In Part: While initial results of the oxygenation of North Twin Lake are promising, the ISRP believes that additional time is needed to fully characterize the costs and benefits of this fishery enhancement effort. One to two years of data may not be enough to adequately characterize the whole-lake response to a restoration at this scale, especially in view of several confounding factors identified below, which occurred during the initial phase of the study. For this reason we feel that proceeding with an oxygen generation plant for both lakes is not scientifically justified at this time. Provided that sufficient oxygen can be obtained from local suppliers for North Twin, additional data should be collected comparing oxygenated North Twin versus non-oxygenated South Twin. Project staff should obtain statistical assistance to determine the point at which results clearly demonstrate that oxygenation is cost-effective before committing to oxygenating both lakes on a regular basis.

Qualified: In the last review, the ISRP requested specific results indicating that external nutrient loading was being reduced, but these results were not included in the proposal or in the last annual report. An update should be added to the proposal quantitatively summarizing the reduction of discharge into the lakes. Has the concept of large tanks that are periodically pumped and hauled away been considered, instead of using septic fields that eventually drain into the lakes?

1. Purpose: Significance to Regional Programs, Technical Background, and Objectives

The project sponsors cite that the project goals follow those in several subbasin plans including the Upper Columbia and Columbia River plans, the CCT Fish and Wildlife Management Plan, and the MERR document guidelines when monitoring and evaluating fish planting strategies. The project is adequately described in the context of regional trout enhancement efforts. In the Annual Report for 2010 (April 2011), one of the goals of this project is stated to be enhancement of the population of interior rainbow ("redband") trout in both North and South Twin lakes so that they can support a sustainable fishery without the need for hatchery augmentation. However, at present both lakes are stocked with hatchery rainbow trout, and the decision to switch from redband trout to rainbow trout needs to be included here.

The objectives (below) are straightforward and measurable - when linked with deliverables.

OBJ-1:Improve the trout fishery in North and South Twin Lakes

OBJ-2:Oxygenate North and South Twin Lakes

 

2. History: Accomplishments, Results, and Adaptive Management (ISRP Review of Results)

The proposal itself presents several graphs pertaining to limnological investigations and net captures, but figure captions and an adequate discussion of the data they portray are needed. More details are in the 2010 annual report. Results indicate that the two lakes are similar in some respects but somewhat different in others. For this reason, the response of fishes and aquatic invertebrates to the proposed oxygenation of South Twin Lake, which was not oxygenated in the past, cannot be predicted with certainty. Results do show, however, that oxygenating North Twin Lake has created conditions more suitable for benthic invertebrates and that trout now use the cool hypolimnion during warm summer months.

It would be easy to assume that increased angler catch rates with oxygenation would make North Twin Lake a better place to fish; however, Table 6 and Table 7 suggest that catch per unit effort in South Twin exceeded that of North Twin in some months, even with the higher carryover rate of trout in North Twin. This raises the question of how stocking has been carried out in the lakes and how hatchery supplementation has influenced harvest during the initial period of oxygenation. It also raises the more general question: will the relatively high cost of oxygenation, especially if the oxygen generating plant is constructed, result in enough fish and/or enough larger fish to justify the expense?

The work in 2009, 2010, and 2011 clearly showed that once North Twin Lake was oxygenated, fish utilized the hypolimnion and survived at a higher rate than at South Twin Lake. Differences were statistically significant. As a result of the success at North Twin Lake, stocking strategies changed which confounds the growth rate and condition factor data collected during the study. Angling pressure, catch-per-unit-effort, survivability of marked release groups of trout, growth and condition of fish have been measured to establish if goals of project have been met. As a result stocking numbers have been reduced by 60%, but the size of fish caught has increased from 230g to 435g, while reducing CPUE by only 10%. The percentage of carryover fish increased by five times and angler satisfaction has increased.

A short paragraph on adaptive management only indicates that the management changes which have occurred have been adjustment of stocking numbers in response to oxygenation effects. However, during the project site visit we were told that a switch in type of fish planted from redband stock to triploid rainbow occurred because the redbands were emigrating from the lakes. This discussion plus the rationale for the switch could/should also be added as an example of adaptive management.

3. Project Relationships, Emerging Limiting Factors, and Tailored Questions for Type of Work (hatchery, RME, tagging)

In general, the project sponsors have made progress in addressing the questions posed by the ISRP. Additional research to understand the limnological processes in the two lakes will be very helpful. One emerging factor that deserves more discussion is the presence of non-native largemouth bass and golden shiners in the lakes. What is being done to monitor the effects of oxygenation on these species?

Several long-term issues are of concern: (1) what are the long-term effects on macroinvertebrates and will changes effect fish growth, and (2) hypolimnetic anoxia is a result of sediment oxygen demand (SOD) and now that external nutrient loading has been reduced, will SOD be reduced as the hypolimnion continues to be oxygenated and will future oxygen supplementation continue to be required? Some evidence indicates that SOD will be reduced, but this needs to be monitored and documented for a longer period of time. Mercury analyses from the two lakes have been confusing to date. More information is needed over time. Another issue of concern is how will the oxygenation affect uptake of methylmercury in fish. Present levels are below EPA cautionary guidelines.

4. Deliverables, Work Elements, Metrics, and Methods

The project should consider expanding the number of sites for continuous oxygen measurements in the lakes. According to the descriptions of the sampling program in MonitoringMethods.org, only a single site from each lake will be continuously monitored. More sampling locations are needed, especially if trout prefer different places in the lakes over the course of a year.

4a. Specific comments on protocols and methods described in MonitoringMethods.org

The methods published in MonitoringMethods.org have sufficient detail for the most part but should also include the stocking regimes for the two lakes, including species and size at release. Additional details on the benthic and plankton surveys would also be helpful.

Modified by Dal Marsters on 4/17/2012 2:55:56 PM.