Change in the foraging strategy of female South American sea lions (Carnivora: Pinnipedia) after parturition

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We analyzed the δ13C and δ15N values in the vibrissae of captive adult breeding South American sea lions (Otaria byronia) fed at a constant diet and then used this information to analyze the change in stable isotope values along the vibrissae from wild individuals. The overall diet‐to‐vibrissa discrimination factor of the captive animals was 3.0‰ ± 0.1‰ for δ13C and 3.6‰ ± 0.1‰ for δ15N, but the stable isotope ratios fluctuated periodically despite constant diet. The δ13C and δ15N values of the captive male declined at the end of the breeding season, whereas the δ13C values of the female increased during the central part of pregnancy and the δ15N values peaked during lactation. The δ13C and δ15N values of adult wild specimens also fluctuated periodically and vibrissae growth rate (0.15 mm/d in both sexes) was slightly lower than in captivity (0.17 mm/d), assuming an annual periodicity for oscillations. Similarities in the amplitude of the cycles of captive and wild males suggested that fasting was probably the main source of periodic variability in the δ15N of wild males, whereas pregnancy and lactation were probably the main source of periodic variability for the δ13C of wild females.

Section: Discussionmentioning

confidence: 97%

mentioning

confidence: 97%

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

Cardona

Vales

Aguilar

et al. 2017

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“…Because during the first months of their lives South American sea lion pups exclusively feed on maternal milk, their isotope values can be used to investigate the adult females' foraging ecology (Drago et al . , Franco‐Trecu et al . ).…”

Section: Methodsmentioning

confidence: 99%

“…During February and March, we carried out fortnightly scan samplings (Martin and Bateson 1991) in each colony to visually recapture the marked pups. Because during the first months of their lives South American sea lion pups exclusively feed on maternal milk, their isotope values can be used to investigate the adult females' foraging ecology (Drago et al 2010b, Franco-Trecu et al 2012. Furthermore, given that serum half-life in endotherms is 3-4 d and that of blood cells is 28-30 d Clark 1993, Hilderbrand et al 1996), the isotopic value of blood cells collected just after birth and that of the serum collected 5-6 wk later can be used as proxies of the South American sea lion female diet in the prepartum and early lactation periods, respectively.…”

Section: Data and Sample Collectionmentioning

confidence: 99%

Postharvesting population dynamics of the South American sea lion (Otaria byronia) in the southwestern Atlantic

Franco‐Trecu

Drago

Baladán

et al. 2014

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Many pinniped populations precipitously declined during the 19th and 20th centuries due to overharvesting. In Uruguay, the South American sea lion (SASL) was harvested until 1986. Birth rates in two nearby breeding colonies have had opposite trends for at least 20 yr. We assessed different mechanisms that could explain opposite trends in birth rates in the two SASL colonies. We compared feeding habits (δ15N and δ13C) of breeding females, birth mass, individual growth rate and early survival of pups and the social structure between colonies. Breeding females from the two colonies did not differ in their feeding habits. However, male and female pups grew faster but had a lower survival in the second month in the smallest colony. We found differences in the social structures, with a higher proportion of males in the smallest colony. The latter is important because peripheral SASL males may abduct and kill pups, which may explain the lower survival of pups in smaller colonies. We believe that the cumulative effects of population extractions have lowered the local SASL population size and disrupted its social structure to the point where Allee‐like effects could become important and hamper the recovery of the Uruguayan SASL population.

“…The Bayesian approach in SIAR circumvents these limitations by allowing for multiple dietary sources as well as associated uncertainties in both isotopic values and Δ (Parnell et al 2010). As such, Bayesian mixing models are more robust in their result than other modeling approaches, generating potential dietary compositions as true probability distributions (Inger and Bearhop 2008, Moore and Semmens 2008, Parnell et al 2008, Drago et al 2010, Parnell et al 2010).…”

Section: Methodsmentioning

confidence: 99%

Modeling the diet of humpback whales: An approach using stable carbon and nitrogen isotopes in a Bayesian mixing model

Witteveen¹,

Worthy

Foy

et al. 2011

Humpback whales are considered generalist predators, feeding on schooling fish, and zooplankton, but variability likely exists among regional feeding aggregations. We explored the diet of one feeding aggregation of humpback whales near Kodiak Island, Alaska, through analysis of the stable carbon (δ13C) and nitrogen (δ15N) isotope ratios of their skin and regional prey sources. Humpback whales were sampled during the summer feeding season over 3 yr (n= 93; 2004–2006). Prey samples were collected from the same region during trawl surveys conducted between 2003 and 2005. Isotope values of humpback whale skin and prey were entered into a Bayesian dietary mixing model to estimate feasible contributions of prey to humpback diets. Diet results indicated that humpbacks feed heavily on euphausiids, but also consume juvenile walleye pollock, capelin, and Pacific sand lance. The diet of humpback whales in 2004 was the most diverse, while diets in 2005 and 2006 showed a higher proportion of euphausiids. Our results reveal annual differences in humpback diets from the Kodiak region due to either individual prey preferences or prey availability. Application of a Bayesian mixing model to stable isotope analysis improves description of regional diets and comparison of these diets to resource availability and quality.