Common dolphins, Delphinus delphis, in the southwestern Atlantic Ocean are subject to incidental mortality in fishing gear.However, no information on trends in abundance or estimates of bycatch mortality are available to evaluate the impact of this threat on the population. This study presents estimates of life history parameters using postmortem data obtained over a 17-year period in Argentina. Ages were determined for 93 specimens, and reproductive organ samples were examined (n = 89).

Populations of the South American sea lion (SASL, Otaria byronia) have been intensely exploited for leather and oil in different parts of its distribution range throughout the 19th and 20th centuries, generating large changes in abundance. In Patagonia, the SASL population was reduced by more than 90% of its original abundance, and it began to recover after sealing ended. The aim of this work was to assess changes in size and shape of the skull related to changes in population abundance during the last 100 years. Using geometric morphometry techniques, we analyzed 145 individuals (68 males and 77 females) from Patagonia. Skulls were classified by sex, time period (harvest vs. postharvest), and decades of individual's birth. Results indicated that there were differences in skull size but not in shape discriminated by time period. Moreover, individuals of the postharvest period showed a decrease in the skull size during the last two decades, coinciding with the recovery in population abundance. Our results suggest the existence of a density‐dependence response in somatic growth of SASL population of Patagonia.

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El Niño-Southern Oscillation (ENSO) and Southern Annular Mode (SAM) indirectly affect tooth growth of marine mammals, through changes in prey abundance, availability, and composition. This is reflected as variation in the dentine deposition, which determines the formation of annual layers, called growth layer groups (GLGs). The aim of this work was to study potential effects of ENSO and SAM on South American sea lion (Otaria byronia) of Patagonia, by examining interannual variability of GLG width. Adapting dendrochronological techniques, we analyzed 97 individuals (60 females and 37 males) and built six chronologies (three for each sex) by using cubic splines with different rigidity.Chronologies were correlated with MEI (Multivariate ENSO Index) and SAM index time series, considering lags in the biological response. The chronologies of females spanned 39 years and only two of these chronologies showed negative correlation with 1 year lagged SAM events. The chronologies of males spanned 23 years, but none showed significant correlation with these indexes. Our results did not indicate any ENSO effects on this species, while positive SAM events could reduce the abundance or availability of South American sea lion's prey, affecting the nutritional status of females and generating thinner GLGs during the next year.

No abstract