PNAS – Proceedings of the National Academy of Sciences of the United States of America
http://www.pnas.org/content/early/
(Accessed 9 July 2016)

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Biological Sciences – Ecology:
Large scale, synchronous variability of marine fish populations driven by commercial exploitation
Kenneth T. Frank, Brian Petrie, William C. Leggett,and Daniel G. Boyce
PNAS 2016 ; published ahead of print July 5, 2016, doi:10.1073/pnas.1602325113
Significance
Large-scale synchronous variation in the abundance of marine fish populations has generally been viewed as a response to coupled atmosphere–ocean forcing. The possibility that commercial exploitation could contribute significantly to these variations has been largely dismissed. We demonstrate, using data from 22 Atlantic cod stocks distributed across the North Atlantic, that fishing pressure can cause synchronous changes in stock abundance at spatial and temporal scales comparable to those attributed to climate forcing. We conclude that an understanding of the underlying causes of the large-scale, often synchronous variability of exploited marine fish populations and their underlying food chains will require greater acceptance of the potential importance of exploitation than has been evident to date.
Abstract
Synchronous variations in the abundance of geographically distinct marine fish populations are known to occur across spatial scales on the order of 1,000 km and greater. The prevailing assumption is that this large-scale coherent variability is a response to coupled atmosphere–ocean dynamics, commonly represented by climate indexes, such as the Atlantic Multidecadal Oscillation and North Atlantic Oscillation. On the other hand, it has been suggested that exploitation might contribute to this coherent variability. This possibility has been generally ignored or dismissed on the grounds that exploitation is unlikely to operate synchronously at such large spatial scales. Our analysis of adult fishing mortality and spawning stock biomass of 22 North Atlantic cod (Gadus morhua) stocks revealed that both the temporal and spatial scales in fishing mortality and spawning stock biomass were equivalent to those of the climate drivers. From these results, we conclude that greater consideration must be given to the potential of exploitation as a driving force behind broad, coherent variability of heavily exploited fish species.