Fatty acid composition suggests leopard seals are no longer apex predators in the WAP ecosystem.

The leopard seal, Hydrurga leptonyx, is an apex predator that has a key role as consumer within the Antarctic ecosystem. Due to the constraints of traditional methods for studying feeding ecology fatty acids (FAs) analysis of blubber has become a useful tool for determining diet since it provides an indication of long-term dietary histories. FAs however, are not distributed uniformly within the blubber so understanding the degree of stratification is important in order to obtain accurate results. The FA stratification in blubber has not been examined for the leopard seal. We used whole blubber core samples from 24 individual leopard seals captured in the Danco Coast region off the Western Antarctic Peninsula (WAP). The cores were sub-sectioned into: outer, middle and inner layers and the FA compositions were compared with potential prey species (krill, fish and penguins). We found 17 FAs present at greater than trace amounts (>0.5%) across all samples. The most abundant FAs were: C18:1ω9, C16:1, C22:6ω3, C16:0 and C18:1ω7 which accounted for approximately 70% of the total. This composition of blubber is similar to other marine mammals, although some differences do exist. Principal Component Analysis confirmed clear separation between inner and outer layers where most of the FAs were present in significantly different amounts between these layers. Monounsaturated FAs (MUFA) dominated the three layers being more abundant in the outer layer. The higher presence of MUFAs, which have comparatively low melting points, in the outer layer, may suggest that this section has a thermoregulatory function. On the other hand, polyunsaturated (PUFA) and saturated FAs (SFA) were more abundant in the inner layer. PUFAs are known to be of dietary origin and SFAs are inert chemically so they can be used as long-term reserve suggesting this layer is associated with dietary intake. Moreover, the FA composition of the inner blubber layer resembles those of the prey more closely than the outer layer. Detailed analysis of the inner layer and the prey species revealed that although they did not overlap completely, inner layer FAs resembled krill FAs more closely than any of the other prey types. This would suggest that seals are eating a combination of prey types, but are using krill more heavily. FA analysis indicates that this top predator is feeding predominantly at lower trophic levels than anticipated; so that, within the WAP food web, the leopard seal is behaving more like a mesopredator rather than an apex predator Fatty acid composition suggests leopard seals are no longer apex predators in the Western Antarctic Peninsula ecosystem. Available from: https://www.researchgate.net/publication/308413191_Fatty_acid_composition_suggests_leopard_seals_are_no_longer_apex_predators_in_the_Western_Antarctic_Peninsula_ecosystem?channel=doi&linkId=57e37e4e08aecd0198dd896a&showFulltext=true [accessed Aug 8, 2017]