Otolith Chemistry Reveals Complex Life History Patterns and Facultative Anadromy in Southwestern Alaska Dolly Varden

Loss of life history diversity is often implicated as a cause for population decline in anadromous fishes. Habitat loss or alterations often prevent studies of fishes where the entire suite of life histories is still present. In these cases we must resort to historical reconstructions or modeling to determine what life histories may have occurred in a given population or watershed. Therefore, population level assessments of life history diversity in undisturbed systems are rare. In the Chignik Lakes watershed of southwestern Alaska, Dolly Varden (Salvelinus malma) are the only large resident fish species, are abundant throughout the watershed, and are virtually unexploited. The small watershed, devoid of habitat alteration by humans, contains diverse habitats (e.g. two lakes, small streams, larger rivers, and a large estuary), all of which are accessible to anadromous Dolly Varden. The high habitat diversity and low species diversity of the Chignik Lakes watershed creates an ideal situation to study movement patterns and life history diversity, particularly with respect to the incidence of anadromy. In this study we address the prevalence and spatial distribution of anadromy using otoliths as a natural recorder of age and habitat use.  Otolith trace elemental signatures (Sr/Ca and Ba/Ca) from the core (natal) to the edge (recent) were analyzed to determine the fish’s migratory history (n = 149), as well as the prevalence of maternal anadromy. Preliminary results indicate a wide variety of migratory histories, from complete freshwater residency to anadromy in the first year of life. Previous studies of coastal Dolly Varden populations predict high levels of maternal anadromy, however, in our study maternal anadromy in the season prior to spawning was only found in 56% of individuals. Seventeen combinations of age at first migration and total number of migrations were present among our collections, indicating a wide range of migration strategies. Additionally, we are using the chemistry of water samples collected throughout the watershed and genetics to determine early life rearing areas for fish captured in mixed stock areas. These results serve as the backbone for further studies of the mechanisms that produce and maintain diversity in anadromy of Chignik Dolly Varden; establishing a model system by which life history diversity could be predicted for other facultatively anadromous species or populations.