Vulnerabilities and fisheries impacts: the uncertain future of manta and devil rays

Abstract

ABSTRACT1. Manta and devil rays of the subfamily Mobulinae (mobulids) are rarely studied, large, pelagic elasmobranchs, with all eight of well-evaluated species listed on the IUCN Red List as threatened or near threatened.2. Mobulids have life history characteristics (matrotrophic reproduction, extremely low fecundity, and delayed age of first reproduction) that make them exceptionally susceptible to overexploitation.3. Targeted and bycatch mortality from fisheries is a globally important and increasing threat, and targeted fisheries are incentivized by the high value of the global trade in mobulid gill plates.4. Fisheries bycatch of mobulids is substantial in tuna purse seine fisheries. 5. Thirteen fisheries in 12 countries specifically targeting mobulids, and 30 fisheries in 23 countries with mobulid bycatch were identified.6. Aside from a few recently enacted national restrictions on capture, there is no comprehensive monitoring, assessment or control of mobulid fisheries or bycatch. Recent listing through the Convention on the This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.International Trade in Endangered Species (CITES) may benefit mobulids of the genus Manta (manta rays), but none of the mobulids in the genus Mobula (devil rays) are protected. 7. The relative economic costs of catch mitigation are minimal, particularly compared with a broad range of other, more complicated, marine conservation issues.

Trophic overlap in mobulid rays: insights from stable isotope analysis

“…Both bycatch and targeted fisheries appear to contribute to global declines in mobulid abundance (Ward-Paige et al 2013, White et al 2015, Croll et al 2016. Targeted fisheries can be managed with legislation banning the capture of mobulids, but bycatch remains a more challenging and persistent threat due to the ubiquity of mobulid bycatch in artisanal and commercial fisheries of all types (Croll et al 2016). The apparent similarity in diets and overlapping isotopic niches between mobulids in this study are consistent with the spatial overlap in bycatch of the various mobulid species (Croll et al 2016).…”

“…Targeted fisheries can be managed with legislation banning the capture of mobulids, but bycatch remains a more challenging and persistent threat due to the ubiquity of mobulid bycatch in artisanal and commercial fisheries of all types (Croll et al 2016). The apparent similarity in diets and overlapping isotopic niches between mobulids in this study are consistent with the spatial overlap in bycatch of the various mobulid species (Croll et al 2016). Identifying the spatial and temporal patterns of mobulids' primary zooplankton prey (for example euphausiids in the Philippines) could aid in predicting their occurrence and relative vulnerability to bycatch-prone fisheries.…”

“…1). We selected these bounding boxes based on the expected distribution of mobulids in each region, which was supported by bycatch data from the eastern equatorial Pacific (Croll et al 2016), interviews with fishermen regarding capture locations in Sri Lanka, and records of long-distance movements in several Mobula species (Thorrold et al 2014, Francis & Jones 2017. We averaged chl a values over the entire bounding box for a given region and smoothed monthly averages into seasonal (3 mo) averages for plotting purposes.…”

“…While these growing targeted fisheries have catalyzed focused conservation and scientific attention for mobulids (Ward-Paige et al 2013, White et al 2015, bycatch of these species likely impacted populations long before large-scale targeted fisheries began. Mobulid rays are vulnerable to incidental capture in gill nets, purse seines, trawls, and even long lines (Croll et al 2016). Moreover, their low annual reproductive output and conservative demographic characteristics make them highly susceptible to fisheries-induced population declines (Dulvy et al 2014, Pardo et al 2016, even when catch rates are low.…”

Basking Shark (Cetorhinus maximus) Movements in the Eastern North Pacific Determined Using Satellite Telemetry

“…Keywords: basking shark, habitat, diel vertical migration, satellite telemetry, Cetorhinus maximus, foraging ecology INTRODUCTION A long history of human interaction has resulted in the decline of many species of marine megafauna including turtles, tunas, cetaceans, rays and sharks (Springer et al, 2003;Lewison et al, 2004;Marshall et al, 2006;Bradshaw et al, 2008;Dulvy et al, 2008;Croll et al, 2016;ISC, 2016). This list includes the second largest shark, the basking shark (Cetorhinus maximus, Gunnerus, 1765), that can reach 12 m in length and is named for its habit of swimming slowly at the surface (Compagno, 1984;Priede, 1984;Sims, 2008;McFarlane et al, 2009).…”