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Marine Ecology Progress Series

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MEPS 600:85-98 (2018)  -  DOI:

Four-year decline in Ostrea chilensis recruits per spawner in Foveaux Strait, New Zealand, suggests a diminishing stock-recruitment relationship

Keith P. Michael1,2,3,*, Jeffrey S. Shima1,2

1School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand
2Victoria University Coastal Ecology Laboratory (VUCEL), PO Box 600, Wellington 6140, New Zealand
3National Institute of Water and Atmospheric Research (NIWA), PB 14901, Wellington 6021, New Zealand
*Corresponding author:

ABSTRACT: Rebuilding and maintaining sufficient spawning stock to ensure recruitment is a key strategy for fisheries management and ecological restoration. We evaluated variation in Ostrea chilensis recruitment across seasons and sites over 4-6 yr in Foveaux Strait (New Zealand) to infer the relative importance of determinants of population recruitment. Recruitment varied significantly between seasons (p < 0.001). Most recruitment in any given year (97.8 ± 0.9%, mean ± SE) occurred in the austral spring and summer (November to February). Recruitment also varied significantly between years (p < 0.001). In a separate fishery-wide study, we investigated the effect of spawner densities on recruitment, relative to other climatic and biological factors. We deployed spat collectors at 6 sites across 3 discrete fishery areas, and estimated densities of spawning-sized oysters from dredge samples. We modelled counts of oyster spat and spawners with a negative binomial regression to evaluate the stock-recruitment relationship. Recruitment varied between years (50.8% of the deviance explained), spawner densities (13.8%), and areas (11.6%), with further 2-way interactions among these factors. Importantly, our analysis showed a continued decline in recruits per spawner, despite similar or increasing densities of spawning-sized oysters. Average recruitment for 2010-11 when spawner densities were highest was 4.6% of the level observed in 2007-08. Our data suggest that factors other than densities of oysters play a major role in the numbers of competent larvae available for settlement. Managing oyster fisheries as a single stock and maintaining oyster densities above management reference points alone may not be sufficient to ensure recruitment to rebuild populations.

KEY WORDS: Recruitment variability · Oysters · Spatial management · Foveaux Strait · Stock-recruitment relationship

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Cite this article as: Michael KP, Shima JS (2018) Four-year decline in Ostrea chilensis recruits per spawner in Foveaux Strait, New Zealand, suggests a diminishing stock-recruitment relationship. Mar Ecol Prog Ser 600:85-98.

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