Growth discontinuity in males of the deep-water giant red shrimp Aristaeomorpha foliacea in the Mediterranean Sea |
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| Authors: | Sergio Ragonese Sergio Vitale Mark Dimech Alberto De Santi |
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| Institution: | 1. Institute for Marine and Coastal Environment, Italian National Research Council, IAMC-CNR, via L. Vaccara, Mazara del Vallo (TP), Italy;2. Malta Centre for Fisheries Science (MCFS), Fort San Lucjan Marsaxlokk, BBG, Malta |
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| Abstract: | The deep-water giant red shrimp, Aristaeomorpha foliacea (Risso, 1827) (Decapoda, Aristeidae), represents a highly valuable resource for bottom trawling in the Mediterranean Sea. Recent assessments have described both a worsening of the status of the traditionally exploited stocks and low levels of annual-based instantaneous natural mortality (M 0.4–0.7 year?1) in the unexploited stocks. The mortality (M) figures, however, are in contrast with the longevity (Tmax) of 3–4-year males and 4–5-year females, estimated from classical length frequency distribution analysis. Reduced growth (after the onset of sexual maturity) and pile-up of older individuals in the larger size classes have been considered to be reasonable explanations for the contrast between M and Tmax. We propose that a discontinuity of the growth models could address this contrast. Because a clear discontinuity in sexual maturity is evident only in males, length frequency distribution data for different sets of males collected from the South of Sicily and the Maltese Islands deep bottoms (400–800 m) were fitted with both the classic (c) and double-phased (d) von Bertalanffy growth formula (VBGF). According to the dVBGF, adult males sharply reduce their growth rate after reaching an age between 1.2 and 1.5 year, which corresponds to the estimates of age at sexual maturity (tm between 1 and 1.5 years). The reduction in growth determines a higher Tmax (7.3–9.5 year) and lower M (0.4–0.6 year?1) than previously derived on the basis of cVBGF estimates (Tmax 3–4 years and M 1.2 year?1). The dVBGF results suggest that sexual dimorphism and length–sex segregation in giant red shrimps reflect an alternative life history strategy that is based mainly on growth reduction in adult males and it might be adopted for implementing more conservative assessments. |
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| Keywords: | Aristaeomorpha foliacea giant red shrimp growth discontinuity Malta Mediterranean Sea Sicily straits |
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