Age and growth of the shortfin mako (Isurus oxyrinchus) in the south-eastern Pacific off Chile
Francisco Cerna A D and Roberto Licandeo B CA División de Investigación Pesquera, Instituto de Fomento Pesquero, Avenuenida Blanco 839, Valparaíso, Chile.
B Departamento de Oceanografía, Universidad de Concepción, Cabina 10, PO Box 160-C, Concepción, Chile.
C Present address: Center for Quantitative Fisheries Ecology, Old Dominion University, 800, West 46th Street, Norfolk, USA.
D Corresponding author. Email: pfcerna@ifop.cl
Marine and Freshwater Research 60(5) 394-403 https://doi.org/10.1071/MF08125
Submitted: 18 April 2008 Accepted: 24 October 2008 Published: 25 May 2009
Abstract
The shortfin mako, Isurus oxyrinchus, is a large pelagic shark with a widespread global distribution. However, very little is known about most aspects of this species for the south-eastern Pacific. In the present paper, the age and growth parameters of the shortfin mako, caught by Chilean swordfish longline fisheries from 2004 to 2005, are reported. Ages were estimated by counting band-pairs from sections of vertebral centra from 547 individuals, ranging from 76 to 330 cm in total length (TL). Trends in the proportion of opaque edges for all ages combined and grouped into ages 0–6 and 7–26 years indicated that they are formed during summer and showed that annually, one band-pair is formed in the vertebrae of shortfin makos. Modal-progression analysis was used to verify the first three age classes (ages 0–2 years). For both sexes, the oldest estimated age was 25+ years. Von Bertalanffy growth parameters were estimated at L∞ = 325.29 cm TL, K = 0.076 year–1 and t0 = –3.18 years for females and L∞ = 296.60 cm TL, K = 0.087 year–1 and t0 = –3.58 years for males. The results indicated that this species is highly vulnerable to exploitation and, thus, urgent conservation measures are required.
Additional keywords: age and growth, longline, mako, south-eastern Pacific, tiburón marrajo.
Acknowledgements
We thank the scientific observers of Instituto de Fomento Pesquero (IFOP) whose effort in collecting data aboard swordfish longline vessels made the present study possible. We also thank Leopoldo Vidal at the Age and Growth Laboratory (IFOP), who prepared the vertebrae sections. Malcolm Francis (NIWA) and Professor Andrew Boulton (Editor of this Journal) made useful comments on earlier versions of this paper. Also thanks to Christina Morgan (CQFE-ODU) for improving the English text. Finally, we want to express gratitude to two anonymous referees who enormously contributed to improve the ideas here. This study was funded by SUBPESCA–IFOP, through the ‘Programa de Investigación Situación Recursos Altamente Migratorios’.
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