Gear Types

Purse Seines

Purse seines are common in both small-scale and industrial fisheries, used to target schooling pelagic fishes such as tunas, anchovies, and sardines.

Purse seines are large nets that are used to encircle large schools of fish before the bottom of the net is closed (pursed). Once the net is pursed, fish cannot escape through the bottom of the large net, and the net walls are pulled in. However, this process also catches a lot of other animals swimming with the schools of target fish. Historically, bycatch mortality rates in purse seine fisheries were high, but through the use of updated practices and gears bycatch mortality rates can be effectively reduced.

How do purse seines find schools of fish in the open ocean?

There are two main classifications for purse seine fisheries, those that set nets around fish aggregating devices (FAD-associated) and those that do not (free-swimming). Finding a school of target fish is the most difficult part of purse seine fishing, and therefore many tools and techniques have been developed to find fish. Over the last two decades, fishers have deployed trackable FADs, which are designed to attract schooling fish. Nets are then set around the FADs, but bycatch can still be high since many other animals are also attracted to FADs.

When the purse seine is closed, vessels can use the “backdown method”, which opens a section of the net on the surface where dolphins, porpoises, and sea turtles can escape.

Purse seine set from vessel.

A purse seine is set.

One way to target fish was to set nets around pods of dolphins and porpoises or whale sharks because they often school with tuna. This practice led to disturbingly high bycatch mortality rates and should be avoided at all times (though it is still legal in many areas).

FADs are more commonly used now.  However, FADs are typically made of plastic (poly ropes and nets) and include hanging structures that can entangle wildlife. If lost or abandoned, these non-biodegradable FADs will continue to entangle wildlife as they drift with currents, potentially for years.  Fortunately, new techniques and gear configurations have been shown to greatly reduce the ETP bycatch impacts of both FAD-associated and free-swimming sets.

ETP Impacts and Fishery Recommendations