Factors Influencing the Abundance, Distribution and Availability of Forage Fish to Predators in Nearshore Marine Ecosystems

During the past decade, our research has focused on understanding predator and prey distribution relative to marine habitat features in nearshore ecosystems, particularly glacial fjords in the Gulf of Alaska. These estuarine fjord systems are rapidly changing as a result of climate change, and they are host to a variety of piscivorous predators, including species of management concern such as the Kittlitz’s murrelet. We employed an ecosystem approach to sampling nearshore waters by measuring predator densities with respect to several important underlying factors that influence their dispersion, including a variety of oceanographic parameters and the abundance of phytoplankton, zooplankton and forage fish. Here we present an overview of our findings on the distribution and habitat relationships of important forage species including euphausiids, lanternfish, capelin, Pacific herring, Pacific sand lance, eulachon, and walleye pollock. In glacial-marine systems, freshwater inflow from glaciers is a structuring feature that strongly influences local temperatures, stratification and sedimentation. Phytoplankton are limited by light availability in surface waters near turbid glacier outflows, but zooplankton and forage fish are often abundant. Forage fish species differ in their response to habitat features. Some species, such as juvenile walleye pollock, exhibit high tolerance to oceanic conditions and are widely distributed whereas others, such as capelin and lanternfish, show greater preference for glacially modified waters and are therefore more limited in their distribution within fjords. Future work will investigate the role of glacier-derived nutrients to nearshore marine food webs in the Gulf of Alaska.