Research Document - 2012/117

Technical Guidelines for the Provision of Scientific Advice on the Precautionary Approach for Canadian Fish Stocks: Section 7 – Invertebrate Species

By S.J. Smith, H. Bourdages, J. Choi, E. Dawe, J.S. Dunham, L. Gendron, D. Hardie, M. Moriyasu, D. Orr, D. Roddick, D. Rutherford, B. Sainte-Marie, L. Savard, P. Shelton, D. Stansbury, M.J. Tremblay, and Z. Zhang

Abstract

This report summarizes progress to date on the development of reference points for the management of various marine invertebrate species commercially harvested in Canada. The implementation of the precautionary approach (PA) to fisheries management in Canada requires the definition of reference points reflecting the productivity and reproductive capacity of a stock. The different invertebrate species commonly fished in Canada exhibit a very diverse range of life history characteristics. For these species, reproductive success will be a function of life history factors such as effective female fecundity, spawning opportunities for females, spatial patterns of age–size structure, the relationship between spawner density and fertilization success — especially for broadcast spawners with sedentary or sessile adults, spatial and temporal aspects of breeding areas, and the relationship between benthic settlement success and habitat suitability. For many species the time period between spawning and actually being able to observe recruits may be long enough so that cumulative environmental influences on survival could radically reduce year-class strength. Also, there is often a mismatch between managed areas and stock area so that recruitment success in one area may be affected by spawning success in another area. The lack of adequate models to account for these complexities has often resulted in the use of empirical methods to define the type of reference points expected by the DFO PA policy. To date, empirical methods have used either an estimate of or an indicator of population biomass or abundance to represent the productivity of the stock. Given that biomass alone is an incomplete measure of productivity, many invertebrate stock assessments rely on secondary indicators such as population size, composition-based and sex ratio-based growth changes, spawner abundance or biomass, abundance of prerecruits, predator abundance, environmental changes and spatial patterns of density, to modify stock status advice. For many sedentary species (e.g., bivalves and echinoderms), primarily spatially-based limits and targets for fisheries may be more appropriate. However, methods for spatial approaches still need to be developed.

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