Quantifying longline bycatch mortality for pelagic sharks in western Pacific shark sanctuaries

Abstract

Marine protected areas are increasingly touted for their role in conserving large marine predators such as sharks, but their efficacy is debated. Seventeen “shark sanctuaries” have been established globally, but longline fishing continues within many such jurisdictions, leading to unknown levels of bycatch mortality levels. Using public data from Global Fishing Watch and Regional Fisheries Management Organizations, we quantified longline fishing within eight shark sanctuaries and estimated pelagic shark catch and mortality for seven pelagic shark species. Sanctuary mortality ranged from 600 individuals (Samoa) to 36,256 individuals (Federated States of Micronesia), equivalent to ~5% of hypothesized sustainable levels for blue sharks to ~40% for silky sharks, with high mortality levels in the Federated States of Micronesia, Palau, and the Marshall Islands. Unsustainable mortality rates were exceeded for silky sharks in two sanctuaries, highlighting a need for additional stock assessments and implementation of bycatch reduction measures. Big data integration workflows represent a transformative tool in fisheries management, particularly for data-poor species.

Seasonal distribution patterns and conservation gaps of blue sharks in the Indo‐Western Pacific Ocean

“…A recent study has indicated that mortality rates of blue sharks are very high in shark sanctuaries near the equator (i.e. Federated States of Micronesia, Palau and Marshall Islands; Shea et al, 2023). Therefore, it is necessary to modify or prohibit fishing gears (e.g.…”

Perceptions and attitudes of residents toward small-scale longline tuna fishing in the Galapagos Marine Reserve: conservation and management implications

“…Contrary to these beliefs, as of May 18th, 2023, 27 longline fisheries have been certified as sustainable by the Marine Stewardship Council, with another 15 under assessment (MSC, 2023). Furthermore, although the 17 global shark sanctuaries, serving as specialized Large Marine Protected Areas (LMPA), prohibit shark fishing and trading, many still allow longline tuna and billfish fisheries (Ward-Paige, 2017; Shea et al, 2023). According to Shea et al (2023), who evaluated eight out of 17 existing sanctuaries, shark mortality produced by longline fisheries varied drastically, from 600 in Samoa to 36,256 in the Federated States of Micronesia.…”

“…Furthermore, although the 17 global shark sanctuaries, serving as specialized Large Marine Protected Areas (LMPA), prohibit shark fishing and trading, many still allow longline tuna and billfish fisheries (Ward-Paige, 2017; Shea et al, 2023). According to Shea et al (2023), who evaluated eight out of 17 existing sanctuaries, shark mortality produced by longline fisheries varied drastically, from 600 in Samoa to 36,256 in the Federated States of Micronesia. Mortality rates in these sanctuaries reached up to 5% of sustainable levels for blue sharks (Prionace glauca), and 40% for silky sharks (Carcharhinus falciformis).…”

“…While some studies advocate for outright longlining bans in "shark sanctuaries" or multiple use MPA (Chapman et al, 2013;Cerutti-Pereyra et al, 2020), others recognize the socioeconomic importance of longlining in these areas, suggesting alternative mitigation strategies (Davidson, 2012;Simpfendorfer and Dulvy, 2017). A recent study examining longline fishing across eight Western Pacific shark sanctuaries and its effects on pelagic shark species acknowledges that an ideal shark sanctuary should prohibit longlining (Shea et al, 2023). However, given the economic and food security roles of longlining in numerous remote island nations, enforcing such bans may not always be feasible.…”

“…However, given the economic and food security roles of longlining in numerous remote island nations, enforcing such bans may not always be feasible. In situations where absolute bans are impractical, Shea et al (2023) suggest adopting bycatch mitigation strategies, such as gear modifications, effort limitations, or temporary or permanent closures of critical habitats, to reduce incidental shark mortalities. A similar management approach has been suggested by Ben-Yami (2001) and Castrejoń and Defeo (2023), who suggest reconsidering the feasibility and efficacy of this regulation in the Galapagos Marine Reserve (GMR) to guarantee the conservation of ETP species.…”