Research Document 2017/078

Towards Regional Benchmarks of Fish Productivity in Nearshore Marine Ecosystems: Model Framework, Habitat Comparisons, and Examination of Regional Data

By Wong, M.C., and Dowd, M.

Abstract

Regional benchmarks of fisheries productivity could guide decision making by the Fisheries Protection Program (FPP) for authorization, compensation, and offsetting of serious harm.  In particular, benchmarks are needed for nearshore marine habitats, which are important for fisheries production.  Here we present a model framework to estimate fish production for the data and information poor situations generally found in nearshore ecosystems.  We also review available fish data for nearshore habitats in Maritimes Canada and comment on the potential for using these data to develop regional benchmarks.

Our model framework estimates fish production using an age-structured Leslie population matrix and is formulated with length-dependent survival and fecundity, coupled with growth and length-weight functions.  Uncertainty quantification is included and accounts for parameter dependence.  We made the simplifying assumption of steady-state populations, scaling the resultant proportional stable age distribution with observed fish density (in at least one age class).  Mortality and growth were estimated from regional values.  Model outputs include species-specific abundance, biomass and production per age class across the entire lifespan of the fish.  We apply the model using data from Eelgrass (Zostera marina) beds, Rockweed (Ascophyllum nodosum) beds, and associated bare habitat on the Atlantic coast of Nova Scotia, Canada.  We present three different candidate metrics of fish production, including production potential, equivalent adults, and area per recruit.  Fish production of most species was higher in Eelgrass or Rockweed relative to bare habitat.  The model framework is general in that it can be adapted and extended as more comprehensive data sets become available, and thus has application beyond that presented here.

Additional datasets of fish assemblages in Eelgrass beds from the southern Gulf of St. Lawrence were examined for their potential in developing benchmarks.  These data were of species-specific capture density, with typically no information on fish biomass or age class.  Use of these data in our model to estimate production would require assumptions of age or size structure.  Differing capture efficiencies of sampling gear would also need to be taken into account.  Regardless, the compiled data can provide insight into various aspects of fish production across different spatial scales, including fish density, community structure, habitat associations, and temporal variability.

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