Diet-to-female and female-to-pup isotopic discrimination in South American sea lions

Abstract

Only the stable isotope ratios in pup blood are good proxies of the individual lactating females. Thus, we suggest that blood components are more appropriate to quantify the feeding habits of wild individuals of this species. Furthermore, because female-to-pup discrimination factors for blood components did not differ between captive and wild individuals, we suggest that results for captive experiments can be extrapolated to wild South American sea lion populations.

Seals and sea lions are what they eat, plus what? Determination of trophic discrimination factors for seven pinniped species

“…For all tissue types, the Δ 13 C values calculated from lipid-corrected prey were within the range of calculated Δ 13 C values from studies where the prey had been lipid-extracted, including the captive sea otter study [39] . The one exception was that our estimates of the diet-to-RBC Δ 13 C values (+1.4 to +1.9‰) were considerably greater than the value of +0.2‰ reported by Drago et al [18] for South American sea lions ( Otaria flavescens ). The similarities among ours and previous studies for estimates of Δ 13 C values calculated using lipid-corrected prey suggest that differences among studies in prey lipid content may partially explain why we observed higher Δ 13 C values from bulk prey than found in previous studies.…”

“…We used whole prey instead of only fish muscle for the prey isotopic composition, whereas several of these previous studies used only fish muscle [6,15,18] . Fish muscle typically has higher δ 15 N values than whole fish [31] , which results in lower TDF values than those calculated using isotope ratios from whole fish [31] .…”

“… a Zhao et al [17] ; b Germain et al [29] ; c Lesage et al [15] ; d Hobson et al [6] ; e Kurle [16] ; f Drago et al [18] ; g Stricker et al [19] ; h Tyrrell et al [36] i Lipid extracted prey samples were used for calculation of Δ 15 N values j The TDF was estimated using the average offset between the δ 13 C and δ 15 N values in whiskers and RBCs in free ranging northern elephant seals collected upon return to the colony from a foraging trip (the present study) k Serum samples were collected twice, approximately one year apart and used to calculate an average TDF l Samples were collected from rehabilitated animals …”

“…Furthermore, factors that fluctuate considerably in free-ranging animals and influence TDFs (i.e., animal diet and condition [12–14] ) can be manipulated in a captive setting. Dietary studies of free-ranging pinnipeds (seals, sea lions, fur seals, and walruses) report stable isotope values from multiple tissues (e.g., whiskers, red blood cells, serum) [6,15–18] , but the TDFs required to interpret these data are limited. TDFs have been quantified for seven of 33 extant pinniped species, and species-specific values have been reported for six of these seven species [15–19] .…”

Temporal variability in stable isotope ratios of C and N in the vibrissa of captive and wild adult South American sea lions Otaria byronia: More than just diet shifts

“…The stable isotope values of the white muscle of the herring ( δ 13 C = −18.6‰ ± 0.3‰; δ 15 N = 12.6‰ ± 0.5‰) and capelin ( δ 13 C = −20.6‰ ± 0.3‰; δ 15 N = 11.7‰ ± 0.5‰) used to feed the captive sea lions had been previously reported by Drago et al . (). Vibrissae were collected during one of the health checks conducted by the veterinary staff of L'Oceanogràfic on 22 February 2012.…”