TUNPOP, a computer simulation model of the yellowfin tuna population and the surface tuna fishery of the Eastern Pacific Ocean

ENGLISH: Mathematical documentation of TUNP0P, an age-structured computer simulation model of the yellowfin tuna population and surface tuna fishery of the eastern Pacific Ocean, is described. Example runs of the model are presented and discussed, and the sensitivity of the model output to changes in various parameters is examined. SPANISH: Se describe la documentación matemática de TUNP0P, un modelo computador de simulación basado en la edad de la población del atún aleta amarilla y de la pesca atunera epipelágíca del Océano Pacífico oriental. Se presentan y se discuten ejemplos de las pasadas del modelo, y se examina la sensibilidad de los resultados de salida con relación a los cambios de varios parámetros. (PDF contains 47 pages.)

TUNPOP: A simulation of the dynamics and structure of the yellowfin tuna stock and surface fishery of the Eastern Pacific Ocean

ENGLISH: Three distinct versions of TUNP0P, an age-structured computer simulation model of the eastern Pacific yellowfin tuna, Thunnus albacores, stock and surface tuna fishery, are used to reveal mechanisms which appear to have a significant effect on the fishery dynamics. Real data on this fishery are used to make deductions on the distribution of the fish and to show how that distribution might influence events in the fishery. The most important result of the paper is that the concept of the eastern Pacific yellowfin tuna stock as a homogeneous unit is inadequate to represent the recent history of the fishery. Inferences are made on the size and distribution of the underlying stock as well as its potential yield to the surface fishery as a result of alterations in the level and distribution of the effort. SPANISH: Se han empleado tres versiones diferentes de TUNP0P, un modelo de simulación de la computadora (basado en la estructura de la edad) de la población y la pesca epipelágica del atún aleta amarilla, Tbunnus albacares, del Pacífico oriental, para revelar los mecanismos que parecen tener un efecto importante en la dinámica pesquera. Se emplean los datos verdaderos de esta pesca para hacer deducciones sobre la distribución de los peces y para mostrar cómo puede influir esta distribución en los eventos de pesca. La conclusión más importante de este estudio es que el concepto de que la población del aleta amarilla del Pacífico oriental es una unidad homogénea, es inadecuado para representar la historia reciente de pesca. Se teoriza sobre la talla y distribución de la población subyacente como también sobre su producción potencial en la pesca epipelágica al cambiar el nivel y distribución del esfuerzo.

Simulation stochastique des structures démographiques. Application aux populations d'albacores, Thunnus albacares

A computer program has been written in order to generate a population of fishes following a Von Bertalanffy growth curve with a random Gaussian variability for birth dates and growth parameters K and L ∞. Standard deviations for these 3 parameters are chosen separately for each run. Fishing and natural mortalities are applied to this population. Using as an input parameters usually taken for yellowfin in the eastern Atlantic, the simulation suggests a standard deviation between 1 and 2 months for the birth dates in this population. It also indicates that increasing levels of fishing mortalities must produce a better agreement between age and length for the larger fish.

Evaluating methods for estimating rare events with zero-heavy data: a simulation model estimating sea turtle bycatch in the pelagic longline fishery

Estimating rare events from zero-heavy data (data with many zero values) is a common challenge in fisheries science and ecology. For example, loggerhead sea turtles (Caretta caretta) and leatherback sea turtles (Dermochelys coriacea) account for less than 1% of total catch in the U.S. Atlantic pelagic longline fishery. Nevertheless, the Southeast Fisheries Science Center (SEFSC) of the National Marine Fisheries Service (NMFS) is charged with assessing the effect of this fishery on these federally protected species. Annual estimates of loggerhead and leatherback bycatch in a fishery can affect fishery management and species conservation decisions. However, current estimates have wide confidence intervals, and their accuracy is unknown. We evaluate 3 estimation methods, each at 2 spatiotemporal scales, in simulations of 5 spatial scenarios representing incidental capture of sea turtles by the U.S. Atlantic pelagic longline fishery. The delta-log normal method of estimating bycatch for calendar quarter and fishing area strata was the least biased estimation method in the spatial scenarios believed to be most realistic. This result supports the current estimation procedure used by the SEFSC.