We show that the distributions of both exploited and nonexploited North Sea fishes have responded markedly to recent increases in sea temperature, with nearly two-thirds of species shifting in mean latitude or depth or both over 25 years. For species with northerly or southerly range margins in the North Sea, half have shown boundary shifts with warming, and all but one shifted northward. Species with shifting distributions have faster life cycles and smaller body sizes than nonshifting species. Further temperature rises are likely to have profound impacts on commercial fisheries through continued shifts in distribution and alterations in community interactions.

The stomach contents of ten species of elasmobranch from the north-eastern Atlantic indicate that most are generalist predators, eating a variety of polychaetes, molluscs, crustaceans and teleosts. Two species, Mustelus asterias and Squatina scjuatina were found to be specialist feeders, consuming portunid crabs and pleuronectids, respectively. Measures for both dietary breadth and dietary overlap are given and the implications of elasmobranch predation on the prey communities and on commercial species are discussed.

Introduction 256Defining extinction 257The routes to extinction in the sea 258Life history and 'rule of thumb' approaches 258Estimating population parameters using life-history invariants 259Life-history benchmarks 259Qualitative ranking using threat correlates 259 AbstractThe decline and disappearance of species from large parts of their former geographical range has become an important issue in fisheries ecology. There is a need to identify which species are at risk of extinction. The available approaches have been subject to considerable debate -particularly when applied to commercially exploited species.Here we have compiled methods that have been used or may be used for assessing threat status of marine organisms. We organize the methods according to the availability of data on the natural history, ecology and population biology of species. There are three general approaches to inferring or assessing extinction risk: (i) correlative approaches based on knowledge of life histories and ecology; (ii) time-series approaches that examine changes in abundance; and (iii) demographic approaches based on age-or stage-based schedules of vital rates and fisheries reference points. Many methods are well suited to species that are highly catchable and/or have relatively low productivity, but theory is less well developed for assessing extinction risk in species exhibiting narrow geographical distributions or ecological specialization. There is considerable variation in both definitions of extinction risk and the precision and defensibility of the available risk assessment methods, so we suggest a two-tiered approach for defining and assessing extinction risk. First, simple methods requiring a few easily estimated parameters are used to triage or rapidly assess large numbers of populations and species to identify potentially vulnerable populations or species. Second, the populations and species identified as vulnerable by this process can then be subject to more detailed and rigorous population analysis explicitly considering sources of error and uncertainty.