Individuality counts: A new comprehensive approach to foraging strategies of a tropical marine predator

Abstract

Foraging strategies are of great ecological interest, as they have a strong impact on the fitness of an individual and can affect its ability to cope with a changing environment. Recent studies on foraging strategies show a higher complexity than previously thought due to intraspecific variability. To reliably identify foraging strategies and describe the different foraging niches they allow individual animals to realize, high-resolution multivariate approaches which consider individual variation are required. Here we dive into the foraging strategies of Galápagos sea lions (Zalophus wollebaeki), a tropical predator confronted with substantial annual variation in sea surface temperature. This affects prey abundance, and El Niño events, expected to become more frequent and severe with climate change, are known to have dramatic effects on sea lions. This study used high-resolution measures of depth, GPS position and acceleration collected from 39 lactating sea lion females to analyze their foraging strategies at an unprecedented level of detail using a novel combination of automated broken stick algorithm, hierarchical cluster analysis and individually fitted multivariate hidden Markov models. We found three distinct foraging strategies (pelagic, benthic, and night divers), which differed in their horizontal, vertical and temporal distribution, most likely corresponding to different prey species, and allowed us to formulate hypotheses with regard to adaptive values under different environmental scenarios. We demonstrate the advantages of our multivariate approach and inclusion of individual variation to reliably gain a deeper understanding of the adaptive value and ecological relevance of foraging strategies of marine predators in dynamic environments.

Regional Variation in Winter Foraging Strategies by Weddell Seals in Eastern Antarctica and the Ross Sea

“…These differences may be due to divergent behavioural traits among individual seals (Toscano et al, 2016;Troxell-Smith and Mella, 2017). Individual behavioural traits under-pins differences in foraging behaviour in other species (Patrick et al, 2014;Toscano et al, 2016;Krüger et al, 2019;DiNuzzo and Griffen, 2020;Steinhoff et al, 2020), and distinct, stable foraging strategies have been identified in many pinnipeds [e.g., Australian sea lions, Neophoca cinerea (Lowther et al, 2011); Galapagos sea lions, Zalophus wollebaeki (Villegas-Amtmann et al, 2008)], consistent with individual traits (Schwarz et al, 2021). In dynamic environments, multiple foraging strategies within a population may reduce resource competition (Lewis et al, 2006;Baylis et al, 2015).…”

Movement patterns and activity levels are shaped by the neonatal environment in Antarctic fur seal pups

“…active and inactive) 5 . HMMs have accordingly been used to analyse animal tracking data in relation to, among others, environmental conditions 52 , anthropogenic activity 53 , sex 54 , ontogeny 55 , and individualised niches 56 .…”

Hormone‐mediated foraging strategies in an uncertain environment: Insights into the at‐sea behavior of a marine predator

“…This closely resembles the benthic diver strategy in the GSL, where benthic divers have higher CORT levels and return repeatably to the same shallow foraging areas which are considered a more reliable habitat but one with lower prey density and quality (Schwarz et al, 2021). Reliability is inferred because the quantity of benthic prey in GSL diets is more common when environmental conditions (e.g., sea surface temperatures) become suboptimal (Páez-Rosas et al, 2020).…”

“…Here, pelagic divers, with greater depths, durations, and total dive times, had significantly higher thyroid T3 levels than their night diving counterparts. As seen in Schwarz et al (2021), night divers exhibit quite diverse and unique behavior in that they mostly taking shallow dives of ~30-60 m with shorter durations compared to pelagic divers. Although night divers are known to show flexibility and occasionally take deeper foraging bouts during the day, they mostly exploit mesopelagic prey that overlap with the shallow pelagic zone at night.…”