Diversity in migration, habitat use, and growth of Dolly Varden char in Chignik Lakes, Alaska

Abstract

Dolly Varden (Salvelinus malma) are a facultatively anadromous salmonid common around much of the north Pacific Rim, but little is known of the factors that determine their migration and life-history patterns. In the Chignik Lakes system on the Alaska Peninsula, Dolly Varden are the only large bodied resident fish species and use nearly all available aquatic habitats at different life stages. In addition, they are often the numerical dominant fish in both freshwater and estuarine habitats. I employed a multifaceted approach to understand variation in Dolly Varden migration timing, growth, habitat use, and variation in anadromy. By integrating daily counts of Dolly Varden ascending rivers and streams throughout the migratory range over a wide temporal scale, I determined upstream migration generally occurs earlier in southern stream and later in northern streams. Interannual variation in ascent timing in southern streams is correlated with sea-surface temperatures, while in northern streams it was not. Plasma insulin-like growth factor 1 concentrations indicate rapid summer growth in estuarine waters compared to freshwater lake habitats. However, the growth benefits of discrete sub-regions of the estuary vary by month. Muscle tissue stable isotope analyses of carbon and nitrogen indicate non-overlapping isotopic signatures of Dolly Varden captured at each estuary sub-region. Therefore there is behavioral spatial separation among estuarine Dolly Varden despite broadly similar body size and diet across the estuarine habitat. Finally, I employed otolith microchemistry (Sr/Ca, Ba/Ca) to evaluate the lifetime migratory history of 366 Dolly Varden captured throughout the watershed. Nearly all Dolly Varden migrate to sea at least once in their life, with most doing so at age four. However, after age four migration rates decline, to near zero by age seven. Fully resident individuals exist within marine-accessible portions of the watershed, and comprise almost 15% of fish over age six. These data demonstrate that Dolly Varden exhibit wide diversity in movement behavior among and within watersheds. These patterns change with ontogeny, and are likely shaped by the size-specific costs and benefits of alternative habitat use and resource availability. Analogous dynamics likely drive life-history diversity in many iteroparous, facultatively anadromous species.