High bycatch rates of manta and devil rays in the “small-scale” artisanal fisheries of Sri Lanka

Abstract

Background Expanding fisheries in developing nations like Sri Lanka have a significant impact on threatened marine species such as elasmobranchs. Manta and devil (mobulid) rays have some of the most conservative life history strategies of any elasmobranch, and even low to moderate levels of bycatch from gillnet fisheries may lead to significant population declines. A lack of information on life history, demographics, population trends, and fisheries impacts hinders effective management measures for these species. Method We report on mobulid fishery landings over nine years between 2011 and 2020 across 38 landing sites in Sri Lanka. We collected data on catch numbers, body sizes, sex, and maturity status for five mobulid species. We used a Bayesian state-space model to estimate monthly country-wide catch rates and total annual landings of mobulid rays. We used catch curve analyses to estimate total mortality for Mobula mobular, and evaluated trends in recorded body sizes across the study period for M. mobular, M. birostris, M. tarapacana and M. thurstoni. Results We find that catch rates have declined an order of magnitude for all species across the study period, and that total annual captures of mobulid rays by the Sri Lankan artisanal fishing fleet exceed the estimated annual captures of mobulids in all global, industrial purse seine fisheries combined. Catch curve analyses suggest that M. mobular is being fished at rates far above the species’ intrinsic population growth rate, and the average sizes of all mobulids in the fishery except for M. birostris are declining. Collectively, these findings suggest overfishing of mobulid ray populations in the northern Indian Ocean by Sri Lankan artisanal fisheries. We recommend strengthening the management of these species through improved implementation of CITES, CMS, and regional fisheries management actions. In addition, we report on the demographic characteristics of mobulids landed in Sri Lanka and provide the first record of M. eregoodoo in the country.

Manta and devil ray species occurrence and distribution in Venezuela, assessed through fishery landings and citizen science data

“…Despite the potential for manta ray‐related eco‐tourism activities to provide sustainable economic benefits to the area, the Venezuelan political and economic situation has hindered the growth of tourism in recent decades (Gutiérrez & Narváez, 2015). Consequently, citizen science data availability for mobulids and other megafauna in Venezuela are few compared to other countries, such as Australia (Armstrong et al ., 2019), the Solomon Islands (Chin et al ., 2020), Maldives (Nicholson‐Jack et al ., 2021; Strike et al ., 2022), Sri Lanka (Fernando & Stewart, 2021) and the Mexican Pacific (Becerril‐García et al ., 2019). Nevertheless, the limited citizen science data the authors were able to source still constitute a base to build knowledge of mobulid species diversity, abundance and distribution in Venezuela.…”

“…Venezuela are few compared to other countries, such as Australia(Armstrong et al, 2019), the Solomon Islands(Chin et al, 2020), Maldives(Nicholson-Jack et al, 2021;Strike et al, 2022), Sri Lanka(Fernando & Stewart, 2021) and the Mexican Pacific(Becerril-García et al, 2019). Nevertheless, the limited citizen science data the authors were able to source still constitute a base to build knowledge of mobulid species diversity, abundance and distribution in Venezuela.The locations identified by Notarbartolo diSciara and Hillyer (1989) in northeastern Venezuela and the locations identified by citizen scientists provide evidence to support Farall on Centinela, Los Roques Archipelago Islands, Chichiriviche de la Costa and Morrocoy National Park as potential manta ray sighting hotspots.…”

Sublethal Injuries and Physical Abnormalities in Maldives Manta Rays, Mobula alfredi and Mobula birostris

“…To address the growing threat of the gill plate trade, both manta species were listed on Appendix II of the Convention on International Trade in Endangered Species in 2013, and they are also listed on Appendices I and II of the Convention on the Conservation of Migratory Species (Lawson et al, 2017). Despite these protective measures, targeted and incidental bycatch of manta rays in small-and large-scale fisheries remains a persistent threat (Dulvy et al, 2014;Croll et al, 2016;Lawson et al, 2017;Fernando and Stewart, 2021). Less directly, impacts of the climate crisis and reef degradation threaten manta ray food supply and habitat (Richardson, 2008;Stevens and Froman, 2019), while unregulated tourism operations can impact feeding, alter behaviour, and inflict lethal and sublethal boat strikes (Anderson et al, 2011a;Venables, 2013;Venables et al, 2016;Murray et al, 2020).…”

Spatially explicit risk assessment of marine megafauna vulnerability to Indian Ocean tuna fisheries

“…The most commonly reported species are silky sharks (Carcharhinus falciformis, Carcharhinidae) in all three gears; blue sharks (Prionace glauca, Carcharhinidae) and oceanic whitetip sharks (Carcharhinus longimanus, Carcharhinidae) in longlines and purse seines; shortfin makos (Isurus oxyrinchus, Lamnidae) and pelagic batoids (e.g. Myliobatidae, Mobulidae) in purse seines and drift nets; pelagic stingrays (Pteroplatytrygon violacea, Dasyatidae) in drift nets and longlines; hammerheads (Sphyrna spp, Sphyrnidae) and crocodile sharks (Pseudocarcharias kamoharai, Pseudocarchariidae) in longlines; and whale sharks (Rhincodon typus, Rhincodontidae) in drift nets (Briscoe, Maxwell, Kudela, Crowder, & Croll, 2016;Clavareau et al, 2020;Escalle et al, 2015;Fernando & Stewart, 2021;Garcia & Herrera, 2018;Moazzam, 2012;Murua et al, 2018). Overall, purse seine fleets reportedly have the lowest by-catch rates per unit of fishing effort (especially for cetaceans), lower mortality for sea turtles and cetaceans, and fewer species that are caught in large numbers compared with drift nets and longlines (Clavareau et al, 2020).…”