Gulf of California IMMA
Size in Square Kilometres
276 011 km2
Qualifying Species and Criteria
Blue whale – Balaenoptera musculus
Criterion A; B (2); C (1, 2)
Fin whale – Balaenoptera physalus
Criterion A; B (1)
Humpback whale – Megaptera novaeangliae
Criterion C (1)
Vaquita – Phocoena sinus
Criterion A; C (1)
Marine Mammal Diversity
Criterion D (2)
Balaenoptera acutorostrata, Balaenoptera borealis, Balaenoptera edeni, Eschrichtius robustus, Berardius bairdii, Eubalaena japonica, Mesoplodon densirostris, Mesoplodon ginkgoden, Mesoplodon peruvianus, Indopacetus pacificus, Ziphius cavirostris, Kogia sima, Kogia breviceps, Pseudorca crassidens, Grampus griseus, Feresa attenuata, Lagenorhynchus obliquidens, Stenella attenuata, Stenella coeruleoalba, Stenella longirostris, Steno bredanensis, Peponocephala electra, Globicephala macrorhynchus, Delphinus delphis, Orcinus orca, Physeter macrocephalus, Tursiops truncatus, Arctocephalus philippi townsendi, Zalophus californianus
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Summary
The Gulf of California is a long and narrow basin approximately 1,400 km long and 150 km wide, bound by the Baja California Peninsula and the mainland of the northwest coast of Mexico. The IMMA hosts 32 species of cetaceans and two pinniped species, the Californian sea lion (Zalophus californianus) which has several reproductive colonies in the IMMA, and the Guadalupe fur seal (Arctocephalus philippii townsendi). Among the cetacean populations present in the Gulf of California, there are resident populations of common bottlenose dolphins (Tursiops truncatus), fin whales (Balaenoptera physalus) and vaquita porpoises (Phocoena sinus), the most endangered species in the world. Other migratory cetaceans such as blue (B. musculus), humpback (Megaptera novaeangliae) and gray whales (Eschrichtius robustus) also use the area as a wintering ground. Other species that are more rare include the Pacific right whale (Eubalaena japonica).
Description of Qualifying Criteria
Criterion A – Species or Population Vulnerability
There is a resident population of fin whales (Balaenoptera physalus) in the Gulf of California, which is genetically and acoustically isolated, with a low genetic diversity (π = 0.00052) (Bérubé et al., 1998; Bérubé et al., 2002). Fin whales are designated as Vulnerable (VU) on the IUCN Red List of Threatened Species (Cooke, 2018). The upper Gulf of California is home to the entire remaining population of the endemic vaquita (Phocoena sinus), which is considered Critically Endangered (CR) on the IUCN Red List of Threatened Species (Rojas Bracho et al., 2022). The estimated rate of decline is extremely high: with an estimated 48% decline in 2017 (95% Bayesian credible interval – CRI, 78% decline to 9% increase) and 47% in 2018 (95% CRI, 80% decline to 13% increase). Estimated total population decline since 2011 is 98.6% making the vaquita porpoise the most endangered species in the world.
Criterion B: Distribution and Abundance
Sub-criterion B1: Small and Resident Populations
Three abundance estimates have been generated for the Gulf of California’s resident population of fin whales: 820 individuals (95% CI 594-3.229) based on line transects carried out in 1993 (Gerrodette and Palacios, 1996); 656 individuals (95% CI 374-938) based on capture-recapture methods based on fieldwork carried out in 2004 (Díaz-Guzmán, 2006); finally, Rivera-León et al. (2019) based on molecular analyses, estimated an “effective population size” of around 250. Based on the presence of females with calves, the main nursery area for fin whales in the Gulf of California are Bahía de La Paz and the San José Channel in both the warm season (May-November) and the temperate season (December-April) (Jiménez López, 2019; Bernot et al 2021). Females with young have only been recorded in the warm season Ángel de la Guarda Island and southern Shark Island (Jiménez López, 2019). There are also three areas where fin whale feeding behaviour has been documented: Bahía de los Ángeles-Canal de Ballenas- Grandes Islas, Bahía de La Paz, and Bahía Kino, with fewer records Bahía de Loreto (Jiménez López, 2019). The entire population of Critically Endangered vaquitas is confined within the limits of this IMMA. In Summer 2018 it was estimated that fewer than 19 vaquitas remained (posterior mean 9, median 8, 95% CRI 6–19; Jaramillo-Legorreta et al., 2019). Acoustic data have shown a substantial reduction in the area used by the remaining vaquitas. In 2019 CIRVA, the international recovery team, called on the Government of Mexico to fully mobilize its enforcement assets to eliminate illegal fishing in this small area where the last few vaquitas remain (12 km x 24 km), called the Zero Tolerance Area (ZTA).
Sub-criterion B2: Aggregations
Within the Gulf of California IMMA, Loreto Bay serves as an important annual aggregation point for blue whales (Gendron, 2002), where females have been seen with young and where feeding has been further documented (Sears et al., 2013). Although blue whales don’t normally demonstrate a preference for a particular habitat, but rather concentrate where there is food biomass (Chávez-Andrade, 2006), it is recognized that the Loreto Bay area is an important aggregation zone for this species.
Criterion C: Key Life Cycle Activities
Sub-criterion C1: Reproductive Areas
The Gulf of California is a nursery area for blue whales of the Northeast Pacific stock. The females, both these with and without calves, return to the Gulf of California which indicates that the area it is also regularly used by females in different reproductive states (Gendron 2002; Sears et al., 2013). Humpback whales (Megaptera novaeangliae) from the North Pacific congregate in the Gulf of California for mating, calving and nursing. Within the IMMA, they are concentrated in the Los Cabos region in the southern end of the Peninsula of Baja California Sur, and in Bahía de Banderas including the coast of Nayarit and Islas Tres Marias (Urbán y Aguayo, 1987; Urbán et al., 2000). The estimated abundance of these aggregations were estimated at 2,188 individuals (95% CI 1861-2612) in 1993 (Urbán et al 1999; Martínez-Loustalot, 2017). Mothers with calves are distributed close to the shore while the singing males and competitive groups have more oceanic distribution. There are movements between aggregations and their main migratory destinations are the west coast of USA and also the Gulf of Alaska and Aleutians (Urbán et al., 2000).
Sub-criterion C2: Feeding Areas
Unlike other baleen whale species with migratory habits, that take them between productive temperate/polar regions and tropical wintering grounds, blue whales in the Gulf of California feed extensively on dense aggregations of krill species, primarily those species of krill of the Nyctiphanes simplex (Gendron, 1990; Del Angel-Rodríguez, 1997). Molecular eschatology revealed that lanternfish of the family Myctophidae were also present in 98% of fecal samples collected from blue whales in the Gulf of California (Jiménez-Pinedo, 2010).
Criterion D: Special Attributes
Sub-criterion D2: Diversity
The Gulf of California IMMA represents an important habitat supporting a wide diversity of marine mammal species of global significance. The IMMA home to California sea lions (Zalophus californianus) and Guadalupe fur seals (Arctocephalus philippi townsendi) (Szteren and Aurioles-Gamboa, 2011). In addition, The Gulf of California also hosts 31 species of cetaceans belonging to seven different families and 21 genera (Urbán, 2010). Numerous species stand out regarding the Gulf’s richness of species: the fin whale (Balaenoptera physalus) and the Bryde’s whale (Balaenoptera edeni) are present throughout the year, while blue whales are present seasonally in the cold season. Four additional baleen whale species present in the Mexican Pacific also use the Gulf of California: the humpback whale, the minke whale (Balaenoptera acutorostrata) and the gray whale (Eschrichtius robustus). Odontocete species that are periodically observed are killer whales (Orcinus orca) and short-finned pilot whales (Globicephala macrorhynchus) (Vidal et al., 1993; Urbán et al., 2005; Urbán, 2010). Sperm whales (Physeter macrocephalus) are also regularly present in association with the presence of squid in the area, particularly the species Dosidicus gigas (Jaquet and Gendron, 2002; Camarillo-Coop et al., 2011).
Supporting Information
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