The use of permanent magnets, electropositive rare earth metals (EPREM) and other electrical measures has been trialled as a means of deterring sharks from approaching baited hooks.
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.
See instead: Light Cues - attractors and deterrents
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.
Seabirds are attracted to fishing vessels to feed on processing waste and discarded fish. Discharging offal on the opposite side to the hauling hatch helps to divert their attention away from the area where hooks return to the surface.
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.
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.
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.
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. In recent years, tuna RFMOs, to varying degrees, have adopted binding measures and data collection protocols to address the issue.
The use of chemical attractants or deterrents in longline and purse seine fisheries aims to exploit differences in sensory biology between target and non-target species, improving the specificity of fishing and thus reducing bycatch.
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.
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.
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; strategies are needed to make them less attractive or invisible to turtles. Gillnet illumination has been shown to reduce both seabird and sea turtle bycatch.
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]. In the BMIS, ‘Depredation Mitigation Devices (DMDs)’ are principally technologies designed to reduce cetacean bycatch through the use of physical barriers.
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.
'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.
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.
Bycatch rates can vary among fishing vessels operating in the same fishery, even after accounting for factors such as vessel size and fishing effort, and these differences can persist from year to year.
Bait condition and bait size play a part in bait sink rate. The faster bait sinks, the less available it is to predatory seabirds during line setting. Bait condition also plays a part in the ease of hooking ('baiting') and whether the bait will stay on the hook (quality).
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.