Publication Date:
2013-10-15
Description:
Wilhelm, M. R., Roux, J-P., Moloney, C. L., and Jarre, A. 2013. Data from fur seal scats reveal when Namibian Merluccius capensis are hatched and how fast they grow. – ICES Journal of Marine Science, 70: . Scat samples were collected regularly at several breeding colonies of Cape fur seals along the Namibian coast. Merluccius capensis otoliths were obtained from these samples, identified, and measured. Cohorts were easily distinguishable using otolith length measurements converted to fish total length. Growth rates of 2- to 21-month-old hake and hatch dates for each of 15 cohorts were estimated from September 1994 to October 2009 (1994–2008 cohorts) using a Schnute growth function and a non-linear mixed-effects model. The function describing growth of these young hake was length L t (cm) at age t (years) L t = 3.17 + (25.0 – 3.17) x [1 – e –0.665 x ( t – 0.140) ]/[1 – e –0.665 x (1.74–0.140) ]. Cohort-specific random effects showed a population hatch date estimate of 31 July (austral winter), varying by 94 days among cohorts, from 31 May (1996 cohort) to 1 September (2004 cohort). The mean growth rate from ages 6 to 12 months was 1.26 cm month –1 for the population, ranging between 0.97 cm month –1 (1996 cohort) and 1.38 cm month –1 (2004 cohort). As this rate is almost double the previously estimated value, which is currently used in the stock assessment models, this result may have major implications for the current stock assessment results and the management of the stock. Re-examination of growth rates needs to be extended to older fish.
Print ISSN:
1054-3139
Electronic ISSN:
1095-9289
Topics:
Biology
,
Geosciences
,
Physics
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