The effects of El Niño on the foraging behavior of lactating California sea lions (Zalophus californianus californianus) during the nonbreeding season

Abstract

We compared the nonbreeding-season foraging behavior of lactating California sea lions ( Zalophus californianus californianus (Lesson, 1828)) at San Miguel Island, California, during El Niño conditions in 1993 and non-El Niño conditions in 1996. Lactating females were instrumented with satellite-linked time–depth recorders between January and March in 1993 (n = 6) and 1996 (n = 10) and data were collected through May in each year. Females foraged northwest of the colony, up to 367 km from it and 230 km from the California coast. Mean dive depths ranged from 19.5 to 279.3 m, but most females achieved dives deeper than 400 m. Most females fed exclusively in the offshore habitat, traveled farther from the colony, spent more time traveling, made deeper and longer dives, and terminated lactation earlier during the 1993 El Niño. The results suggest that prey were concentrated in the offshore habitat and located farther from the colony and deeper in the water column during El Niño. Females did not change their foraging direction, foraging-trip duration, foraging effort, or prey species consumed.

Age, body mass and environmental variation shape the foraging ontogeny of Galapagos sea lions

“…Similar adjustments were found in other otariid species comparing years with higher and lower productivity (McCafferty et al 1998, Georges et al 2000, Costa 2008, Melin et al 2008. Studies off the coasts of Peru and Chile suggest that fish species groups like sardines, anchovies and silversides either migrated to other locations or withdrew to deeper depths in El Niño conditions (Arntz et al 1991).…”

Navigating under sea ice promotes rapid maturation of diving physiology and performance in beluga whales

“…These depths are about 150 m shallower than maximum depths recorded for free-ranging adult belugas (Hauser et al, 2015). Based on this theoretical assessment, beluga may have little flexibility to alter foraging behaviors because marine mammals that operate at their physiological limits cannot increase dive duration or depth (Costa et al, 2001), which is how marine mammals typically respond to decreased prey availability (Feldkamp et al, 1989;Crocker et al, 2006;Melin et al, 2008).…”

Foraging strategies of a generalist marine predator inhabiting a dynamic environment

“…The minimum criterion for a bout was five dives with a maximum surface interval of 10 min or less between dives. Transiting bouts were identified as those with a mean dive depth of 8 m or less; these bouts (and all dives within) were excluded from further analysis (Melin et al 2008).…”

“…This sensitivity is likely because female sea lions have a restricted distribution during an energetically expensive time period (lactation), alternating foraging trips to sea (1-7+ days) with onshore nursing (1-2 days) at the rookery for the 10-to 11-month lactation period (Melin et al 2000;Kuhn and Costa 2014;Harris 2016). Despite their abundance and importance as an indicator species, there have been relatively few published studies on the at-sea behavior of adult female California sea lions (Feldkamp et al 1989;Antonelis et al 1990;Melin et al 2008;Kuhn and Costa 2014). Previous studies have focused on describing population-level trends, although Melin et al (2008) and Kuhn and Costa (2014) noted that adult females from the two largest US rookeries exhibited considerable individual variation in their at-sea behavior.…”

“…Despite their abundance and importance as an indicator species, there have been relatively few published studies on the at-sea behavior of adult female California sea lions (Feldkamp et al 1989;Antonelis et al 1990;Melin et al 2008;Kuhn and Costa 2014). Previous studies have focused on describing population-level trends, although Melin et al (2008) and Kuhn and Costa (2014) noted that adult females from the two largest US rookeries exhibited considerable individual variation in their at-sea behavior.…”