Effects of Fishing and Fishing Closures on Beach Clams: Experimental Evaluation across Commercially Fished and Non-Fished Beaches before and during Harvesting.

Charles A Gray,Ulrike Gertrud Munderloh

doi:10.1371/journal.pone.0146122

Abstract

Management responses to reconcile declining fisheries typically include closed areas and times to fishing. This study evaluated this strategy for a beach clam fishery by testing the hypothesis that changes in the densities and size compositions of clams from before to during harvesting would differ between commercially fished and non-fished beaches. Sampling was spatially stratified across the swash and dry sand habitats on each of two commercially fished and two non-fished beaches, and temporally stratified across three six-week blocks: before, early and late harvesting. Small-scale spatio-temporal variability in the densities and sizes of clams was prevalent across both habitats and the components of variation were generally greatest at the lowest levels examined. Despite this, differences in the densities and sizes of clams among individual beaches were evident, but there were few significant differences across the commercially fished versus non-fished beaches from before to during harvesting. There was no evidence of reduced densities or truncated size compositions of clams on fished compared to non-fished beaches, contrasting reports of some other organisms in protected areas. This was probably due to a combination of factors, including the current levels of commercial harvests, the movements and other local-scale responses of clams to ecological processes acting independently across individual beaches. The results identify the difficulties in detecting fishing-related impacts against inherent levels of variability in clam populations. Nevertheless, continued experimental studies that test alternate management arrangements may help refine and determine the most suitable strategies for the sustainable harvesting of beach clams, ultimately enhancing the management of sandy beaches.

Highlights

Fishing has had detrimental impacts on wild populations and assemblages of aquatic organisms of various phyla across a spectrum of habitats throughout the world [1,2,3,4]
Populations of clams on all four beaches were inherently variable across both habitats with significant differences in densities consistently occurring across individual sites sampled each day, as well as among days sampled within each period on each beach
The components of variation were consistently greatest across the smallest spatial scale sampled; among replicate samples taken at each site on each day and they were generally high for the factors Site and Day. These results exemplify the need for future assessments of beach clams to adequately account for small-scale variability in sampling strategies to avoid potential confounding of larger scale comparisons [33]

Summary

Introduction

Fishing has had detrimental impacts on wild populations and assemblages of aquatic organisms of various phyla across a spectrum of habitats throughout the world [1,2,3,4]. Initiatives to reconcile the effects of fishing and provide greater protection to wild organisms and habitats include areas and times either fully or partially closed to fishing [13,14], fishing gear restrictions and modifications [15], catch and bycatch quotas and size and bag limits [16]. Several such measures have been shown to be effective across different fisheries and landscapes. The success or failure of such management measures should be evaluated experimentally as part of an adaptive management regime [21,22]

Methods

Results

Conclusion