Western Baja California Lagoons and Coastal Waters IMMA
Size in Square Kilometres
17 834 km2
Qualifying Species and Criteria
Gray whale – Eschrichtius robustus
Criterion B (2); C (1, 3)
[Western gray whale subpopulation]
Criterion A; B (2); C (1, 3)
Blue whale – Balaenoptera musculus
Marine Mammal Diversity
Balaenoptera edeni, Megaptera novaeangliae, Orcinus orca, Tursiops truncatus, Delphinus delphis, Lagenorhynchus obliquidens, Arctocephalus philippii townsendi, Zalophus californianus, Mirounga angustirostris, Phoca vitulina
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The Western Baja California lagoons and coastal waters IMMA includes two separate lagoon features, and one lagoon complex: Ojo de Liebre Lagoon, San Ignacio Lagoon, and the Bahía Magdalena-Bahía Almejas (BM-BA) complex. The area also includes an ocean corridor that connects these three sites. Two gray whale (Eschrichtius robustus) populations use this IMMA during the Northern Hemisphere winter months for mating, calving, and nursing. While the Eastern North Pacific (ENP) population that migrates to the IMMA from the Westcoast of North America is considered Least Concern (LC) on the IUCN Red List of Threatened Species, the Western gray whale subpopulation that migrates from feeding grounds off the Kamchatka Peninsula and Sakhalin Island is Endangered (EN) by the IUCN Red List. Individuals of both populations may interbreed in this reproductive area. The IMMA also supports blue whales (Balaenoptera musculus) and a diverse array of other marine mammals, including four species of pinnipeds, four species of dolphins, and four species of baleen whale.
Description of Qualifying Criteria
Criterion A – Species or Population Vulnerability
The western subpopulation of gray whales is considered Endangered (EN) on the IUCN Red List of Threatened Species with a 2016 estimate of between 51 and 72 reproductive females (Cooke et al., 2018). Western gray whales feed in the Okhotsk Sea off Sakhalin Island, Russia, and in nearshore waters of the south-eastern Kamchatka Peninsula (southwestern Bering Sea). Historically this population was believed to migrate to breeding grounds in Asian waters (Japan/Korea), however it is unknown whether these wintering grounds are still used, and Cooke et al. (2019) estimated the proportion of the Sakhalin feeding population that migrates to the Eastern North Pacific (ENP) breeding grounds to be 45-80%. Although they have the opportunity to interbreed with Eastern North Pacific gray whales in this IMMA, they still appear to be genetically and demographically distinct (Cooke et al., 2018).
Blue whales are listed as Endangered (EN) on the IUCN Red List of Threatened Species (Cooke, 2018). The presence of blue whales on the western coast of Baja California has been known since the mid-nineteenth century when some specimens were captured (Scammon, 1874). From 1913 to 1914 Norwegian whalers hunted 83 blue whales outside Magdalena Bay. A decade later, in the same area, they captured almost half of all the blue whales hunted in the Northeast Pacific (Tonnessen and Johnsen, 1982). Blue whales are currently documented in locations near the western coast of Baja California during all seasons of the year. They were observed off the southwestern coast of Baja California in February, outside Magdalena Bay in June, and along the entire west coast of Baja California, in June, August, and October. In addition, according to reports from the Norwegian whaling fleet, the months of March to June represented the best whaling season along this coast, where 989 blue whales were hunted between 1924-1929 and 1935 (Tonnessen and Johnsen, 1982). The months and locations of these hunts coincide with more recent observations of blue whale congregations (Gendron, 2002).
Criterion B: Distribution and Abundance
Sub-criterion B2: Aggregations
Eastern North Pacific (ENP) gray whales winter in the lagoons and adjacent waters of Baja California, Mexico, and then migrate northward in spring along the west coast of North America to feed in the Bering and Chukchi Seas during summer (Rice and Wolman, 1971). Photographic and genetic evidence indicates that at least 54 gray whales migrate from the feeding ground in Russia to the eastern Pacific and the wintering grounds encompassed by this IMMA in Baja California (Weller et al., 2012; Mate et al., 2015; Urbán et al., 2012). These whales represent close to 20% of the known Sakhalin Island gray whale population (Martínez-Aguilar et al., 2022).
Criterion C: Key Life Cycle Activities
Sub-criterion C1: Reproductive Areas
Gray whales from both the Eastern North Pacific (ENP) and the Western Gray Whale subpopulation spend about 3 months in the Mexican wintering areas, where they mate and give birth between December and April (Jones and Swartz, 1984; Swartz, 1986). Gray whale calving areas along the west coast of the Baja California Peninsula are Laguna Ojo de Liebre (Scammon’s Lagoon); Laguna Guerrero Negro (at times when its entrance is open); Laguna San Ignacio; and Bahía Magdalena and adjacent waters (from Estero Las Animas to Bahía Almejas). About the 70% of documented mothers with calves stay at Laguna Ojo de Liebre, 14% in Laguna San Ignacio and 16% in the Bahía Magdalena-Bahia Almejas (BM-BA) complex. The average duration in a breeding lagoon for adults is 10 days, although females with calves may stay a month or longer in one area (Urban et al., 2003). Most whales have departed from the Baja lagoons by late March. Genetic studies suggest interbreeding between Eastern and Western populations during the winter breeding season (Brüniche-Olsen et al., 2018; Lang et al., 2021).
Sub-criterion C3: Migration Routes
Individuals of both the eastern and western feeding populations have been photo-identified in the breeding lagoons in Mexico (Weller et al., 2012). The southward migration initiates in the autumn, lead by females in late pregnancy, followed by adults and immature females, and lastly by immature males. The trip averages 2 months, during which mating begins and continues in the winter congregation areas (Jones and Swartz, 1984, Urbán et al., 2021). The gray whales using the three lagoon (systems) travel following the coastline between lagoons during the course of the breeding season. Between 2012 and 2022, 42% of mothers with calves that were photo-identified in Bahía Magdalena were recaptured later in the season in Laguna San Ignacio (Annual Reports Laguna San Ignacio Ecosystem Science Program, 2022). As such, the Pacific coastal portions of this IMMA serve as an important migratory corridor for gray whales during the breeding season.
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