Power of monitoring surveys to detect abundance trends in depleted populations: the effects of density-dependent habitat use, patchiness, and climate change

• Published in: ICES Journal of Marine Science
• Main Authors: Blanchard, JL, Maxwell, DL, Jennings, S
• Format: Article in Journal/Newspaper
• Language: English
• Published: Academic Press Ltd Elsevier Science Ltd 2008
• Subjects: Environmental Sciences; Environmental Science and Management; Conservation and Biodiversity; Northeast Atlantic
• Online Access: https://doi.org/10.1093/icesjms/fsm182; http://ecite.utas.edu.au/100507

Traditionally, trawl surveys were designed to collect fishery-independent data for assessing the population dynamics of commerciallyexploited species. However, trawl survey data are increasingly used to describe the abundance, distribution and ecology of a wide rangeof species in studies of climate change and fishing effects. These new uses of survey data suggest that improved understanding of thevalue and limitations of existing survey designs is required. We compared the power of different survey designs (where stations arefixed, fixed stratified, random, or random stratified) to detect known trends in the abundance of depleted populations. Modelledpopulations were characterized by different temperature preference, density-dependent habitat selection, and patterns of small-scaleaggregation (patchiness). Temperature preferences and local patchiness had an influence on the power of different surveys todetect increases in abundance, and in some scenarios, survey-area indices would consistently underestimate or overestimate trendsin overall abundance. As the distributions of many fish populations have shifted in response to climate change, exhibit distribution-abundance relationships, and have been depleted by fishing, we conclude that survey indices may provide partial or unreliableinformation on changes in the true abundance of the wider range of species now of interest. To disentangle the effects of fishing,climate, and biology on the abundance of fish populations, and to monitor the depletion and recovery of species threatened byfishing, there should be greater emphasis on coordinating the timing, areas of coverage, and methods of sampling of surveys ofthe Northeast Atlantic continental shelf.