Bycatch Mitigation Information System

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Mitigation Method
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Mitigation Method Description

Underwater setting techniques

Underwater setting techniques are means of deploying baited hooks below the surface of the sea, out of the sight and reach of foraging seabirds.
Examples of underwater setting techniques include:
- the underwater bait setter, also known as a bait setting capsule or underwater bait launcher; and
- underwater setting tubes or chutes.
While versions of the latter have been trialled in pelagic longline fisheries, they are currently used only in demersal longline fisheries (see Birdlife International Factsheet 6 Demersal Longline: Underwater setting chute) and are not discussed here. Likewise, underwater setting funnels or lining tubes apply to demersal longline fisheries.
The underwater bait setter for pelagic longline fisheries deploys a baited hook underwater through a stainless steel capsule. Development has progressed through several stages. The current Mk2 incorporates:
    • a demountable track (attaches to the transom) which extends 1.4 m underwater. The track is stored inboard when transiting to and from fishing;
    • the capability for the Skipper to set maximum depth and cycle time from the wheel-house; and
    • modular construction comprising a box with hydraulic motors and winches, de-mountable track section and electronic control system and data logger operated from the wheel-house.
Research to-date has shown that the underwater bait setter has no impact on catch rates of target and non-target fish. Preliminary evidence suggest that underwater setting to 10 m depth prevents albatross and petrel mortality without the need for other mitigation measures (e.g., night setting; bird scaring lines). There is evidence that a small, residual, mortality exist with hooks set at 6 m depth but more data is required on effects of hooks set to this depth (and to 8 m depth). The final proof-of-concept experiment is scheduled for the southern autumn and winter of 2014.
Note: Click on the web link found under 'More Information' to view a stylised drawing of the prototype underwater bait setter.

Vessel-specific management

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. However, it is very difficult to separate out the factors influencing vessel performance. Likely factors include the skill with which mitigation measures are implemented, the vessels' fishing patterns compared to the spatial and temporal distribution of bycatch species, and their willingness to move away when bycatch rates increase.

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.

Bait size and condition

Refer also to these Mitigation Method descriptions:
  1. Line weighting and bait sink rate. Bait condition is usually discussed in conjunction with these factors.
  2. Fish not squid bait. Bait size is intrinsically linked to bait species. Bait species affects the probability of catching different bycatch species.
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).
Bait Condition
Bait Life Status
Live bait sinks more slowly than dead bait; using it increases the likelihood seabirds will be caught. Recent research recommends the use of dead bait only.
Bait Thaw Status
In fisheries where lead weights are added to branch lines, as long as bait (fish, squid) are thawed to an extent that permits hooks to be inserted without undue force, bait thaw status has no effect on sink rates. In fisheries where leaded swivels are not added to branch lines, the use of unthawed bait slows sink rates. However, the difference is minor and less important than other factors that affect gear sink rates.
Bait Size (and species)
Small species of fish bait should be used in preference to squid bait. This is because larger squid bait sinks considerably more slowly than small fish bait. Common fish baits are pilchards, sardines and various species of mackerel (Japanese, blue, yellow-tail). The difference in sink rates between large and small fish baits of the same species is minor.
Hooking position
Bait hooking position is important. To ensure fast sink rates, baits should be hooked in either the head (fish) or tail (fish and squid), not in the middle of the back or top of the mantle (squid).
December 2014

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.
The economics of adopting corrodible hooks requires examination. Corrodible hooks would need to be replaced more often than the low-grade stainless steel hooks currently used in fishing operations, however, they cost less than stainless hooks. No extra skill is required to secure a corrodible hook, compared with a stainless steel hook.

Smart Tuna Hook

Note: The similarly named 'Smart Hook' is a hook designed to deter sharks from approaching longline baits; see 'Magnetic, E+ metals and Electrical deterrents'.
The Smart Tuna Hook system has been developed over the past few years by Hans Jusseit. The premise of the Smart Tuna Hook system is that it 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. The shield and the pin are both made of a metal alloy which dissolves, leaving no contaminants.
There are two components to the system - the hook and the shield. The Smart Tuna Hook is a modified tuna longline hook made to the size and pattern (including circle hooks) required by the fisher. It attaches to branch lines in the same way as regular tuna hooks and lasts just as long. The single-use Smart Hook Shield is applied manually (no applicator required) to the baited Smart Hook.
A recent Australian Fisheries Management Authority funded pilot study1 evaluated the efficacy of the system in mitigating seabird and turtle bycatch in a longline fishery. The system was found to be very effective at preventing seabirds and turtles from being hooked when setting baited longlines, using a range of bait (fish and squid) and hook types.
Assessment of the operational performance of the system in a commercial fishing operation was positive. Setting time did not increase and the system was perceived to improve both the ease of casting and bait retention (bait retained on the hook when casting and entering the water).  Promising increases in bait sink rates were demonstrated and similarly, an increase in catch rates of target species was noted. The increase in sink rates may eliminate the need for lead sinkers, which would reduce gear costs and improve fisher safety (where snapped branch lines can turn sinkers into missiles).
The pilot study concludes that a more extensive evaluation of the system under commercial fishing operations is needed. Should the system be proved successful on a large scale, it may enable access for fishing vessels to restricted regions where, for example, night-time setting is stipulated, and areas currently closed to fishing, e.g., due to their delineation as seabird or turtle hotspots. It may reduce or eliminate the need for multiple mitigation methods, e.g., Tori lines plus line weighting.
Thus the Smart Tuna Hook system shows promise for increasing economic returns to fishers while reducing or eliminating incidental catch of seabirds and turtles.
See for further information.

Sliding Leads (optional illumination)

Refer also to these Mitigation Method descriptions:
1. Line weighting and bait sink rate
2. Yamazaki double-weight branchline
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.
Lumo Leads are a variant on Sliding Leads, with additional advantages. These include an encapsulating 2 mm luminescent nylon sheath that glows for up to 6 hours, attracting fish to the hook, and which also prevents the crew from handling exposed lead during gear rigging, setting and hauling.
Technical details are discussed on the commercial website
July 2013

Yamazaki Double-Weight Branchline

This device is 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.
The Yamazaki double-weight configuration consists of two leads placed at either end of a 1 to 1.5 m section of wire or wire trace. This weighted section is inserted into a monofilament branchline 2 meters above the hook. The weight nearest the hook is free to slide along the branchline while the second lead is fixed. The double weight reduces the danger of weight recoil injury by: 1) spreading the mass of the weights (two smaller weights are better than one) across the wire trace, 2) including a sliding weight that dampens the speed at which the weight can recoil; including a 1 to 1.5 meter section of stretch resistant line (wire) which serves to also reduce recoil energy; and positioning the larger of the two weights in or near the hands of a crewman as the fish is under maximum tension as it approaches the sea door.
In 2010, over 95,000 branch lines with the Yamazaki double weight system were hauled with no injuries to fishermen, reducing seabird bycatch by 89% more than un-weighted branch lines, with no effect on fish catch rates.
February 2015

Hook Pod

Refer also to these Mitigation Method descriptions:
1. Bait size and condition
2. Light attractors
3. Line weighting and bait sink rate
4. Smart Tuna Hook
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. The pod is retrieved during hauling, closed and stored until the next set.
The hook pod incorporates a light emitting diode (LED) light source that is triggered by a magnetic switch when the device opens at depth. The LED is incorporated as an alternative to disposable chemical light sticks (reducing marine debris) and electric fishing lights.
Experimental research on the efficacy of the hook pod in reducing bycatch of seabirds has been conducted across a range of pelagic fisheries (southern Brazil, South Africa and Australia) over a four-year period, evaluating variables including bait type, hooking position and hook sink rate [2,4]. It has been shown to significantly reduce seabird bycatch without negatively affecting target catch rates [2,3].
ACAP?s Seabird Working Group (SBWG) agreed in May 2016 to recommend the Hook Pod as a stand-alone mitigation measure for pelagic longline fishing [1].
Effect on other bycatch species
Research conducted in three different regions showed that the hook pod did not increase bycatch of other taxa. Preliminary findings suggest hook pods may reduce marine turtle bycatch but further data is needed to validate this [2].
June 2016
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