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.
Coastal habitats are crucial to pinnipeds for resting, molting, and reproduction. We examined terrestrial habitat preferences of four pinniped species (California sea lion, Guadalupe fur seal, harbor seal, and northern elephant seal) on the islands off the western coast of the Baja California Peninsula, Mexico. Boat‐based surveys were conducted while circumnavigating 10 islands or archipelagos during summer and winter in 2009 and 2010. Habitat selection was inferred based on generalized linear models using animal counts and four habitat descriptors (substrate type, tide pools, bathymetry, and surf protection). The interspecific overlapping was analyzed using the Morisita index. Sea lions, fur seals, and harbor seals used sheltered beaches and rocky platforms as breeding sites. Cobblestone and sandy beaches were the most important substrates for elephant seals. Cliffs were the least preferred habitat by all species. Although substrate preferences were similar among species, segregation was observed in most islands except at the San Benito Archipelago, where sea lions co‐inhabit with elephant seals and fur seals. In the context of a recolonization process, these results could provide insights about the location of future colonies and information on habitat use, which can be used when designing conservation strategies for the islands.
Community marine reserves are geographical areas closed to fishing activities, implemented and enforced by the same fishermen that fish around them. Their main objective is to recover commercial stocks of fish and invertebrates. While marine reserves have proven successful in many parts of the world, their success near important marine predator colonies, such as the California sea lion (
Zalophus californianus
) and the Pacific harbor seal (
Phoca vitulina richardii
), is yet to be analyzed. In response to the concerns expressed by local fishermen about the impact of the presence of pinnipeds on their communities’ marine reserves, we conducted underwater surveys around four islands in the Pacific west of the Baja California Peninsula: two without reserves (Todos Santos and San Roque); one with a recently established reserve (San Jeronimo); and, a fourth with reserves established eight years ago (Natividad). All these islands are subject to similar rates of exploitation by fishing cooperatives with exclusive rights. We estimated fish biomass and biodiversity in the seas around the islands, applying filters for potential California sea lion and harbor seal prey using known species from the literature. Generalized linear mixed models revealed that the age of the reserve has a significant positive effect on fish biomass, while the site (inside or outside of the reserve) did not, with a similar result found for the biomass of the prey of the California sea lion. Fish biodiversity was also higher around Natividad Island, while invertebrate biodiversity was higher around San Roque. These findings indicate that marine reserves increase overall fish diversity and biomass, despite the presence of top predators, even increasing the numbers of their potential prey. Community marine reserves may help to improve the resilience of marine mammals to climate-driven phenomena and maintain a healthy marine ecosystem for the benefit of both pinnipeds and fishermen.
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