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

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.