In 2011, Cook Inlet RCAC submitted a proposal to the Kenai Peninsula Borough (KPB) to address categories of research needs expressed by the Cook Inlet beluga whale Conservation Plan, as well as in the KPB Cook Inlet Beluga Whale Research Study. The intent of those initiatives is to identify potential threats that might be impeding recovery of the endangered Cook Inlet beluga whales. Our proposed study specifically addressed biological diversity, abundance, and hydrocarbon contaminants of potential beluga whale prey items in known beluga winter habitat areas. Our proposal, Oil-related contamination and prey availability in winter habitat of Cook Inlet beluga whales (Delphinapterus leucas), was a collaboration between Cook Inlet RCAC, Mote Marine Laboratory, and the Alaska Department of Fish & Game (ADF&G). Although information about beluga summer distribution, habitat attributes, and prey availability was reasonably available, due to the harsh conditions under which whales must survive and forage in winter, the Conservation Plan noted a need to better understand winter prey availability and diversity, as well as contaminant levels. This study will provide such information to managers and scientists.
The overall goals of our proposed study were to (1) measure contaminants in potential Cook Inlet beluga whale winter prey species and assess data in the context of environmental conditions, and (2) assess biodiversity and relative abundance of potential winter prey in two general areas where beluga whales have been observed feeding in either late fall or winter.
Due to ice conditions in winter, sampling took place in late fall and early spring. Benthic trawl surveys were conducted in April and October 2012 from the research vessel Pandalus and opportunistic sampling for potential pelagic prey was conducted in April from the Kahtnu. Thirty four taxonomic groups were captured in the bottom trawl and eleven in the mid-water trawl. The mean biomass density of non-sessile animals in April was dominated by starry flounder (Platichthys stellatus), eulachon (Thaleichthys pacificus), sevenspine bay shrimp (Crangon septemspinosa), Pacific tomcod (Microgadus proximus), and Pacific sandfish (Trichodon trichodon). The dominance of Starry flounder was from one station in the southeast part of area. In October, the catches were dominated by starry flounder, spiny dogfish (Squalas acanthias), jellyfish (Cyanea sp.), sevenspine bay shrimp, Pacific halibut (Hippoglossus stenolepis), walleye Pollock (Theragra chalcogramma), and Pacific tomcod.
Our data indicate that the biomass and individual sizes of benthic fauna available to beluga whales are very low in much of the sampled area, although both are greater in the southeast study area near the lower Inlet, and the biomass likely declines over the winter. Given the small body sizes and apparent low density of benthic fauna in much of the area, belugas may not be acquiring a maintenance ration during winter, consistent with previous observations that belugas in the spring have much lower fat reserves than after feeding on abundant summer eulachon and salmon. Analyses of hydrocarbons in selected prey tissues showed non-detectable levels, in contrast to earlier analyses of their summer prey. Our study results provide some of the only information available on winter habitat and prey and will inform other Cook Inlet beluga whale life history studies and the recovery team, as well as enhance decisions by managers.
A report was presented to the Kenai Peninsula Borough in early 2014 and a presentation provided at a KPB-sponsored Cook Inlet Beluga Whale Workshop. To download the Assessment of the Prey Availability and Oil-related Contaminants in Winter Habitat of Cook Inlet Beluga Whales report, click here. For more information on NOAA Fisheries Beluga Whale Research and Reports, click here.
