UNIT 24 

 MARINE MAMMALS OF THE ATLANTIC REGION AND THE GULF OF MEXICO 



to recover. Kr.uis (1990) estimated mottality in 

 the fifst 4 yeats of life at between 2% and 17%, 

 with at least a thitd attributable to ship collisions 

 and entanglement. Photographs of 1 1 8 identified 

 individuals showed that 57% possessed scarring 

 indicative of entanglement (Kraus, 1990). Sources 

 of ship strikes are generally unknown, but are pri- 

 marily large commercial vessels; regrettably, many 

 of the right whale's major habitats in the western 

 North Atlantic are adjacent to, or even straddle, 

 major shipping lanes. Given this population's de- 

 pendence upon ncarshore habitat tor much oi its 

 lite cycle, intensive coastal development in this and 

 other portions ot the range poses additional threats 

 to recovery. 



Studies showing relatively low genetic diver- 

 sity in the western North Atlantic population 

 (Schaeff et al., 1993, 1997) suggest that inbreed- 

 ing may be inhibiting recover)-, but this is diffi- 

 cult to interpret without a knowledge of historic 

 genetic structure. The latter topic is currently be- 

 ing investigated using DNA extracted from his- 

 toric baleen samples (Rosenbaum et al., 1997, 

 1998). 



This is a strategic stock. PBR was specified as 

 the product of minimum population size (29S), 

 one-half the maximum productivity rate (0.02), 

 and a recovery factor of 0.1 because this species is 

 listed as endangered under the ESA. PBR for the 

 northern right whale is therefore 0.4 whales. Over 

 the past several years, known human-caused mor- 

 talit\' has consistently exceeded PBR. This is a cause 

 for concern, given the critically endangered status 

 of the stock and its apparent failure to recover. 



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257 



