Research Document - 2003/061

Fish productivity and habitat productive capacity: definitions, indices, units of field measurement, and a need for standardized terminology

By Randall, R.G.

Abstract

Effective aquatic resource conservation involves the management of fish populations and their habitat. Differences between habitat and fisheries science in the use of terms like productivity and productive capacity are highlighted to emphasize that a common terminology should be adopted. Habitat evaluation should occur, implicitly or explicitly, at a spatial scale that encompasses entire fish populations. Knowledge of the population level spatial scale is poorly known in most instances but the spatial scale of many habitat projects is likely smaller than the population scale. This mismatch is a challenge for science. Productive capacity is a characteristic of fish habitat, while productivity is a characteristic of populations. The concepts and measurement units of fish production (kg ha-1 yr-1), productivity (survival, e.g., recruits per spawner) and habitat productive capacity (kg ha-1) are defined and explained in a manner that bridges both habitat and fisheries science. Fish production is measured for fisheries assessment of individual populations, but it is usually not measured for habitat management. Rather, biological indices of production (density, biomass, richness, IBI, HPI ) and physical habitat surrogates (area, cover, substrate, depth, pools, riffles, Defensible Methods) of productive capacity are used. The indices and surrogates can apply to species, assemblages or whole communities; the latter is paramount for resource management as maintaining natural biodiversity is a primary mandate of Fisheries and Oceans Canada. Habitat biologists must be mindful of the limitations and implied assumptions when indices or surrogates are used to assess the productive capacity of fish habitat. Research to provide science support for habitat and fisheries management is mutually beneficial, and the objectives often overlap. The Canadian Science Advisory Secretariat (CSAS) publication series provides a national forum for reporting both science and management advisories, and highlights the parallels between habitat and fisheries science.

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