Effects of High-Seas Driftnet Fisheries on the Northern Right Whale Dolphin Lissodelphis Borealis

Abstract

The United Nations (U.N.) resolutions concerning high-seas driftnets called for moratoria by July 1992, unless appropriate conservation measures could be enacted. The analyses presented here show that the population of northern right whale dolphin has been affected by driftnets and that no apparent conservation measures are available. A number of points emerge: (1) Simple "worst-case" estimates of depletion highlight the importance of accurate estimates of population abundance. Current abundance is 24-73% of the abundance in 1978, depending upon which estimate of current population is assumed. The enormous variability associated with the estimates of current population size will create difficulties for "statistically sound analysis" of management plans, as called for by the U.N. resolutions. In addition, depletion caused by high-seas driftnet fisheries could even be greater than the worst-case estimate reported at a scientific review in June 1991 (Anonymous 1991). (2) The catches of driftnets are highly aggregated. Reporting a kill rate of a fraction of an animal per unit of effort assumes that driftnets "cull" the population of animals and masks the more important effect of large, simultaneous kills of large fractions of pods, families, or other reproductive units. In addition, aggregated catches may lead to underestimates of the necessary level of observer effort. However, the operational characteristics of high-seas driftnet fisheries make impossible any management or conservation plan in which highly aggregated catches do not occur. (3) Any "statistically sound analysis" must include discussion of statistical power. To date, this has not been done. The importance of statistical power is that it places the burden of proof upon the fishing nations that wish to claim either no effect or a successful management plan. In summary, this study of northern right whale dolphin illustrates the following broad points concerning resource protection and conservation: abundance estimates (or trends in abundance) are key to advising on the problem, the statistical characterization of the data must take into account the observed patterns, and statistical power needs to be evaluated to clarify results.