Derelict fishing line provides a useful proxy for estimating levels of non-compliance with no-take marine reserves.

Richard D Evans,Jos K Hill,Daniela M Ceccarelli,Garry R Russ,David H Williamson

doi:10.1371/journal.pone.0114395

Abstract

No-take marine reserves (NTMRs) are increasingly being established to conserve or restore biodiversity and to enhance the sustainability of fisheries. Although effectively designed and protected NTMR networks can yield conservation and fishery benefits, reserve effects often fail to manifest in systems where there are high levels of non-compliance by fishers (poaching). Obtaining reliable estimates of NTMR non-compliance can be expensive and logistically challenging, particularly in areas with limited or non-existent resources for conducting surveillance and enforcement. Here we assess the utility of density estimates and re-accumulation rates of derelict (lost and abandoned) fishing line as a proxy for fishing effort and NTMR non-compliance on fringing coral reefs in three island groups of the Great Barrier Reef Marine Park (GBRMP), Australia. Densities of derelict fishing line were consistently lower on reefs within old (>20 year) NTMRs than on non-NTMR reefs (significantly in the Palm and Whitsunday Islands), whereas line densities did not differ significantly between reefs in new NTMRs (5 years of protection) and non-NTMR reefs. A manipulative experiment in which derelict fishing lines were removed from a subset of the monitoring sites demonstrated that lines re-accumulated on NTMR reefs at approximately one third (32.4%) of the rate observed on non-NTMR reefs over a thirty-two month period. Although these inshore NTMRs have long been considered some of the best protected within the GBRMP, evidence presented here suggests that the level of non-compliance with NTMR regulations is higher than previously assumed.

Highlights

Overharvesting and habitat degradation caused by destructive fishing methods are among the greatest threats to the health and productivity of marine ecosystems [1,2,3]
During the 2009 Underwater visual census (UVC) surveys of reefs in the Palm, Whitsunday and Keppel Island groups, derelict fishing lines were recorded within old (1987) No-take marine reserves (NTMRs), new (2004) NTMRs and in non-NTMR zones that are legally open to fishing
In the Palm Islands, line densities were significantly higher in new NTMRs than in old NTMRs (Tukey HSD, p,0.05), but there was no significant difference in the density of lines between non-NTMRs and both old and new NTMRs (Fig. 2)

Summary

Introduction

Overharvesting and habitat degradation caused by destructive fishing methods are among the greatest threats to the health and productivity of marine ecosystems [1,2,3]. Hook-and-line is a commonly used fishing method on coral reefs and rates of gear loss are often relatively high, when fishing over highly complex reef slope habitats, with steep walls, overhangs, caves and high hard coral cover [6, 10, 12]. The direct impacts of hook and line fishing are generally lower than more habitat-destructive fishing methods [2, 13], derelict fishing line can be detrimental to the health of corals and other benthic invertebrates [5, 9, 14]. Once entangled on coral reefs, derelict fishing lines eventually become overgrown by benthic invertebrates and they are embedded in the reef matrix [5]

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Conclusion