Milk fatty acids predict the foraging locations of the New Zealand fur seal: continental shelf versus oceanic waters

Abstract

Lactating New Zealand fur seals Arctocephalus forsteri utilise 2 ecological regions: continental shelf habitats and oceanic habitats associated with the Subtropical Front. Using milk fatty acids (FA) obtained from 29 satellite-tracked fur seals, we characterised the FA composition of seals that foraged on the continental shelf, and those that foraged in oceanic waters. Seals that foraged within oceanic waters were characterised by milk being comparatively high in monounsaturated fatty acids (MUFA; 47.4 ± 4.4%, mean ± SD), and lower in polyunsaturated fatty acids (PUFA; 23.8 ± 4.0%) when compared to seals that foraged in continental shelf waters (MUFA 36.7 ± 5.4 and PUFA 31.4 ± 5.5%). Based on FA compositions, we predicted the likelihood that milk samples collected at random (n = 131) represented individual seals having foraged either on the continental shelf or in distant oceanic waters. Results indicated that 74% (n = 97) of seals were likely to have foraged in oceanic waters, with 26% (n = 34) likely to have foraged within continental shelf waters. These results were supported by the small sub-sample of 29 satellite-tracked seals, which indicated that 62% of seals had foraged in oceanic waters. FA analysis and satellite-tracking results contrasted with scat analyses, from which only 7% of scats contained prey remains from oceanic waters. The results suggest scats were biased toward females foraging on the continental shelf. To further understand the diet of New Zealand fur seals, additional information on potential prey species that inhabit waters associated with the Subtropical Front south of Australia is required, as well as the continued development and application of alternative dietary techniques. KEY WORDS: Milk fatty acids · New Zealand fur seal · Subtropical Front · Continental shelf Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 380: [271][272][273][274][275][276][277][278][279][280][281][282][283][284][285][286] 2009 sent diet and to assess trophic interactions, the ability to separate dietary information from different ecological regions utilised by marine predators is required.Traditionally the diets of marine predators have been largely inferred using scat, regurgitation and stomach samples. Although these methods have proven to be invaluable, it is often assumed they are only representative of the last foraging bout, and inherent biases associated with differences in the rates of passage of food through the gut and in the digestibility of particular prey are well established (Dellinger & Trillmich 1988, Bodley et al. 1999, Staniland 2002. As such, the accuracy at which traditional methods are able to reconstruct the diet of wide-ranging marine predators is dependant, to some degree, on the characteristics of their foraging trips (such as distance and duration), which vary temporally (i.e. seasonal) and spatially (colony location) and between individuals (e.g. Beauplet et al. 2004, Gremillet et al. 2004, Robson et al. 2004, Staniland et...

Fine‐scale diet of the Australian sea lion (Neophoca cinerea) using DNA‐based analysis of faeces

“…Pinniped dietary information has been derived from analyses of prey hard-parts recovered from regurgitates, faeces or stomach contents and from predator tissues containing dietary fatty acids (FAs) or stable isotopes (SIA). Analysis of digesta for hard-parts is mostly noninvasive and can provide species-level taxonomic identification from undigested prey remains, and composition ratios of FAs and SIAs incorporated into a predator's tissues can be used to distinguish prey consumed over time, but these methods have well understood problems (Childerhouse et al 2001;Iverson et al 2004;Meynier et al 2008Meynier et al , 2009Baylis & Nichols 2009a;Baylis et al 2009b). For example, the remains of prey hard-parts are subject to species-specific erosion and digestive retention, which can bias results (Tollit et al 1997(Tollit et al , 2003.…”

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

“…Fatty acid signatures in milk samples have been used to classify the foraging area (continental shelf waters vs . oceanic) as well as identifying seasonal shifts in female Australian sea lions and New Zealand fur seals (Baylis and Nichols , Baylis et al . ).…”

PCR‐based techniques to determine diet of the Australian sea lion (Neophoca cinerea): a comparison with morphological analysis

“…; Gibbs ). Other non‐destructive dietary methods such as fatty acid and stable isotope analysis have offered broader trophic‐level insights into prey utilization and habitat use, but owing to broad similarities in chemical signals amongst prey, these have provided little fine‐scale taxonomic information on the species consumed (Baylis & Nichols Peter ; Baylis et al . ; Lowther & Goldsworthy ; Lowther et al .…”

“…cartilaginous fish). As a result, dietary analysis using these methods is challenged by the potential to under-or over-estimate the importance of the prey taxa consumed, leaving estimates of diet often incomplete (Dellinger & Trillmich 1987;Tollit et al 1997;Kvitrud et al 2005;Casper et al 2006;Baylis & Nichols Peter 2009a).…”

“…Dietary analyses based on hard parts have indicated that Australian sea lions exploit a range of benthic species including cephalopods, fish, crustaceans and occasional elasmobranchs, but few remains survive digestion and, of those which do, are rarely defined to species (Walker & Ling 1981;Richardson & Gales 1987;Gales & Cheal 1992;Ling 1992;McIntosh et al 2006;Gibbs 2008). Other non-destructive dietary methods such as fatty acid and stable isotope analysis have offered broader trophic-level insights into prey utilization and habitat use, but owing to broad similarities in chemical signals amongst prey, these have provided little fine-scale taxonomic information on the species consumed (Baylis & Nichols Peter 2009a;Baylis et al 2009b;Lowther & Goldsworthy 2010;Lowther et al 2012).…”