Ecology And Evolution Of Heavily Exploited Fish Populations

Commercial harvest of fish stocks and their appropriate management requires an understanding of their population dynamics and of their ability to sustain exploitation. Here, some ecological and evolutionary consequences of excessive exploitation are examined. In Chapter 2 I evaluate the knowledge base and status of commercially exploited marine populations that undergo formal stock assessment. Despite a bias towards industrialised countries and stocks of commercial importance, I show the pervasiveness of overexploitation and, by using reference points of stock status, identify important regional differences in the effectiveness of fisheries management. In Chapter 3 I develop a data format suitable for ecological analyses to best disseminate the valuable information contained in scientific trawl surveys. This data format is suitable for inclusion into the public Ocean Biogeographic Information System (OBIS) and provides detailed observations that are suitable to the reconstruction of important fisheries-independent stock indices. In Chapter 4 I examine the spatiotemporal dynamics of groundfish populations. A positive abundance-occupancy relationship was estimated for the majority of groundfish populations examined suggesting that this well-described terrestrial pattern is also pervasive in the marine environment. Spatial hysteresis was exhibited by numerous populations, indicating that the spatial distribution of individuals failed to recover despite recoveries in abundance. In Chapter 5 I estimate the demographic consequences of changes in growth and maturation characteristics. The ability of a population to sustain harvest, and its ability to recover from previous depletions can be overestimated because of trends towards earlier maturation and slower growth. In Chapter 6 I conclude the thesis by discussing the implications of my research to fisheries science and management. I argue that trends in the spatial distribution and the overall productivity of populations must be accounted for when determining sustainable fishing levels and when predicting recovery trajectories under various catch abatement scenarios. While successful management measures have been implemented in a number of marine ecosystems, this thesis highlights the importance of improving our capacity to understand the dynamics of exploited populations and to fully use the wealth of available monitoring and assessment data. xiii List of Abbreviations and Symbols Used Bmsy Biomass at MSY BRP Biological reference point CCGS Canadian Coast Guard Ship CPUE Catch-per-unit-of-effort DFO Fisheries and Oceans Canada DiGIR Distributed Generic Information Retrieval EEA European Environment Agency EEZ Exclusive Economic Zone FAO Food and Agricultural Organization of the United Nations F Fishing mortality GCMD Global Change Master Directory GLM Generalized linear model IATTC Inter-American Tropical Tuna Commission ICCAT International Commission for the Conservation of Atlantic Tuna ICC Intraclass Correlation Coefficient ICES International Council for the Exploration of the Seas ITIS Integrated Taxonomic Information System LME Large Marine Ecosystem xiv MTL Mean Trophic Level MSY Maximum Sustainable Yield NAFO Northwest Atlantic Fisheries Organization NEFSC Northeast Fisheries Science Center NMFS The National Marine Fisheries Service of the United States National Oceanic and Atmospheric Administration NOAA The United States National Oceanic and Atmospheric Administration NSERC Natural Sciences and Engineering Research Council of Canada OBIS Ocean Biogeographic Information System RAM Ransom Aldrich Myers RFMO Regional Fisheries Management Organization R Recruits r Finite population rate of increase SQL Structured Query Language SSB Spawning stock biomass SPRFMO South Pacific Regional Fisheries Management Organisation TB Total biomass TC Total catch TL Total landings Umsy Exploitation rate at MSY VPA Virtual Population Analysis xv WCPFC Western and Central Pacific Fisheries Commission