Ecological studies of exploited populations of whales and rock lobsters

Abstract

The humpback whale and the western rock lobster are widely separated in phylogeny, morphology and physiology. At first sight they have little in common except a marine habitat. Both have a relatively high longevity and when undisturbed appear to attain fairly stable population levels determined by responses to environmental pressures. However, in most other respects their life cycles differ greatly, as shown by the summary in Table 1. Despite these differences, when populations of either species are exploited commercially, a similar rationale is applied to management. Compensatory changes are expected to occur to some extent in birth rate, growth rate, and/or survival as the population is reduced (usually selectively) from some maximal level. Where the interactions of these parameters are optimised giving greatest recruitment to the fishable stock, a fishery can be continued indefinitely at a level classically known as the maximum sustainable yield. Thus in spite of the widest of differences between these species, the responses of their populations to fishing pressure are expected to be similar in principle if not in extent. The research upon humpback whales is brought together in paper 14, while the implications of the findings on the western rock lobster are discussed in paper 26. Following the presentation of research papers, the above hypothesis is examined ln the light of data collected from populations of humpback whales and the western rock lobster as these were exposed to high rates of exploitation.