Cetaceans of the oceanic northern Gulf of Mexico: Distributions, group sizes and interspecific associations

Abstract

The Gulf of Mexico is a subtropical ocean basin with a diverse oceanic cetacean community. Cetacean research in the Gulf of Mexico has been driven by mandates of the US Marine Mammal Protection Act as well as concerns over the rapidly expanding oil and natural gas industry and related potential threats (e.g. seismic surveys, increased ship traffic, oil spills). Previously, cetacean distribution and abundances for specific Gulf of Mexico areas or species have been described based on work over periods of several years, and recently abundance estimates were made for the entire oceanic northern Gulf of Mexico (1996-2001). For each cetacean species, the paper describes distribution, group size, associated sea surface temperature and water depth and interspecific associations based on surveys conducted over 11 years that span the entire northern Gulf of Mexico. This dataset is the most comprehensive to date for the oceanic northern Gulf. Nine ship surveys totalling 45,462km of effort were conducted during spring seasons (1991-2001) in continental shelf-edge and oceanic waters ( 100m) of the northern Gulf of Mexico. Eighteen species were identified from 1,868 sightings. Cetaceans were found throughout the area although some species had localised distributions or occurred in restricted ranges of water depths. Spinner dolphins (Stenella longirostris) had the largest mean group size (n = 40, x – = 151.5, SE = 30.90), followed by melon-headed whales (Peponocephala electra), clymene dolphins (S. clymene), pantropical spotted dolphins (S. attenuata), Fraser’s dolphins (Lagenodelphis hosei) and striped dolphins (S. coeruleoalba) (range of means 46.1-99.6). Beaked whales (Ziphiidae), Bryde’s whales (Balaenoptera edeni/brydei), sperm whales (Physeter macrocephalus) and pygmy/dwarf sperm whales (Kogia spp.) were found in the smallest groups (x – < 3). Twenty-seven sightings (1.4% of all sightings) were composed of two cetacean species. Common bottlenose dolphins (Tursiops truncatus) were recorded in mixedspecies groups with more species than any other cetacean. Forty-five cetacean sightings (2.4% of all sightings) were associated with at least one bird species, and 21 (1.1% of all sightings) were associated with schools of fish. Contrary to previous reports, pantropical spotted dolphins were observed in association with both fish (including surface tunas) and seabirds, although to a lesser extent than for other tropical oceans. No mixed pantropical spotted and spinner dolphin groups were sighted despite their regular co-occurrence in other tropical oceans.

Cetacean‐mediated vertical nitrogen transport in the oceanic realm

“…Cetaceans occupy important ecological roles in oceanic ecosystems as predators, prey, foraging facilitators, and nutrient vectors (Bowen 1997, Roman et al 2014, Kiszka et al 2015. Their frequent diving behavior to deeper layers and assumed ubiquitous distribution throughout the oceanic Gulf of Mexico (Davis et al 1998;Maze-Foley and Mullin 2006) suggests that cetaceans provide positive feedback loops throughout the oligotrophic ocean basins via the influx of nutrients. This has also been suggested in other ecosystems for several large cetaceans, such as blue (Balaenoptera musculus) and sperm whales, supplementing iron concentrations and promoting primary production in the Southern Ocean (Lavery et al 2010(Lavery et al , 2014.…”

“…A small portion of the Caribbean Sea was included within the study area based on a habitat suitability model recently developed for the region (Ramírez‐León et al 2021). The continental shelf region (landward of 200‐m isobath) was not included in this analysis because of the importance of the continental shelf break in dividing cetacean stocks and species' distributions (Maze‐Foley and Mullin 2006; Ramírez‐León et al 2021), making these regions distinct from an ecological standpoint. The model consisted of 19 cetacean species (Table 1), with species' abundances simulated as random integers from lognormal distributions.…”

“…This randomization and constraint process means that there were more simulations with modeled abundances near the minimum population size estimate than the maximum population size estimate, but was intended for all simulations to have a possible abundance (determined by stock assessment confidence intervals) and the mean species' abundance from all model iterations to closely represent the stock assessment mean population size. All species were divided into groups with group sizes determined by the means, and standard errors of group sizes in the Gulf of Mexico (Table 1; Maze‐Foley and Mullin 2006). Each group was composed of one or more individuals of the same species that shared the same morphological and ecological characteristics (i.e., dive behavior, diet, and body size).…”

Drones Assist in the First Report of a Mixed-Species Group of Tursiops truncatus (Common Bottlenose Dolphin) and a Stenella frontalis (Atlantic Spotted Dolphin) along the Southeast Florida Coast

“…data). Reports of MSGs between Atlantic Spotted Dolphins and Common Bottlenose Dolphins exist throughout other portions of their range: the Azores (Clua and Grosvalet 2001), the Gulf of Mexico (Maze-Foley and Mullin 2006), oceanic waters off the coast of southeastern and southern Brazil (de Lima et al 2021), and many reports in the Bahamas (Cusick and Herzing 2014, Eireman et al 2019, Elliser and Herzing 2015, Herzing 1996, Herzing and Johnson 1997, Herzing et al 2003, Melillo et al 2009, Volker and Herzing 2021). Until now, to our knowledge, there have been no reported observations of these types of interactions along the southeast Florida coast in the literature.…”

“…In the Gulf of Mexico, aggressive behaviors such as jaw snaps and head-butting have been observed within MSGs of Atlantic Spotted Dolphins and Common Bottlenose Dolphins during 2 of 9 sightings (Maze-Foley and Mullin 2006). In the Bahamas, WDP has observed MSGs composed of Atlantic Spotted Dolphins and Common Bottlenose Dolphins engaged in social behavior, such as aggression, including behaviors such as side-mounting and copulation between males of both species (Cusick and Herzing 2014, Volker and Herzing 2021).…”