Mitigation Techniques

    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, Sea Turtles , Sharks and Rays
    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. Illustrated Guides and more general literature have been collected in the BMIS.

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

    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, 'move-on' guidelines), or requiring that particular mitigation techniques be adopted in an area. They include fleet or vessel communication schemes, such as the Hawaii-based 'Turtlewatch', a dynamic means of avoiding bycatch 'hotspots'.

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

    FAD design & management

    Fish aggregating devices, or ‘FADs’, are floating objects, either natural or artificial, that attract and aggregate fish, including tuna schools. Silky and oceanic whitetip sharks are the main bycatch species in purse seine fisheries, incidentally caught when vessels fish on drifting FADs or entangled in the netting beneath FADs. Sea turtles are occasionally caught in seines and may be snared in the netting on, or under, FADs. Bycatch can be significantly reduced through effective FAD design (non-entangling, biodegradable) and management (e.g., limit FAD numbers & fishing seasons, shift a percentage of fishing effort to free schools, fish sharks from the net with handlines and release, target tuna schools greater than 10 tonnes, release sharks from deck using safe handling and release techniques).

    Species Groups
    Sea Turtles , Sharks and Rays
    Fishing Gear
    Purse Seine

    Deep / shallow setting

    Deep setting is a longline fishing technique where hooks are set below a critical depth, out of range of most bycatch species, but within the range that target species are usually captured. Deep setting has been shown to decrease bycatch of sea turtles. Deep-set buoy gear has been trialed recently in a US swordfish fishery, with promising results.

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

    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, Sea Turtles, Sharks and Rays
    Fishing Gear
    Longline

    ALDFG - management of abandoned, lost, discarded fishing gear

    Management of abandoned, lost, discarded fishing gear (ALDFG) refers to the management of fishing gear (onboard and deployed, e.g., FADs) and retrieval of lost gear as a means of reducing fisheries bycatch and environmental damage. Tuna RFMOs have adopted binding measures and data collection protocols, as well as encouraging voluntary measures, to address the issue.

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

    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
    Sea Turtles, Seabirds, Sharks and Rays
    Fishing Gear
    Longline

    Hookpod

    The Hookpod (Hookpod-LED & Hookpod-mini) 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. ACAP (October 2021) recommends that approved hook-shielding devices can be used as stand-alone measures or with other measures, such as bird-scaring lines and night setting.

    Species Groups
    Sea Turtles, Seabirds
    Fishing Gear
    Longline

    Lightsticks / light attractors

    Light attractors, including chemical lightsticks and battery-powered light-emitting diodes (LEDs), are attached near baited hooks on branchlines to attract fish. They also appear to attract sea turtles and sharks.  Strategies are needed to make longline lightsticks less attractive or visible to these species groups. Research is limited but has considered factors such as light colour,  hook depth and fishing according to lunar phase.

    Another important consideration is the contribution of lost or discarded chemical lightsticks to marine pollution, both the plastic and the toxic contents.

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

    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, Sea Turtles, Sharks and Rays
    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 in reducing bycatch of seabirds, turtles and sharks, except in limited circumstances. In the main, this is because the feasibility and long-term effectiveness of an acoustic deterrent is affected by habituation. Acoustic deterrents (e.g., pingers) are used with some success for marine mammals, in particular, cetaceans.

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

    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.

    Note: The similarly named 'Smart Hook' is a hook designed to deter sharks from approaching longline baits; see 'Magnetic, E+ metals and Electrical deterrents'.

    Species Groups
    Sea Turtles, 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, or it may be that seabirds are simply less interested in blue-dyed bait compared with undyed controls. Due to practical issues of dyeing bait at-sea and the inconsistent results of experimental trials, this technique is considered unproven and is not recommended.

    Species Groups
    Sea Turtles, Seabirds
    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). Trials with 'Looming Eye Buoys', to deter seabirds from gillnets, are underway.

    Species Groups
    Sea Turtles, Seabirds
    Fishing Gear
    Longline, Gillnet

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

    Gear switching

    Gear switching in a fishery refers to changing from using a relatively high-threat to a relatively low-threat gear type. For example, switching from traditional gillnets to either sub-surface gillnets or longlines to reduce cetacean bycatch in Pakistan's tuna fisheries.

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