Energy and prey requirements of California sea lions under variable environmental conditions

Abstract

Quantifying energy demands and prey consumption of marine mammals is important to understand the population dynamics of species and their ecological role in marine ecosystems. We developed a bioenergetic model to quantify the energy and prey requirements of adult female California sea lions Zalophus californianus, an abundant predator that has recently experienced several years of poor reproductive success presumably associated with oceanographic changes. We also examined how changes in at-sea field metabolic rates and the proportion of time at sea-2 mechanisms that female otariids use to compensate for changes in prey availabilityaffected energy requirements. Mean gross energy requirements (± SD) ranged from 12 500 ± 1900 to 21 000 ± 2200 MJ yr −1 , depending on reproductive status, resulting in prey consumption estimates of 1700−3000 to 2900−5000 kg prey yr −1 , respectively. California sea lions had energy requirements that were 3 to 4 times higher than phocid seals because of high metabolic rates and the considerable cost of lactation. Behavioral changes resulted in a 3 to 25% change in energy requirements, depending on the type and magnitude of the change, time period, and lactation status. Energy requirements may therefore increase during periods of reduced prey availability, assuming that a female does not reduce milk energy delivery to her pup. These results highlight the importance of considering behavioral responses to environmental conditions when developing and applying results from bioenergetic models to understand the relationships between energy requirements, prey availability, and reproductive success.

Climate variability and life history impact stress, thyroid, and immune markers in California sea lions (Zalophus californianus) during El Niño conditions

“…Physiological limitations due to smaller body size may restrict juvenile CSL in our study area to small home range sizes (McHuron et al , 2018a), and the spatial abundance of forage fish during the study period was limited (McClatchie et al , 2016). Foraging otariids continuously maintain high field metabolic rates (Costa, 1991), and confinement to areas of reduced prey availability leads to increases in energy requirements and metabolic rates (McHuron et al , 2017) and physiological challenges to juvenile CSL. Although we were not able to determine exact age or breeding success within individual adult males in this study, we also found increases in thyroid hormones measured directly after the conclusion of the breeding season.…”

Characterizing habitat suitability for a central‐place forager in a dynamic marine environment

“…In a warming ocean, alterations to suitable habitat—smaller in extent and further from the breeding colonies—may have severe consequences on the population dynamics of this species. Prolonged environmental change will result in increased energetic costs and decreased reproductive success with potentially long‐term population declines (Hazen et al., ; Lowry et al., ; McHuron, Mangel, Schwarz, & Costa, ; Melin et al., , ). Recent studies have documented an increasing number of pups born on Año Nuevo Island, an important central California haul‐out site that supports a small breeding population (Lowry et al., ; McHuron, Block, & Costa, ).…”

“…For exam- Thomas & Brickley, 2006;Trillmich et al, 1991). Suboptimal conditions require females to alter foraging and attendance patterns, with females moving further offshore and north of Monterey Bay to find food (Kuhn & Costa, 2014;Melin et al, 2008), which may result in pup abandonment (Melin et al, 2008) (Hazen et al, 2012;Lowry et al, 2017;McHuron, Mangel, Schwarz, & Costa, 2017;Melin et al, 2008Melin et al, , 2012. Recent studies have documented an increasing number of pups born on Año Nuevo Island, an important central California haul-out site that supports a small breeding population (Lowry et al, 2017;McHuron, Block, & Costa, 2017).…”

Understanding the population consequences of disturbance

“…() examined the relation between foraging activity and energy stores (estimated from changes in buoyancy) of female southern elephant seals ( Mirounga leonina ) over the course of a foraging trip. Other applications have inferred changes in energy stores from models of foraging activity that either treat energy explicitly using a bioenergetic approach (Beltran, Testa, & Burns, ; Christiansen & Lusseau, ; Farmer, Noren, Fougères, Machernis, & Baker, ; McHuron, Costa, Schwarz, & Mangel, ; McHuron, Mangel, Schwarz, & Costa, ; Noren, ; Pirotta, Mangel, et al., ; Villegas‐Amtmann et al., , ) or use an arbitrarily scaled energy metric that represents an underlying motivational state (Nabe‐Nielsen et al., , ; New, Harwood, et al., ; Pirotta, Harwood, et al., ; Pirotta, New, Harwood, & Lusseau, ). Although technologies that can measure the morphometrics of individuals remotely may make it easier to estimate changes in body condition directly (e.g., Christiansen, Dujon, Sprogis, Arnould, & Bejder, ; Miller, Best, Perryman, Baumgartner, & Moore, ), extensive health assessment in cetaceans will probably remain limited to a few closely monitored coastal populations, due to logistical constraints (Wells et al., ).…”