Bycatch refers to the incidental catch of non-target species in fisheries. This occurs when fishing methods are non-selective and unable to differentiate between target and non-target species. Bycatch is a major concern as it can negatively impact non-target species populations, biodiversity, and ecosystems. Understanding what the most common bycatch species are can help fisheries better mitigate bycatch through improved fishing strategies and technologies.
What is bycatch?
Bycatch is defined as the incidental catch of non-target species in a fishery. This includes both commercial and recreational fisheries. Bycatch can include fish, marine mammals, seabirds, sea turtles, and other species. It occurs for a number of reasons:
- Fishing gear like trawls, gillnets, and longlines are non-selective – they do not effectively differentiate between target and non-target species.
- Fishing sometimes occurs in areas frequented by non-target species.
- Non-target species are attracted to fishing vessels and gear.
Bycatch species may be discarded at sea due to having low commercial value, regulations, or lack of storage space. Bycatch that is discarded, usually dies. Even species that are released alive after being caught often suffer stress and injury during capture which can negatively impact populations. Bycatch is a global issue affecting both small scale local fisheries and large industrial operations.
Why is bycatch a problem?
Bycatch can have many harmful impacts including:
- Overexploitation of non-target species – bycatch may be unsustainable for some populations leading to declines.
- Changes in food web dynamics – declining bycatch species may impact predator-prey relationships in ecosystems.
- Loss of biodiversity – bycatch contributes to reduced biodiversity in marine environments.
- Waste – discarded bycatch represents lost economic potential, wasted resources and reduced efficiency.
- Threats to endangered species – bycatch exacerbates pressures on vulnerable species like sea turtles.
Mitigating bycatch is an important fisheries management goal. Steps include improving gear selectivity, spatial and temporal closures, bycatch limits and quotas, and using fishing techniques that reduce bycatch. However, bycatch remains a complex global problem.
Most common global bycatch species
The most comprehensive global bycatch data comes from the Sea Around Us project database. This analysis found the taxa most commonly caught as bycatch worldwide from 1950-2014 were:
| Bycatch Taxa | Total Bycatch (tonnes) |
| Sharks and rays | 45,392,031 |
| Crabs | 19,919,284 |
| Squid | 18,451,633 |
| Theragra chalcogramma (Alaska pollock) | 15,176,163 |
| Miscellaneous coastal fishes | 12,443,965 |
| Miscellaneous demersal fishes | 10,385,524 |
| Salmons, trouts, smelts | 8,930,173 |
| Miscellaneous pelagic fishes | 8,713,497 |
| Miscellaneous marine crustaceans | 7,408,166 |
| Sea stars and sea urchins | 6,979,596 |
Sharks and rays are the most common global bycatch taxon. They are caught across many gear types and fisheries worldwide. Their life history characteristics like slow growth, late maturity, and low fecundity make them vulnerable to overexploitation as bycatch. Crabs, squid, Alaska pollock, and coastal/demersal/pelagic fishes are also very common bycatch species globally.
Most common bycatch species in the United States
For United States fisheries, the most recent analysis of bycatch rates comes from the 2011 NOAA National Bycatch Report. The top bycatch species were:
| Bycatch Species | Total Bycatch (mt) |
| Spiny dogfish | 27,187 |
| Unspecified skates | 18,006 |
| Haddock | 13,583 |
| Atlantic herring | 12,167 |
| Unspecified sharks | 11,459 |
| Yellowtail flounder | 10,057 |
| Acadian redfish | 9,070 |
| Summer flounder | 8,072 |
| Atlantic cod | 7,828 |
| Monkfish (Goosefish) | 7,624 |
Again sharks and rays dominate, with spiny dogfish, skates, and unspecified sharks as the top species. Groundfish like haddock, yellowtail flounder, Acadian redfish, summer flounder, Atlantic cod, and monkfish are also frequent bycatch in U.S. fisheries. Herring and other forage fishes are common bycatch species as well.
Bycatch mitigation strategies
There are a variety of strategies and techniques fisheries can use to reduce bycatch including:
- Improved gear selectivity – modifications like larger mesh sizes allow escapement of non-target species.
- Spatial closures – closing high bycatch areas reduces interactions and protects species.
- Seasonal closures – closing during spawning or migrating times protects vulnerable species.
- Bycatch quotas – setting limits on how much bycatch is permissible can constrain mortality.
- Bycatch reduction devices – allow escapement from nets through exits or escape panels.
- Avoiding bycatch hotspots – using real-time data to avoid high bycatch areas.
- Alternative gear types – fixed gears like pots and traps have lower bycatch rates than mobile trawls.
Bycatch mitigation has had some successes but remains an ongoing challenge. Further innovation in fishing technology and management strategies is still needed to reduce bycatch worldwide.
Conclusion
Bycatch remains a significant threat to marine biodiversity and sustainable fisheries globally. The main taxa caught as bycatch worldwide are sharks and rays, crabs, squid, and groundfish species. In the United States, spiny dogfish, skates, haddock, herring, and flounder are common bycatch species. While some progress has been made, there is more work to be done improving fishing selectivity and developing robust bycatch management strategies. Understanding what the most vulnerable bycatch species are can help focus mitigation efforts on priority species and lead to healthier oceans.
