Abstract:
North Atlantic right whales (NARW), Eubalaena glacialis, were
nearly exterminated by historical whaling. Their abundance
slowly increased up until 2010, to a maximum of fewer than
500 whales, and since then they have been in decline. We
assessed the extent to which the relatively slow increase
demonstrated by NARW was intrinsic, and how much could
be due to anthropogenic impacts. In order to do so, we first
compared calf counts of three populations of Southern right
whales (SRW), E. australis, with that of NARW, over the
period 1992–2016. By this index, the annual rate of increase
of NARW was approximately one-third of that of SRW. Next
we constructed a population projection model for female
NARW, using the highest annual survival estimates available
from recent mark–resight analysis, and assuming a four-year
calving interval. The model results indicated an intrinsic rate
of increase of 4% per year, approximately twice that
observed, and that adult female mortality is the main factor influencing this rate. Necropsy records demonstrate that anthropogenic mortality is the primary cause
of known mortality of NARW. Anthropogenic mortality and morbidity has limited the recovery of
NARW, and baseline conditions prior to their recent decline were already jeopardizing NARW
recovery.
