FISHERY BULLETIN: VOL. 84, NO. 2 



of humpbacks in the southwest Gulf of Maine 

 reasonably explains the present distribution of 

 humpbacks within the Gulf of Maine. However, it 

 does not adequately explain the paucity of hump- 

 backs on Georges Bank (Table 2) and throughout the 

 remaining shelf waters of the northeastern United 

 States (Hain et al. 1981; Kenney et al. 1981; Payne 

 et al. 1984), areas where sand eel have also increased 

 since 1975. The nonsignificant correlation between 

 humpbacks/effort and the log-mean catches of sand 

 eel/tow on Georges Bank suggests that factors other 

 than simply food concentrations, perhaps behavioral 

 or environmental, may influence the humpback's 

 feeding strategy and location. 



Sutcliffe and Brodie (1977) reported that hump- 

 backs are led into ecological or oceanographic bound- 

 aries (i.e., isopleths or shelf-edges) and feed in 

 patchy areas of dense prey aggregations along these 

 boundaries. A change in depth on the shelf is often 

 accompanied by a concentration of near-surface zoo- 

 plankton; in general, the more abrupt the change, 

 the greater the concentration (Sutcliffe and Brodie 

 1977). Concentrations are especially noticeable 

 along the edge of banks where the availability of 

 prey is most affected (Jaansgard 1974). Reay (1970) 

 found that sand eel concentrations are greatest on 

 the edges of sandy banks where currents and prey 

 (zooplankton) are optimum; thus the whales, in seek- 

 ing the highest concentrations of prey, feed most 

 frequently along the edges of the banks (Sutcliffe 

 and Brodie 1977; Brodie et al. 1978). Observations 

 of feeding humpbacks in the Gulf of Maine have oc- 

 curred primarily along the edge of submarine banks 

 or canyons (Hain et al. 1982; CETAP 1982). 



If bottom topography influences feeding behavior 

 of humpbacks (by concentrating prey), then the 

 paucity of humpbacks on Georges Banks and 

 throughout the mid-Atlantic Bight regions becomes 

 more understandable. The floor of the broad mid- 

 Atlantic Bight is gently sloping continental shelf 

 with no relief until it steepens sharply at the shelf 

 break, at about 200 m depth, to form the continen- 

 tal slope. Since the feeding behaviors for humpbacks 

 described by Hain et al. (1982) occur principally over 

 a shelf-floor with rugged relief, the strategies used 

 by humpbacks seem most efficient in these waters. 

 This also explains the present lack of sightings in 

 the mid-Atlantic shelf waters and the offshore 

 migration route between calving and feeding areas. 

 It seems energetically advantageous for the hump- 

 back, a relatively slow-moving whale, to migrate 

 over deep water with little apparent feeding, then 

 feed on the densely concentrated prey along the bot- 

 tom profiles of the Gulf of Maine. 



We maintain that humpbacks are merely utilizing 

 the first concentrations of prey available to them 

 in spring, after they reach shelf-waters from their 

 offshore migration route between winter-calving 

 and summer-feeding grounds. The humpbacks seem 

 to use the Great South Channel as an entry-exit in- 

 to the Gulf of Maine (as hypothesized by Kenney et 

 al. (1981)), and follow the bottom profile northward, 

 using this profile to their feeding advantage until 

 they reach the dense concentrations of sand eel 

 available within the southwest Gulf of Maine. The 

 quantities of sand eel available to humpbacks at this 

 location have allowed the whales to remain through- 

 out the feeding season; therefore, the recent paucity 

 of sightings in the northern Gulf of Maine. 



ACKNOWLEDGMENTS 



The authors wish to thank T. R. Azarovitz, S. K. 

 Katona, P. Major, M. P. Pennington, M. P. Sissen- 

 wine, G. Waring, H. Whitehead, and anonymous 

 reviewers for criticizing previous drafts of this 

 manuscript. The study was funded by the National 

 Marine Fisheries Service, Northeast Fisheries 

 Center, Woods Hole, MA. 



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