Records of Southern elephant seals (Mirounga leonina) in the southern Mexican Pacific

Abstract

Antarctica (Hindell & McMahon, 2000; Hofmeyr, 2015). Most adult females feed in pelagic zones, while adult males feed in both pelagic and benthic zones (Hindell et al., 1991). The diet of this pinniped includes different species of fish and squid, with changes that are proportional according to the season and feeding areas (Bradshaw et al., 2003). Southern elephant seals perform long-range movements, coupled with the absence of oceanographic barriers and currents that could hinder their displacement. This has resulted in relatively frequent records on the Brazilian coasts, with almost 50 individuals observed between 1958 and 2008 (de Moura et al., 2010). There are records of this species toward northern latitudes, whose frequency has increased recently or has been documented for the first time (e.g., Alava & Aurioles-Gamboa, 2017; Páez-Rosas et al., 2018; Elorriaga-Verplancken et al., 2020; de Vos, 2021; Alava et al., 2022). These unusually long-range movements by this species involve juvenile and subadult males, as these seem not to choose resting or hauling sites as selectively as older and more experienced animals (Mulaudzi et al., 2008). In this regard, the continental edge of the southeast Pacific is narrow and relatively close to the coast, which favors juveniles and subadults to move along this coast and its productive waters, heading to northern and distant latitudes (Acevedo et al., 2016). This article reports the presence of two Southern elephant seals on the coasts of Chiapas and Oaxaca, Mexico. Both individuals were taxonomically identified based on the large size of the specimens, compared with animals of the same sex and age class as the Northern elephant seal (M. angustirostris). Other useful features for identification included a thick neck relative to head size, and proboscis length and size which is shorter, smaller, and with nostrils tending to be more forward-facing compared to males of the Northern elephant seal, whose proboscis is much larger and rounded (Reeves et al., 2002; Páez-Rosas et al., 2018). The first individual was observed on 15 December 2020 at Santuario Playa, Puerto Arista (SPPA), 2.9 km southeast of the Puerto Arista town (15°55’41.96” N, 93°48’10.02” W; Fig. 1). Its presence was reported by the staff of the local turtle camp. The individual, which was molting, had no external injuries nor evidence of interaction with human activities such as fishing. The Southern elephant seal (Mirounga leonina) has a generally circumpolar distribution in the Southern Hemisphere. Four populations are distinguished based on their genetic attributes. One inhabits Argentina and Chile, including the Valdés Peninsula, the Falkland Islands, the Strait of Magellan, and the Chilean Antarctic region (Capella et al., 2017); the second ranges in the Atlantic Ocean along South Georgia, South Orkney, South Shetland, Bouvetøya, and Gough islands; the third, in the Indian Ocean on the Kerguelen, Crozet, Heard, and Prince Edward islands; and the fourth, in the Pacific Ocean on Macquaire, Campbell, and Antipodes islands, near New Zealand (Slade et al., 1998). The total population size of this species has been estimated at approximately 750,000 individuals in the year 2000 (Hindell et al., 2016; Hindell, 2018) and the species is listed as “Least Concern” by the International Union for the Conservation of Nature (Hofmeyr, 2015). The Southern elephant seal feeds mainly between 40° S and