Changing Seasonality of Arctic Hydrology Disrupts Key Biotic Linkages in Arctic Aquatic Ecosystems

Arctic grayling (Thymallus arcticus) are an important circumpolar species that provide a model system for understanding the impacts of changing seasonality on arctic ecosystem function. Grayling serve as food for other biota, including lake trout, birds and humans, and as top-down controls in stream ecosystems suggesting that changes to their populations will have effects that reverberate throughout the arctic ecosystems. Our objective is to assess how shifting seasonality of Arctic river hydrology may disrupt key biotic linkages within and between lake and stream components of watersheds on the North Slope of the Brooks Mountain Range, Alaska. Because Arctic tundra streams will often freeze solid in the winter, many resident grayling populations are dependent on deep lakes and large rivers for overwintering habitat. We hypothesize that grayling migration timing into overwintering lakes may be later due to a longer open water season, but could be disrupted by drought due to increased fall variability in discharge. In turn, a shorter overwintering season will reduce lake trout predation on migrating grayling, which we hypothesize rely on the seasonal inputs of stream nutrients, in the form of migrating grayling, into these oligotrophic lakes. In 2010, we undertook new surveys of grayling migration dynamics using Passive Integrated Transponder (PIT) tags, coupled with stream-side antenna units to monitor grayling migration timing into winter lakes. Initial results indicate day length may prime grayling migration readiness, but that flooding events may be the cue the grayling use to initiate migration. Many fish used high water in the stream as an opportunity to move into lakes. Stream and lake derived stable isotopes also indicate that lake trout rely on these seasonally transported inputs of stream nutrients for growth. Improved understanding of these processes will advance our general understanding of the role of animals in ecosystem dynamics, life-history evolution and ecosystem management.