A spatial model for fishery age-selection at the population level

Different age-classes do not generally experience the same rates of fishing mortality. The processes that result in age- (or length-) selection operate at several scales. At the broadest 38 scale population-selection measures the age-specific probability of capture, whilst at the finest scale contact-selection describes the vulnerability of fish that encounter the fishing gear. Population-selectivity is the process most relevant to fish population dynamics and stock assessment but it has received far less attention than processes operating at gear specific scales. Despite wide recognition of the diverse shapes possible for population selectivity, the processes determining these shapes are poorly understood. This paper develops a reasonably simple model of population-selectivity from a set of survival equations, coupled to allow movement between subpopulations, and explores the conditions necessary to produce different shaped population-selection curves. Important factors influencing the population-selectivity model are the gear-specific selection characteristics of the fleets, their effort levels relative to one another, the spatial distribution of fishing mortality and the movement of fish between subpopulations. The model can generate quite complicated curves and has surprising properties. For example, even though the same asymptotic gear-selectivity applies in all subpopulations the overall population-selectivity will be dome-shaped unless fishing mortality is uniform across all subpopulations.

SAMPSON David;  SCOTT Robert; 

2011-07-12

NATL RESEARCH COUNCIL CANADA-N R C RESEARCH PRESS

JRC58969

0706-652X,   

http://www.nrcresearchpress.com/doi/pdf/10.1139/f2011-044,    https://publications.jrc.ec.europa.eu/repository/handle/JRC58969,   

10.1139/F2011-044,