Evaluating an alternative larval assessment and stream selection method
The budget of the lamprey control program must be divided among several areas, including larval assessment and control. Assessment is conducted annually on a subset of streams to determine which streams will require chemical treatment in the following year. This assessment involves quantifying larval lamprey density and length composition at the time of survey, and applying regional growth and metamorphosis models to predict the number of larvae that will transform into parasitic juveniles in the following year. Streams are ranked in order of predicted number transformers killed per treatment dollar spent, and streams are treated in rank order until the control budget is exhausted.
The GLFC currently allots a considerable amount of money to assessment in an attempt to reduce the uncertainty surrounding estimates of larval abundance. However, a great deal of uncertainty still exists in the abundance estimates and predictions of transformers due to variations across streams and across years. One option to reduce uncertainty surrounding which streams are the most important to treat is to spend more money on more rigorous assessment in order to be more confident in the larval abundance estimates. However, more money spent on assessment reduces money available to actually treat streams. An alternative, somewhat counterintuitive, strategy is to spend minimal money on assessment and accept a high level of uncertainty surrounding predictions of larval and transformer abundance, but then have the funds available to treat more streams and theoretically kill more lamprey. This alternative strategy is the approach used in this research.
The goals of this project were to develop an alternative method of larval assessment and stream selection and to compare its effectiveness to the current assessment method by:
- Implementing the new assessment method (known as RA) throughout the Great Lakes basin using an adaptive management approach;
- Comparing the rank list of streams that would be treated as a result of each assessment method;
- Comparing the number of larvae and transformers killed as a result of making stream treatment decisions based on each method using population estimates generated from the surveys themselves;
- Using mark-recapture studies to further compare the number of larvae and transformers killed in a subset of streams that would be ranked for treatment based on only one assessment method.
This study is ongoing, but
after two years of conducting RA and one year of mark-recapture
studies, it appears that the use of RA results in higher numbers of
larvae and transformers killed than the use of current assessment
methods.
