Impacts of fisheries bycatch on marine turtle populations worldwide: toward conservation and research priorities

Bryan P Wallace,Larry B Crowder,Connie Y Kot,Tina Lee,Andrew D Dimatteo,Rebecca L Lewison

doi:10.1890/es12-00388.1

Abstract

Fisheries bycatch is considered the most serious threat globally to long‐lived marine megafauna (e.g., mammals, birds, turtles, elasmobranchs). However, bycatch assessments to date have not evaluated population‐level bycatch impacts across fishing gears. Here, we provide the first global, multi‐gear evaluation of population‐level fisheries bycatch impacts for marine turtles. To compare bycatch impacts of multiple gears within and among marine turtle populations (or regional management units, RMUs), we compiled more than 1,800 records from over 230 sources of reported marine turtle bycatch in longline, net, and trawl fisheries worldwide that were published between 1990–2011. The highest bycatch rates and levels of observed effort for each gear category occurred in the East Pacific, Northwest and Southwest Atlantic, and Mediterranean regions, which were also the regions of highest data availability. Overall, available data were dominated by longline records (nearly 60% of all records), and were non‐uniformly distributed, with significant data gaps around Africa, in the Indian Ocean, and Southeast Asia. We found that bycatch impact scores—which integrate information on bycatch rates, fishing effort, mortality rates, and body sizes (i.e., proxies for reproductive values) of turtles taken as bycatch—as well as mortality rates in particular, were significantly lower in longline fishing gear than in net and trawl fishing gears. Based on bycatch impact scores and RMU‐specific population metrics, we identified the RMUs most and least threatened by bycatch globally, and found wide variation among species, regions, and gears within these classifications. The lack of regional or species‐specific patterns in bycatch impacts across fishing gears suggests that gear types and RMUs in which bycatch has the highest impact depend on spatially‐explicit overlaps of fisheries (e.g., gear characteristics, fishing practices, target species), marine turtle populations (e.g., conservation status, aggregation areas), and underlying habitat features (e.g., oceanographic conditions). Our study provides a blueprint both for prioritizing limited conservation resources toward managing fishing gears and practices with the highest population impacts on sea turtles and for enhancing data collection and reporting efforts.

Highlights

Minimizing bycatch, or the unintended capture of non-target organisms during fisheries operations (Hall et al 2000, Soykan et al 2008), is a key component of sustainable fisheries management that maintains marine biodiversity (Veitch et al 2012)
Of the data records that contained both BPUE and fishing effort information (n 1⁄4 1,467), more than 59% were longline records, while the remainder was split between nets (26%) and trawls (15%) (Fig. 1)
This study is the first attempt to quantify potential impacts of fisheries bycatch on marine turtle regional management units (RMUs) worldwide by compiling and analyzing available bycatch data from multiple fishing gears in a population context

Summary

Introduction

Minimizing bycatch, or the unintended capture of non-target organisms during fisheries operations (Hall et al 2000, Soykan et al 2008), is a key component of sustainable fisheries management that maintains marine biodiversity (Veitch et al 2012). Marine megafauna bycatch research has increased exponentially in recent years (Soykan et al 2008), highlighting cases of acute bycatch problems (e.g., Peckham et al 2007, Alfaro-Shigueto et al 2011), the relative magnitude of bycatch at broad scales (e.g., Lewison et al 2004a, b, 2005, Read et al 2006, Casale 2010, Wallace et al 2010a), and the need for development and implementation of bycatch reduction strategies (Cox et al 2007, FAO Fisheries Department 2009, Gilman et al 2009). Various types of information are necessary to characterize bycatch patterns and to understand population impacts on taxa affected by bycatch, including bycatch rates, amounts of fishing effort on which these rates were based, rates of mortality associated with bycatch interactions, among others. Bycatch studies typically focus on specific areas, time periods, and gear types, limiting their generality (Lewison et al 2009), or are global-scale assessments of megafauna bycatch that are unable to describe fine-scale patterns to guide effective bycatch management at local scales (e.g., Wallace et al 2010a)

Objectives

Methods

Results

Discussion

Conclusion