198 



Fishery Bulletin 93(1), 1995 



Results 



Mortality 



A total of 38 stranded humpback whales were re- 

 corded between 1 January 1985 and 31 December 

 1992 (Table 1). One animal (4/14/85) was not included 

 in the analyses because body condition ("mummifi- 

 cation") indicated death or stranding, or both, oc- 

 curred prior to the study period. The number of 

 strandings by year was as follows: in 1985, 2 in 

 1986, in 1987, 1 in 1988, 3 in 1989, 8 in 1990, 7 in 

 1991, and 16 in 1992. Significantly more animals 

 stranded during the period 1989 to 1992 (n=34), than 

 from 1985 to 1988 (n=3) (Mann- Whitney U: Z=-2.32, 

 P=0.02). Of the strandings recorded in our database, 

 92% (34/37) occurred after January 1989. 



Significantly more strandings occurred along 170 

 km of coastline between Chesapeake Bay, Virginia, 

 and Cape Hatteras, North Carolina (x 2 =70.67, df=l, 

 P<0.01), than occurred in the rest of the study area. 

 In this region, which represents 7.3% (170 km/2,319 

 km) of the coastline within the study area, 43% (16/ 

 37) of all strandings occurred. A second cluster of 

 strandings occurred along the coast of northern 

 Florida; however, this grouping was not found to 

 be significant (x 2 =5.98, df=l, P=0.25). The region, 

 which represents 4.7% (110 km/2319 km) of the study 

 area's coastline, contained 13.5% (5/37) of all 

 strandings. 



The number of strandings per state was highly 

 variable (Table 2). Numerically, the highest number 

 of strandings occurred in North Carolina (n-15), but 

 the incidence of strandings (strandings per kilome- 

 ter of coastline) was greatest in Virginia (SIR=0.055, 

 n=10), followed by North Carolina (SIR=0.031). South 

 Carolina had the lowest incidence of strandings 

 (SIR=0.003, n=l). The stranding incidence ratio for 

 the entire study area was 0.016. All states recorded 

 at least one stranding. 



There were no significant differences in stranding 

 occurrence by season (x 2 =4.22, df=3, P=0.24) (Fig. 

 2). However, only 8% (3/37) of all strandings occurred 

 during the summer (July-September). Strandings oc- 

 curred with the greatest frequency in April (n=6) fol- 

 lowed by February, March, and October (n=5 each), 

 and least in July and August (n=0 each). In 1992 (the 

 most recent year of the study), strandings were 

 spread over a greater number of months than any of 

 the seven previous years. 



Data on body length were available for 25 animals. 

 Body length indicated all animals were sexually im- 

 mature but none were dependent calves. Sixty-eight 

 percent (17/25) of the animals were considered newly 

 independent calves. Information on gender was avail- 

 able for 26 animals. Fifty percent (13/26) were fe- 

 male and 50% (13/26) were male. 



Of the 37 animals, an advanced stage of decomposi- 

 tion eliminated 13 from analysis for potential cause 

 of death. Four additional animals were insufficiently 

 examined or information was inadequately reported 

 to determine a cause of death or the presence or ab- 

 sence of injury or scars. Of the 20 remaining ani- 

 mals, 30% (6/20) had major injuries potentially at- 

 tributable to a ship strike and 25% (5/20) had inju- 

 ries consistent with possible entanglement in fish- 

 ing gear. One animal exhibited scars consistent with 

 past entanglement or ship strike, or both, and was 

 emaciated at the time of stranding. Thus, up to 60% 

 (12/20) of the sufficiently inspected animals showed 

 signs that anthropogenic factors may have contrib- 

 uted to or been directly responsible for their death. 

 However, the possibility that some animals sustained 

 body trauma after death can not be ruled out. Unfor- 

 tunately, few animals were sufficiently necropsied 

 to establish an unequivocal cause of death. 



Discussion 



These results suggest that stranding of humpback 

 whales along the mid-Atlantic and southeast coastal 

 areas of the United States has increased. All stranded 

 animals were sexually immature and males and fe- 

 males stranded with equal frequency. However, natu- 

 ral mortality may show a gender bias that has been 

 obscured by the high number of deaths potentially 

 due to anthropogenic factors. Strandings occurred 

 throughout the fall, winter, and spring seasons, but 

 few strandings occurred during the summer months. 

 There are several possible explanations for the 

 apparent increase in strandings, including changes 



I .hi 



JA FE MA AP MY JU JL AU SP OC NO DE 

 MONTH 



Figure 2 



Humpback whale, Megaptera novaeangliae, strandings by 

 month, 1985 through 1992. 



