Relative abundance of derelict fishing gear in the Hawaii-based pelagic longline fishery grounds as estimated from fishery observer data

Amy V Uhrin,William A Walsh,Jon Brodziak

doi:10.1038/s41598-020-64771-1

Abstract

Derelict fishing gear (DFG) is abundant across the remote North Pacific Ocean, accumulating in convergence zones that coincide with the fishing grounds of the Hawai’i-based pelagic longline fishery. Longlines are prone to snagging DFG, providing an opportunistic, yet regular, reporting mechanism by longline fishery observers (fishery-dependent data). We apply a zero-inflated negative binomial model previously used to standardize catch per unit effort (CPUE) for bycatch and incidentally caught species in this fishery to estimate DFG relative abundance and qualitative trends within the longline fishing grounds. During 2008–2016, observers reported 1326 marine debris items intercepted by longlines, dominated by DFG at nearly 90%. Modeling results suggest that the relative abundance of DFG has declined ~66% from 2008–2016. DFG standardized CPUE was higher for longlines fished inside the North Pacific Subtropical Convergence Zone (versus outside) and increased moving eastward and northward toward the Great Pacific Garbage Patch. Despite substantially less effort in the shallow-set sector of the fishery (∼60 m depth), DFG standardized CPUE was four-fold greater than that of the deep-set sector (∼250 m) suggesting that marine debris observer reporting focused in this sector may be most effective. Some fishermen voluntarily stow snagged debris; incentivizing at-sea removal may elicit further cooperation.

Highlights

Derelict fishing gear (DFG) is abundant across the remote North Pacific Ocean, accumulating in convergence zones that coincide with the fishing grounds of the Hawai’i-based pelagic longline fishery
Recent estimates suggest that derelict fishing nets comprise 46% of debris by mass reported within the boundaries of the Great Pacific Garbage Patch[9], a known collection of marine debris entrained within the eastern boundary of the North Pacific Subtropical Gyre
Onboard observations of species-specific catch and other operational details from vessels participating in this fishery have been made since 1994 as part of the NOAA Pacific Islands Region Observer Program (PIROP)[20]

Summary

Introduction

Derelict fishing gear (DFG) is abundant across the remote North Pacific Ocean, accumulating in convergence zones that coincide with the fishing grounds of the Hawai’i-based pelagic longline fishery. Despite substantially less effort in the shallow-set sector of the fishery (∼60 m depth), DFG standardized CPUE was four-fold greater than that of the deep-set sector (∼250 m) suggesting that marine debris observer reporting focused in this sector may be most effective. Commercial vessels operating under the purview of the Hawai’i-based pelagic longline fishery exploit the seasonally migrating North Pacific Subtropical Convergence Zone[13,15,16], an area of both high biological productivity and zone of DFG accumulation which shifts latitudinally between the extremes of 23–37◦N17. PIROP maintains 20% annual observer coverage of deep sector trips and 100% observer coverage of shallow sector trips

Methods

Results

Conclusion