“A growth model for Indo-Pacific sailfish, Istiophorus platypterus, in the eastern tropical Pacific Ocean using mixture distributions from length frequency data to statistically discern age groups”
Fitchett, M.D. and N.M. Ehrhardt
The Indo-Pacific sailfish, Istiophorus platypterus, has been subjected to heavy exploitation throughout the eastern tropical Pacific as non-target catch in industrial high-seas longline and purse seine fisheries in additional directed fisheries in localized artisanal longline and drift net fisheries. In order to accurately assess population processes and mortality by discernable natural and fishery sources, a growth model is imperative. At present, reliable growth models for the species are absent in the region. In this study, spatially explicit observed sailfish length data series (n=9321 measurements eye-forklength in cm) from widespread purse seine fisheries in the eastern tropical Pacific from 1991 to 2007 are used to develop a growth model for sailfish. Methods include fitting mixture distributions representative of age groups partitioned by singular statistical distributions among length-frequency data in the R Statistical Computing environment (R Development Core Team 2010). A simulator is developed to utilize outputs from a series of fitted mixture distributions to recreate length at age by a series of Monte Carlo simulations for each simulated age class. A series of simulated von Bertalanffy growth functions are fitted as a result to estimate much needed growth parameters for the species. Resulting fits yield a von Bertlanffy growth function with asymptotic growth maxima for sailfish to be 207.05 cm eye forklength, with intrinsic Brody growth rate coefficient of 0.59, and a fitted age at size 0 to be -0.04 years. Combined simulated length at age distributions statistically fit to the original length frequency data series for which they are estimated from (Kolmogorov–Smirnov, p > 0.5) thus verifying the validity of the simulation procedure.
Why study growth?
Understanding sailfish growth is paramount in assessing the population dynamics of the species. Mortality estimations and migratory patterns are contingent on age and size of the animals. In order to assess the age composition, animals need to be sampled and assessed by observations of length and weight, thus rendering the immediate need to link age with the size of the fish.
Alvarado-Castillo, R., Felix-Uraga, R., 1998. Growth of Istiophorus platypterus (Pisces: Istiophoridae) from the mouth of the Gulf of California. Rev. Biol. Trop. 46, 115–118.
Beverton, R.J.H. and Holt, S.J. 1957. On the dynamics of exploited fish populations. Fish. Invest. Ser. II, Vol. 19. 533 pp.
Cerdenares-Ladrón De Guevara, G., Morales-Bojórquez, E., and R. Rodríguez-
Sánchez (2011): Age and growth of the sailfish Istiophorus platypterus (Istiophoridae) in the Gulf of Tehuantepec, Mexico, Marine Biology Research, 7:5, 488-499
Chiang, W.-C., Sun, C.-L., Yeh, S.-Z., 2004. Age and growth of sailfish (Istiophorus playtypterus) in waters off eastern Taiwan. Fish. Bull. 102, 251–263
Ehrhardt, N. M and M.D. Fitchett. 2006. On the seasonal dynamic characteristics of the sailfish, Istiophorus platypterus, in the Eastern Pacific off Central America. Bull. Mar Sci., 79(3) 589-606
Ehrhardt, N.M and M. D. Fitchett 2008. Report to the Government of Costa Rica : Evaluation and recommendations regarding recreational sport fisheries targeting billfishes and their exploitation. In Spanish. Unpublished report.
Formacion, S.P., Rongo, J.M. and Sambilay, V.C. 1991. Extreme value theory applied to the statistical distribution of the largest lengths of fish. Asian Fish. Sci. 4, 123±135.
Fournier, D. A., Sibert, J. R., Majkowski, J., and Hampton, J. 1990. MULTIFAN: a likelihood-based method for estimating growth parameters and age composition from multiple length frequency data sets illustrated using data for southern bluefin tuna (Thunnus maccoyii). Canadian Journal of Fisheries and Aquatic Sciences 47, 301-17.
Fournier, D. A., Hampton, J., and Sibert, J. R. 1998. MULTIFAN-CL: a length-based, age-structured model for fisheries stock assessment, with application to South Pacific albacore, Thunnus alalunga. Canadian Journal of Fisheries and Aquatic Sciences 55, 205-16.
Macı´as-Zamora R, Vidaurri-Sotelo AL, Santana-Herna´ndez H, Valdez-Flores JJ, Beltra´n-Pimienta R. 2001. Pez vela. In: SAGARPA, editors. Sustentabilidad y pesca responsable en Me´xico Evaluacio´n y Manejo. Me´xico: SAGARPA, p 389-410
Nakamura I. 1985. FAO Species Catalogue. Vol. 5. Billfishes of the World. An Annotated and Illustrated Catalogue of Marlins, Sailfishes, Spearfishes and Swordfishes known to date. Rome: FAO Fish Synopsis 5: 65 pages.
Joseph, J., W. L. Klawe, and C. J. Orange. 1974. A review of the longline fishery for billfishes in the Eastern Pacific Ocean. Pages 309–331 in R. S. Shomura and F. Williams (Eds.). Proceedings of the International Billfish Symposium Kailua-Kona, Hawaii, 9–12 August 1972. Part 2. Review and contributed Papers. NOAA Tech. Rep. NMFS SSRF-675.
Prince, E. D., and C.P. Goodyear. 2006. Hypoxia-base habitat compression of tropical pelagic fishes. Fish. Oceanogr. 15 6: 451–464.
R Development Core Team. 2010. R Statistical Computing environment.
Siegfried, K. I. and Sanso´, B. 2006. Two Bayesian methods for estimating parameters of the von Bertalanffy growth equation. Environmental Biology of Fishes