Social and Behavioural Factors in Cetacean Responses to Overexploitation: Are Odontocetes Less “Resilient” Than Mysticetes?

Table 1

Possible mechanisms by which direct exploitation affects odontocete cetaceans, beyond the simple effect on population dynamics of removing individual animals.

(a) Mechanisms for which there is some evidence
Deficit of reproductive-age females (killer whales)
Deficit of adult males leading to lower pregnancy rate in females (sperm whales)
Lowered birth rate from disruption of mating systems (spinner and pantropical spotted dolphins)
Physical separation of cow/calf pairs from chase and encirclement leading to death of calves (spinner and spotted dolphins)
(b) Additional mechanisms suggested by the species’ social systems
Loss of cultural knowledge concerning, for example, types of alternative prey, areas where prey can be found, and ways to capture different types of prey under varying circumstances (killer whales, sperm whales, belugas, narwhals, and pilot whales)
Increased risk of ice entrapment due to loss of cultural knowledge (belugas and narwhals)
Disruption of social networks by removal of key individuals leading to dispersal and potentially higher mortality rates (bottlenose dolphins and killer whales)
Loss of an important nonreproductive role played by older females (pilot whales, killer whales, and sperm whales)
Increased predation risk due to loss of social connection and “babysitting” by nonrelatives (sperm whales)