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On the Probable Distribution of Stock-Recruitment Steepness for Western and Central North Pacific Swordfish
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2020
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Series: PIFSC working paper ; WP-20-005
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Description:The resilience of a stock-recruitment relationship is a key characteristic for modeling the population dynamics and fishery productivity of living marine resources. Steepness determines the expected resiliency of a fish stock to harvest and is important for the estimation of biological reference points such as maximum sustainable yield. Stock-recruitment steepness was a primary uncertainty for the determination of stock status and biological reference points in the most recent stock assessment (ISC 2018) of Western and Central North Pacific swordfish (Xiphias gladius). To address this uncertainty, we applied the method of Mangel et al. (2010) and Brodziak et al. (2015) to quantify the probable distribution of steepness for swordfish using new information on the mean batch fecundity, spawning frequency, and spawning season duration. Results indicated that, under an assumption of Beverton-Holt stock-recruitment dynamics, the median steepness of swordfish was 0.95 with a 95% probable range of (0.89, 0.99). This suggested that Western and Central North Pacific swordfish was highly resilient to reductions in spawning potential. Results also indicated that variation in some reproductive and life history parameters had an important influence on the distribution of steepness. In particular, sensitivity analyses showed that steepness was most sensitive to body girth, mean egg weight, and most importantly, early life history stage survival. Sensitivity analyses also confirmed that the effects of changes in life history parameters on steepness were consistent with expected increases or decreases in reproductive output due to changes in body weight or fecundity.
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Rights Information:Public Domain
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