Steller sea lion feeding habits in the Russian Far East, 2000-2003

Abstract

During the breeding seasons of 2000-2003 we collected 1,724 scats from seven rookeries and eighteen haul-outs on the Kamchatka Peninsula and in the Kuril Islands, Okhotsk Sea, and Commander Islands to analyze the diet of Steller sea lions (Eumetopias jubatus) in the Russian Far-East. The most frequently encountered prey items in all scats combined were Atka mackerel (Pleurogrammus monopterygius), walleye pollock (Theragra chalcogramma), salmon (Oncorhynchus sp.), sculpins (Cottidae), cephalopods, Pacific sand lance (Ammodytes hexapterus), Pacific herring (Clupea pallasii), Northern smoothtongue (Leuroglossus stilbius), snailfish (Liparidae), and Pacific cod (Gadus macrocephalus). Spatial differences were analyzed by comparing frequency of occurrence (FO) values on a site-by-site basis for each year and all years combined. Breeding-season collection sites were grouped into seven geographic regions based on FO similarities using cluster analysis. Diet diversity was calculated for each of these geographic regions. No significant relationship was found between diet diversity and population trend (P = 0.886). Significant differences in diet composition were found between geographic regions (P < 0.001 for all regions). Significant seasonal differences were also detected at two haul-outs on the Kamchatka Peninsula from which an additional 93 scats were collected during the fall molt (P < 0.001 for both locations).

Spatial and temporal variation in the diet of Steller sea lions in the Kodiak Archipelago, 1999 to 2005

“…In concordance with previous studies, the prey identified in the present study indicate that Steller sea lions Eumetopias jubatus are adept at foraging on a variety of prey including demersal, semi-demersal, and pelagic prey (Sinclair & Zeppelin 2002, Waite & Burkanov 2006, Trites et al 2007b). The size range of prey consumed by sea lions was also wide, with prey up to ~70 cm FL taken.…”

“…suggested that as diet diversity increased, the rate of population decline decreased; therefore, the higher diversity measured for Kodiak may reflect reduced rates of population decline between the 1990s and the period of this study (1999 to 2005). However, this trend was not demonstrated in diet studies conducted between 2000 and 2003 in Russian waters at the western extent of the population range, where some of the areas with the highest diversity also had the highest levels of population decline (Waite & Burkanov 2006).…”

“…For example, diet diversity in spring on the west side of Kodiak was low (mean H' = 2.3) compared to in other regions, but was dominated by energy-rich herring. As highlighted by Waite & Burkanov (2006), little can be inferred about the foraging success of populations from diet diversity measures without further information on prey availability and on the quality and quantity of prey consumed.…”

“…Critical to the development of such models are data on the diet of Steller sea lions. Diet composition of Steller sea lions is known to vary geographically and seasonally (Sinclair & Zeppelin 2002, Waite & Burkanov 2006). However, due to insufficient data most models have assumed that diet remains constant throughout the year and is similar over broad geographic areas.…”

Environmental and biological factors influencing maternal attendance patterns of Steller sea lions (Eumetopias jubatus) in Russia

“…The exception was Lovushki Island, on which scats were collected in 2005 and 2007 (Waite 2010; Waite and Burkanov 2006). In addition, we supplemented the data set with scats collected outside the attendance study period: on Lovushki in Brat Chirpoev, Raykoke, and Antsiferov in 2003;and Yamsky in 2004.…”