White sturgeon Acipenser transmontanus, like many sturgeon species worldwide, have declined in abundance and distribution (Birstein 1993; Rosenthal 2008; IUCN 2011; Beamesderfer et al. 1995; Musick et al. 2000; UCWSRI 2002; McAdam et al. 2005). The Kootenai(y) River population was listed as endangered under the both the U.S. Endangered Species Act (ESA) (USFWS 1999; Ireland et al. 2002; Paragamian et al. 2005) and the Canadian Species at Risk Act (SARA) (Wood et al. 2007). The upper Fraser River, Nechako River, and Columbia River populations were also listed as endangered under SARA. Declines in white sturgeon populations have been variously attributed to hydropower development (i.e. changes in the hydrograph, habitat loss, water quality degradation, blockages, predation), over-harvest, and contaminants (Parsley and Beckman 1994; Kruse and Scarnecchia 2002; Paragamian et al. 2001; Parsley et al. 2002; UCWSRI 2002; Gadomski and Parsley 2005a; McAdam et al. 2005; Paragamian et al. 2005).

In addition to being listed as endangered in Canada under SARA, the subpopulation in the upper Columbia River above Grand Coulee Dam is classified as Critically Endangered (CE) by the IUCN (2011) due to persistent recruitment failure. Recruitment failure in the upper Columbia River between Grand Coulee and Hugh Keenleyside dams (hereafter termed the Transboundary Reach) white sturgeon population was first documented during studies conducted in the early 1990’s in the Canadian portion of the Reach (hereafter termed the Keenleyside Reach) (Hildebrand and English 1991; R.L.&L.1994; Hildebrand et al. 1999). Similar results were obtained in 1998 in the Washington portion of the Reach (hereafter termed the Roosevelt Reach; Figure 1) during a cooperative setline and gill net survey conducted by the Washington Department of Fish and Wildlife (WDFW), Oregon Department of Fish and Wildlife (ODFW), and the Spokane Tribe of Indians (STOI) that sampled an aged white sturgeon population (Devore et al. 2000) (Figure 2). In that same year, a trawl survey completed by the U.S. Geological Survey (USGS) (Kappenman et al. 2000) in the upper stretches of the Roosevelt Reach failed to capture white sturgeon sub-yearlings or juveniles.

Figure 1.  The Roosvelt Reach of the Columbia River.

Figure 2. Length-frequency distributions of white sturgeon captured during pre-LRSRP Transboundary Reach stock assessment surveys (setline and gill net) that demonstrated the lack of natural recruitment. Figure taken from UCWSRI (2002).

In response to increasing concerns over the threat of extinction, the Upper Columbia White Sturgeon Recovery Initiative (UCWSRI) was formed in 2000. The UCWSRI is an international organization with members from state, provincial, and federal fisheries agencies, Canadian First Nations, U.S. Tribes, and industry stakeholders in British Columbia and Washington State. The Initiative produced an Upper Columbia White Sturgeon Recovery Plan (UCWSRP) that is compatible with the ESA and SARA legislation (UCWSRI 2002). The goal of the UCWSRI, as defined in the UCWSRP (UCWSRI 2002), “is to ensure the persistence and viability of naturally-reproducing populations of white sturgeon in the upper Columbia River and restore opportunities for beneficial use if feasible.”

The UCWSRP includes short-, medium-, and long-term objectives for achieving recovery. The short-term (within 5 years) objective is “to assess population status and act to prevent further reductions in white sturgeon distribution, numbers, and genetic diversity within the current geographic range.” The medium-term (within 10 years) objective is “to determine survival limitations (bottlenecks) for remaining supportable populations and establish feasible response measures to reduce or eliminate limitations.” The long-term (within 50 years) objective is “to re-establish natural population age structure, target abundance levels, and beneficial uses through self sustaining recruitment in two or more recovery areas.” The UCWSRP also outlined measures required to meet the recovery objectives (UCWSRI 2002) that included controlling direct sources of mortality, immediate implementation of a conservation aquaculture program, assessment of the existing population including genetic stock structure, and a research program directed at diagnosing and correcting recruitment failure.  Since the implementation of the UCWSRP, substantial progress, summarized below, has been made toward achieving short-term objectives.

CONTROLLING MORTALITY

Direct sources of mortality were controlled through regulations prohibiting angling and regulation enforcement, and as well as improved operations at hydropower facilities in British Columbia. Recreational angling for white sturgeon in the Keenleyside Reach was prohibited beginning in 1996. The WDFW prohibited the harvest of white sturgeon in the Roosevelt Reach in 1995, but catch and release fishing was allowable until it was finally prohibited in 2001. While protection of white sturgeon spawning stock through harvest regulations has been successfully employed to increase production in some populations following stock collapse (i.e. the populations below Bonneville Dam [Columbia River], Hells Canyon Reach of the Snake River, and, to a lesser degree of success, in the mid-Columbia River impoundments downstream from McNary Dam), other stocks continue to decline despite catch and release regulations or complete closures (e.g. the Transboundary Reach of the Columbia River and the Kootenai(y) River populations [Parsley et al. 2002]).

POPULATION STATUS

Age-0 juvenile to adult (wild fish)

Initial assessments of population status in the Roosevelt Reach following the completion of the UCWSRP have been accomplished through a combination of setline, gillnet, and acoustic telemetry.

LRSRP stock assessment surveys using standardized baited setlines were conducted in in 2004, 2005, 2007, 2008, and 2009.  The initial 2004 and 2005 surveys (Howell and McLellan 2007a; Howell and McLellan 2007b) were performed during the early spring (April and May) and were confined to the upper third of the Roosevelt Reach.  Efforts were limited to this area based on: 1) insufficient funding to sample the entire reservoir; 2) the observation that the majority of fish (92%) were capture in this area during the 1998 summer/fall reservoir setline survey (DeVore et al. 2000); and 3) previous telemetry studies that indicated sturgeon overwinter in this area (Brannon and Setter 1992) and thus spring sampling would therefore likely provide a representative geographic sample of the general population. 

Surveys in 2007, 2008, and 2009 setline surveys were undertaken to address the potential sources of bias in the 2005 and 2006 surveys and evaluate previous assumptions about sturgeon distribution within the Roosevelt Reach. Whereas the 2004 and 2005 surveys utilized a haphazard sampling strategy in order to maximize catch rates, surveys 2007-2009 incorporated a spatially balanced, general random tessellation stratified design (GRTS; Stevens and Olsen 2003).  The 2007 survey covered the lower third of the Roosevelt Reach (Grand Coulee Dam to the Spokane River confluence, including the Sanpoil River Arm), the 2008 survey covered the middle third of the Roosevelt Reach (Spokane River confluence to Gifford, including the Spokane River Arm), and the 2009 survey covered the upper third of the Roosevelt Reach (Gifford to the International Border).

Fall (October) gill net surveys have been conducted annually in the Roosevelt Reach since 2001 to monitor levels of natural recruitment and, secondarily, collect data on hatchery origin juveniles released as part of ongoing conservation aquaculture supplementation efforts.  Gear type and survey area have varied through time.  In years 2004, 2005, 2006, 2008, 2009, 2010, and 2011 gear was identical to that used for sub-yearling recruitment indexing in the mid Columbia and lower Snake impoundments (Burner et al 2000) consisting of 300ft long by 12 ft deep nets with 2” stretch nylon webbing.  From 2001-2003 gear used was similar in mesh size (2 inch stretch) but net dimensions were smaller (150 ft long by 6 ft deep).  Sampling in 2007 utilized nets of same dimension as described by Burner et al (2000) but incorporated panels of 2”, 4” and 6”.  Survey areas have generally been limited to the upstream third of the Roosevelt Reach for similar reasons given above for the 2004 and 2005 setline surveys.  However, the 2008 survey sampled the entire Roosevelt Reach.  Prior to 2007, sample site selection was haphazard in nature but beginning in 2008, surveys employed spatially balanced, GRTS designs (Stevens and Olsen 2003).

Sturgeon movements, habitat usage, and spawning migrations have been further assessed using biotelemetry.  Since 2003, approximately 450 sturgeon of various sizes/ages have been acoustic tagged and subsequently monitored with a longitudinal array of hydrophone receivers operated throughout the Transboundary Reach by various entities (Figure 3; Howell and McLellan 2011).  Finer scale telemetry studies using the VEMCO positioning system (VPS; VEMCO, Halifax, Nova Scotia) application has also been employed to evaluate habitat use by sturgeon in the Marcus area (McLellan et al. 2011).  Based on the success of VPS work in the Marcus area, in 2011 the LRSRP conducted a pilot study to investigate the feasibility of installing a VPS system at the Northport spawn area to document habitat use and spawning behavior at a fine scale (WDFW, unpublished data).

Figure 3.  Overview of automated acoustic telemetry stations in the Transboundary area in 2008-2009 operated by various agencies in Washington and British Columbia (from Howell and McLellan 2011).

Demographics

As previously described, the catch of white sturgeon during Transboundary Reach stock assessment surveys conducted prior to implementation of the UCWSRP was dominated by large, old fish (R.L.&L. 1996, 1998a, Devore et al. 2000; Howell and McLellan 2005, 2007a, 2007b, 2008; Irvine et al. 2007).  The length distribution of white sturgeon captured during the LRSRP setline stock assessments in 2004 and 2005 was similar to earlier studies although a small cohort (<10%) of wild juveniles ~100 cm FL was also represented indicating a recent recruitment event (Figure 4).  Preliminary examinations of fin ray spines collected from this cohort indicated they were 1997 year class, a year when spring and summer river discharge was abnormally high in the Columbia River basin.  Supporting evidence that these fish were born in 1997 was the incidental capture of wild juveniles (<40 cm FL) during routine fish monitoring surveys in Lake Roosevelt in 1998 (STOI, unpublished data; WDFW, unpublished data).  The length of these fish was similar to those of age 1 white sturgeon in other areas of the Columbia and Snake Rivers, as well as the age 1 upper Columbia River hatchery sturgeon (Howell and McLellan 2007a, 2007b, 2008, 2011).  Data collected during the 2009 LRSRP setline survey showed the wild component of the population was still represented by large (range 100-279 cm FL; median=202 cm FL; mean=194 cm FL), presumably older fish and that the median length of the adult cohort (≥150 cm FL) was greater than documented in previous surveys thereby demonstrating ongoing limited recruitment (Figure 4). 

Figure 4.  Fork length frequencies of wild sturgeon captured during setline surveys of the Roosevelt Reach in 1998, 2004, and 2009 (from Howell and McLellan in prep).

Fall gill net sampling conducted in the Transboundary Reach annually since 2001 has failed to capture any wild sub-yearling or older juvenile white sturgeon, with the exception of the 1997 cohort (Golder 2003a, 2005a, 2006a, 2006b, 2007; Lee and Underwood 2002; Lee and Pavlik 2003; Howell and McLellan 2005, 2007a, 2007b, 2008, 2011).  Collectively, the setline and gill net survey data confirms that natural recruitment of white sturgeon in the Transboundary Reach is a rare event, consistent with recruitment collapse.

Abundance

The abundance of wild white sturgeon (all sizes) in the Keenleyside Reach was estimated to be 1,157 (414-1,900 95% CI) using mark-recapture data collected between 1990 and 2004 (Irvine et al. 2007) (Table 1). Irvine et al. (2007) estimated survival of wild white sturgeon in the Keenleyside Reach was 0.973 (0.918-0.991 95% CI) for the 1993-2004 time period (Table 1). No comprehensive stock assessment surveys have been conducted in the Keenleyside Reach since the early 2000’s.  Abundance of wild white sturgeon (>70 cm FL) in the Roosevelt Reach was estimated to be 2,037 (1,093-3,223 95% CI) using mark-recapture data collected during the 2004 and 2005 surveys (Howell and McLellan 2007b) (Table 1).  No estimates of abundance or survival have been undertaken in the Roosevelt Reach since 2005.

Table 1.  The estimates abundance (N) and survival (S) of wild and hatchery origin white sturgeon in the Transboundary Reach (WA/BC) of the upper Columbia River.

Growth and condition

Based on von Bertalanffy growth (VBG) modeling of length at age data derived from analysis of pectoral fin sections collected during the reservoir wide setline survey in 1998, Devore et al. (2000) found that the asymptotic fork length (L_∞) of sturgeon (255 cm) in the Roosevelt Reach was substantially less than observed in mid-Columbia impoundments (John Day = 382 cm; The Dalles = 340 cm; Bonneville = 311 cm; Beamesderfer et al. 1995; Kern et al. 2002) and in the lower Columbia River (311 cm FL; Devore et al. 1995), but similar to sturgeon in the Keenleyside Reach (RL&L 1994, 1996).   Whereas the theoretical maximum size of sturgeon in the Roosevelt Reach was less than that of downstream populations, the estimate of growth co-efficient, K, predicted growth trajectories for fish <30 years of age in the Roosevelt Reach sturgeon were comparable to lower Columbia and mid Columbia impoundments (Figure 5). 

Figure 5. (Upper panel) Estimates of mean annual growth in length for 610 sturgeon captured or released (hatchery) and subsequently recaptured in the Roosevelt Reach 1998-2009 (Howell and McLellan in prep).  Time at large ranged 1.0-11.0 years (mean=2.8). (Lower panel) comparison of von Bertalanffy growth curves for Columbia River sturgeon populations based on aging from fin spines (Beamesderfer et al 1995; DeVore et al. 1995; DeVore et al. 2000; RL&L 1996) and mark-recapture data (LRSRP; Howell and McLellan in prep).

VBG estimates of theoretical maximum size based on mark-recapture data (Fabens 1965) collected from wild and hatchery sturgeon in the Roosevelt Reach by the LRSRP through 2009 was similar to length-at-age based estimates by DeVore et al. (2000) (Howell and McLellan in prep).  However, the estimate of growth co-efficient, K, was substantially greater in magnitude, and resulting growth trajectories predicted that sturgeon in the Roosevelt Reach attain larger sizes at younger ages than observed in other areas of the Columbia River (Howell and McLellan in prep; Figure 5).  The discrepancies in growth parameter estimates of Roosevelt Reach sturgeon from age-at-length and mark-recapture analyses is likely due to the inclusion of juvenile growth information from hatchery releases in the latter.  Parameter estimation by DeVore et al. (2000) was based on a data set that included relatively few juvenile sturgeon due to their paucity in the catch of the 1998 survey.  Growth models can be severely distorted if growth data from all size classes are not included in the analyses (Spencer 2002). 

Comparisons of direct estimates of growth in large (adult) sturgeon between areas based on mark-recapture studies is difficult due to lack of available data since relatively few large fish are marked and recaptured during setline stock assessments in other areas of the Columbia basin.  However, the mean annual growth calculated from mark-recapture data of sturgeon in the Roosevelt Reach (2.8 cm yr-1; >150 cm FL; Howell and McLellan, in prep), was less than the 5.0 cm yr^-1 (FL > 137 cm) reported for the John Day reservoir by Kern et al. (2002), similar to 2.7 cm yr^-1 reported for sturgeon in the Keenleyside Reach (Golder 2002), and greater than 1.5 cm yr^-1 (FL 116-160 cm) and 0.6 cm yr^-1 (FL>160 cm) reported for the Kootenay River population (Paragamian and Beamesderfer 2003).

Devore et al. (2000) found that the condition (mean relative weight [Wr] = 91%; Beamesderfer 1993) of Roosevelt Reach sturgeon was the lowest recorded for any Columbia River population. They attributed slow growth (from their VBG analyses) and poor condition to the northerly location of the population (reduced growing season, colder average water temperature) and lack of food resources such as an anadromous forage base, as well as the large seasonal drawdowns and low water retention times characteristic of the Roosevelt Reach that tend to decrease densities of benthic invertebrates (Griffith and Scholz 1991).

More recent LRSRP setline surveys found wild sturgeon condition to be improved over 1998. Mean population Wr’s in 2003 (November survey; Howell and McLellan 2005), 2004 (April/May survey; Howell and McLellan 2007a), and 2005 (May survey; Howell and McLellan 2007b) were estimated at 117%, 101%, and 98%, respectively. Howell and McLellan (2007b) speculated that the low mean Wr observed in 1998 may have been the result of sampling during the summer months (most fish were captured in August) when numbers of recently spawned out fish were likely present in the catch.  This hypothesis was supported by the 2009 setline survey results (also conducted during August) when mean Wr of the adult component (>150 cm FL) was again found to be low at 93% (Howell and McLellan, in prep).

Reproductive potential

During the LRSRP spring (prior to spawning timeframe) stock assessments in 2004 and 2005, 147 sturgeon (148-232 cm FL) were surgically examined for gender and stage of maturity.  For fish positively identified as females (n=70; range 148-232 cm FL, mean=198), 20% were pre-vitellogenic (range 148-219 cm FL; mean=186), 59% were vitellogenic (range 173-227 cm FL; mean=200) and 21% were post vitellogenic (pre-spawn; range 169-232 cm FL; mean=206).

Theoretically, the reciprocal of the ratio of vitellogenic to post-vitellogenic (pre-spawn) females should approximate the duration of gonadal development.  Thus, Roosevelt Reach collections indicate a gonadal development time between 2-3 years. Welch and Beamesderfer (1993) concluded that white sturgeon mid Columbia River impoundments were physiologically capable of spawning about every three years, with the spawning cycle consisting of a two-year period of oocyte development and a one-year resting period prior to re-initiation of gonadal development. 

Howell and McLellan (2007b) did not attempt to quantify median length at maturity for the Roosevelt Reach population (sensu Welch and Beamesderfer 1993; Beamesderfer et al. 1995 DeVore et al. 1995); however general comparisons indicated that sturgeon achieve maturity at similar sizes and rates reported for other areas of the Columbia.   For example, Howell and McLellan (2007b) found that 59.6% of females >166 cm FL were either mature or maturing when fish where sex could not be determined during surgical assessment were assumed to be female (Figure 6).  Excluding fish where sex could not be positively identified, 82.3% of females in this size interval were either maturing or mature.  By comparison, Welch and Beamesderfer (1993) found only 47% of fish identified as females >166 cm FL were mature/maturing when using similar methods of fish collection and surgical gonad inspections.

Figure 6.  The proportion of females by size interval that were vitellogenic or post-vitellogenic (maturing or mature) when surgically examined during LRSRP setline surveys in 2004 and 2005.  Data includes individuals whose sex could not be determined during surgical assessment and assumes them to be female.  Thus some males may be represented in the plot, particularly at shorter fork lengths.  Numerals above the bars indicate sample size.

The combined number of adult sturgeon in the Transboundary Reach is likely greater than in any of the three mid-Columbia River impoundments (i.e. Bonneville, The Dalles, John Day) where abundance estimates for fish >166 cm have not been reported to exceed 1,000 individuals (North et al. 1999). Despite this, sturgeon in these areas are able to support limited levels of exploitation through periodic recruitment whereas the Transboundary Reach population has experienced almost total recruitment failure since the mid 1970’s. 

Based on the preliminary assessments of reproductive potential outlined above, we do not currently believe that recruitment failure in the Transboundary Reach population is due to limited numbers of spawners in any given year.  The relative ease with which the transboundary conservation aquaculture programs are able to collect broodstock indicates that fish in spawning condition are relatively abundant.  Further, removal of pre-spawners from the system for aquaculture purposes does not appear to have an appreciable impact as evidenced by spawn monitoring efforts (Golder 2007, 2008a, 2008b) and collections of large numbers of post-hatch life stages in plankton nets (Howell and McLellan 2007a, 2007b, 2008, 2011, in review).

Distribution and movements

Data collected during various setline, gillnet, and telemetry surveys in the Transboundary Reach indicate that sturgeon primarily reside in the upper third of the Roosevelt Reach and in the Keenleyside Reach.  Summer time setline surveys (when sturgeon would be expected to be most widely distributed) in 1998 (DeVore et al. 2000) and 2007-2009 (Howell and McLellan in prep) found few sturgeon downstream of Gifford (Figure 7).  Acoustic telemetry studies independently confirmed limited use of lower reservoir habitat by sturgeon (Figure 8; Howell and McLellan 2011).

Figure 7.  The spatial catch distribution of sturgeon in the Roosevelt Reach during reservoir wide summer time setline surveys 1998 (DeVore et al 2000) and 2007-2009 (Howell and McLellan in prep.).  Each red symbol indicates a location where sturgeon catch was >0.

Figure 8.  Annual number of unique acoustic tag codes (applied to sturgeon 104-227 cm FL) detected by automated receiver stations 2004-2007; black circles denote Columbia River locations; white circles denote Kootenay River locations.  Data from some closely located stations was combined. Plots demonstrate limited use of lower reservoir habitat by sturgeon (From Howell and McLellan 2011).

During the 2007-2009 Roosevelt Reach summer setline surveys, sub-adults (100-150 cm FL) and adults (>150 cm FL) were distributed throughout the area upstream from Gifford, whereas juveniles (<100 cm FL; primarily hatchery origin) were concentrated in the river-reservoir transition zone from Marcus upstream (Figure 9; Howell and McLellan in prep).  Juveniles were similarly distributed during the fall timeframe based on LRSRP gill net surveys 2004-2009 where few nets set downstream from the mouth of the Colville River captured fish (Figure 10; Howell and McLellan 2007a, 2007b, 2008, 2011, in review, in prep).  Whereas juveniles showed little distributional differences between seasons, older fish (>100 cm FL) were more widely distributed in the summer months than during the early spring (i.e. at the tail-end of overwintering) when fish were most heavily concentrated in the area between the Colville River mouth upstream through the Marcus area (Figure 11).

Figure 9.  Distributions and catch rates of three size classes of sturgeon during spatially balanced summer time setline surveys of the Roosevelt Reach 2007-2009.  The <100 cm FL size class is primarily represented by hatchery origin juveniles.

Figure 10.  The distribution of hatchery origin juvenile sturgeon (<100 cm FL) captured during LRSRP fall gill net surveys 2004-2009.  Downstream bounds of survey areas are shown except 2008 when the entire Roosevelt Reach was surveyed (Howell and McLellan in prep.)

Figure 11.  Seasonal differences in sturgeon (>100 cm FL) catch distribution during reservoir wide setline surveys of the Roosevelt Reach in 1998 and 2004.

Finer scale (<10 m) movement data from a VPS study in the Marcus area 2009-2010 indicated that there were seasonal differences in coarse-scale habitat use by white sturgeon (McLellan et al. 2011).  In this study, sturgeon occupied the original Columbia River channel for significantly longer periods than out of channel areas (i.e. flooded river terrace areas) in the winter and spring whereas habitat use was more dispersed in summer and fall (McLellan et al. 2011).  Acoustic telemetry data collected from the longitudinal array showed that sturgeon in the Transboundary Reach ranged most widely during the period May-October with few long distance movements observed from Nov-April (Howell and McLellan 2011; Figure 12).

Figure 12.  Monthly summaries of detected range (furthest upstream detection minus furthest downstream detection) for wild white sturgeon outfitted with Vemco V16 acoustic tags in the Transboundary Reach.  Boxes indicate the 25^th and 75^th percentiles, whiskers indicate 10^th and 90^th percentiles, light solid lines are the median, heavy solid lines are the mean, and closed circles are outliers.  Diamond symbols indicate the sample size.  Fluctuations in sample size reflect additions through tagging efforts and reductions from expiring tags. From Howell and McLellan 2011.

Genetics

One of the UCWSRI recovery measures is to maintain genetic diversity (including rare allele frequencies) at current levels (UCWSRI 2002).  A nuclear DNA genetic study was conducted to examine both current (post-dam) and historic (pre-dam) stock structure of white sturgeon within the Transboundary Reach and Arrow Lakes Reservoir to 1) inform current and future management and recovery activities and 2) assist with recruitment failure diagnosis research. The study indicated that the genetic diversity (215 alleles; n=350) of Transboundary Reach sturgeon was similar to other Columbia River populations (below Bonneville Dam, 234 alleles, n=99; McNary Dam to Chief Joseph Dam 202 alleles, n=90) (Drauch Schreier et al. 2010). The Kootenai River population, which is small and experiencing recruitment failure, has low genetic diversity (95 alleles, n=268) (Drauch Schreier et al. 2009).  Drauch Schreier et al. (2010) found that there was little evidence of stock structure in the Transboundary Reach white sturgeon population and that it can be considered one genetic population.

Spawning

In the Keenleyside Reach, white sturgeon spawning has been detected in the tailrace of Waneta Dam at the confluence of the Pend Oreille and Columbia rivers in each of the 16 years that sampling was conducted between 1993 and 2011 (no monitoring in 1997 or 1999) (R.L.&L. 1996, 1997, 1998b, 2001; Golder 2002, 2003b, 2004, 2005b, 2006c, 2008a; Golder, unpublished data). A second white sturgeon spawning area was recently identified in the upper Keenleyside Reach, as evidenced by the collection of white sturgeon larvae near Castlegar, British Columbia annually since 2007 (Golder 2008b, 2009; Golder, unpublished data; BC Hydro, unpublished data).

In the Roosevelt Reach the LRSRP used radio and acoustic telemetry of mature sturgeon to identify a potential additional spawning area in the U.S. located near to the town of Northport, WA and this was subsequently confirmed by the collection of eggs and free embryos using artificial substrates and D-ring plankton nets in 2005 (Howell and McLellan 2007b).  Spawning at this location was confirmed in 2006-2008 with egg mats (Howell and McLellan 2008, 2011, in review) and implied from 2009-2011 through capture of spawned out adults during broodstock collection efforts at Northport and through collections of free embryos in D-ring plankton nets (Howell and McLellan in prep; WDFW, unpublished data).  A second, likely more minor, spawning area was identified in the vicinity of China Bend through collections of eggs and free embryos in D-ring plankton nets in 2007 and 2008 (Howell and McLellan 2008, 2011, in review).  In contrast to most other white sturgeon spawning documented to date in the Columbia basin (Chapman and Jones 2011; Hildebrand 1999; Parsley et al. 1993, 1994, 2000), spawning in the Roosevelt Reach is noteworthy in that it is not closely associated with a hydropower facility tailrace. The only other instance of this is found in the Kootenay River (Paragamian et al. 2001).

The spawning timeframe in the Transboundary Reach is somewhat later (late June through July; Golder 2007, 2008a, 2008b; Howell and McLellan 2007b, 2008, 2011) than observed in downstream areas of the Columbia (May-June; Parsley et al 1993; Parsley and Beckman 1994) due to more slowly warming water temperatures in the upper Columbia.  Similar to other areas of the Columbia, sturgeon spawning in the Transboundary Reach generally occurs when water temperatures reach about 14^oC (Parsley et al 1993; Parsley and Beckman 1994; Golder 2007, 2008a, 2008b; Howell and McLellan 2007b, 2008, 2011).

Post hatch

Post-hatch sturgeon up to the first-feeding life stage have been captured during LRSRP D-ring plankton net surveys of the riverine and upper river-reservoir transition zone areas of the Roosevelt Reach annually since 2004 (no sampling was conducted in 2009) (Howell and McLellan 2008, 2011; WDFW, unpublished data; Figure 13).  Total catch varied from 26 in 2004 to 10,391 in 2011.  Variability in annual catch was due to various factors that included 1) increasing experience of the research team, 2) improvements in sampling equipment, and 3) differences in levels of effort and sample site location.  Thus, no conclusions can be drawn about annual larval production.  However, plankton net catch data indicates that conditions in the Transboundary Reach are suitable for successful incubation of embryos and that substantial numbers of larvae survive to the point of exogenous feeding in most years.  Golder (2006c, 2007, 2008a, 2008b) demonstrated high survival to hatch of embryos collected at the Waneta spawn area on egg mats and incubated in situ in incubation capsules.

Figure 13.  Locations of LRSRP plankton net stations in the upper Roosevelt Reach 2005-2010.

Despite documented annual spawning and hatch success, no sub-yearling sturgeons have been captured during Transboundary Reach fall gill net surveys suggesting that the primary survival bottleneck resulting in recruitment failure occurs sometime during the period between the onset of exogenous feeding and recruitment to sub-yearling juvenile (i.e. within the first four months of life).  Further information gained from LRSRP early life history studies is discussed below in the context of recruitment failure research.

RECRUITMENT FAILURE RESEARCH

The medium-term objective of the UCWSRP is to identify and correct the sources of recruitment failure (UCWSRI 2002). There are numerous factors suspected to limit natural recruitment of upper Columbia River white sturgeon; however, they can be narrowed into five general categories (Gregory and Long 2008): 1) changes in flow patterns and turbidity, 2) diminished habitat (primarily substrate) downstream of spawning areas, 3) changes in the fish community resulting in increased predation, 4) contaminants, and 5) food availability.  Under each of these potential limiting factors, a suite of mechanisms impacting survival have been identified which are either associated with direct mortality of embryos, larvae, and early juveniles or reduced growth, condition, and reproductive potential of older juveniles, sub-adults, and adults and many of the factors are likely related and interact.

Hydro-ops

In the Transboundary Reach, river discharge appears to influence white sturgeon recruitment. The timing of sturgeon recruitment failure corresponded with the construction of mainstem dams in British Columbia that substantially reduced the magnitude and duration of discharge during the typical sturgeon spawning, incubation, and larval dispersal period (June–August; UCWSRI 2002).  As discussed above, the only detectable recruitment event in the Transboundary Reach within the last two decades occurred in 1997 when the magnitude and duration of the discharge in the June-July period were similar to levels observed prior to mainstem dam construction in Canada.

White sturgeon research in the lower Columbia River and mid-Columbia impoundments demonstrated that annual recruitment is related to river discharge during the spawning period and that the operation of the hydropower system can have large effects on the extent of white sturgeon spawning habitat (Parsley and Beckman 1994; Parsley et al. 1993). Parsley and Beckman (1994) found that recruitment to subyearling juveniles in the mid-Columbia impoundments was poor during 1987-1989, when river discharges were low, and improved with the increased discharges during 1990 and 1991. They also found that the effects of river discharge, and thus hydropower system operation, on white sturgeon spawning habitat varies among areas. For example, Bonneville Dam tailrace provides high-quality habitat for spawning white sturgeons at discharges lower than those needed to provide even low- to medium-quality habitat in the tailraces of the mid-Columbia dams. The researchers attributed this to lower gradients in the tailraces of the mid-Columbia dams compared to below Bonneville Dam due to backwater effects from the downstream projects.

While production in the mid-Columbia appears directly related to river discharge, hydropower operations, and the resulting availability and quality of spawning habitat, it remains unclear exactly what mechanisms are acting to limit recruitment.  In the case of the Kootenai(y) River population, flow augmentation through manipulation of operations at Libby Dam to more closely mimic the natural spring freshet resulted in increases in spawning activity and the collection of viable eggs (Paragamian et al. 2001). However, apparent improvements in spawning intensity have not resulted in subsequent increases in natural recruitment (Paragamian et al. 2001; Paragamian and Wakkinen 2002).  The majority of spawning in the Kootenai(y) River occurs over sand substrate (Paragamian et al. 2001; Paragamian and Kruse 2001 which is hypothesized to reduce egg survival and thus limit recruitment. In laboratory experiments, Kock et al. (2006) found that white sturgeon embryo survival was significantly lower when covered in sediment of 5 mm depth or greater when compared to controls at “low” and “high” velocities. They also reported embryo survival was negatively correlated with increased duration of sediment coverage. In addition, survival of white sturgeon eggs was diminished when incubated in contact with sediments collected from the Kootenai(y) sturgeon spawning area.  Reduced survival was attributed to contaminants within the substrate (copper and the PCB Aroclor 1260) (Kruse and Scarnecchia 2002). Thus, recruitment failure in the Kootenai(y) population appears more likely related to substrate composition in the spawning area(s) than to magnitude of river discharge.

We do not believe recruitment failure in the Transboundary Reach population is due either to limited spawning habitat in years with low (relative to historic) discharge as is observed in mid-Columbia impoundments, or to substrate conditions in spawning areas as is observed in the Kootenai.   As previously discussed, regardless of river discharge conditions, each year relatively high numbers of adults are in spawning condition,  spawning is documented at multiple locations over a protracted period of time, and substantial numbers of dispersing larvae are captured downstream of the spawning areas.  Instead we contend that river discharge and hydro-operations primarily impact survival of the larval stage by limiting their ability to effectively disperse. We suspect that hydro-operations in most years inhibit the dispersal of early larvae to suitable rearing habitats and this leads to high mortality and, ultimately, recruitment failure.

The ontogenetic behavior of many species of sturgeons, including white sturgeon, includes a drift or dispersal phase, although there is substantial variation in the manifestation of the drift behavior (Kynard and Horgan 2002; Kynard et al. 2002; Zhuang et al. 2002, 2003; Kynard and Parker 2004, 2005; Kynard et al. 2010; Braaten et al. 2008). There are even differences in the ontogenetic behavior of different populations of white sturgeon. Laboratory studies of early life history of white sturgeon from the Sacramento, lower Columbia, and Kootenai(y) rivers collectively indicate that upon hatching, some free embryos enter the water column and undergo a short (1-3 d), weak dispersal (Brannon et al. 1985; Kynard and Parker 2005; Kynard et al. 2010). This initial dispersal phase is followed by a hiding phase (approximately 7 d in duration) when free-embryos seek the substrate for places that provide cover while the yolk-sac is absorbed. At or around yolk-sac absorption, fish re-emerge from hiding. Lower Columbia River and Kootenai River white sturgeon initiate a strong downstream dispersal following re-emergence, presumably to be distributed to suitable rearing habitats (Brannon et al. 1985; Kynard et al. 2010) whereas larvae of Sacramento River white sturgeon do not migrate but forage on the substrate until the early juvenile stage at which point they initiate downstream dispersal (Kynard and Parker 2005).  

Plankton nets are a passive type of sampling gear, and catch composition should therefore reflect early life stage behaviors.  The catch compositions of annual LRSRP plankton net sampling to date were bimodal with small peaks occurring at the early free-embryo stage and larger peaks at the first-feeding larval stage (Figures 14 and15; Howell and McLellan 2011) indicating that the early ontogenetic behaviors of Transboundary Reach white sturgeon are similar to those of lower Columbia River and Kootenai River populations i.e. they exhibit a weak post-hatch dispersal followed by a strong downstream dispersal during the early larval phase.

Figure 14. Catch composition of white sturgeon collected with D-ring style plankton nets in the Roosevelt Reach 2006-2008.  Fish that could not be definitively staged according to Dettlaff et al. (1993) were assigned to a general group: EFE (early stage free-embryo; stages 36-41), LFE (late stage free embryo/larva; stages 42-45), or UNK (unknown – distinguishable as a sturgeon but too damaged or decomposed to assign a stage). For reference, developmental stages are illustrated in Figure 15.

Figure 15.  White sturgeon development from hatch (stage 36) through first feeding (stage 45) at a constant water temperature of 17 ^oC.  Fish were progeny of adults captured during broodstock collection efforts in the Northport area in June 2010.  Fertilization and rearing occurred at WDFW Region 1 fish laboratory in Spokane Valley, WA.  All fish are to same scale.  hpf denotes hours post-fertilization. Taken from Howell and McLellan in review.

Dispersal of sturgeon larvae to appropriate rearing habitats is critical for successful recruitment. Kynard and Parker (2005) speculated that recruitment failure in white sturgeon populations might be due to habitat mis-match resulting from dispersal behaviors and altered habitat due to hydropower development. Disruption of the dispersal of pallid sturgeon Scaphirhyncus albus larvae has been implicated in that species’ recruitment failure in the Missouri River system (Braaten et al. 2008).

Based on LRSRP spawn monitoring and plankton net data, sturgeon larvae begin to emerge from the substrate in the upper river-reservoir transition zone of the Roosevelt Reach in mid-late July coincident with rapidly declining river discharge, and following completion of reservoir refill in early July (Figure 16). These factors may collectively limit the extent of larval dispersal and confine them to upper transition zone habitat by diminishing water velocities in this area of the river.  Further, hydropower facilities begin load shaping by mid-July that can substantially reduce discharge - and therefore water velocities - at night when white sturgeon larval dispersal intensity is greatest (Kynard et al. 2010; WDFW,unpublished data; Figure 17).  Kynard et al. (2010) reported that in a laboratory study, dispersal of larval Kootenai(y)River white sturgeon was initiated earlier and was of greater duration and intensity at higher experimental water velocities (0.169 versus 0.234 m s-1).  Thus, low velocities in the river-reservoir transition zone of the Roosevelt Reach in normal flow years may result in less intense, shorter duration, and delayed dispersal by early larvae.  LRSRP plankton netting data support this assertion by showing that the relative abundance of post-hatch sturgeon progressively declines downstream in the transition zone (Figure 18; Howell and McLellan 2007a, 2007b, 2008, 2011, in review).  As well, various trawling efforts have failed to capture any larval sturgeon in downstream habitats where plankton nets are ineffective due to low velocities (Kappenman et al 2000; Howell and McLellan 2011, in prep).  Collectively then, these observations suggest that dispersal extent is limited and that larval stages may be confined to upper transition zone habitat in most years.  If this is the case, then the lack of subyearling captures during fall gill net surveys indicate that conditions in this area are not conducive to larval survival.  Further, the occurrence of limited recruitment in years when very high river discharge coincides with emergence of first feeding larvae (e.g. 1997) provides further support for dispersal as a primary mechanism influencing survival (Figure 19). 

Figure 16.  Daily total catch of post-hatch white sturgeon during LRSRP plankton net surveys of the Roosevelt Reach 2006-2008.  Sampling was concluded at the end of July in 2006 and 2007, and 24 July in 2008; post-hatch sturgeon were likely present after these times.  The duration of spawning, as documented by egg mat sampling at the Waneta and Northport spawn areas (gray horizontal bars), is protracted; however spawning intensity was greatest during the last week of June and first week of July in each year.  Note the onset of power-peaking in July coincident with presence of post-hatch sturgeon.

Figure 17.  Box plot comparisons of post hatch sturgeon (predominantly larvae at or around first-feeding) catch rates in plankton nets by time interval during LRSRP conservation aquaculture larval collection efforts in the upper Roosevelt Reach 25 July through 2 August, 2011.  Sunrise and sunrise times during the collection effort were, approximately, 0530 and 2030 PDT.  Numerals indicate sample size (WDFW unpublished data).

Figure 18.  Mean (SD = error bars) relative abundance of post-hatch sturgeon and mean (SD = error bars) water speeds calculated from flowmeter readings during D-ring plankton net sampling at four locations in the upper Roosevelt Reach in June-July 2008 (see figure 13 for overview map of 2008 plankton net locations).  Note that sampling stations were located in areas of channel constriction and thus estimated water velocities likely represent the upper range for this area of the river.  Numerals indicate sample size.

Figure 19.  Comparisons of Columbia River discharge at the U.S.-Canada border pre- and post- mainstem dam construction in Canada, and in 1997 - a year when a detectable level of white sturgeon recruitment occurred.  Water temperatures at the international border reached 14^oC (i.e. optimal spawning temperature) in mid-late June 1997 and thus first feeding larvae would likely have been abundant by mid-July coincident with the large secondary peak in discharge that may have aided dispersal to nursery habitats further downstream in the Roosevelt Reach.

While the transition zone may generally represent unsuitable nursery habitat for larval white sturgeon, the mechanisms resulting in poor survival are unknown but may be related to a lack of food (starvation), predation, contaminants, or likely some combination of all of those factors.  

Food availability

The onset of exogenous feeding constitutes a critical period of potentially high mortality (Parsley et al. 2002). According to the habitat “Match-Mismatch” hypothesis (Cushing 1974, 1990; Houde 2008), dispersing larvae must arrive at the right location at the right time to ensure survival (i.e. the place where food is, when the food is there). Braaten et al. (2008) suggested that it is important for sturgeon to settle in habitat patches with abundant food resources as they transition to exogenous foods.

Available data from the mid- and lower Columbia indicate that larval and subyearling juvenile white sturgeon are typically captured over sand (McCabe and Tracy 1994; Parsley et al. 1993). Most of the food items observed in the guts of early larvae collected by the LRSRP in the Roosevelt Reach to date consist of Diptera (Chironimidae), which are generally found in fine substrates (Howell and McLellan 2011, in review). However, current limited information indicates that in the area of the Roosevelt Reach where larval abundance is greatest, the substrate is typified by coarse sediments (gravel, cobble, boulder; Weakland et al. 2011; CH2M Hill and Ecology Environment, Inc. 2006).  Extensive areas of fine grained (sand/silt) sediments are only found from the Marcus area downstream - areas where trawl efforts to date have failed to capture larval stages (Kappenman et al. 2000; Howell and McLellan 2011; Howell and McLellan in prep).

Based on samples collected during LRSRP plankton netting efforts in 2005, 2006, 2007, and 2008, approximately 0%, 16%, 26%, and 23%, respectively, of larvae that had exhausted their yolk contained prey items (Howell and McLellan 2007b, 2008, 2011, in review).  By comparison, Muir et al. (2000) found that of 64 larvae averaging 21 mm in length (i.e. a similar size and stage of development as the late free embryos/early larvae collected in Roosevelt Reach studies) only one was found to have an empty stomach.  These observations could suggest that prey availability, feeding success, or both, in the upper transition zone of the Roosevelt Reach is comparatively low.

However, it should be noted that the larvae collected by Muir et al. (2000) were captured with actively towed trawl gear while those collected in the Roosevelt Reach were captured in passively fished plankton nets. Since larvae with empty stomachs may be more actively dispersing in search of suitable foraging habitat, these individuals may be disproportionately represented in the catch of stationary gear. Furthermore, since most larvae collected in the Roosevelt Reach and examined for diet were captured in long duration (overnight) sets, there is potential for complete prey digestion and expulsion between time of entry to the collection bucket and specimen preservation.  Alternatively, feeding may have occurred within the collection bucket following capture.

It is also questionable if researchers have captured white sturgeon larvae in the Roosevelt Reach old enough to exhibit the effects of starvation.  The oldest sturgeon larvae captured in the Roosevelt Reach to date were approximately 15 dph and relatively few fish had exhausted their yolk supply (Figure 20).  Mortality of food-deprived green sturgeon A. medirostris, larvae was not appreciable until 28-31 dph (Gisbert and Doroshov 2003) and food deprived white sturgeon larvae reared in a laboratory under a thermal regime that mimicked that of the Transboundary Reach exhibited 50% mortality within 13-21 dph and 100% mortality within 22-29 dph (Parsley 2010; Parsley et al. 2011). Current information is not sufficient to suggest starvation is a primary cause of larval mortality, but this requires more investigation.

Figure 20.  Length frequency (upper panel) and length-weight relationship (lower panel) of post-hatch sturgeon captured with D-ring plankton nets in the Roosevelt Reach in 2008. From Howell and McLellan in review)

Predation

Early larvae involved in extended searches for food could potentially experience an increased vulnerability to predation. Early life stages of white sturgeon are subject to predation by other fishes (Miller and Beckman 1993; Gadomski and Parsley 2005a, 2005b). White and green sturgeon deprived of food had slower growth and lower condition which may make them more vulnerable to predation (Gisbert and Williot 1997; Gisbert and Doroshov 2003). However, predator diet studies to date have failed to identify large numbers of white sturgeon larvae or juveniles consumed. Stomach samples (n=520) from 13 species of potential predators collected in the upper Roosevelt Reach during the sturgeon spawning and larval dispersal period did not contain any white sturgeon young (Howell and McLellan 2007a, 2007b). Similarly, predator diet studies in lower Columbia River reservoirs have only identified one instance of predation on juvenile sturgeon (Gadomski and Parsley 2005a). However, these results do not definitively rule out predation as a limiting factor since electrofishing was the method used to capture potential predators. Electrofishing collects only fish distributed in near shore shallow habitats, while current data indicates most sturgeon larvae are located in deep, mid-channel habitats. Further, lab studies indicate larval sturgeon are digested more rapidly by predators than similar sized salmonids thereby limiting the likelihood of identifying them in diet sampling (Garner 2006).

The abundance of potential predators is relatively high in the upper Roosevelt Reach during the times when early life stages of sturgeon are present (Beckman et al. 1985; Hall et al. 1985; Peone et al. 1990; Griffith and Scholz 1991; McLellan et al. 2002). Among those predators suspected to pose the greatest risk are walleye and sculpins. Walleye are one of the most abundant species of fish in the Roosevelt Reach (Peone et al. 1990; Griffith and Scholz 1991; Underwood and Shields 1996; Lee et al. 2006) and their proliferation corresponds with the decline in sturgeon recruitment failure (Nielsen 1975). In addition, the decline of numerous other native species populations in the Roosevelt Reach corresponds with the expansion of the walleye population (Earnest et al. 1966; Scholz et al. 1986). Introductions of walleye have led to sharp declines in native fish populations in other reservoirs as well (McMahon and Bennett 1996). Consumption of age-0 sturgeon by walleye has been demonstrated in the laboratory, and sturgeon of this age appeared to be preferred over both rainbow trout Oncorhynchus mykiss and kokanee O. nerka while age-1 sturgeon were not consumed  (Garner 2006).

In 2008 an acoustic telemetry study of walleye behavior was conducted to explore the spatio-temporal overlap between walleye and early post-hatch life stages of white sturgeon in the upper Roosevelt Reach (Howell and McLellan, in review). Walleye exhibited diel depth migrations occupying deeper water habitat during the day and shallower water at night.  Night time depths were typically shallower than 15 m whereas in the same area, white sturgeon larvae were most often captured in the main channel (>20 m) near the bottom and were more active at night (Howell and McLellan, in review). Since walleye are bentho-pelagic by nature, this implies that while they seek depth during the day, they may remain in areas peripheral to the main channel, thereby potentially limiting interactions with sturgeon larvae.

Sculpins, another fish observed to consume white sturgeon larvae and subyearling juveniles in lab studies (Gadomski and Parsley 2005a, 2005b), are also abundant in the upper Roosevelt Reach as indicated by the catch in trawl surveys (Howell and McLellan 2007b). Large sculpin, those presumably more likely to consume sturgeon larvae, are distributed in the area where D-ring sampling is conducted, whereas small sculpin are distributed further downstream (Howell and McLellan 2007b).  A mottled sculpin (75 mm TL) captured in a plankton net set during the 2010 LRSRP conservation aquaculture larval collection effort had consumed 13 sturgeon larvae (WDFW, unpublished data). Further, in November 2011, a subyearling sturgeon (~10 cm FL) was collected from the gut of a walleye Sander vitreus (31.5 cm TL) captured during a gill net based walleye population monitoring study in the upper Roosevelt Reach (Figure 21; WDFW, unpublished data).  Thus, predation on sturgeon early life stages does occur in the Roosevelt Reach.

Figure 21.  A wild subyearling white sturgeon (~10 cm FL) found in the gut of a walleye (31.5 cm TL) captured in a gill net set at the mouth of Flat Creek (located just downstream from China Bend) on 4 November 2011.

Reduced discharge may influence predation rates on sturgeon larvae in the Transboundary Reach by reducing velocities and turbidity, and thus improving predator efficiency. Gadomski and Parsley 2005c demonstrated an inverse relationship between predation rate on white sturgeon larvae and turbidity levels.  Upstream impoundments have likely reduced turbidity in the Transboundary Reach (UCWSRI 2002) and velocities are lower than they were historically as previously discussed.   LRSRP sampling in 2011 (a relatively high flow year) demonstrated that turbidity levels were very low during the sturgeon spawning and larval dispersal period (Figure 22).

Figure 22.  Turbidity readings collected from various sites in the upper Roosevelt Reach in 2011.  Each point represents the mean of three subsamples.

Contaminant exposure

Exposure to contaminants may also limit survival of early life stage white sturgeon. According to the UCWSRI (2002):

There are several sources of contaminants to the Upper Columbia River watershed in British Columbia and the United States, including Cominco Ltd. at Trail, B.C., Celgar Pulp Company at Castlegar, B.C., municipal sewage treatment plants, abandoned mines, and tailing dumps. Many of these sources have made substantial effort to establish cleaner operating procedures within the last 25 years; however, a great deal of contaminant input occurred prior to these upgrades and potential effects to sturgeon are unknown. Cominco has been operating since 1906 (MacDonald Environmental Sciences Ltd. 1997). However, over the past 25 years, the industry has initiated a long-term program to modernize and expand its operations at the Trail plant. Some of the major improvements include an effluent treatment plant, zinc electrolyte stripper, mercury removal plant, drainage controlsystem, heat exchanger, elimination of phosphate-based fertilizer plant, and a slag containment facility. These modernization projects have significantly reduced loading of metals to theColumbia River. Accidental discharges currently comprise the majority of contaminant inputs. Between January 1987 and January 1993, there were a total of 56 spills from ComincoLtd., into the Upper Columbia River. These spills released multiple tons of compounds containing sulphuric and phosphoric acid, zinc (various forms), gypsum, mercury, copper sulphate, ammonia, coal dust, furnace and compressor oils, sodium bisulphite, phosphate, ammonium sulphate, arsenic, cadmium oxide, chlorine, lead, slag, oxide dust, and various undetermined solutions.

Exposure to contaminants has been suggested to cause direct mortality of sturgeon larvae. Kruse and Scarnecchia (2002) suspected contaminant exposure (copper and the PCB Aroclor 1260) led to decreased survival of white sturgeon eggs. Sand-sized water-granulated fumed slag released from the Cominco Ltd. (now Teck Metals Corporation) lead and zinc smelter in Trail, British Columbia is distributed throughout the Roosevelt Reach, but primarily in the upper portion with a major depositional area at Marcus (CH2M Hill and Ecology Environment, Inc. 2006). Slag contains elevated levels of several trace elements, such as arsenic, cadmium, copper, lead, and zinc (Majewski et al. 2003). Preliminary acute toxicity studies with larval (30 dph) white sturgeon indicated LD50’s occurred at much lower concentrations of copper (3.1-4.9 μg/L) than similar aged rainbow trout (USFWS 2008). However, Vardy et al. (2011) reported that chronic concentrations (LC20) for white sturgeon larvae (up to 66 dph) exposed to copper (5.5 μg/L), zinc (112 μg/L), and cadmium (1.5 μg/L) were similar to other sensitive salmonids. Smelter effluent which contained lead (mean=21.6 ug/L at 100%), zinc (mean=166 ug/L at 100%), copper (mean=2.5 ug/L at 100%), and cadmium (mean=2.55ug/L at 100%) was lethal to white sturgeon larvae (11-14 and 32-35 dph) at high effluent concentrations of 100% and 50%, but at low concentrations (1%) mortality did not differ significantly from controls (Bruno 2004).

While there may be some direct mortality from exposure to metals, the annual catch of relatively large numbers of post hatch sturgeon in the Roosevelt Reach suggest that acute toxicity may not be a root cause of recruitment failure. However, contaminant exposure may result in sublethal effects that influence survival of sturgeon during early life stages. Exposure to elevated levels of copper from slag deposited throughout the upper Roosevelt Reach may impair sensory function and behavior of larval sturgeon. Exposure to copper has been shown to impair the olfactory system of coho salmon O. kisutch and steelhead (Baldwin et al. 2003; Sandahl et al. 2007) and larval zebrafish Danio rerio experienced damage to peripheral mechanosensory (lateral line) cells when exposed to copper (Linbo et al. 2006).  Sensory impairment may reduce the ability of larvae to locate food, ultimately resulting in starvation, or could result in an increase in searching behavior or reduced growth and condition, both factors that could potentially increase predation risk. Contaminant exposure may also alter a sturgeon’s ability to detect or respond to predation risk: coho salmon exposed to copper (>2.0 μg/L) did not initiate “predator avoidance behaviors” (Sandahl et al. 2007).  Heavy metal contamination in the upper Roosevelt Reach may also reduce the variety and abundance of food available to first feeding white sturgeon larvae. Copper and Zinc can negatively impact benthic macro-invertebrate diversity and abundance (Roch et al. 1985; Clements 2004).  Habitat depauperate in suitable forage could, in concert with sensory/behavioral impairment, severely limit larval white sturgeon survival.  Recruitment of sturgeon in the Transboundary Reach may thus be dependent upon successful dispersal of larvae to nursery habitats downstream of the primary slag depositional areas although more research is required to map the spatial distribution of slag as well as evaluate exposure effects of this substance on the early life stages of sturgeon.

Concern has also been raised about the physical effects of slag on sturgeon free embryos and larvae since slag particles are glass-like and very angular (CH2M Hill and Ecology Environment, Inc. 2006) and contact with slag could result in physical trauma. Evidence of early larvae incidentally ingesting slag particles (attached to prey) has been confirmed through the examination of the gut contents of the plankton net catch (Howell and McLellan 2011) (Figure 23).  Parsley et al. (2010) examined the gut contents of 37 hatchery origin juvenile white sturgeon captured by the LRSRP in upper Lake Roosevelt (rkm 1,120 to 1,170) that had been at large for 1–4 growing seasons and found that 78% contained slag particles. Histological examination of the digestive tracts indicated significantly greater chronic inflammation relative to controls (fish reared without exposure to ingestible substrate). It is unknown if the inflammatory response would occur in sturgeon ingesting inert sand-sized substrate or if it results in reduced survival, growth, or condition. The relatively high survival, growth, and condition of hatchery sturgeon in the Transboundary Reach (discussed above) suggest that it does not.

Figure 23. Granulated industrial slag particle found in the gut of a larval sturgeon. A) Stage 45 individual (19.9 mm TL) captured in a benthic plankton net. B) Left-lateral view of excised digestive tract; prey items and slag/sand grains can be clearly seen. C) Prey items and slag/sand grains removed from stomach. D) Detail of the slag (left) and sand (right) grains. Taken from Howell and McLellan, in review.

The effects of contaminants on older life stages are unknown at this time. White sturgeon are long lived, and thus they have greater risk of negative effects due to contaminants as a result of bioaccumulation (Beamesderfer et al. 1995). Exposure to some contaminants has been suggested to reduce reproductive potential of white sturgeon (Feist et al. 2005). Kruse and Webb (2006) indicated that copper can bioaccumulate in the eggs of upper Columbia River white sturgeon. As discussed above, copper can have both acute and potentially sublethal effects on white sturgeon early life stages that may result in low survival. Hatchery sturgeons from the Roosevelt Reach were provided to the USFWS in 2008 and 2009 for an analysis of contaminant burden; however, ongoing litigation has prevented public release of the results. Additional work is needed to determine the patterns and rates of contaminant bioaccumulation by sturgeons in the Transboundary Reach.

Critical habitat

The availability of suitable substrate for the hiding phase of development has been implicated as a potential factor limiting recruitment of white sturgeon in the Roosevelt Reach. Fine substrates, including slag, filling interstitial spaces may reduce available habitat for sturgeon free embryos during their hiding phase.  Brannon et al. (1985) noted that substrate composition may influence the settling response of free embryos such that coarser substrates provide more suitable cover for the hiding phase than fines. McAdam (2011) found in a laboratory study that free embryos hid immediately when provided coarse substrate, whereas over sand they entered the drift suggesting free embryo drift was indicative of poor hiding habitat. Gravel was identified by Bennett et al. (2007) as the preferred hiding habitat of white sturgeon free embryos.   In the context of the Roosevelt Reach, the relatively low catch rate of early free-embryos relative to first-feeding larvae in plankton net catches indicates that substrate suitable for the free-embryo hiding phase is available. However, there is a need to undertake comprehensive sediment facies mapping of the upper Roosevelt Reach, in order to quantify the availability of this and other critical habitats.

CONSERVATION AQUACULTURE

The Upper Columbia White Sturgeon Conservation Aquaculture Program is a critical component of the UCWSRP with the intention of preserving the remaining demographic and genetic diversity of the transboundary population and rebuild the natural age-class structure (UCWSRI 2002, Recovery Plan Measure 5.5.3).  The program is particularly critical to Canadian UCWSRI members, as white sturgeon are listed as endangered under the Species At Risk Act (SARA) in Canada.  The Canadian National Recovery Strategy (NRTWS 2007) has identified aquaculture as a priority activity to protect the upper Columbia River white sturgeon population in the recovery strategy; “prevent extirpation of white sturgeon in each of the four identified populations [including the upper Columbia River Transboundary Reach population] by preventing net loss of reproductive potential”. 

Conservation aquaculture programs were established in British Columbia and Washington in 2001 and 2003, respectively. Collectively, the programs have released a combined total of 118,412 juvenile white sturgeon into the Transboundary Reach between 2002 and 2011 (Figure 24; Table 2). 

Figure 24.  Number of hatchery juvenile sturgeon released in to the Transboundary Reach by brood year.  Fish were sourced for rearing by direct gamete take (DGT) from broodstock collected in British Columbia (BC) and Washington (WA) and by wild larval collection (WLC).

Table 2. Release summary for hatchery reared sturgeon into the Roosevelt Reach of the Columbia River by the LRSRP conservation aquaculture program.

The Washington program began in 2003 when surplus juveniles from the British Columbia program were transferred to WDFW’s Columbia Basin Hatchery (CBH) for rearing and to act as a failsafe group.  In 2004 and 2005, fertilized eggs and larvae were transferred from Canada to CBH where they were successfully reared and subsequently released (Howell and McLellan 2005, 2006).  In 2006 the LRSRP implemented a full-scale white sturgeon conservation aquaculture program that included all aspects of husbandry from broodstock collection and spawning to rearing and subsequent release (Howell and McLellan 2008).  That year, an interim broodstock holding facility was developed at WDFW’s Sherman Creek Hatchery (SCH) and pre-spawn adults were collected from near the documented spawning area at Northport, WA (Figure 25).  Adults were transferred to SCH where they were successfully spawned and later released.  The resulting embryos were transferred to CBH where they were again successfully reared for release in 2007. 

Figure 25.  Overview map of key sites related to LRSRP conservation aquaculture.

The LRSRP aquaculture program subsequently operated in this manner until 2011 when the program suspended direct gamete take in favor of collecting naturally produced larvae for rearing and stocking purposes.  This shift was motivated by the following: 1) recent research demonstrating that lake sturgeon offspring produced from direct gamete take were more related and exhibited lower genetic diversity than offspring produced from larvae collected while dispersing from spawning areas (Crossman et al. 2011); 2) collection of naturally produced eggs and post-hatch live stages for conservation aquaculture purposes was identified as a potential option in the UCWSRP; 3) plankton net sampling as part of LRSRP early life history studies from 2004 to 2008 indicated that substantial numbers of post-hatch sturgeon could be collected alive and therefore potentially be reared in a hatchery environment; 4) broodstock collection would become more logistically challenging over time due to growth (i.e. length and weight) of the existing adult cohort; 5) concerns over the potentially deleterious effects of sampling procedures on broodstock fish (i.e. capture, transport, spawning).

The LRSRP initiated a pilot study in 2010 to collect post-hatch sturgeon and transfer them to SCH for rearing on river water.  A total 2,744 larvae were collected from the river between 11-25 July and transferred to Sherman Creek Hatchery for rearing.  Rearing was successful and 522 sub-yearling juveniles were released in to the Roosevelt Reach on 1 December 2010.  Based on the success of the 2010 study, broodstock collection was suspended in 2011 in favor of a full scale larval collection effort.  From 26 July – 2 August 2011 a total of 10,295 larval sturgeon were collected from the river and transported to SCH.  Rearing success in 2011 (34.9% survival to release) was substantially improved over 2010 (19.0% survival to release) and 3,598 sub-yearling juveniles were released into the Roosevelt Reach on 30 November 2011.

uring the 2004 LRSRP setline survey, only three hatchery sturgeon were captured in 162 overnight setline sets, whereas 225 hatchery sturgeon were captured in 219 overnight setline sets during the 2009 survey, dominating the catch ((Figure 26; Howell and McLellan 2007a; Howell and McLellan, in prep;).  Thus supplementation efforts are successfully restoring a more natural size structure.  Various survey efforts indicate that hatchery fish condition and growth is generally very good (Golder 2005a, 2006a, 2007, 2009; Howell and McLellan 2007a, 2007b, 2008, 2001, in review, in prep).  Indeed, as discussed above, VBG modeling based on mark-recapture data collected in the Roosevelt Reach indicate that growth during the juvenile phase is markedly greater than observed in other areas of the Columbia River downstream.  However, some spatial trends in fish condition and growth have been observed that may represent variation in habitat quality or density dependent effects.  In the Roosevelt Reach hatchery juvenile condition declines moving upstream towards the international border from the Marcus area (Figure 27) and this trend continues in the lower Keenleyside Reach but reverses such that fish condition is very good in the area immediately downstream from HLK Dam (Golder 2006a). 

Figure 26.  Length frequency distribution, length-weigh relationship, and relative weight of hatchery and wild white sturgeon captured between Gifford and the international border during the 2009 LRSRP setline survey.

Figure 27.  Relative weights of hatchery origin juveniles (23-127 cm FL) by capture location during various LRSRP surveys 2003-2009 (WDFW unpublished data).  The plot shows declining fish condition moving upstream from the Marcus area.

In response to these trends, the LRSRP has adapted its juvenile release strategy.  From 2004-2006, the LRSRP distributed hatchery releases among three locations (Northport, North Gorge, Nancy Creek; Figure 25).  Following initial observations that juvenile growth and condition were decreased in upstream areas of the river-reservoir transition zone, releases at Northport and North Gorge were suspended in 2007 and fish were instead released further downstream at the Kettle Falls Marina and Nancy Creek sites (Figure 25).  Since 2008, LRSRP release sites have been further limited to the Kettle Falls Marina location only (Figure 25).  Concerns over potential over-stocking have also led to reductions in the annual number of fish released into the transboundary area.  Beginning with BY 2008, annual target release numbers were reduced in the Keenleyside Reach and equalized with the Roosevelt Reach at 4,000 fish per area (Figure 24).

Formal analyses seeking to evaluate hatchery juvenile survival post-release have been limited.  Using catch data from both the Keenleyside and Roosevelt Reaches, Golder (2007) estimated survival of hatchery sturgeon to be 0.28 (0.11-0.54 95% CI) for the first 6 months post release and 0.88 (0.35-0.99 95% CI) between 2 and 5 years post release (Table 1). When viewed the context of the long juvenile phase of sturgeon, the very low precision of the Golder (2007) estimates limits their usefulness as inputs for modeling exercises attempting to project future rates of recruitment to the adult life stage.  Thus there is a need for more intensive and coordinated sampling efforts to capture sufficient numbers of fish to generate more precise estimates of survival.

PROPOSED LRWSCH 3-STEP PROJECT WORK PLAN 2013-2017

During the 2013-2017 funding period we intend to complete conceptual planning for a dedicated U.S. conservation white sturgeon aquaculture facility under the NPCC 3-Step Review Process (NPCC 2006-21).  Activities will include development of a master plan that includes a description of the regional significance of the project with a detailed background on current and historical status of biota in the project area, a Hatchery and Genetic Management Plan, a description of the upper Columbia River white sturgeon harvest objectives, a monitoring and evaluation plan, an appropriate and comprehensive environmental assessment, and a precise estimate of project cost (construction, operations, maintenance, monitoring).