Instant sinking hooks will save seabirds in tuna longline fisheries

New line weighting regimes for commercial longline fisheries can significantly reduce seabird deaths on baited hooks. The challenge now is to encourage uptake.

Thousands of albatrosses and petrels drown on commercial fishing hooks in the southern hemisphere each year.

Some fisheries are well regulated, especially those overseen by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), and incorporate a range of seabird bycatch mitigation methods into their operations. These include seasonal closures, night setting of fishing gear, streamer lines that scare birds when the gear is being set, and line weights that rapidly draw baited hooks below the diving depth of seabirds.

In the mid-2000s these measures saw seabird bycatch decline by up to 100% in toothfish fisheries throughout most of the Southern Ocean. However, seabirds are still at risk in many poorly regulated or unregulated tuna and billfish fisheries operating in sub-tropical waters.

Australian Antarctic Division seabird ecologist Dr Graham Robertson has worked with the fishing industry for decades to help develop practical and effective technologies and strategies to save seabirds, without compromising fish catch rates (see 'A life dedicated to saving seabirds'). His work feeds into CCAMLR, various regional fisheries bodies, Australia’s domestic fisheries regulations, and the Agreement on the Conservation of Albatrosses and Petrels (ACAP), which coordinates international activity to mitigate known threats to seabird populations.

He said one of the biggest barriers to the uptake of seabird bycatch mitigation measures in tuna fisheries is the reluctance to change traditional fishing practices, coupled with a lack of incentives to adopt seabird friendly practices.

‘Fishing industries are generally wary of changes that could affect their catch rates,’ Dr Robertson said.

‘But it’s part of the job of scientists and policy-makers to work with fishers and demonstrate that there are better ways of doing things that benefit both their operations and seabirds. This is a slow, cooperative process involving industry leaders, engineering and experimental manipulation, data analysis and reporting. But when things work well, the results are adopted by management organisations and embedded in fisheries management regulations.’

One of Dr Robertson’s latest successes is the development of a new line weighting regime for pelagic (open ocean) longline fisheries, in collaboration with a Queensland tuna fisherman, the Australian Fisheries Management Authority and an engineering company in the United Kingdom that specialises in manufacturing bycatch mitigation technologies.

While the new regime is being voluntarily adopted by fishing operators in Queensland, it is a conceptual step-change on current best practice line weighting recommendations and it may take time to convince the international community of its merits.

‘The idea involves using a new type of sliding lead weight at the hook; or near the hook in regions where shark bite-offs are common,’ Dr Robertson said.

‘It sounds quite simple, but the new regime had to offer improved, cost-effective seabird deterrence via rapid sink rates, improved crew safety, and no reduction in fish catch. It also had to facilitate in-port inspection of gear for compliance purposes. Getting all these elements to align was a challenge.’

To understand why the new weighting regime is significant requires a short historical deviation.

According to ACAP, best-practice line weighting offers fishers three weighting options that position different sized lead weights at different distances from the hook. The weighting regimes all involve long ‘leaders’ (the distance between the lead weight and baited hook), resulting in slow sink rates. The regimes were developed in the days when longlines were unweighted and resistance to the addition of weight was fierce, due to fears the weights would reduce fish catch.

‘A compromise was needed. So we embarked on a stepped approach working with progressive fishers and did some trials testing the effect of lead weights at six metres from the hook, then at four metres and eventually at two metres,’ Dr Robertson said.

In 2011, the Queensland fisherman Dr Robertson was working with suggested they try putting the lead at the hook.

‘He was taking a big risk; for all we knew his fish catch and income may have been reduced and he had a family to support,’ Dr Robertson said.

The pair sketched some designs and approached bycatch mitigation technology company, Fishtek Marine, who added their ideas and eventually manufactured a sliding lead that they called the ‘Lumo Lead’.

Unlike conventional swivel leads which are tied or ‘crimped’ into the line, sliding leads are attached in such a way that if the line breaks under tension, the lead slides off the line, rather than flying back like a cannon ball at the person on the other end.

Fishtek Marine also designed a luminescent nylon sheath for the lead (conferring the name Lumo Lead), with the potential to attract fish. Because the leads sit just above the hook and don’t need to be crimped in, the lines are faster and easier to construct and the weights do not get tangled within the coils of line. The leads are also clearly visible when they’re sitting in bins on the deck, making it easy for compliance observers to see whether weights are being used. And the luminescent coating prevents deckhands from contacting the lead.

‘Our trials showed that lines with lead at the hook sank instantly, giving seabirds little time to attack the baits. And there were significant operational advantages to crews as well, which helped voluntary uptake by fishers,’ Dr Robertson said.

Because the at-risk seabird species do not occur in Queensland waters, the trials were unable to determine the impact of the sliding leads on seabird bycatch. However, at about the same time Dr Robertson’s trials were underway, another study was being conducted by Uruguayan researchers in the south-western Atlantic, where major seabird bycatch events have been recorded. The Uruguayan trials looked at the impact of reducing the distance between the lead weight and the hook on seabird bycatch and pelagic fish catches. The team provisionally reported a 50% reduction in seabird bycatch on lines using 65g weights at one metre from the hook, with no other mitigation measures.

‘The Uruguayan data helps show that if you have fast sinking lines, you’re going to save seabird lives, without any other mitigation,’ Dr Robertson said.

‘Based on my experience in Queensland, where tuna operators are voluntarily adopting the new line weighting regime, we can be fairly confident that this approach to line weighting has great promise.

‘It’s time to be pragmatic about unregulated fisheries. Many fishermen resent using streamer lines and 95% of the time there are no independent observers onboard vessels to ensure compliance. With this new line weighting, fishers can’t take the leads out when they’re at sea, and inspectors can simply walk around the docks and check the gear for compliance.’

It may take some years yet for Dr Robertson’s vision to be realised, but the technology, research, political will and environmental climate are beginning to align.

Wendy Pyper
Corporate Communications, Australian Antarctic Division