Project Description
NMML, in conjunction with the Marine Mammal Division of the SWFSC, will conduct a medium-format aerial photographic survey of Steller sea lions in Alaska. This survey will provide counts of either pups (young of the year) or non-pups (adults and juveniles) used to track the trends in population abundance for the endangered western stock of Steller sea lions. In FY08, NMML will conduct a non-pup survey in the range of the eastern and western stocks in Alaska during June and early July 2008. NMML will work cooperatively with the Alaska Department of Fish and Game regarding survey effort within the range of the threatened eastern stock in SE Alaska.
Issues & Justification
Nutritional limitation has been presented as one hypothesis for mediating survival of juvenile and fecundity of adult female Steller sea lions through ecosystem changes or competition with fisheries. It is critical that NMFS monitor the status and trend of the western stock of Steller sea lion to obtain a complete understanding of potential responses to changing environmental conditions. One way NMML monitors the status and trend of the western Steller sea lion population is by counting pups (young of the year) and/or non-pups (adults and juveniles) on haul-out and rookery sites from photographs taken during aerial surveys. Medium-format aerial photographic surveys also provide information on the age/sex structure of the non-pup population which is useful in demographic modeling. A subset of all sites has been consistently counted since the late 1970s; these index, or trend, sites are useful for assessing population trend. Pup production is also assessed using medium format aerial surveys; pup surveys are conducted approximately 2 weeks later than non-pup surveys to insure that they occur after the vast majority of pups are born. Counts of pups and non-pups are necessary to monitor recovery of the western Steller sea lion population and the survey is a Priority 1 research item in the draft Recovery Plan. Failure to meet this objective would mean that the agency is unable to provide an up to date population estimate such that previous estimates must be used for management decisions.
Goals
- Conduct an aerial survey during June to count non-pup Steller sea lions on haulouts and rookeries throughout their range in Alaska (this was attempted in both FY06 and FY07, but not completed because of weather and logistical difficulties; this will be done again in FY08)
- Conduct an aerial survey during late June-early July to count Steller sea lion pups on rookeries and large haul-outs throughout their range in Alaska (this will be done in FY09)
Methods
Medium format (MF) surveys are conducted with a high-wing aircraft capable of flying at relatively slow speeds and taking photographs of sea lions on rookeries and haulouts with a belly-mounted medium-format cameras (i.e., vertical orientation, with motion compensation). To count non-pups, surveys are conducted from 1000-1600 each day (peak time for sea lions on-land) in mid-June. All haul-out and rookery sites are photographed and Steller sea lions are counted and assigned to one of 4 age/sex groups: juveniles, adult females, sub-adult males and adult (territorial) males. Trends in non-pup abundance are assessed by analysis of counts at groups of trend sites that have been consistently surveyed since the late 1970s (N=96) or 1990 (N-173). Age-sex structure of the population is used in demographic modeling studies.
To count pups, surveys are conducted in late June-early July after the vast majority of pups have been born. Only rookery and large haul-out (where more than 10 pups have been counted in previous surveys) sites are photographed. Aerial pup production estimates will be compared with ground counts (where available) made the same year.