UNITED

NATIONS


Regional Workshop of Experts on the Development of the Marine Mammal Action Plan for the Wider Caribbean Region

Bridgetown, Barbados, 18-21 July 2005

DISTRIBUTION AND STATUS OF MARINE MAMMALS OF THE WIDER CARIBBEAN REGION: AN UPDATE OF UNEP DOCUMENTS

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Distribution and Status of Marine Mammals of the Wider Caribbean Region:

An Update of UNEP Documents

Randall R. Reeves, Okapi Wildlife Associates, 27 Chandler Lane, Hudson, Quebec J0P 1H0, Canada

Abstract

The purpose of this paper is to “update” two documents – Marine Mammals of the Wider Caribbean Region: A Review of their Conservation Status (by Ward and Moscrop, 1999) and Elements for the Development of a Marine Mammal Action Plan for the Wider Caribbean: A Review of Marine Mammal Distribution (by Ward, Moscrop, and Carlson, 2001). Although it is frequently stated that “little is known” about marine mammals in the WCR (a familiar refrain in many other regions and contexts as well), enough is known to make some broad generalizations and to generate working hypotheses to inform the conservation planning process. It is proposed here that the region’s marine mammal populations should be ranked in some way to reflect their significance to global biodiversity conservation. The basis for such ranking could involve such things as: endemism, resident vs. migratory population(s), continuous vs. fragmented distribution, current relative to historic abundance, and global status of the species (e.g., with reference to the IUCN Red List, the CMS appendices). These factors would, of course, need to be balanced against other concerns, such as economic valuation (e.g., whalewatching), cultural traditions (e.g., hunting), and immediacy or severity of threats. As a working hypothesis, it is suggested that manatees (Antillean subspecies in particular) rank highest (assuming that the West Indian monk seal is extinct), but determining which species or populations should fall “next in line” is bound to be a challenge.

Introduction

The two main background documents for the WCR action plan initiative – Ward and Moscrop (1999) and Ward et al. (2001) – summarize much of the relevant literature, specify the marine mammal species known from the region, describe their distribution, ecology, and conservation status, and identify threats, socio-economic opportunities, and research needs. In this paper, I attempt mainly to do two things. First, I review some information that has become available since those documents were prepared and that I consider relevant to the workshop’s needs. Second, I propose an approach for ranking species and populations for attention under the draft plan. I have made no attempt to update information on manatees, on the understanding that other presenters would be covering that species.

New Information of Relevance

Pinnipeds

Ward and Moscrop (1999) and Ward et al. (2001) correctly (in my judgment) considered the West Indian monk seal (Monachus tropicalis) to be extinct, despite the fact that Boyd and Stanfield (1998) offered “circumstantial evidence” for its possible continued existence. Definite evidence is now available that hooded seals (Cystophora cristata) occasionally wander from their Subarctic and Arctic range to occur as vagrants in the WCR, e.g. in Puerto Rico and Guadeloupe. Unlike California sea lions (Zalophus californianus), which are truly exotic in the region, having arrived through human agency, the occasional occurrence of hooded seals represents natural dispersal by a North Atlantic endemic. The occasional appearance of stray harp and harbor seals (Pagophilus groenlandicus and Phoca vitulina, respectively) from the northern North Atlantic might also be expected.

Baleen Whales

It appears, on present evidence, that only one species of baleen whale depends on the WCR for food resources, namely the common Bryde’s whale, Balaenoptera cf. brydei. Whether it migrates seasonally into and out of the region remains to be discovered. Two other species that are regular non-residents, the humpback whale (Megaptera novaeangliae) and the common minke whale (B. acutorostrata), are considered seasonal migrants at the winter (breeding) end of their annual cycle – definitely in the case of the humpback, probably in the case of the minke. The other balaenopterids that have been recorded – blue, fin, and sei (B. musculus, B. physalus, and B. borealis) – are probably “just visiting,” but the possibility cannot be ruled out that their visitation is more regular and frequent in unstudied or poorly studied parts of the region, or that the WCR is a significant portion of the normal range of one or more populations of these species. Similarly, the rare reports of North Atlantic right whales seem to suggest that they are, in some sense, “extralimital.” However, in view of recent occurrences of right whales in the region, this conclusion deserves careful reconsideration.

At the 2004 Workshop on Shortcomings of Cetacean Taxonomy (Reeves et al. 2004:9), participants concluded that one of three high-priority subjects in relation to baleen whales was the need to obtain “immediate clarification” of the borealis-edeni-brydei-omurai complex. The present IUCN Red List classification of the Bryde’s whale as “data deficient” is owing mainly to the problem of taxonomic uncertainty. According to R.G. LeDuc of the Southwest Fisheries Science Center in La Jolla, California (pers. comm., June 2005), he and the cetacean genetics group there are especially interested in obtaining more tissue samples of Bryde’s whales from the WCR for DNA analyses. Their preliminary findings based on a small number of samples suggest that further comparisons of Caribbean animals with those from the western North Pacific and elsewhere will be highly informative to the overall phylogeography of Bryde’s whales, and indeed of the borealis-edeni-brydei-omurai complex. Two activities would seem timely in this regard. First, an updated review and synthesis of records of finner whales (Balaenoptera spp.) in the WCR is needed (cf. Mead 1977). Second, a concerted effort should be made to obtain tissue samples, whether from strandings, sightings (biopsy darting), or animals killed opportunistically by Caribbean whalers.

With regard to humpback whales, the recent findings of Swartz et al. (2003) deserve critical evaluation. Having acknowledged that their study was not designed to obtain abundance estimates, those authors nevertheless reached conclusions implying that they had adequate quantitative information to make comparisons between current (2000) and pre-exploitation abundance of humpbacks in different parts of the WCR. The statement in their abstract that “the species continues to occupy its historical range” is inconsistent with the statement in their main text (p. 205), that “apparent low abundance of whales in the formerly important breeding habitats of the eastern and southeastern Caribbean suggests failure to reoccupy their former range despite … protection….” Moreover, their suggestion that the “abundance of humpbacks using the eastern and southeastern Caribbean … remains low” would seem to require a better understanding not only of actual abundance, but also of how individual whales may circulate during the 4- or 5-month winter season (January-May) – between the “primary breeding aggregations” in the northern Greater Antilles and the extreme southern limits of the population’s distribution along the northern coast of South America. Perhaps the most important result of their study was the failure to find any evidence of present-day use by humpbacks of the Gulf of Paria and waters along the southern coast of Trinidad, which they attributed to “the effects of disturbance and noise associated with the development of extensive oil and gas production facilities … and to heavy commercial shipping traffic since the turn of the 20th century” (p. 205). If this finding is borne out in the light of all other evidence, it would represent one of the few empirical examples available of the outright loss of cetacean “breeding” habitat from ocean urbanization.

Toothed Cetaceans

In terms of science and conservation, research on two species or species groups of cetaceans in the WCR has particular prominence globally: the sperm whale (Physeter macrocephalus) and the beaked whales (Ziphiidae). Ongoing studies of sperm whales around Dominica by Hal Whitehead and his students from Dalhousie University promise to add important insights on the species’ social structure and behavior, particularly when used in comparative analyses with their results from the eastern Pacific. Of more immediate applied importance is the diverse program of research on sperm whales in the northern Gulf of Mexico that includes satellite telemetry, photo-identification, monitoring of dive behavior and physiology, and controlled-exposure experimentation to assess the effects of underwater sound (e.g., Miller et al. 2004a, 2004b; Thode et al. 2002). This work’s significance derives from global concern about the effects of acoustic disturbance on sperm (and other) whales, especially that from offshore oil and gas development.

Long-term studies of beaked whales have been undertaken in just two areas of the world – The Gully off Nova Scotia, Canada (northern bottlenose whale, Hyperoodon ampullatus), and the Bahamas (Blainville’s beaked whale, Mesoplodon densirostris). In the latter area, the work of Claridge and Balcomb (2001) was key in documenting the vulnerability of beaked whales exposed to military sonar under particular circumstances. Given the general rarity of opportunities for observational studies of beaked whales, and the high profile of the controversy surrounding the effects of high-intensity underwater sound on this group of whales, it is important that research effort in the Bahamas be maintained and, if possible, expanded.

Another point worth highlighting, although already noted by Ward et al. (2001:23), concerns the habitat requirements of beaked whales. Contrary to the usual descriptions of various species’ distributions as “cosmopolitan” or “worldwide” in deep offshore waters, it appears that their distributions are considerably more specialized and thus limited. The Bahamas studies provided the first good evidence of this for the mesoplodonts, as summarized by Ward et al. There, Blainville’s beaked whales generally occur only in depths between 200-1000 m and near areas with particular bottom topography. It should be noted in this context that similarly analyses of habitat preferences of other odontocetes have been conducted in the northern Gulf of Mexico (e.g., Baumgartner et al. 2001). Thus, the WCR has become a focal region of research on several species, including the beaked whales, the sperm whale, and several tropical to warm temperate delphinids.

The aforementioned 2004 workshop (Reeves et al. 2004) ranked taxonomic uncertainty as high for killer whales (Orcinus sp.) and called for a global inventory of specimen material for that genus. It seems clear from the records summarized by Ward et al. (2001) that at least some of the killer whales in the WCR are mammal and sea turtle predators, but in the absence of rigorous analysis of morphological, dietary, and other types of data from the region, it remains impossible to judge whether more than one ecotype (and thus possibly eventually subspecies or species) is present. A regional inventory of sighting, stranding, and take records, perhaps followed by a directed effort to obtain and analyze biological materials from killer whales in specific parts of the WCR (via biopsy), could be a significant contribution to ongoing global analyses. The same can be said of Blainville’s beaked whales and Cuvier’s beaked whales (Ziphius cavirostris), both of which the workshop described as “warranting special attention to resolve taxonomic uncertainty” (p. 10). Their vulnerability to underwater noise as well as entanglement in drift gillnets was noted, as was the fact that Dalebout (2002) found strong evidence of population structure in Cuvier’s beaked whale, suggesting that there could be isolated regional populations. Its apparently widespread and regular occurrence in the WCR makes Cuvier’s beaked whale a candidate for focused effort along the same lines as mentioned above for killer whales.

The subject of population structure of odontocetes within the WCR has hardly begun to be addressed, but judging by findings elsewhere, considerable structure is likely present (e.g., island-associated near-shore populations and farther-ranging offshore populations). Given the long history of exploitation of some near-shore species in some parts of the WCR (Caldwell and Caldwell 1975; Price 1985; Reeves 2002), this could mean that a number of populations have already been substantially depleted or even entirely eliminated. In the absence of even rudimentary survey data for most of the region (except U.S. waters of the northern Gulf of Mexico), uncertainty concerning population structure, abundance, and conservation status is the norm.

Ranking

How should the various marine mammal species and populations in the WCR be ranked as conservation priorities? One possibility is to develop a matrix that allows multiple criteria to be taken into account. Such an approach could be pursued at two levels or in two separate contexts – one of global biodiversity and the other at a regional scale. For the first of these, the criteria could include:

  • Endemism, i.e., to what extent do a species’ or a population’s range and number of individuals fall within the WCR?
  • Residency, i.e., does the population remain year-round in WCR waters? If not, how critical is the WCR, as a migratory destination, to the population’s persistence?
  • What is the officially recognized status of the species or population according to global listing schemes, e.g., IUCN Red List, appendices or annexes of conservation conventions? Such listings may provide useful guidance but should not necessarily be accepted uncritically.
  • Potential for contributing to scientific understanding relevant to conservation (this can refer to either a global or a regional level).

Another set of criteria could be developed at the regional level, to include:

  • Socio-economic importance, e.g., is the population subject to human use of any kind (e.g., revenue from tourism or live-capture, as a food source)?
  • National biodiversity conservation policy, i.e., does a legal framework exist that obligates authorities to take management action?
  • Known or suspected threats, e.g., deliberate exploitation (killing or live-capture), offshore military or industrial activity, fisheries operating in the area (especially gillnets or trawls). Such threats can be in the past, ongoing, or anticipated for the near-term future.
  • Historical evidence suggests that the species is present in the region, but little or no recent information exists on its status, i.e., there is high uncertainty.

It would be appropriate for the Action Plan workshop to consider these and other criteria, and attempt to integrate them in setting priorities for proposed actions. The presumably extinct monk seal is the only endemic marine mammal in the region. Populations (subspecies?) of manatees probably would rank high on the basis of a scheme such as the one proposed here. It seems likely that the humpback whale, possibly the Bryde’s whale, the sperm whale, the common bottlenose dolphin, the short-finned pilot whale, and the sperm whale would also rank relatively high based on current understanding. Several others, such as some beaked whales, the killer whale, the clymene dolphin (Stenella clymene), and the marine tucuxi (Sotalia fluviatilis guianensis), would likely rank high according to at least some of the criteria.

References

Balcomb, K.C. and Claridge, D.E. 2001. Mass stranding of cetaceans caused by naval sonar in the Bahamas. Bahamas Journal of Science 4:2-12.

Baumngartner, M.F., Mullin, K.D., May, L.N. and Leming, T.D. 2001. Cetacean habitats in the northern Gulf of Mexico. Fishery Bulletin 99:219-239.

Boyd, I.L. and Stanfield, M.P. 1998. Circumstantial evidence for the presence of monk seals in the West Indies. Oryx 32:310-316.

Caldwell, D.K. and Caldwell, M.C. 1975. Dolphin and small whale fisheries of the Caribbean and West Indies: occurrence, history, and catch statistics – with special reference to the Lesser Antillean island of St. Vincent. Journal of the Fisheries Research Board of Canada 32:1105-1110.

Dalebout, M.L. 2002. Species identity, genetic diversity and molecular systematic relationships among the Ziphiidae (beaked whales). Ph.D. thesis, School of Biological Sciences, University of Auckland, New Zealand.

Mead, J.G. 1977. Records of sei and Bryde’s whales from the Atlantic coast of the United States, the Gulf of Mexico, and the Caribbean. Report of the International Whaling Commission (Special Issue) 1:113-116.

Miller, P.O. Miller, P.J.O., Johnson, M.P. and Tyack, P.L. 2004a. Sperm whale behaviour indicates the use of echolocation click buzzes 'creaks' in prey capture. Proceedings of the Royal Society of London B 271:2239-2247.

Miller, P.J.O., Johnson, M.P., Tyack, P.L. and Terray, E.A. 2004b. Swimming gaits, passive drag and buoyancy of diving sperm whales Physeter macrocephalus. Journal of Experimental Biology 207:1953-1967.

Price, W.S. 1985. Whaling in the Caribbean: historical perspective and update. Report fo the International Whaling Commission 35:413-420.

Reeves, R.R. 2002. The origins and character of ‘aboriginal subsistence’ whaling: a global review. Mammal Review 32:71-106.

Reeves, R.R., Perrin, W.F., Taylor, B.L., Baker, C.S. and Mesnick, S.L. (eds.). 2004. Report of the Workshop on Shortcomings of Cetacean Taxonomy in Relation to Needs of Conservation and Management, April 30 – May 2, 2004, La Jolla, California. NOAA Technical Memorandum NMFS-SWFSC-363.

Swartz, S.L., Cole, T., McDonald, M.A., Hildebrand, J.A., Oleson, E.M., Martinez, A., Clapham, P.J., Barlow, J. and Jones, M.L. 2003. Acoustic and visual survey of humpback whales (Megaptera novaeangliae) distribution in the eastern and southeastern Caribbean Sea. Caribbean Journal of Science 39:195-208.

Thode, A., Mellinger, D.K., Stienessen, S., Martinez, A., and Mullin, K. 2002. Depth-dependent acoustic features of diving sperm whales (Physeter macrocephalus) in the Gulf of Mexico. Journal of the Acoustical Society of America 112:308-321.

Ward, N. and Moscrop, A. 1999. Marine mammals of the Wider Caribbean Region: a preliminary review of their conservation status.

Ward, N., Moscrop, A. and Carlson, C. 2001. Elements for the development of a marine mammal action plan for the Wider Caribbean: a review of marine mammal distribution.

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