Comparative statistical analysis of incidental dolphin mortality, during fishing trips of the Mexican purse seine tuna fishery in the Eastern Pacific Ocean recorded by two scientific observer programs

Michel J Dreyfus-Leon,Elena Solana-Arellano

doi:10.22370/rbmo.2019.54.3.2032

Abstract

Scientific observer programs in fisheries are being deployed worldwide in order to obtain robust data for fishery studies, and in relation to its interaction with target and bycatch species. A comparison between two observer programs in Mexican purse seine tuna fishery in the Eastern Pacific ocean is performed considering the incidental mortality per trip as a metric recorded by both observers programs from 1999 to 2016. A Bayesian t-test approximation was used for the comparison between the two methods since, due to its probabilistic nature reduces uncertainty. The analysis showed a very low probability of differences for the estimated bycatch rate between both programs.

Highlights

The assessment of the impact of fisheries on marine ecosystems is complicated because historically emphasis or attention has been placed on obtaining reliable statistics through logbooks in order to report data of fishing effort, location and target catch magnitude
The “La Jolla Agreement” was signed by many members of the Inter American Tropical Tuna Commission (IATTC), which is a regional organization in charge of tuna management in the eastern Pacific Ocean
Since the main objective was to compare the performance of these programs in the Mexican purse seine fishery in the eastern Pacific Ocean hereinafter called PA and PB, the mortality of fishing dolphins was used as a measure

Summary

Introduction

The assessment of the impact of fisheries on marine ecosystems is complicated because historically emphasis or attention has been placed on obtaining reliable statistics through logbooks in order to report data of fishing effort, location and target catch magnitude. Observer programs provide high-quality bycatch data (Lewinson et al 2004), especially if these observers have adequate training and academic background to identify species interactions with the fishery and the preparation to appropriately quantify the amounts of incidental mortality. Due to incidental dolphin mortality in the USA tuna fishery fleet in the Eastern Pacific, the National Marine Fisheries Service of the USA, initiated an observer program in 1966 (Chivers 2018). Starting in 1992 and under the “La Jolla Agreement” the observer program reached a 100% coverage for vessels above 363 tons of carrying capacity (IATTC 1998). One of the main goals was to quantify instead of estimate dolphin mortality and to keep track of fishing

Objectives

Methods

Results