The rise and fall of autumn-spawning herring (Clupea harengus L.) in the Celtic Sea between 1959 and 2009: Temporal trends in spawning component diversity
KeywordComplex stock structure
Celtic Sea herring
Seasonal spawning components
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AbstractSub-stock components of highly exploited migratory fish species exhibit different life-history traits and can thus show variation in productivity and vulnerability to fishing pressure. Celtic Sea herring comprises both autumn and winter-spawners that are targeted by the same fishery. The current study investigated if the relative abundances of the two components in the Celtic Sea have changed over time, and whether this could explain marked long-term trends in size-at-age. The study utilized a remarkably long time-series of biological data from commercial landings (1959–2009). Based on the maturity state of the gonads at the time of sampling, herring were assigned to seasonal spawning components. Significant temporal variations in spawning component dominance were found, even after potential bias due to fishing history patterns were accounted for. Strong directional changes in the relative proportion of spawning components consisted of autumn spawning herring proportions reaching a peak in the 1990s before drastically declining. Winter spawning herring had lower mean lengths- and weights-at-age than autumn spawning herring. The recent decline in the autumn spawning component did not fully explain the observed decline in size-at-age in the catches, with both spawning components showing similar decreases in mean-size parameters over time. Response of spawning components to environmental changes may have consequences for the fishery, especially in light of the observed influence of temperature on spawning components. Life-cycle diversity in herring stocks may confer resilience to potential climate-induced changes. Therefore, it is suggested that the relative proportions of spawning components should be monitored and diversity should be preserved as part of the management of fisheries for this species, which is characterized by stock complexity.
DescriptionNOTICE: this is the author’s version of a work that was accepted for publication in Fisheries Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Fisheries Research, [VOL121-122, (June 2012)] doi: 10.1016/j.fishres.2012.01.005, http://www.sciencedirect.com/science/article/pii/S0165783612000367