KENNEY and WINN: CETACEAN HIGH-USE HABITATS 



and white-sided dolphins likely do so as well (CETAP 

 1982; Mayo 1982; Mitchell 1975b). The sand lance 

 populations of the western North Atlantic have in- 

 creased dramatically since the mid-1970's (Sherman 

 et al. 1981). Meyer et al. (1979) described the west- 

 ern Gulf of Maine, especially Stellwagen Bank and 

 east of Cape Cod, as an area of extremely dense sand 

 lance populations. Data from the National Marine 

 Fisheries Service 1979-1981 groundfish surveys (T. 

 R. Azarovitz 5 ) also shows peak Ammodytes abun- 

 dance in the Stellwagen Bank-Jeffreys Ledge area. 

 A second area of high sand lance abundance shown 

 oy these data corresponds to the midshelf east of 

 the Chesapeake, which was identified above as a 

 region of high use by piscivorous cetaceans. It is 

 likely that sand lance distributions are a primary 

 controlling factor in the pattern of high-intensity 

 habitat use shown here for the western Gulf of 

 Maine. 



Ammodytes is not the only cetacean prey species 

 which can be shown to have a strong effect on pat- 

 terns of cetacean habitat use within the western Gulf 

 of Maine, although it is the major one The right 

 whale feeds primarily upon copepods (Nemoto 1970; 

 Watkins and Schevill 1976). Right whales are a major 

 component of the cetaceans in the southeasternmost 

 portion of the high-use area in the western Gulf of 

 Maine, in the vicinity of the Great South Channel, 

 where they congregate in response to extremely 

 dense spring concentrations of Calanus finmar- 

 chicus (CETAP 1982). 



The other high-use cetacean habitat we have iden- 

 tified is the edge of the continental shelf. The ceta- 

 cean assemblage of this region has been analyzed 

 in detail by Hain et al. (1985). The primary species 

 of the shelf edge are sperm whales, pilot whales, gray 

 grampus, saddleback dolphins, bottlenose dolphins, 

 and striped dolphins. Less common species include 

 the various beaked whales and other dolphin species. 

 This assemblage does not specialize on one or two 

 prey species as we have suggested for the Gulf of 

 Maine, but is highly diverse in prey taken, although 

 individual species may exhibit quite narrow dietary 

 specializations. Food items include a wide variety of 

 squids and fishes (Kenney et al. 1985). Furthermore, 

 the shelf edge assemblage on Georges Bank includes 

 sei whales, which feed primarily on copepods and 

 secondarily on euphausiids (Jonsgard and Darling 

 -;977; Mitchell 1975a, 1975b; Nemoto 1970). Sei 

 whales occur primarily on the southwest and eastern 



portions of Georges Bank. The CETAP data also 

 show sightings of other baleen whales— primarily fin 

 whales, but also minke, humpback, and right whales 

 —near the southern edge of Georges Bank during 

 some times of the year. The shelf edge, although used 

 less intensely than the western Gulf of Maine, sup- 

 ports a cetacean fauna which is much more diverse 

 in terms of both cetacean species and variety of prey 

 taken. 



We have interpreted our results in this study as 

 indicating control of cetacean distributions by the 

 distributions of the most important prey species. 

 This is almost certain to be the case on a microscale 

 level, but may or may not be true at the general level. 

 It is unknown how migratory cetaceans orient or 

 navigate to their feeding grounds, but it may be that 

 physical cues from the environment are used in this 

 process, in effect determining or influencing the 

 general pattern of distribution. Another alternative 

 could be that there is a significant traditional or 

 historical component of the return to the same 

 general vicinity each year, with microscale distribu- 

 tions within that region directly related to prey den- 

 sity. In each of these cases the ultimate controlling 

 factor is food, but the proximate factors are some- 

 thing different. 



We have limited our discussion of individual species 

 mostly to the descriptive level. One factor, however, 

 should be noted. Because we are dealing with bio- 

 mass of cetaceans, these patterns are dominated by 

 the large whales for the most part. Because fin 

 whales are easily the most common whale in the 

 region, they are the dominant factor in patterns of 

 cetacean biomass distribution (Kenney et al. 1985; 

 Scott et al. fn. 4). The most common species num- 

 erically were white-sided and saddleback dolphins, 

 with estimated populations of each exceeding 30,000 

 individuals (CETAP 1982), but their contributions 

 to the patterns shown here are smaller because of 

 their relatively smaller sizes. One must refer to the 

 distribution plots in the 1982 CETAP report for the 

 details of individual species distribution patterns. 



We have purposely avoided the use of the term 

 "critical habitat" in this analysis. Besides the legal 

 aspects of the term under the Endangered Species 

 Act and Marine Mammal Protection Act, Ray and 

 Miller 6 have pointed out that there are many dimen- 

 sions to the concept of critical habitat. These include 

 the biological vulnerability of a species, the ecological 

 processes which support the species, and the poten- 



B T. R. Azarovitz, Northeast Fisheries Center Woods Hole Labora- 

 tory, National Marine Fisheries Service, NOAA, Woods Hole, MA 

 02543, pers. commun. December 1982. 



6 Ray, G. C, and R. V. Miller. 1982. Critical habitats of marine 

 mammals. Paper presented at 1982 annual meeting, International 

 Council for the Exploration of the Seas, ICES CM. 1982/N:7. 



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