Abstract
The spatial pattern in hydro-plankton and fish distributions and their relationship were analysed based on the spring 2000 fisheries acoustic survey. The importance of this survey was that it was a multi-disciplinary platform which collected an extensive set of parameters in the hydro-plankton leading to a potentially finer description of hydro-plankton conditions and fish habitats. More than 50 variables were measured on a grid of stations, in four compartments of the ecosystem: hydrology, nutrients, primary producers and meso-zooplankton. First, a joint analysis of all hydro-plankton compartments was performed using multiple factor analysis (MFA). The method was used to estimate a compromise factorial space common to all compartments in which the stations were grouped by hierarchical clustering. The groups were represented spatially and a strong spatial pattern was evidenced. The fish and their spawned eggs were sampled along transect lines using acoustics and CUFES (continuous underway fish egg samplers). The distribution of the fish and their eggs was analysed in relation to the hydro-plankton groups of stations and difference in fish density across hydro-plankton conditions was tested by a pair-wise multiple comparison procedure. Anchovy was associated with a lesser number of hydro-plankton conditions than sardine. Eggs of both species were also associated with a lesser number of conditions than the fish. Finally, the gain provided by using the extensive set of hydro-plankton parameters for mapping large-scale hydro-plankton conditions was analysed in comparison with the situation in which a small set of parameters was available. The extensive set of parameters allowed more hydro-plankton conditions to be identified but only in the coastal area and not on the shelf. Size fractionated chlorophyll was determinant for tracking river plume hydro-plankton condition. However, the fish did not respond to the variety of the coastal hydro-plankton conditions.
Highlights
Fisheries resource monitoring surveys provide a platform for monitoring the ecosystem on a large spatial scale and allow patterns to be characterised in the geographical distribution of the fish as well as in that of some environmental parameters
SUMMARY: The spatial pattern in hydro-plankton and fish distributions and their relationship were analysed based on the spring 2000 fisheries acoustic survey
The importance of this survey was that it was a multi-disciplinary platform which collected an extensive set of parameters in the hydro-plankton leading to a potentially finer description of hydro-plankton conditions and fish habitats
Summary
Fisheries resource monitoring surveys provide a platform for monitoring the ecosystem on a large spatial scale and allow patterns to be characterised in the geographical distribution of the fish as well as in that of some environmental parameters. Taking the fish distribution as a dependent variable and the environmental parameters as explanatory variables, the statistical analysis results in a static distribution model of fish habitat. Such an approach, which differs from a mechanistic approach, assumes equilibrium in the habitat occupation and results in the characterisation of realised habitats (Guisan and Zimmerman, 2000). Implementation of the regression methodology generally involves some difficulties related to noise in the data and to the choice of the environmental parameters. We tested how fish abundance related to this environmental pattern, building a simple habitat statistical model. Rather than particular environmental parameters, we used structure in the set of parameters, relating the general pattern in the environment with that in the fish
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