Mitigation Techniques

    Artificial bait

    Artificial baits are an experimental technology in pelagic longline fisheries. Research in the field has been very limited, with mixed success. Although they have the potential to both reduce bycatch and bring other efficiencies to the fishery (e.g. enhanced selectivity, waste reduction, etc.), much work remains to be done before artificial baits are a viable alternative to natural baits.

    Species Groups
    Marine Mammals, Sharks and Rays, Sea Turtles
    Fishing Gear
    Longline

    Auditory deterrents and attractors

    Using sound to discourage or distract bycatch species from interacting with fishing gear. Auditory deterrents are not generally considered useful, except in limited circumstances, in reducing bycatch of seabirds, turtles and sharks. In the main, this is because the feasibility and long-term effectiveness of an acoustic deterrent is affected by habituation.

    Species Groups
    Seabirds, Marine Mammals, Sharks and Rays, Sea Turtles
    Fishing Gear
    Longline, Purse Seine

    Bait caster

    A Bait Casting Machine (BCM) is a hydraulically operated device designed to deploy baited hooks during pelagic longline setting (prior to the development of BCMs, individual hooks were cast by hand). BCMs are commonly used in high seas pelagic fisheries and are an integral part of the line setting process.

    Species Groups
    Seabirds
    Fishing Gear
    Longline

    Circle hooks

    Using wide circle hooks has been shown to significantly reduce sea turtle interactions without compromising catch rates of target species. Switching from J hooks to circle hooks may increase shark catch rates but lower at-vessel mortality rates - this is an area of active research.

    Species Groups
    Marine Mammals, Sharks and Rays, Sea Turtles
    Fishing Gear
    Longline

    Corrodible hooks

    Corrodible hooks are fishing hooks composed of material other than stainless steel. They may be made from different alloys, with different coatings, which all affect how long they last. The hook may dissolve quickly, within a couple of days, or more slowly over weeks or months. The premise behind the use of corrodible hooks is that they should improve the mortality rate of bycatch released with a hook attached. However, this needs to be tested through tagging studies.

    Species Groups
    Seabirds, Marine Mammals, Sharks and Rays, Sea Turtles
    Fishing Gear
    Longline

    Decoys

    Shark decoys have been shown to work as sea turtle 'scarecrows', though these decoys also frightened-off target finfish species (tunas, billfish, mahi-mahi). However, there remains potential to develop decoys which maintain target species catch rates while deterring sea turtles from approaching baited longline hooks.

    Species Groups
    Sea Turtles
    Fishing Gear
    Longline

    Double-weight branchlines

    Double-weight branchlines are designed to reduce seabird bycatch in pelagic longline fisheries when used in combination with tori lines and in some cases night setting. The double-weight configuration is designed to 1) sink pelagic longline hooks beyond the range of seabird attacks within the aerial extent of a tori line during line setting, and 2) reduce injuries to crew should a hook come free while under tension in the landing process and recoil back at the vessel.

    Species Groups
    Seabirds
    Fishing Gear
    Longline

    Dyed bait

    In theory, dyeing bait blue reduces the contrast between the bait and the surrounding seawater making it more difficult for foraging seabirds to detect. Alternative theories suggest that seabirds are simply less interested in blue-dyed bait compared with undyed controls. Practical issues of dyeing bait at-sea and the inconsistent results of experimental trials suggest that blue-dyed bait is not an appropriate primary mitigation measure.

    Species Groups
    Seabirds, Sea Turtles
    Fishing Gear
    Longline

    FAD design & management

    It has long been known that natural floating objects, such as logs, palm leaves or dead animals, attract fish. Fish Aggregating Devices (FADs), made of either natural or man-made materials, are deployed to exploit this phenomenon and help catch pelagic fish. In fisheries management literature, the term 'FAD' often encompasses both man-made, deployed FADs and naturally occurring flotsam [27].
     
    Species Groups
    Sharks and Rays, Sea Turtles
    Fishing Gear
    Purse Seine

    Gear configuration - other

    'Gear configuration - other' is a catch-all for changes in the deployment of fishing gear (aimed at reducing bycatch) that are not covered by other mitigation methods listed in this database. They are generally not well studied, for example, decreasing the number of hooks between floats to decrease shark catch rates.

    Species Groups
    Seabirds, Marine Mammals, Sharks and Rays, Sea Turtles
    Fishing Gear
    Longline, Purse Seine

    Hook Pod

    The hook pod is an emerging mitigation technique which protects the point and barb of baited hooks from seabird attack during line setting. Branch line weighting at the hook maximises hook sink rate. When a predetermined depth is reached a pressure release system ensures that the pod opens, releasing the hook to begin fishing.

    Species Groups
    Seabirds, Sea Turtles
    Fishing Gear
    Longline

    Line shooter

    A line shooter is a hydraulically operated device designed to deploy the mainline at a speed faster than the vessel’s forward motion, which removes tension from the longline. This allows the mainline to enter the water immediately astern of the vessel, rather than up to 30 m behind the vessel. It has been demonstrated that variation in tension on the mainline will affect the sink rates of baited hooks and therefore the risks to seabirds.

    Species Groups
    Seabirds
    Fishing Gear
    Longline

    Monofilament / Wire Leaders

    Monofilament (nylon) line is used widely in the fishing industry. It is commonly used for both the mainline (the longline) and branchlines (which hang off the main longline and are also known as snoods or gangions/ganglions). Branchlines may incorporate a section of line (of variable length) known as a leader, with a lead weight at one end and the baited hook at the other. Leaders made of wire have implications for sharks and seabirds.

    Species Groups
    Seabirds, Sharks and Rays, Sea Turtles
    Fishing Gear
    Longline

    Night / day setting

    Night or day setting refers to the times of day when longliners set, soak and haul their lines. These variables are inherently linked to the duration of the soak (the period that the longline is in the water). Timing depends principally on the target species, but also varies among fleets and regions.

    Species Groups
    Seabirds, Marine Mammals, Sharks and Rays, Sea Turtles
    Fishing Gear
    Longline

    Safe handling & release

    Safe handling and release refers to using best practice methods for dealing with bycatch species, to maximise their chances of survival after interacting with fishing gear. It can also include vessel manoeuvring to avoid taking bycatch species, for example, avoiding setting purse seines on whale sharks.

    Species Groups
    Seabirds, Marine Mammals, Sharks and Rays, Sea Turtles
    Fishing Gear
    Longline, Purse Seine

    Seabird Saver

    The Seabird Saver is a recently developed technology combining a laser and an optional acoustic deterrent. It can be used in a range of fishing situations, including longlining, purse seining and trawling, to scare seabirds from interacting with bait, catch or discards.

    Species Groups
    Seabirds
    Fishing Gear
    Longline, Purse Seine

    Side-setting

    Side-setting requires the longline hook setting operation to move to the side of the vessel. Birds are unable or unwilling to forage for bait close to the side of a vessel. Additionally, side-setting avoids setting baited hooks into the propeller wash, which slows the sink rate of stern set hooks.

    Species Groups
    Seabirds
    Fishing Gear
    Longline

    Sliding Leads (Lumo Leads)

    Sliding Leads are an alternative to leaded swivels. They are designed to increase branch line sink rates (to get baited hooks rapidly out of the range of feeding seabirds) and protect crew safety. Sliding Leads slide away from crew during bite offs or when the line breaks under tension, thereby greatly reducing the incidence of dangerous fly-backs towards the vessel, as can occur with leaded swivels.

    Species Groups
    Seabirds
    Fishing Gear
    Longline

    Smart Tuna Hook

    The Smart Tuna Hook system prevents hooking of seabirds and turtles during line setting by protecting a baited hook with a metal shield, which is held in place with a biodegradable pin. The pin dissolves once the hook is below the feeding depth of seabirds (25 m) and turtles (100 m). Once the pin dissolves, the shield is released and the baited hook is ready for fishing.

    Species Groups
    Seabirds, Sea Turtles
    Fishing Gear
    Longline

    Soak duration

    Soak duration is the length of time that pelagic longlines remain in the water, between line setting and line hauling. Average soak time varies among fisheries and is dependent on factors such as the target species, number of hooks deployed and the time required to bring them aboard.

    Species Groups
    Marine Mammals, Sharks and Rays, Sea Turtles
    Fishing Gear
    Longline

    Spatial & temporal measures

    Spatial and temporal measures aim to avoid or minimise bycatch by either temporarily or permanently moving fishing out of an area (e.g., time and area closures, marine protected areas), or requiring that particular mitigation techniques be adopted in an area. They are predominantly mandatory (i.e., fisheries regulations) but can be voluntary and the areas that they apply to may be dynamic, e.g., around an ocean front, or static, e.g., around a seamount or below a specified latitude.

    Species Groups
    Seabirds, Marine Mammals, Sharks and Rays, Sea Turtles
    Fishing Gear
    Longline, Purse Seine

    Stealth fishing gear

    Stealth fishing gear refers to fishing gear and bait that have been camouflaged to deceive predatory species. For bycatch species such as marine turtles and seabirds, the aim is to reduce the detection of bait. For target species, such as swordfish and tunas, the aim is to reduce the detection of the fishing gear and thus increase catch rates.

    Species Groups
    Seabirds, Marine Mammals, Sharks and Rays, Sea Turtles
    Fishing Gear
    Longline

    Streamer (tori) lines

    A streamer line (also called a tori or bird scaring line) is a line with streamers that is towed from a high point near the stern of a vessel as baited hooks are deployed. They are the most commonly prescribed seabird bycatch mitigation measure for longline fisheries. However, recent evidence shows that they are not fully effective unless combined with other mitigation measures, i.e., branchline weighting and night setting.

    Species Groups
    Seabirds
    Fishing Gear
    Longline

    Weak Hooks

    'Weak hooks' refers to weak circle hooks, constructed of thinner gauge stock wire than standard circle hooks of the same size, and designed to straighten at a lower strain (pull) level than standard hooks, thereby allowing large hooked animals to escape while retaining the target catch.

    Species Groups
    Marine Mammals
    Fishing Gear
    Longline