Life History and Genetic Variability of Larval Lampreys in Interior of Alaska Rivers

Lampreys share many of the same habitats as salmonids in freshwater ecosystems, yet receive comparatively little management or research attention.  This paucity of information currently limits the development of management and conservation plans for lamprey species in Alaska.  For this research, we examined the species assemblage, distribution, relative abundance, life history, and habitat requirements of larval lampreys in the Chatanika and Chena rivers.  Sampling was conducted during the 2010 and 2011 growing seasons using a low voltage Model ABP-2 backpack electrofishing unit that is specifically designed for the collection of larval lampreys. Although it was believed that two lamprey species resided in this system (Arctic lamprey Lampetra camtschatica and Alaskan brook lamprey Lampetra alaskense), a combination of morphological, meristic, mitochondrial DNA haplotype, and multi-locus microsatellite genotype data indicated that the degree of genetic diversity in the populations sampled were low and that only a single species (Arctic lamprey) was present.  In both river systems, no lampreys were collected in upper river locations, where habitats were characterized as having primarily gravel, cobble, and small boulder substrates and swift flow (range, 0.11-0.53 m/s).  Middle and lower river sites all supported larval lampreys, with catch-per-unit effort of larvae ranging from 0.41 to 5.10 lampreys per minute electrofishing.  Habitats that supported larval lampreys were characterized as having predominantly silt or sand substrates with woody debris and slow flow (range, 0.0-0.1 m/s).  Based on combined length-frequency and statolith age analyses, an age-length key was developed and the age structure of larval lampreys was determined to range from ages 0 to 8.  Organic detritus comprised most of the diet ash-free-dry-mass (AFDM) of the gut contents of larval lampreys, averaging greater than 95% of the organic fraction of the diet.  Although assimilation efficiency was high (> 50%), gut fullness was low, suggesting that larval lampreys can effectively utilize a low-quality food source (organic detritus) that is consistently available in stream ecosystems.  Larval lampreys also exhibited very slow growth rates which, when coupled with cold water temperatures and a very short growing season (approximately 5 months in duration) in Alaska, results in a protracted larval period.  With the information collected during this study, our understanding of larval lampreys in interior of Alaska rivers has increased significantly, thereby allowing for the development of appropriate and science-based management and conservation decisions.