An introduction to mitigation measures for fishing vessel crew involved in longline fisheries.


Surface and bottom longline commercial fisheries occur throughout New Zealand waters. Longline fisheries are generally considered a more selective fishing method than some net fisheries (e.g. set nets and trawl). Longline fisheries are known to interact, and impact upon, a wide range of marine protected species.

There are a range of mitigation devices and practices that longline vessels can employ to reduce harm or mortality to protected species. Some of these measures are compulsory under the :

Other measures are voluntary and recommended best practice. Seabirds are generally caught either on the set, haul, or during the soak depending on how close the hooks are to the surface. Below is a basic introduction to some mitigation measures that can be employed in the longline fishery. 

Sink rates

Sink hooks quick. Birds are most at risk between the time when hooks leave the vessel to when they sink below the diving range of seabirds. Limiting the availability of baited hooks to seabirds will have a significant impact on captures. Weighting close to the hooks and setting speed are both essential components to making sure your sink rates are effective.

Guiding Principles for improving sink rate - bottom longline (2022) (PDF 1,636 K)

Tori or streamer lines

A tori line is an essential mitigation tool in longline fisheries. The purpose of this device is to scare the birds away from the mainline and therefore the hooks as they sink. The condition, position and aerial extent of the tori line will determine how effective they are. Aerial extent is determined by the height at attachment point, the drag device used at the end of the line and the setting speed.

Tori Line Design and Guiding Principles – surface longline (2021) (PDF, 1,120 K)

Tori Line Design and Guiding Principles – bottom longline (2021) (PDF, 261 K)

Discard management

The discharge of offal and fish waste acts as an attractant to seabirds to areas of high risk, managing when and where this discharge occurs will greatly reduce the chance of injury or capture of protected species.

Light management

Night setting can greatly reduce the incidental capture of seabirds. Despite this, the moon phase effects light levels at night-time which can increase nocturnal birds ability to detect and locate baited hooks. Keeping deck lighting to a minimum will reduce seabird attraction to fishing vessels.

Further information on light management.

Research and innovation

Research is continually underway to develop mitigation practices and devices in order to reduce the incidental capture of protected species in longline fisheries. Hook shielding devices are one such innovation currently on the market. This device shields the hooks from seabirds when setting the line by covering the barb of hooks until the baited hook is below the diving range of seabirds.

Other research includes sink rate testing onboard vessels using time depth recorders (TDRs) and ongoing trials of bait and line setters which take fishing gear to depth quickly, limiting the chance of diving seabirds becoming hooked.

Though many of the mitigation measures above focus on reducing seabird interactions, other marine protected species are also at risk to longline fisheries, e.g. seals and turtles. DOC currently provides turtle de-hookers to vessels so they can quickly and safely remove fishing gear while the animal is in the water, limiting further negative impact. Fishers are responsible for handling all protected species appropriately in order to maximise the chance of survival. More more information on best practice methods of protected species bycatch and handling, check out the handling and release guide.

Commercial fishers are legally obliged to report any captures and releases of protected species, as well as noting the status of survival of the animal. It is not illegal to capture a protected species however it is illegal not to report it.

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