Mitigation Techniques

    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

    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

    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

    Depredation Mitigation Device

    Depredation - the removal of bait and damage of hooked fish by sharks and cetaceans - is a major issue for pelagic longline fleets, with a negative impact on their economic profitability [1,2] and a risk of mortality to the animals from either retaliation by fishermen or hooking or entanglement in fishing gear [3]. In the BMIS, ‘Depredation Mitigation Devices (DMDs)’ are principally technologies designed to reduce cetacean bycatch through the use of physical barriers to protect target catch.

    Species Groups
    Marine Mammals, 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

    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

    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

    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

    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

    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