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<p>At the edge of their distribution, populations are more susceptible to habitat changes and have higher risk of abundance decline. In the northeast Pacific Ocean, the harbor seal’s southernmost distribution occurs in the southern California Current Large Marine Ecosystem, off the Baja California Peninsula, which includes nine islands and archipelagos, and some sites on the coast. A decrease in abundance in 2016 at coastal colonies has been associated to an increase in pebble extraction activities at some beaches. The present study analyzed seal counts spanning 2016–2022 and evaluated them as a function of sea surface temperature 50&#xa0;km around each colony, and of pebble extraction occurrence. We found a consistent decrease in the number of the species during the study period for all colonies off the Baja California Peninsula, coinciding with an increase in SST that could indicate lower habitat suitability. However, the decline of seal numbers on the islands of Todos Santos, San Jeronimo, San Benito, Natividad, and San Roque was slower, possibly because they are surrounded by more productive waters. Additionally, the loss of several seal colonies on the coast seemed associated to disturbances caused by pebble extraction activities nearby. The present study provides evidence of the effect of ocean warming and disturbance on harbor seal relative to distribution and abundance. Since it is a protected species under Mexican law, future conservation policies should account for climate change effects, and include pebble extraction management along the western coast of the Baja California Peninsula.</p>

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Decrease in Pacific harbor seal counts in the Southern California current large marine ecosystem

  • 期刊论文

  • 发表日期：

    2025年4月21日

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  • María Guadalupe Ruiz-Mar,
  • Mario A. Pardo,
  • Yolanda Schramm,
  • Denise Lubinsky-Jinich,
  • Alejandro Arias-Del-Razo,
  • Sofía Daniela Flores-Mejía,
  • Gisela Heckel

摘要

At the edge of their distribution, populations are more susceptible to habitat changes and have higher risk of abundance decline. In the northeast Pacific Ocean, the harbor seal’s southernmost distribution occurs in the southern California Current Large Marine Ecosystem, off the Baja California Peninsula, which includes nine islands and archipelagos, and some sites on the coast. A decrease in abundance in 2016 at coastal colonies has been associated to an increase in pebble extraction activities at some beaches. The present study analyzed seal counts spanning 2016–2022 and evaluated them as a function of sea surface temperature 50 km around each colony, and of pebble extraction occurrence. We found a consistent decrease in the number of the species during the study period for all colonies off the Baja California Peninsula, coinciding with an increase in SST that could indicate lower habitat suitability. However, the decline of seal numbers on the islands of Todos Santos, San Jeronimo, San Benito, Natividad, and San Roque was slower, possibly because they are surrounded by more productive waters. Additionally, the loss of several seal colonies on the coast seemed associated to disturbances caused by pebble extraction activities nearby. The present study provides evidence of the effect of ocean warming and disturbance on harbor seal relative to distribution and abundance. Since it is a protected species under Mexican law, future conservation policies should account for climate change effects, and include pebble extraction management along the western coast of the Baja California Peninsula.