Population Status and Food Habits of Steller Sea Lions in Oregon

Identification Information

Citation

Originator: Brown, Robin F., Susan D. Riemer, and Bryan E. Wright

Publish Date: 2002

Online Link: None

BPA Project #:

Contact Information

Agency: Oregon Department of Fish and Wildlife

Name: Cedric Cooney

Job Position: Natural Resources Data and Systems Manager

Telephone: 503-947-6094

E-Mail Address: cedric.x.cooney@odfw.oregon.gov

Description

Abstract: The abundance of Steller sea lions (Eumetopias jubatus) has declined significantly throughout much of the species’ range in the North Pacific since the mid-1970s (Braham et al. 1980, Merrick et al. 1987, National Marine Fisheries Service 1992, National Marine Fisheries Service 1995). From an original population of nearly 300,000 animals, abundance dropped 50-60% to an estimated 116,000 animals by 1989 (Loughlin et al. 1992). As a result of these observed declines, Steller sea lions were listed as “threatened” range-wide under the Endangered Species Act in 1990. Subsequent genetic analyses suggested that the population consists of two stocks (eastern and western) separated at 1440 W longitude in the Gulf of Alaska (Bickham et al. 1996, Loughlin 1997). Steller sea lions in the western stock continued to decline in abundance at about 5% per year during the 1990s (Loughlin and York, in press). In 1997 the western stock was listed as “endangered”, while the eastern stock remained classified as “threatened”. In recent years, counts of Steller sea lions in the eastern stock (Southeast Alaska to Oregon) have increased at several percent per year (Strick et al. 1997, Sease et al. 1999, Sease and Loughlin 1999, P. Olesiuk, Dept. of Fisheries and Oceans, unpubl. Data, Riemer et al. 2001.) Explanations for the initial decline of the western Steller sea lion stock that have been considered and determined to be unlikely ultimate causes include population redistribution, commercial and subsistence harvest, predation, effects of pollution and entanglement in marine debris (Merrick et al. 1987). It is possible that some of these factors may now be important at the current lower population levels. Sea lion mortalities incidental to commercial fisheries and shooting of animals may have contributed to the decline but are not thought to be significant at present. Currently the National Marine Fisheries Service (NMFS) and others are focusing attention on what may be declines in the quality and/or quantity of the prey base available to younger sea lions, possibly resulting in reduced nutritional condition and increased susceptibility to mortality from disease, parasitism and predation (J. Sease, National Marine Mammal Laboratory, NMFS, pers. comm.). For these reasons, the collection and analysis of data on the distribution, abundance, population trends and food habits of Steller sea lions in parts of the range where declines have not occurred may be of important comparative value. The two rookeries in southern Oregon and a single rookery just south of the border in northern California constitute the largest reproductive aggregation of Steller sea lions in U.S. waters south of Alaska. The Oregon Department of Fish and Wildlife (ODFW) has monitored Steller sea lion abundance and distribution at Orford Reef and Rogue Reef rookeries and at eight haul-out areas in Oregon annually by aerial photographic surveys since 1976. Surveys of sea lion abundance at the St. George Reef rookery have been conducted since 1987. Since the mid-1980s, ODFW has also collected sea lion scat (fecal) samples from rookeries in order to describe prey selection and food habits of Steller sea lions in this region. In July of 2000, ODFW entered into a contract with Oregon State University (OSU) to continue this research on Steller sea lion population status and food habits in Oregon. The following report summarizes: 1) field work conducted for aerial surveys and food habits sample collections (July 2000 - June 2001), and 2) laboratory analysis and summary of food habits information and statewide population trends (July - December 2001).

Purpose:

Time Period of Content: 2000-2001

Geographic Extent: Oregon

Status: Final

Use Constraints:

Format: PDF

Data Quality Information

Lineage-Source: Contract Report to: Oregon State University In fulfillment of requirements of Subcontract No.: F0225A-001 North Pacific Marine Science Foundation Grant No.: MA96FX0124

Data Information

No data information was supplied.

Entity and Attribute Information

Attributes Description: Field attribute information is available in the attached file(s).

Is a physical copy maintained for reference at Headquarters? Unknown