Foraging diversity in lactating New Zealand sea lions: insights from qualitative and quantitative fatty acid analysis

Abstract

Lactating New Zealand (NZ) sea lions (Phocarctos hookeri) exhibit different foraging patterns during their foraging trips, with benthic divers spending more energy at sea than mesopelagic conspecifics. We compared blubber fatty acids (FAs) of 14 benthic and 12 mesopelagic females captured at the Auckland Islands, NZ subantarctic, in late January 2000 using an analysis of similarities (ANOSIM). FA profiles between foraging types were significantly different (global R = 0.30, p = 0.001), suggesting a different use in prey resources. We then compared the diet predictions by quantitative FA signature analysis (QFASA) by using a prey FA library available in the region. Overall, diet predictions were significantly distinct between benthic and mesopelagic females (global R = 0.17, p = 0.022), although the diets consisted of the same prey but in different contributions. The results suggest benthic females do not compensate their higher foraging costs by feeding on prey with higher energy densities. Foraging areas of benthic females are not exploited by the trawling fishery; therefore, the benthic tactic might be a trade-off between a higher foraging cost and less resource competition.Résumé : Les lionnes de mer de Nouvelle Zélande (NZ) lactantes utilisent des tactiques de chasse en mer différentes : les individus chassant sur le benthos dépensant plus d'énergie que les individus mesopélagiques. Nous avons comparé avec une ANOSIM les acides gras (AG) du lard de 14 lionnes de mer benthiques et 12 mesopélagiques capturées aux Iles Auckland (région subantarctique de la NZ) fin janvier 2000. Les profiles d'AG entre les comportements de chasse présentent des différences significatives (global R = 0.30, p = 0.001), probablement dues à une utilisation différente des ressources entre ces deux groupes. La composition du régime alimentaire a été estimée par l'analyse quantitative des profiles d'AG (QFASA), en utilisant un catalogue d'AG de proies venant de la même région. Les régimes alimentaires des deux types de chasse comprennent les mêmes espèces de proies mais avec des proportions significativement différentes (global R = 0.17, p = 0.022). Il semble donc que les femelles chassant sur le benthos ne compensent pas leurs dépenses énergétiques plus élevées en mer par des proies de qualité supérieure. Les zones de chasse des femelles benthiques ne sont pas exploitées par les pêcheries; ces individus pourraient chercher un compromis entre une dépense énergétique élevée et une compétition faible pour la ressource.

Stable isotope signatures of whisker and blood serum confirm foraging strategies for female New Zealand sea lions (Phocarctos hookeri) derived from telemetry

“…Foraging research has shown this is the case for female NZ sea lions (Chilvers and Wilkinson 2009). The results from this research and Meynier et al (2014), confirms that these foraging ecotypes are also represented by differing stable isotope signatures and therefore likely prey or proportions of prey in diet. Being able to collect and analyse stable isotope composition and therefore identify likely foraging ecotype from blood or a whisker from a female NZ sea lion is a far faster, less invasive and more cost effective option than undertaking foraging studies, meaning the foraging ecotypes of more individuals could be determined.…”

“…fin fish compared with cephalopods). This difference has been suggested from foraging behavioural studies (Chilvers and Wilkinson 2009) and shown in fatty acid analysis (Meynier et al 2014). The mesopelagic foraging females predominantly forage in the waters above the western slopes of the Auckland Island shelf (Chilvers and Wilkinson 2009), which matches the prey distribution of hoki (Macruronus novaezelandiae (Hector, 1871)), and rattails (Coelorinchus spp.…”

“…This research did not sample prey for stable isotope nor attempt to estimate the prey species related to the stable isotope signatures or their potential proportions in each foraging ecotypes diet. NZ sea lions have been shown to consume a wide variety of prey, and the D r a f t species is considered to be a generalist predator (Meynier et al 2009;Meynier et al 2014). In the present study, mean δ15N values from blood serum ranged from 11.1 to 13.6‰.…”

“…Individual females show either benthic (foraging on the sea floor) or mesopelagic (foraging at various, but usually deep, depths in the water column) diving behaviours (Chilvers and Wilkinson 2009), with individuals showing strong fidelity to these foraging areas and strategies within and between breeding seasons (here defined as December-February each year; Chilvers et al 2005Chilvers et al , 2006Chilvers 2008aChilvers , 2008bChilvers and Wilkinson 2009). This consistent fidelity occurs even with differences in prey distribution and environmental conditions between years (Chilvers 2008a(Chilvers , 2008b and has been indicated in differences in diet through qualitative and quantitative fatty acid analysis (Meynier et al 2014). ).…”

Variation in milk, serum, and blubber fatty acids in young, free‐ranging Steller sea lions

“…; Meynier et al . , ; Fowler et al . ), are being used to investigate the diet and foraging ecology of marine predators.…”