Climate change and the northern elephant seal (Mirounga angustirostris) population in Baja California, Mexico

Abstract

The Earth′s climate is warming, especially in the mid- and high latitudes of the Northern Hemisphere. The northern elephant seal (Mirounga angustirostris) breeds and haul-outs on islands and the mainland of Baja California, Mexico, and California, U.S.A. At the beginning of the 21st century, numbers of elephant seals in California are increasing, but the status of Baja California populations is unknown, and some data suggest they may be decreasing. We hypothesize that the elephant seal population of Baja California is experiencing a decline because the animals are not migrating as far south due to warming sea and air temperatures. Here we assessed population trends of the Baja California population, and climate change in the region. The numbers of northern elephant seals in Baja California colonies have been decreasing since the 1990s, and both the surface waters off Baja California and the local air temperatures have warmed during the last three decades. We propose that declining population sizes may be attributable to decreased migration towards the southern portions of the range in response to the observed temperature increases. Further research is needed to confirm our hypothesis; however, if true, it would imply that elephant seal colonies of Baja California and California are not demographically isolated which would pose challenges to environmental and management policies between Mexico and the United States.

Declines and recovery in endangered Galapagos pinnipeds during the El Niño event

“…California sea lions ( Zalophus californianus ) and Guadalupe fur seals ( Arctocephalus townsendi ) also showed a decline in the pups’ production during the El Niño event 2014–2015, which, in both otariids, was associated with nutritional stress in females and the potential impact on reproductive success 15 . While northern elephant seals ( Mirounga angustirostris) populations of Baja California show a decline in their abundance because the animals are not migrating as far south to avoid thermal stress (metabolic rate increases) that is associated with warming sea and its effect on air temperature 71 . Thus, it is essential to establish accurate population trends in pinnipeds during the presence of anomalous oceanographic events to predict potential changes under climate change scenarios.…”

Land-dependent marine species face climate-driven impacts on land and at sea

“…In temperate regions, land-dependent marine populations may have more opportunities to survive within the context of a changing climate by shifting poleward. Northern elephant seal colonies are decreasing in Baja California (García-Aguilar et al 2018), while the colony in the Channel Islands of California is increasing (Fig. 3c) (Lowry et al 2014).…”

“…This pattern is likely due to climate change and increased atmospheric temperatures as heat dissipation on land becomes an issue for northern elephant seals. This species cannot pant nor do they have sweat glands, instead thermoregulating via cold water edges and cool, moist sand (García-Aguilar et al 2018). As SST and air temperatures continue to increase, the Baja California northern elephant seal colony will likely continue to shrink, while the Channel Islands population will continue to grow (Fig.…”

Causes of mortality in northern elephant seal pups on San Miguel Island, California

“…13 However, several small elephant seal rookeries off the coast of Baja California, Mexico, located near fishing villages are reported to have been declining since the 1990s, possibly because of climate change. 6 The growing numbers of elephant seals inhabiting California rookeries benefit from legal protection from human harassment, and the seals still have a reliable, adequate, and nutritionally balanced food supply. Given that elephant seals forage on mesopelagic prey offshore in extremely deep waters (500–1,500 m) over a large region of the eastern North Pacific, their food base may not be as affected by commercial fishing and climate change as the food base for other marine mammals and birds that usually feed within the first 100–150 m of the water column, which is heavily fished.…”

“…Sharp trauma or bite wounds were not found in any of the pups in our study. Abdominal trauma resulting in a fractured liver and hemoabdomen (6), trauma to the chest causing hemothorax (2), and head trauma with severe subdural hemorrhage (1) were documented (Supplementary Table 1). In 6 of 9 cases, other concurrent predisposing conditions (idiopathic myopathy [5] and omphalophlebitis with mild hydrocephalus [1]) were present.…”