NOTE Wiley et al.: Stranding and mortality of Megaptera novaeangliae 



203 



tor in the change in whale distribution suggested 

 here. While data on changes in prey distribution were 

 not available, the first observations of winter feed- 

 ing humpbacks were documented in the nearshore 

 waters of Maryland (deGroot 10 ) and Virginia (Swingle 

 et al., 1993), during the winters of 1991 and 1992. 



An additional possibility is that the humpback 

 whale population in the western North Atlantic may 

 be increasing and expanding its range such that habi- 

 tats historically occupied are being recolonized. Sev- 

 eral authors (Katona and Beard, 1990; Sigurjonsson 

 and Gunnlaugsson, 1990) have reported numerical 

 increases for this population, although this may be 

 due to increased effort resulting in more accurate 

 estimates of abundance. 



Humpback whales may have always been present 

 during winter in offshore waters of the study area, 

 but a shift in prey abundance or distribution, or both, 

 may have brought them into areas where death 

 would result in stranding, rather than have caused 

 them to be lost at sea. However, offshore concentra- 

 tions were not detected during 1978-82 aerial sur- 

 veys (CeTAP 11 ) or during 1980-88 ship board sur- 

 veys (Payne et al. 12 ). 



While juvenile whales can be expected to exhibit 

 higher mortality than adults (Sumich and Harvey, 

 1986; Kraus, 1990a), the absence of adult animals 

 from the stranding record may provide support for 

 the suggestions of Swingle et al. (1993) that winter 

 or migratory segregation, or both, is occurring. For- 

 aging opportunities on the breeding grounds are rare 

 (Dawbin, 1966; Baraff et al., 1991), and it may be 

 adaptive for some juvenile animals to remain and 

 feed in mid-latitude areas, rather than to migrate 

 with adults. If occupying the breeding grounds is the 

 preferred behavior, individuals remaining in higher 

 latitude areas may be those that failed to obtain suf- 

 ficient resources during the feeding season. Such 

 nutritionally stressed animals may be more suscep- 

 tible to all forms of mortality, natural or anthropo- 

 genic. Nutritionally stressed juveniles and newly 

 weaned calves in particular may be vulnerable to the 

 effects of the parasitic nematode Crassicauda boopis 

 (Lambertsen, 1992). 



10 deGroot, G. 1992. A fluke of nature. The Annapolis Capital- 

 Gazette. 10 March, p. 1. 



11 CeTAP. 1982. A characterization of marine mammals and 

 turtles in the mid- and North Atlantic areas of the U. S. outer 

 continental shelf. Final Rep. to the Cetacean and Turtle As- 

 sessment Program, Univ. Rhode Island, Bur. Land Manage., 

 Contract AA551-CT8-48. U.S. Dep. Int., Wash., DC, 450 p. 



12 Payne, P. M., W. Heinemann, and L. A. Selzer. 1992. A distri- 

 butional assessment of cetaceans in shelf/shelf-edge and adja- 

 cent slope waters of the northeastern United States based on 

 aerial and shipboard surveys, 1978-1988. Natl. Mar. Fish. 

 Serv., Northeast Fish. Sci. Cent,, Woods Hole, MA 02543. 

 Unpubl. manuscr., 108 p. 



If winter foraging opportunities are sufficient, ju- 

 veniles may delay their return to traditional feeding 

 areas and may eventually occupy new habitat. This 

 may be one mechanism by which a species establishes 

 itself in new areas or reoccupies historic sites. This 

 process may be reflected in the stranding record. 

 There seems to be a progressive trend not only for 

 an increased number of strandings but for strandings 

 to take place in a greater variety of months. 



A high percentage of animals exhibited signs that 

 anthropogenic interactions could be implicated in 

 their death. However, there are reasons to believe 

 that mortality estimates based on available strand- 

 ing data could under- or overestimate the impact of 

 human interaction. For example, stranded animals 

 on 16 and 22 April 1992 exhibited no external signs 

 of trauma. However, necropsies indicated internal 

 injuries consistent with a ship strike (McLellan 13 ; 

 Thayer 14 ), suggesting that such injuries could have 

 escaped notice during more cursory examinations. 

 The lack of external body trauma on animals which 

 thorough necropsy revealed to have been killed by a 

 ship strike has also been noted for the northern right 

 whale, Eubalaena glacialis (Kraus 15 ). 



Alternatively, references to rope or net marks did 

 not always specify whether such marks were of re- 

 cent origin or due to past entanglement from which 

 the animal escaped. Baleen whale entanglement does 

 not always lead to immediate mortality (Kraus, 

 1990a); however, the effect of escaped entanglement 

 on long-term survivorship or reproductive success, 

 or both, is unknown. If rope or net marks noted in 

 the stranding reports were of past origin, they may 

 have been independent of the animal's death or the 

 animal may have succumbed to the long-term effects 

 of past entanglement. Reduced foraging efficiency 

 during the entanglement period may be a factor in- 

 fluencing animals to engage in winter feeding behav- 

 ior, such as that observed in the study area by 

 Swingle et al. (1993). 



The apparent high rate of interaction with com- 

 mercial fishing and shipping, may be due, in part, to 

 the age class inhabiting the area. Juvenile animals, 

 and newly independent calves in particular, may be 

 more susceptible to ship strikes or fishing gear en- 

 tanglements, or both, owing to a lack of experience 

 with either factor (Lien, in press). Commercial ship- 

 ping and military traffic to and from the Chesapeake 

 Bay passes by much of the area where strandings 



13 McLellan, W. James Madison Univ., Harrisonburg, VA 22807. 

 Personal commun., March 1993. 



14 Thayer, V. Natl. Mar. Fish. Serv., Beaufort, NC 28516. Per- 

 sonal commun., March 1993. 



15 Kraus, S. New England Aquarium, Boston, MA 02110. Per- 

 sonal commun., March 1993. 



