Banderas Bay and Islands of Nayarit IMMA
Size in Square Kilometres
2 174 km2
Qualifying Species and Criteria
Humpback whale – Megaptera novaeangliae
Criterion A; C (1)
Marine Mammal Diversity
Criterion D (2)
Balaenoptera edeni, Eschrichtius robustus, Kogia sima, Megaptera novaeangliae kuzira, Orcinus orca, Pseudorca crassidens, Physeter macrocephalus, Stenella attenuata attenuata, Stenella attenuata graffmani, Stenella longirostris orientalis, Steno bredanensis, Tursiops truncatus, Ziphius cavirostris
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Summary
Banderas Bay and the Nayarit Islands encompasses the Isla Isabel National Park and Islas Marías UNESCO biosphere reserve. It is situated below the entrance to the Gulf of California, which is considered one of the most biodiverse marine ecosystems in the world. It is at the juncture where several biogeographic areas meet. Bordered by the Middle-America Trench, deep and shallow waters combine with warm and cool mixing currents, this create a unique marine environment that supports high cetacean diversity. In total, 13 cetacean species are regularly encountered in the area, with year-round sightings of false killer whales (Pseudorca crassidens), killer whales (Orcinus orca), and a resident population of dwarf sperm whales (Kogia sima) found in the southern area of the IMMA. The threatened Mexican Distinct Population Segment (DPS) of North Pacific humpback whales (Megaptera novaeangliae kuzira) assemble in large numbers during the winter months to breed, calve and nurse, while humpback whales from the endangered Central America DPS migrate through the IMMA.
Description of Qualifying Criteria
Criterion A – Species or Population Vulnerability
Humpback whales that migrate to the region are part of the Mexico Distinct Population Segment (DPS), which in 2016 was classified as “Threatened” by the US Government’s National Oceanic and Atmospheric Administration (NOAA) as part of the Endangered Species Act (NOAA, 2016). Additionally, humpback whales of the Central America DPS, which were classified as “Endangered” (NOAA, 2016), migrate through the region on the way to their breeding areas further south (Calambokidis et al., 2008; Mate et al., 2018). Justification for these “At Risk” DPS status’s were that for the Mexico DPS there is an absence of regional information on population growth in the last decades, and that whales of the DPS are considered to be threatened significantly by fishing gear entanglement (NOAA, 2016). The Central America DPS was considered to be at risk of extinction due to the low abundance estimate of ~600 non-calf individuals (Calambokidis et al., 2008; NOAA, 2016), although Bettridge et al. (2015) noted there was “considerable uncertainty about the actual population size”. A recent study, using a one-dimensional spatial capture-recapture model, has estimated the population to be significantly larger – at approximately ~1500 non-calf individuals (Curtis et al., 2022) – although still much smaller than estimates of the neighbouring Mexico DPS (Calambokidis et al., 2008).
Criterion C: Key Life Cycle Activities
Sub-criterion C1: Reproductive Areas
Most populations of humpback whales undertake extensive migrations each year between high latitude summer cold-water feeding areas, to low-latitude winter tropical breeding areas (Dawbin, 1966). Nineteenth Century whaling data show that humpback whales have been visiting this IMMA seasonally for several hundred years (Townsend, 1935). The first research surveys, which were conducted in the 1960s (after heavy harvesting of the species and eventual international protection), found humpback whales distributed throughout the region although at a very low abundance of an estimated few hundred animals (Rice, 1966). Today, the population has grown significantly and each year during winter and early spring humpback whales assemble around the islands and in the shallow coastal waters of the IMMA to mate, calve and nurse their young (Calambokidis et al., 2008; Espinoza Rodríguez et al., 2021; Zavala-Alarcón et al., 2021). Using mark-recapture models and data collected between 2004 – 2006 the mainland Mexico breeding area was estimated to host approximately ~3000 – 5000 non-calf individuals with increases of approximately 5 – 6 % annually (Martínez-Aguilar et al., 2018). Males are commonly encountered singing in the region (Darling et al., 2019) and competitive courtship behavior is regularly observed (Espinoza Rodríguez et al., 2021; Ransome et al., 2021; Zavala-Alarcón et al., 2021; Ransome et al., 2022). Humpback whale births have been documented in the Banderas Bay region of the IMMA (Ransome et al., 2021), and females have extended seasonal residencies of five or more weeks when nursing their calves (Ransome et al., 2022). Additionally, atypical feeding by large aggregations of humpback whales was first documented during the La Niña year of 2011/2012 in Banderas Bay (Frisch-Jordán et al., 2019), and observations of feeding have been continued in years of colder sea surface temperatures (Nicola Ransome, unpublished data).
Criterion D: Special Attributes
Sub-criterion D2: Diversity
Most of the focus of cetacean research has been in the south of the IMMA in Banderas Bay and its near waters. Between 1981 – 2015, 954 research trips, comprising over 4631 hours of survey effort and covering more than 2000km documented 20 marine mammal species (2 pinniped species and 18 cetacean species) involving 5232 unique sightings (Arroyo Sánchez, 2017). Of these, 11 species of cetaceans were documented over 10 times. The most commonly encountered was the humpback whale (~4000 sightings) followed by the coastal pantropical spotted dolphin (Stenella attenuata graffmani) (~1000 sightings) and the common bottlenose dolphin (Tursiops truncatus) (~1000 sightings). The other seven frequently encountered species were dwarf sperm whales (Kogia sima) (~100 sightings) rough toothed dolphins (Steno bredanensis) (~100 sightings), Bryde’s whales (Balaenoptera edeni) (~30 sightings), gray whales (Eschrichtius robustus) (~30 sightings), eastern spinner dolphins (Stenella longirostris orientalis) (~20 sightings), false killer whales (Pseudorca crassidens) (~20 sightings), killer whales (Orcinus orca) (~20 sightings) and Cuvier’s beaked whales (Ziphius Cavirostris) (~10 sightings) (Arroyo Sánchez, 2017). Additionally, increased observations of sperm whales (Physeter macrocephalus) during vessel surveys and aerial surveys have been made in the IMMA during the last five years, including groups of up to 30 animals (Nicola Ransome, unpublished data).
Supporting Information
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