Project Description
This project was designed to investigate whether cooperative biomass assessments and surveys can be an effective way to manage fisheries at the local scales that are important to predators such as Steller sea lions. The long-term vision is that one or more commercial fishing vessels conducts hydroacoustic surveys in specific areas of Steller sea lion critical habitat prior to commercial fishing beginning in these areas. Biomass estimates from these surveys would then be used to set a quota for the area surveyed that does not jeopardize the foraging success of Steller sea lions in the area. To design an effective cooperative biomass survey, we need to know whether the survey data collected by commercial vessels is of sufficiently high quality and resolution, and sufficiently low variability to conduct a biomass assessment at local scales. We also need to know where the fishery would be expected to operate and where Steller sea lions rely on pollock for foraging. We will address these information needs by conducting replicated wintertime acoustic surveys of pollock in the central Aleutian Islands from a NOAA acoustic research vessel and from commercial vessels equipped with scientific quality ES60 echosounders. We will also collect data on sea lion distribution and diet during the pollock surveys. The sea lion data will indicate the relative importance of haul-outs near pollock spawning areas and near fished areas.
Issues & Justification
The Alaska population of Steller sea lions has declined by more than 80% since the 1970s (Loughlin 1998). In 1997 the western population (west of longitude 144Aø W) was listed as endangered under the Endangered Species Act (ESA). In November 2000 the ESA consultation prepared by the National Marine Fisheries Service (NMFS) concluded that the Alaska groundfish fishery posed a threat to the recovery of the Steller sea lion population (NMFS 2000). A suite of protection measures was put in place to mitigate potential competition between fisheries and sea lions. These measures included trawl exclusion zones around sea lion rookeries and haulouts to protect sea lion critical habitat (National Research Council 2003). Implicit in the designation of the trawl exclusion zones, which are 10- to 20-nmi in radius, is that competition between fisheries and sea lions is expected to occur at local scales. Global control rules are used to manage rates of fishing mortality at the basin scale (i.e., Bering Sea or Gulf of Alaska), and thus help preserve sufficient prey for sea lions at the large scale. However, there remains concern that local fisheries effects, such as localized depletion or disruption of sea lion prey could impact sea lion foraging success. Thus, advances in Alaska groundfish fisheries management with regard to their impacts on Steller sea lions require new management strategies for assessing groundfish abundance and allocating catch at local scales.
Goals
- Determine the spatial and temporal variability of pollock aggregations in the Aleutian Islands in winter
- Describe the spatial distribution of sea lions on haul-outs with respect to pollock aggregations
- Examine the diet of sea lions (scat analysis from haulouts) in winter in the Aleutian Islands with respect to the distribution of pollock aggregations
Methods
Aerial surveys of Steller sea lions in the Aleutian Islands will be conducted twice during this study using an aircraft equipped with a belly-mounted digital camera (Canon 1DS Mark II or Nikon D1). Survey methods will be the same as those described in Fritz & Stinchcomb (2005) used for the breeding season surveys used to monitor population trend. Non-breeding season counts are useful for relative distribution within a year in the Aleutian Islands as well as to assess variation in sea lion response by age or sex. The number of adult and juvenile (non-pup) Steller sea lions on each terrestrial haul-out will be counted off photographs; sea lions will be assigned to one of the following age and sex categories: adult males, sub-adult males, adult females, and juveniles (of both sexes). The survey will cover terrestrial haul-outs from Amukta Pass (~172AøW) to Amchitka Pass (~180AøW), a larger survey area that encompasses the focused area of the cooperative pollock survey. The sea lion aerial surveys will be conducted in mid-March and early April in order to be synchronous with the pollock survey. Replicate surveys are necessary in order to collect information on variability of site usage over short time intervals due to changes in the weather, as well as distributions of fish and fisheries. Covariates such as wind speed and direction will be evaluated to determine their effect on haul-out patterns and variability. We propose to analyze sea lion distribution at haul-outs at a variety of scales, including individual sites, sums and proportions (by age-sex category) within 1, 2, and 4Aø longitude blocks, and sums and proportions on the lee and windward sides of islands. This will enable us to begin a detailed examination of the relative effects of weather, fish, and oceanographic variables on the use of terrestrial haulouts by Steller sea lions in the central Aleutian Islands in winter.
Samples of Steller sea lion scat from terrestrial haul-outs will be collected to obtain information on diet. Scats will be collected and analyzed as described by Sinclair & Zeppelin (2002) and Zeppelin et al. (2004). Researchers approach the haul-out from the water by skiff, go ashore, and spook the animals off the land into the water as slowly and gently as possible making all attempts to avoid a stampede response. Scats will initially be stored in plastic bags, frozen when returned to the lab in Seattle, and processed using standard procedures to separate bones and other prey hard parts used to identify individual species consumed (Sinclair & Zeppelin 2002).