Improving larval sea lamprey assessment in the Great Lakes using adaptive management and historical records

Sea lampreys in the Great Lakes are managed by treating tributaries with lampricides that target the larval stage. A resource-intensive but imperfect larval assessment process (Quantitative Assessment Sampling, QAS) is currently used to determine which streams to treat annually. I developed an alternative assessment method (Rapid Assessment, RA) that requires fewer resources, and compared the costs and benefits of RA vs. QAS by conducting both methods on all wadeable streams requiring assessment in 2005 and 2006 and ranking streams for treatment priority. The use of RA resulted in more treated streams, and based on population estimates generated by QAS and by capture-recapture experiments, the use of RA would allow greater suppression of sea lampreys basin-wide. Assessment expenses could also be reduced through the incorporation of historical knowledge. Some tributaries are highly regular in their need for treatments, while others vary widely. I analyzed data collected from 1959-2005 using mixed-effects models to test for differences in recruitment and growth to age-1 between regularly and irregularly treated streams. Recruitment was twice as large in regular streams than in irregular streams, indicating that year class strength is established early in the sea lamprey life cycle. I found no consistent differences in growth to age-1 among categories of streams; however, a variance components analysis showed that Lake Superior streams that are treated irregularly also exhibit more irregular size at age-1 than streams treated regularly.