A purse seine is a large wall of netting deployed around an entire area or school of fish.
The seine has floats along the top line with a lead line threaded through rings along the bottom. Once a school of fish is located, a skiff encircles the school with the net. The lead line is then pulled in, "pursing" the net closed on the bottom, preventing fish from escaping by swimming downward.
The catch is harvested by either hauling the net aboard or bringing it alongside the vessel.
- Purse seines can reach more than 6,500 ft (2,000 m) in length and 650 ft (200 m) in depth, varying in size according to the vessel, mesh size, and target species.
- Finding a school of fish is one of the most difficult steps of this fishing technique and include:
- Natural cues such as a congregation of seabirds, ruffling of surface water and/or fast moving groups of dolphins.
- Helicopters scanning the water for natural cues from the air to direct boats toward schooling fish.
- Using radar fish finders to help identify the exact location and size of a school.
Target Species
- Schooling pelagic fish of all sizes, from small sardines to large tunas.
- Squid
Fishery Regions
Throughout U.S. waters, including Alaska and Hawaii.
Risks to Sea Turtles
Purse seining is a non-selective fishing method that captures everything that it surrounds, including protected species.
Sea turtles can be captured by a purse seine as it is set and then become entangled in the net mesh as it is hauled in. Entangled turtles may sustain injuries to their flippers and shells due to the force of the net as it is hauled.
In a large catch, turtles risk being crushed under the sheer weight of the tow. Captured turtles can be released alive if they are quickly retrieved and removed from the net.
Risks to Marine Mammals
Purse seines can easily encircle marine mammals along with target species as the net is set.
Historically, dolphin pods were even used as a natural cue visually leading purse seiners toward areas of abundant schooling fish (called "setting on dolphins").
Once the netting has been set, encircled marine mammals cannot escape and can become entangled, injured, or stressed. Even with quick retrieval, marine mammals' sensitive bodies and internal organs cannot usually withstand the weight of the catch or the impact of being placed on the vessel.
In U.S. fisheries, species most commonly captured include bottlenose dolphins and humpback whales.
Bycatch Reduction
Currently no regulations exist for minimizing bycatch of protected species in purse seine fisheries.
Employing fisheries observers who scan the water prior to setting nets is the most effective way of minimizing incidental capture.
More Information
Leatherback turtle in the Kei Islands. Credit: Scubazoo/Jason Isley
A hawksbill sea turtle swimming above a coral reef in western Maui in the Hawaiian Islands. Credit: NOAA Fisheries/Don McLeish. Photo taken under permit #21260.
The Pacific leatherback sea turtles have existed in their current form without scales and a hard shell since the age of the dinosaurs, but threats from bycatch, egg harvesting, and degradation of nesting habit have made this species endangered. Photo credit: Jason Isley, Scubazoo.