Spatial variation in fishing intensity and its effect on yield

• Published in: Canadian journal of fisheries and aquatic sciences Vol. 65; no. 4; pp. 588 - 599
• Main Authors: Ralston, Stephen, O'Farrell, Michael R
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01.04.2008; National Research Council of Canada; Canadian Science Publishing NRC Research Press
• Subjects: Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Compensation; Density dependence; Exploitation and management of natural biological resources (hunting, fishing and exploited populations survey, etc.); Fish populations; Fish production; Fishing; Fundamental and applied biological sciences. Psychology; Heterogeneity; Mortality; Simulation; Sustainable yield; Thinning; Canada; Aquatic environment; Yield; Fishing; Spatial variation
• ISSN: 0706-652X; 1205-7533
• DOI: 10.1139/f07-174

Fishing mortality is rarely, if ever, evenly distributed over space, yet this is a common assumption of many fisheries models. To evaluate the effect of spatial heterogeneity in fishing mortality on yield, we constructed age-structured models that allowed for differing levels of fishing in three regions within the boundaries of a stock and explored alternative assumptions about the life stage in which density-dependent compensation operates. If the fishing mortality rate (F) is not excessive (i.e., F ≤ F MSY defined for the spatially homogeneous case; MSY, maximum sustainable yield), simulations demonstrated that minor to moderate spatial variation in fishing intensity does not impact sustainable yield. However, if fishing mortality is excessive (F > F MSY ), spatial variation in fishing intensity often improves yield and can actually produce yields in excess of MSY when compensation occurs after dispersal, and the density-dependent recruitment rate is a function of the local density of adults. The yield premium generated in these simulations by postdispersal density dependence is due to a low level of compensatory mortality in heavily fished areas coupled with dispersal of propagules into these areas from lightly fished adjacent regions.