A hunted population in recovery: Effective population size for South American sea lions from Patagonia

Abstract

Effective population size {Ne) is a parameter of central importance in evolutionary biology and conservation. Factors such as unequal sex ratios of breeding individuals, pedodic fluctuation in population size and vadance in reproductive success can affect the Ne in general. At present. South Amedcan sea lions, Otariafiavescens, from northem Patagonia, Argentina, belongs to one of the several populations that are recovedng from overhunting which occurred in the early 20* century. Here, we present the estimate of Ne for this population that takes into account the effects of their polygynous mating system and vadation in population size through time. The resultant overall A^^' s were 4171 ± 2450 or 4745 ± 2681 breeding animals depending on the inclusion of pedpheral adult males. The estimated Ne's are not cdtical, because they are close to the average mean minimum viable population for vertebrates (5000 breeding adults). Even though the northem Patagonian population of O. ßavescens is increasing its abundance is stiU far below its histodcal numbers. The Ne estimated should be considered the minimum range to be maintained, especially in light of bycatch related to fishery interactions along the Patagonian coast. We emphasise the importance of estimating A^^ for future management plans of the species within different populations.

Isotopic niche partitioning between two apex predators over time

“…) while increasing in northern Patagonia (Grandi et al . ). Nevertheless, the Río de la Plata estuary (with the adjacent Atlantic Ocean coast) and northern Patagonia currently support very different ecosystems (Acha et al .…”

“…Nevertheless, the contribution of demersal prey to the diet of South American fur seals in northern Patagonia is negligible but they represent 16-37% of the biomass consumed by fur seals in areas influenced by the R ıo de la Plata estuary (Uruguay-Argentina) (Naya, Arim & Vargas 2002;Franco-Trecu et al 2013;Vales et al 2014Vales et al , 2015. Such a pattern might be related to the opposite trends in size of the sympatric populations of South American sea lions in these two regions, as the sea lion population is declining in both the R ıo de la Plata and the adjoining Atlantic while increasing in northern Patagonia (Grandi et al 2012). Nevertheless, the R ıo de la Plata estuary (with the adjacent Atlantic Ocean coast) and northern Patagonia currently support very different ecosystems (Acha et al 2004;Saporiti et al 2015); therefore, differences in the diet of South American fur seals in these two regions might be because of other ecosystem attributes and deserve further research.…”

Shifting niches of marine predators due to human exploitation: the diet of the South American sea lion (Otaria flavescens) since the late Holocene as a case study

“…Preventing extinction due to human activity is the first step in wildlife conservation, but restoring the role of species in ecosystem dynamics has to be the long-term goal (Jackson and Hobbs 2009; Terborgh and Estes 2010; Bullock et al 2011). Legal protection has certainly allowed the partial recovery of the population of South American sea lions in Argentina (Dans et al 2004; Schiavini et al 2004; Grandi et al 2012), but has not restored the ecological role of the species (this study). Fishing is currently the major ecological driver of coastal ecosystems in the southwestern Atlantic (Koen-Alonso and Yodzis, 2005) and has established a new carrying capacity for South American sea lions (Drago et al 2010).…”

“…The data also reveal the twentieth century as the period when most of the change in the trophic level of South American sea lions happened, following the massive removal of individuals by hunting along the coast of Argentina (Dans et al 2004; Schiavini et al 2004; Grandi et al 2012). Major changes also occurred in southern Patagonia during the early nineteenth century, as all the samples fell outside the mixing polygon formed by the stable isotope ratios of modern prey, even after correction for a shift in the isotope baseline.…”

Population Structure and Dynamics

“…In the case of the vaquita, low genetic variability, coupled with its restricted range, suggests a persistent effect of small effective population size (or a founder event; see above and Rosel and Rojas-Bracho, 1999). In small populations, it is important to recognize that total abundance alone is not sufficient for assessing the well-being and future trends that are likely because not all individuals will contribute to the next generation, particularly in polygynous species (see Grandi et al 2012).…”