ACAP Small Grant 2023-10

Manufacture of a new concept pelagic longline heavy hook to improve line weighting acceptance and seabird bycatch mitigation performance

Project Leader: Nigel Brothers.

Co-investigators: Igor Debski, Department of Conservation, New Zealand.

Amount Awarded: AUD 38,000

Of the three ACAP recommended best practice measures for pelagic longline, line weighting has the advantage of being more consistently implemented. In most pelagic longline fisheries line weighting has become an unavoidable operational necessity for seabird bycatch mitigation requirements. For various reasons, current weighting options tend to be perceived by fishing operators as operationally unfavourable, as well as used in ways that diminish the overall effectiveness of mitigation.

In recognition of the clear mitigation benefit of appropriately weighted lines, the improved effectiveness of weight close to the hook, and the need for more acceptable methods of line weighting (to improve reliable uptake), investigation is underway into the incorporation of weight into the hook itself (SBWG10 Inf 09, SBWG11 Doc 15). If the concept proves viable, there are likely to be substantial operational, economic and mitigation gains (both in terms of effectiveness and ease of compliance monitoring).

Following the manufacture and trialling of a prototype heavy hook (named Procella) in 2022/23, industry interest in advancing development was ascertained. This has already led to collaborative hook redesign with industry, based upon familiarity with the trial hook prototype, along with agreement reached as to the design preference, and ongoing commitment by selected operators to further trials, should hook manufacture and supply proceed. While the original Procella weight was 52 g, the new Procella will weigh 62 g in lieu of hook weighting-specific indecision by SBWG11 (AC13 Doc 11 Rev1), so as to ensure adherence to ACAP recommended weighting specifications. This directly impacted feasibility of acceptable hook redesign and will add further manufacturing plus shipping cost without altering expected mitigation performance much, if at all. Nevertheless, the hook trial participants are amenable to using this amount of weight at (on) hooks, the ACAP weighting Best Practice equivalent of 40 g weights being at hooks, rather than (as allowed) up to 0.5 m away.

Prototype Procella failed to meet operational expectations purely because of manufacturing-related strength issues although other physical aspects of design (visual appearance) have since been altered. As a consequence, an entirely new or different process to conventional tuna hook fabrication is likely to be required. Because tuna fishery hooks are somewhat expendable (ongoing losses to sharks etc), it is necessary to try to establish from the outset, the lowest cost of heavy hook type. For these reasons, and with knowledge from the previous Procella fabrication and trial, it is deemed that a budget sufficient to cover 10,000 to 20,000 hooks is a minimum necessity. Cost estimate is on the basis of conventional hook value around 70 cents and allowing for double the cost, with the order quantity adjusted to fit the budget. The aim at this stage is for manufacture to occur in early 2024.

Hook performance will be measured on three, possibly more, voluntarily committed vessels in New Zealand through 2024 and beyond, focussing initially on comparative vessel catch records supplemented by dedicated operator hook monitor records. Vessels will be using AC14 Inf 01 Agenda Item 15.4 12 required mitigation measure options additional to the weighting of lines and Procella will be weight-compliant with 40g having been essentially added to a standard 22g tuna hook. Although actual mitigation performance of simply applying established ACAP weighting best practice in a different way should not be in doubt, the sink rate characteristics of Procella will be determined.

If proven operationally and economically viable, the aim is for Procella to then be routinely manufactured and become widely available commercially so as to progressively lead to a preference for this hook type. This line weighting option will be much easier in terms of compliance and help to remove many of the current operational drawbacks inherent in conventional line weighting practices. As an alternate line weighting method, it will be much more compatible with the variety of longline methods employed by the different fishing entities. SBWG11 Doc 15 provides a more detailed account of real or perceived (requiring substantiation) benefits as well as potential risks, including industry resistance to uptake, irrespective of actual evidence of viability.

See SBWG12 Inf 02 for more information.