Michael P. Sissenwine

Is MSY an Adequate Foundation for Optimum Yield

Abstract Traditionally, maximum sustained yield (MSY) has been estimated from surplus production models. A second approach has been to calculate MSY as the product of average recruitment and maximum yield per recruit. These approaches to MSY are an inadequate foundation for optimum yield. Surplus production models are fit to catch and effort data under the assumption that the rate of expenditure of effort is proportional to fishing mortality rate. Often, this assumption is not valid. Furthermore, the most common method of fitting surplus production models to data may falsely indicate that the model satisfactorily describes the fishery. Because of the random fluctuations in productivity of fisheries, the fishing mortality rate corresponding to MSY will produce an average yield less than MSY. Maximizing yield per recruit may lead to a severe depletion of spawning stock size and recruitment failure. For multispecies fisheries, independent management of several species aimed at achieving MSY for each may be s...

Marine reserve effects on fishery profits: a comment on White et al. (2008).

A recent study (White et al. 2008) claimed that fishery profits will often be higher with management that employs no-take marine reserves than conventional fisheries management alone. However, this conclusion was based on the erroneous assumption that all landed fish have equal value regardless of size, and questionable assumptions regarding density-dependence. Examination of an age-structured version of the White et al. (2008) model demonstrates that their results are not robust to these assumptions. Models with more realistic assumptions generally do not indicate increased fishery yield or profits from marine reserves except for overfished stocks.

An Overview of Some Methods of Fish Stock Assessment

Abstract Stock assessments, which evaluate the effects of fishing on a fishery, are one basis of fishery management decisions. Stock assessments are based on fisheries data (a description of the catch and catching process), research vessel survey data, and qualitative information drawn from the observations of the harvesters and other knowledgeable observers. The fundamental model used as a basis for stock assessments and fishery management decisions takes account of four forces affecting biomass of the exploited population. These are growth, recruitment, natural mortality, and fishing mortality. Recruitment is the major source of variability in production of a fish population. The magnitude of past recruitment is estimated by application of virtual population analysis (VPA) to fisheries data. Future recruitment is predicted from current research vessel survey data and the relationship between survey catch rates and VPA estimates of recruitment during past years.

Environmental science, environmentalism and governance

Most environmental scientists care about the state of nature. They are concerned about loss of biodiversity, degradation of ecosystems services and threats to sustainability. Do such concerns and the values they reflect make an environmental scientist an environmentalist? Should they be environmentalists?

Report of the Fisheries Ecology Meeting, June 8-11, 1981

Prepared for the National Oceanic and Atmospheric Administration~ the Andrew W. Mellon Foundation, and the Pew Memorial Trust.