Why a hook and line and not a trawl net?

Adam and Leef setting a bottom longline from the FV Southern Cross (Source: Lesley Hamilton, Seafood NZ).

The behavioural characteristics of many fish species determines what type of fishing method, or methods, is most suited to the target species. For example, trawling is generally used for species that swim in schools of various sizes or that are not attracted to baited hooks. Hook and line methods are used for fish that tend to swim alone and may also be found on rough bottom that we aim to avoid when trawling.

The longline method can either be used near the surface for pelagic fish or closer to the seafloor when targeting demersal or semidemersal fish. Both surface and bottom longline fishing methods are commonly used throughout New Zealand.

A bottom longline set up consists of a length of mainline with baited hooks attached by short branch lines called snoods. The mainline is set with intermittent weighting to keep it on or near the seafloor. Grapnel anchors at either end hold the longline in position and buoys are attached to the start and end of the line to mark the longline location. Hauling is done by use of hydraulic winches with fish retrieved and hooks cleaned and reset for the next shot. The baiting of the hooks can either be done by hand or a machine.

A tori line flying from a small longline vessel (Photo credit – DOC Conservation Services Programme project MIT2015-02)

When shooting or setting the longline over the stern of the vessel, there is a period of time when the baited hooks are near the surface before they sink. At these times, seabirds attracted to the bait are at risk of capture. By limiting their access to those baited hooks, the risk of incidental captures is reduced. The one way fishers do this is by weighting their lines so they sink faster. This can be done by using a mainline with a metal core covered by rope material, or attaching independent weights to the mainline at set intervals between the hooks to ensure the line and hooks sink as quickly as possible beyond the diving range of seabirds.

In addition to line weighting, fishers use a tori or streamer line to scare any birds away from the mainline and baited hooks as it is set. The tori line, with colourful streamers (see Figure 3) at 5 metre intervals, is suspended above the hooks while they are at shallow depths but sinking, and are able to be targeted by seabirds. The quicker it sinks the less risk to seabirds. The tori line is an essential mitigation tool and its use is required by law, when shooting a longline.

Every coastal longline vessel has a Protected Species Risk Mitigation Plan, which details the mitigation options that vessel will use when fishing. One size does not fit all when it comes to mitigation options. Department of Conservation

Liaison Officers assist in the preparation of those plans, provide materials for mitigation, and support fishers to review their mitigation when seabirds are captured. Use of the plans is vetted by Fisheries NZ observers and will in the future be vetted through the cameras, once they are installed on all longline vessels.

Diagram of the commercial bottom longline sink rate regulations, where the slowest sinking hook must reach a 5m depth within the aerial extent of the tori line (Resource developed by Dave Goad & Zak Olsen with support through the DOC Conservation Services Programme).

The commercial industry works closely with the Department of Conservation and Fisheries NZ to maintain operational procedures that provide an agreed structured approach for mitigation and assessment of risk, relevant to bottom longline and other fishing methods. These may be found on the Fisheries Inshore NZ webpage, along with the additional details for line setting and aerial extent requirements of tori lines.

Commercial fishers are advised to download this 2-page flyer to assist with their gear setup from inshore.co.nz/fileadmin/user_upload/BLL_ Sink_Rate_Guide_2022.pdf.

The National Plan of Action (NPOA) – Seabirds and web links to commercial longline regulations and fisher advice can be found at mpi.govt.nz/fishing-aquaculture/sustainable-fisheries managing-the-impact-of-fishing-on-protected-species/reducing-deaths-of-seabirds/

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