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All tuna fishing methods have some degree of impact on the marine environment, including on other species, such as sharks, sea turtles, rays, and seabirds. We research those impacts and evaluate efforts by Regional Fisheries Management Organizations (RFMOs) to mitigate them.

ISSF also publishes science-based best practices — often in collaboration with commercial tuna skippers — for reducing bycatch. Bycatch is the catch of any species that is not the main reason for which the skipper is fishing, whether the catch is retained or discarded.

To help fishers avoid unintentional catches of non-target species, our scientists investigate changes in fishing gear and other methods, including aspects of fish aggregating device (FAD) design and management. We also test and refine safe handling-and-release techniques that skippers can use when marine animals are accidentally caught.


There are three major areas of concern when it comes to sharks – observed bycatch, unobserved mortality due to entanglement in fishing gear, and shark finning practices.

Sea Turtles

ISSF supports multiple initiatives to track, report on, and minimize the bycatch of sea turtles in purse-seine and longline tuna fisheries.


Minor changes in both fishing approaches and bycatch handling practices could lead to major improvements for the survival of accidentally caught manta and devil rays in tuna fisheriesISSF 2024-03: Tuna Fisheries’ Impacts on Non-Tuna Species and Other Environmental Aspects: 2024 Summary — among the ocean’s slowest-growing, most vulnerable species.


Many seabirds in tuna fisheries are endangered — and at risk of harm from baited tuna-fishing hooks. ISSF researches seabird bycatch risk and prevention, and our longline skippers guidebooks show fishers how to avoid attracting and hooking them.

Other Bycatch Species

In FAD tuna fisheries, other species at risk of becoming bycatch are the “minor tunas” (such as little tunny, bullet tuna, and kawakawa); other bony fishes (including mahi-mahi, triggerfish, and rainbow runners); and billfishes like Atlantic marlin.


Scientific Research

In our scientific reports, we publish data and analysis on a range of bycatch issues — from summaries of our at-sea research projects, international workshops, and collaborations with skippers to bycatch rates by fishery type and species-specific bycatch mitigation procedures. We publish a report that specifically reviews tuna fisheries’ impacts on non-tuna species.

ISSF is researching how acoustic discrimination of tuna species at FADs, using echosounder technology, may help fishers to more precisely target certain tuna species and avoid catching bycatch species. Our scientists publish their findings in peer-reviewed articles.

Watch our videos for an introduction to our bycatch research.

Conservation Measures

As we identify key challenges in and potential solutions for reducing bycatch of all species in tuna fisheries worldwide, we create conservation measures to address them.

ISSF conservation measures affect how leading seafood companies operate and source tuna, and also how certain vessels fish — including the type of equipment they use.

Among our 11 measures focused on bycatch mitigation, for example, we address anti-shark-finning efforts, tuna retention, non-entangling FADs, and more.

Fisher Collaboration & Education

In collaborative workshops with tuna fishers, we explore bycatch-mitigation equipment and techniques as well as more sustainable Fish Aggregating Device (FAD) designs and management approaches.

To support skippers in protecting sharks and other bycatch species in tuna fisheries, we offer bycatch-education opportunities and resources:

We also share research about set times and technology that can help vessels to fish more selectively and minimize unintentional catches.

RFMO Advocacy

We turn our scientific insights about sustainable fishing approaches into conservation and policy recommendations for Regional Fisheries Management Organizations (RFMOs), governing bodies, and other oversight agencies.

For instance, our advocacy experts develop position statements to petition RFMOs about bycatch-mitigation requirements for fleets in their ocean regions. We recommend steps RFMOs can take to make their measures align with best practices, including electronic monitoring and reporting of bycatch, and we assess their progress.

We also circulate joint letters to RFMOs, co-signed by seafood companies, retailers, and environmental organizations.


Fishing Impacts on Non-Tuna Species

Our report ISSF 2024-03: Tuna Fisheries’ Impacts on Non-Tuna Species and Other Environmental Aspects: 2024 Summary covers non-target species, habitats, and Endangered, Threatened or Protected (ETP) species.

Species Identification Guides

The ISSF Guidebooks site contains guides, in several languages, to help fishers identify different species of tuna.

We also offer identification guides for bycatch species such as sharks, rays, billfish, sea turtles, seabirds, and non-tuna finfish.