Reproductive biology and population dynamics of the shortfin mako, Isurus oxyrinchus Rafinesque, 1810, off the southwest Portuguese coast, eastern North Atlantic |
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| Authors: | A Maia N Queiroz H N Cabral A M Santos J P Correia |
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| Institution: | Departamento de Biologia Animal and Instituto de Oceanografia, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, Lisboa, Portugal;;CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Campus Agrário de Vairão, Vairão, Portugal;;Oceanário de Lisboa, SA, Esplanada D. Carlos I –Doca dos Olivais, Lisboa, Portugal |
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| Abstract: | A total of 262 shortfin mako sharks, Isurus oxyrinchus, was sampled from the swordfish longliners operating in the eastern North Atlantic. Most were juveniles, with only 3.4% mature. Based on cohort analysis, average growth was determined as 61.1 cm year−1 for the first year and 40.6 cm year−1 for the second year. There was a marked seasonality in growth, with average monthly rates of 5.0 cm month−1 in summer and 2.1 cm month−1 in winter. Cohort analysis also indicated summer as the probable parturition season, with sharks close to birth size caught in May 2003 and July 2004. Length at maturity for males was estimated at 180‐cm fork length using the Schnute model. No females between 210 and 290‐cm fork length were caught, although this appears to be the interval where maturation occurs. Gear selectivity was considered as the probable cause for the low number of mature females sampled. |
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