Balaenoptera edeni (Gulf of Mexico subpopulation)
|Scientific Name:||Balaenoptera edeni (Gulf of Mexico subpopulation)|
|Taxonomic Notes:||The Gulf of Mexico Whale (Balaenoptera edeni unnamed subspecies) is a distinct evolutionary lineage within the Eden’s Whale (B. e. edeni)/Bryde’s Whale (B. e. brydei) complex (Rosel and Wilcox 2014). The taxonomy of the Bryde’s Whale complex is unsettled, but it comprises three distinct lineages: Gulf of Mexico Whale, Eden’s Whale, and Bryde’s Whale, each of which is clearly distinct. Whether these clades represent subspecies of B. edeni or full species remains disputed (e.g., Wada et al. 2003, Sasaki et al 2006). The Committee on Taxonomy of the Society for Marine Mammalogy has indicated that the Gulf of Mexico Whale represents at least a separate subspecies (Rosel et al. 2016), based on the information presented in Rosel and Wilcox (2014). However, in view of its limited known range and small numbers, this taxon is assessed as a subpopulation provisionally assigned to B. edeni.
|Red List Category & Criteria:||Critically Endangered D ver 3.1|
|Assessor(s):||Corkeron, P., Reeves, R. & Rosel, P.|
|Reviewer(s):||Brownell Jr., R.L. & Taylor, B.L.|
|Facilitator/Compiler(s):||Lowry, L., Chiozza, F.|
The Gulf of Mexico Whale subpopulation is believed to be geographically, demographically, and genetically isolated from all other lineages of the Bryde’s Whale complex, with known year-round residency in the northeastern Gulf of Mexico; there are no verified data on the current presence of these whales elsewhere in the Gulf of Mexico or the northern Caribbean Sea. Estimates of historical population size are unavailable. Whaling records indicate that the historical range of the subpopulation may have included the north-central and southern Gulf of Mexico, implying a substantial range contraction over the past 150 years although there has been little recent search effort in the southern Gulf of Mexico. The best estimate of current total abundance, based on a vessel line-transect survey in 2009, is 33 (CV (coefficient of variation) 1.07) individuals of all age classes or stages. Taylor et al. (2007) estimated the portion mature to be 51% for Bryde's Whale populations which indicates that the number of mature individuals could be as few as 17. The basis for a Critically Endangered listing is that the subpopulation is geographically and genetically distinct and very likely contains fewer than 50 mature individuals which meets IUCN Red List criterion D.
|Range Description:||The current known distribution of the Gulf of Mexico Whale is the northeastern Gulf of Mexico along the continental slope primarily between the 100 m and 400 m isobaths (Rosel et al. 2016). A Biologically Important Area (BIA; as defined by the US National Oceanic and Atmospheric Administration; https://data.noaa.gov/dataset/biologically-important-areas-for-cetaceans-within-u-s-waters) for the Gulf of Mexico Whale has been delimited based on sightings from aerial and shipboard surveys (LaBreque et al. 2015). This BIA has an area of ~23,500 km² (Ferguson et al. 2015). However, it excludes a portion of the known range, based on sightings, along the continental slope to the west as far as approximately Mobile Bay, Alabama, USA (Rosel et al. 2016). In addition, multiple stranded whales have been recovered in southeastern Louisiana (Mead 1977, Rosel et al. 2016). A habitat model of the subpopulation's distribution has been developed based on the same visual survey data that were used to delineate the BIA (Roberts et al. 2016). The ranges determined by delineating the smallest region that captured 90% and 95% of the total predicted abundance were 21,600 km² and 29,500 km² respectively, bracketing the size of the BIA. The one Gulf of Mexico Whale that has been instrumented with a satellite-linked radio tag, which transmitted for 32 days, spent the duration of the tag’s deployment within, or just beyond, the 300 m isobath of the BIA area (Soldevilla et al. 2017).|
The logbooks of whaling ships that visited the Gulf of Mexico between 1780 and 1870 were reviewed for records of “finbacks” (Reeves et al. 2011). As the infrequent records of Fin Whales (Balaenoptera physalus) in the Gulf of Mexico are considered extralimital in the 20th century (Jefferson and Schiro 1997), it is unlikely that these are records of anything other than Gulf of Mexico Whales although the possibility that more boreal species such as Fin, Sei (Balaenoptera borealis), and Common Minke Whales (Balaenoptera acutorostrata) were more common in the Gulf of Mexico then than they are today cannot be ruled out. The geographic locations where “finbacks” were recorded in the whaling records as either sighted or killed suggest that the historical range of Gulf of Mexico Whales included continental slope waters of the north-central and southern Gulf of Mexico (Reeves et al. 2011). Survey effort in US waters of the north-central and western Gulf of Mexico between the early 1990s and the present has not yielded any sightings of Gulf of Mexico Whales, and very little effort has been dedicated to determining whether these whales still occur in the southern Gulf of Mexico.
Although the Gulf of Mexico Whale’s range is presently believed to be restricted to the northeastern Gulf of Mexico, there are a few records of Bryde’s Whales stranded on the southern section of the U.S. Atlantic coast (Rosel et al. 2016). Genetic analysis of two of these specimens identified them as members of the Gulf of Mexico Whale clade (Rosel and Wilcox 2014). There have been no sightings that can be definitively identified as members of the Eden’s/Bryde’s Whale complex in surveys conducted in Atlantic waters of the US Exclusive Economic Zone (Roberts et al. 2015). Analyses of the acoustic monitoring programs in US Navy training ranges off North Carolina in 2011-2012 (Debich et al. 2014) and off Florida in 2013-2015 (Debich et al. 2015, Frasier et al. 2015) found no evidence of calls known to be produced by Gulf of Mexico Whales (Širović et al. 2014).
Native:United States (Alabama, Florida)
|FAO Marine Fishing Areas:|
Atlantic – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||The best population estimate for the Gulf of Mexico Whale is 33 (CV 1.07) based on a large-vessel line transect survey conducted in 2009 (Garrison 2016). Previously published estimates based on large-vessel line transect surveys are: 35 (CV 1.10) for the period 1991-1994 (Hansen et al. 1995); 40 (CV 0.61) for 1996-2001 (Mullen and Fulling 2004); and 15 (CV 1.98) for 2003-2004 (Mullin 2007). All of these estimates appear to support the conclusion that there are fewer than 50 mature individuals remaining in the population, even considering the following caveats.|
The above estimates do not include a multiplier for animals on the trackline that were not observed because they were unavailable for sighting (i.e., underwater). Also, the various estimates in the time series are not directly comparable, as the original (1991-1995) analysis did not apply habitat stratification whereas the later analyses did (Hansen et al. 1995, Mullen and Fulling 2004).
Roberts et al. (2015, 2016) produced an abundance estimate based on the habitat model discussed above. This estimate, 44 (CV 0.27), integrates data from 1992 to 2009 and includes a correction for animals likely unavailable for sighting. This model-based estimate is derived from the same visual survey series that resulted in the estimates above, but produced an aggregate estimate over time.
Finally, an abundance estimate of 26 (95% confidence interval (CI) 12-56) was generated for the Deepwater Horizon (DWH) oil spill damage assessment by combining all visual survey data between 2003 and 2009 and using somewhat different geographical boundaries than were used for the 2009 estimate (DWH MMIQT 2015, DWH NRDA Trustees 2016).
|Current Population Trend:||Decreasing|
|Habitat and Ecology:|
Gulf of Mexico Whales are currently known to occur in the northeastern Gulf of Mexico, primarily in the vicinity of De Soto Canyon, between the 100 m and 400 m isobaths (Rosel et al. 2016). There is little information on their foraging behaviour. Eden’s and Bryde’s Whales feed primarily on small schooling fish and euphausiids (Kawamura 1977, Urbán and Flores 1996, Best 2001, Thongsukdee et al. 2014). The same may be true of Gulf of Mexico Whales. In 2015, a female Gulf of Mexico Whale was tagged using a suction-cup time-depth recorder that remained in place for almost three days. During that time, the whale engaged in deep dives during the day and shallow dives at night. That individual appeared to be foraging near the sea floor (Soldevilla et al. 2017).
|Continuing decline in area, extent and/or quality of habitat:||Unknown|
The Deepwater Horizon (DWH) oil spill of 2010 occurred close to the primary habitat of Gulf of Mexico Whales. It is estimated that 48% of the subpopulation was exposed to oil, that 22% (95% CI 10–31) of females suffered from reproductive failure, and 18% (95% CI 7–28) of the overall population suffered adverse health effects (DWH MMIQT 2015). Population modelling suggests a maximum possible decline in the subpopulation of 22% (i.e., 5-6 whales from a population estimated for the oil spill damage assessment of 26). Two Gulf of Mexico Whales stranded dead in 2012, a time when impacts on cetaceans from the DWH oil spill were still being documented, but the state of decomposition of the two carcasses was such that cause of death was impossible to determine (Waring et al. 2016).
Entanglement in fishing gear is a well-known problem for all large whales in US waters, with lethal (Cassoff et al. 2011) and sublethal (van der Hoop et al. 2017) effects. In 2003, an adult whale, genetically identified as a Gulf of Mexico Whale, that stranded in North Carolina died from a chronic entanglement (Cassoff et al. 2011). Another individual that live-stranded in 1974 on an island off Florida’s Gulf coast was an entangled immature male (Mead 1977).
Ship strike is a known population-level threat to at least one other small population in the Bryde’s/Eden’s Whale complex (Constantine et al. 2015). In 2009, a lactating female Gulf of Mexico Whale was killed by ship strike (Waring et al. 2016). The northern Gulf of Mexico experiences considerable vessel traffic, particularly in the north-central and western regions where oil and gas exploration and development are concentrated (Rosel et al. 2016). Vessel densities are highest in shipping lanes near ports and around oil and gas platforms. Several shipping lanes cross the Gulf of Mexico Whale BIA described above.
Anthropogenic ambient noise in the northern Gulf of Mexico is chronically elevated, and seismic surveys make a significant contribution to noise levels (Estabrook et al. 2016). Anthropogenic noise in general (Clark et al. 2009), and noise generated by seismic surveys in particular (Nowacek et al. 2015), is a concern for baleen whales. Although the population-level impacts of chronically elevated anthropogenic noise on baleen whales remain poorly understood (Estabrook et al. 2016), this stressor is of concern in the case of Gulf of Mexico Whales.
The Bryde’s Whale species complex (B. edeni and subspecies) is included in Appendix I of the Convention on International Trade in Endangered Species (CITES). The species complex (B. edeni and subspecies) is listed in Appendix II of the Convention on Migratory Species (CMS). The US National Marine Fisheries Service is currently assessing whether Gulf of Mexico Whales should be listed as Endangered or Threatened under the Endangered Species Act (see Rosel et al. 2016).
There are closures on pelagic longline fisheries in the region of De Soto Canyon (Rosel et al. 2016). However, there is concern that these whales forage at the bottom (Soldevilla et al. 2017) in an area of bottom longline fishing. A moratorium on oil exploration and development within approximately 200 km of the coast of Florida and east of 86° 41'W is set to expire in 2022 (Rosel et al. 2016). This means that in much of the Gulf of Mexico Whale’s present habitat the risk of entanglement has been reduced, as has the risk of ship strike (at least from vessels servicing oil platforms) compared with much of the rest of the Gulf of Mexico (at least within US waters). Although these spatially explicit actions were not put in place to help conserve Gulf of Mexico Whales, they provide some de facto protection to them.
|Citation:||Corkeron, P., Reeves, R. & Rosel, P. 2017. Balaenoptera edeni (Gulf of Mexico subpopulation). The IUCN Red List of Threatened Species 2017: e.T117636167A117636174.Downloaded on 20 August 2018.|
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