%0 Journal Article
%T Social and Behavioural Factors in Cetacean Responses to Overexploitation: Are Odontocetes Less ¡°Resilient¡± Than Mysticetes?
%A Paul R. Wade
%A Randall R. Reeves
%A Sarah L. Mesnick
%J Journal of Marine Biology
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/567276
%X Many severely depleted populations of baleen whales (Mysticeti) have exhibited clear signs of recovery whereas there are few examples in toothed whales (Odontoceti). We hypothesize that this difference is due, at least in part, to social and behavioural factors. Clearly, a part of the lack of resilience to exploitation is explained by odontocete life history. However, an additional factor may be the highly social nature of many odontocetes in which survival and reproductive success may depend on: (a) social cohesion and organization, (b) mutual defence against predators and possible alloparental care, (c) inter-generational transfer of ¡°knowledge¡±, and (d) leadership by older individuals. We found little evidence of strong recovery in any of the depleted populations examined. Their relatively low potential rates of increase mean that odontocete populations can be over-exploited with take rates of only a few percent per year. Exploitation can have effects beyond the dynamics of individual removals. Four species showed evidence of a decrease in birth rates following exploitation; potential mechanisms include a deficit of adult females, a deficit of adult males, and disruption of mating systems. The evidence for a lack of strong recovery in heavily exploited odontocete populations indicates that management should be more precautionary. 1. Introduction In a 1993 paper, Best [1] examined increase rates in severely depleted stocks of baleen whales (Mysticeti). Of 44 that had been depleted to less than 10% of their original abundance, 12 were being adequately monitored to determine trends, and of those, ten exhibited significant positive rates of increase. In effect, Best concluded that there was no clear evidence for a ¡°lag¡± in the response to protection (e.g., due to depensation or so-called ¡°Allee effects¡±) and that apparent delays in recovery by some stocks were more likely due to the inadequacy of monitoring effort than to impaired reproduction or recruitment failure. Further, he offered the hypothesis that in many stocks ¡°a combination of range retraction and underestimation of the extent of depletion has hindered detection of a recovery.¡± In the nearly 20 years since Best¡¯s analysis, a number of the 32 severely depleted stocks that he judged to have been inadequately monitored have now shown clear signs of increase. For example, there is evidence for increases in blue whale (Balaenoptera musculus) abundance [2] in the Antarctic and fin whale (Balaenoptera physalus) abundance in central California [3]. Bowhead whales (Balaena mysticetus) in eastern
%U http://www.hindawi.com/journals/jmb/2012/567276/