If not in the winter breeding lagoons, where are all 20,000 gray whales?
We are frequently asked “If there are an estimated 20,000 gray whales in the Eastern North Pacific (ENP) population, but at the peak of their winter breeding season in Baja California, Mexico only 2,100 to 2,600 whales occupy the three primary breeding lagoons (1,500 to 1,800 whales in Laguna Ojo de Liebre, 400 to 500 in Laguna San Ignacio, and an estimated 200 to 300 in the Bahía Magdalena area).
So…where are the rest of the gray whales?”
To understand this disparity in the numbers of gray whales, we need to understand their distribution along the Pacific coast of North America during migration, the timing of their fall and spring migrations, the time required to undertake these migrations, the segregation of age-sex classes of whales during the migrations, and the duration of stay of whales in the winter range.
The gray whale’s migrations are dynamic, with several age, sex, and reproductive sub-groups migrating at different times and circulating within in many areas during their winter breeding season. Their 10,000-km fall southward migration route takes them from their summer feeding areas in the Bering, Chukchi, and Arctic seas to their winter breeding areas along the Pacific coast of Baja California, Mexico. In spring their northward migration returns them to summer feeding areas, for a total annual round-trip of approximately 20,000 km, one of the longest migrations known for any mammal species. Traveling at 7-km/hr., the entire population passes the NOAA census counting station at Granite Canyon in central California during a 90-day period from December through February each year.
Rather than traveling in one large group, the migrating population is distributed along the Pacific coast of North America with different sub-groups arriving at different locations at different times. The leaders of the fall southward migration are the near-term pregnant females that will birth their calves during the last portion of their migration or in the lagoons and coastal aggregation areas of Baja California. They are followed by adult males and females that will mate during the migration or in the coastal areas of Baja California. These females will give birth to their calves the next year following a summer on the feeding grounds in the North Pacific, Bearing and Chukchi Seas. During the spring northward migration, the leaders are adult females that presumably have just conceived, then adult males, immatures, and lastly lactating females with calves of the year. Adult breeding whales without calves circulate among the breeding lagoons and aggregation areas of Baja California, and on average spend only 7-days in a specific lagoon. In contrast, lactating females with calves spend an average of 30-days in or near the lagoons, with some remaining for up to 3-months.
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