Project Description
Permanently marking Steller sea lion pups with an individual identification mark and then resighting those animals throughout their life forms the basis for this project. Pups at selected rookeries in the western stock in Alaska are hot-branded for permanent identification during June and July each year. Resight effort by ship or land-based personnel is used to determine age/sex/cohort/rookery specific survival, as well as age at first reproduction and reproductive rates. Since 2000, NMML has branded pups in Alaska at Ugamak, Marmot, Sugarloaf, Seal Rocks, and Fish Islands in the western stock. This is part of a coordinated branding-resighting program with other NMML-funded projects in California, Oregon, and Russia, with the Alaska Department of Fish and Game (ADFG) in SE Alaska and Prince William Sound, and with the Alaska SeaLife Center in the Chiswell Islands. The NMML alternates years such that particular sites are only visited every other year to reduce disturbance. There was no marking of pups by NMML in either 2006 or 2007.
Issues & Justification
The determination of basic vital rates is fundamental to understanding any potential cause of the Steller sea lion decline in Alaska and provides a mechanism to monitor their recovery. These data can only be obtained by following individual sea lions over long periods of time (longitudinal studies). Mark-recapture information is the best way to determine survival rates of the population by sex, age, region, and cohort to identify and determine which segment has been most affected by changing environmental conditions. The collection of basic life history attributes of Steller sea lions in Alaska is one of the top priorities of NMML Steller sea lion research and requires a long term commitment to marking and resighting those same animals as they become reproductive.
Goals
- Brand ~250 pups (total at all rookeries) per year at two of the following rookeries: Ugamak Island, Marmot Island, Sugarloaf Island, and Seal Rocks.
- Conduct resight effort on dedicated cruises and during other ship or land-based field work (e.g., field camps)
- File cruise reports within 1 month after completion
- Produce field camp data report within 4 months of completion of field work
Methods
In 1987-88, NMML branded a total of 800 pups at Marmot Island. Branding studies were reinitiated in 2000 at Marmot and Sugarloaf Islands, and in 2001 at Ugamak, Fish, and Seal Rocks in Alaska. In 1989, over 700 Steller sea lion pups were branded on 4 rookeries in the Russian Kuril Islands: Brat Chirpoyev, Lovushki, Srednego, and Raykoke. Branding activities started again in Russia in 1996 at Antsiferov, but were expanded to 7 rookeries in 1998. NMML also began branding eastern stock pups at Rogue Reef, Oregon in 2001 and at St George Island, California in 2002. The ADFG re-initiated branding studies in 2001 (after branding 799 pups on Forrester Island in 1994-95) in the range of the eastern stock at Forrester, Hazy, White Sisters, and Graves Rock. The Alaska Sea Life Center also brands pups annually at the Chiswell Islands rookery in Prince William Sound. All researchers in Alaska use the same techniques and marking procedures. Pups are branded with individually identifiable numbers and letters on their left shoulder and then observed in subsequent years to determine vital rates. Observers are stationed at some of the branding sites in subsequent years to monitor sea lion survival and determine female fecundity.
Brand-resight effort occurs on dedicated cruises throughout the spring and summer months in order to maximize opportunity to obtain fecundity data, as well as by personnel living in field camps during the breeding season, during the pup enumeration/branding/condition cruise, and at any other time personnel are in the field (e.g., juvenile/adult capture trips). During brand-resight cruises, numerous rookeries and haulouts are visited to look for branded animals and to collect scat for food habits analyses. Survival rates by sex, age, location, and cohort are estimated (along with the probability of resighting) using the program MARK developed at Colorado State University. This is an ongoing long-term study and is expected to last at least 10 years. A considerable commitment of time and energy over many years from both the NMML and ADFG is required. These studies are a continuation of several initiated in the 1970s by the ADFG and NMML, and were recommended by the Steller Sea Lion Recovery Team peer review panels. Branding of sea lions on rookeries in Alaska did not occur in 2006 and only was completed at the Chiswell Islands in 2007 due to permitting restrictions. Plans are underway to reinitiate some branding during the summer of 2008.