An attempt to improve size selection in pelagic longline fisheries for haddock

Published source details Huse I. & Soldal A.V. (2000) An attempt to improve size selection in pelagic longline fisheries for haddock. Fisheries Research, 48, 43-54.
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This study is summarised as evidence for the following.

	Action	Category
	Modify longline configuration Action Link
	Use a different bait type Action Link
	Use a different hook type Action Link

Modify longline configuration

A replicated, controlled study in 1995–1996 of two coastal pelagic areas in the Norwegian Sea, north Norway (Huse & Soldal 2000) found that increasing the lead weight on mid-water longlines to increase the sinking rate, did not typically reduce the catches of undersized haddock Melanogrammus aeglefinus compared to longlines with normal lead weight. The proportion of haddock below legal size (44 cm) was similar for both weights in three of four trials (double weight: 17–25%, normal weight: 16–21%) and catch rates were also similar (double: 52–70 fish/100 hooks, normal: 46–74 fish/100 hooks). In one of four trials however, the proportion of haddock below legal size was lower with double lead weight (double: 13%, normal: 17%) and haddock catch significantly higher (double: 91 fish/100 hooks, normal: 68 fish/100 hooks). Trials were carried out in July 1995 and June/July 1996 by two commercial longliners. Four separate trials were done, one by each vessel in one area both years. Each vessel fished a different number of hooks/rigging configuration (see paper for specifications), all baited with mackerel. The lead weight on sets of longlines was doubled and the sets deployed alternately with lines with normal lead weight. A total of 14,022 and 26,353 hooks were set for modified lines and normal lines respectively. Numbers of fleets deployed, or their distances apart, were not specified. Numbers and lengths of captured haddock were recorded.

(Summarised by: Natasha Taylor)
Use a different bait type

A replicated, controlled study in 1996 of two coastal pelagic areas in the Barents Sea, off north Norway (Huse & Soldal 2000) found that longline catches of undersized haddock Melanogrammus aeglefinus were lower in two of six comparisons of four different bait types with normal bait. In one trial, the proportion of haddock below the legal size (44 cm) was lower on restructured sandeel Ammodytes spp. bait (5%) and large mackerel Scomber scombrus bait (9%) compared to normal mackerel bait (16%), but similar on restructured mackerel bait (17%) or large restructured mackerel bait (14%). Overall catch rates were similar on all five bait types (51–76 fish/100 hooks). In another trial, restructured baits of sandeel and mackerel caught similar proportions of haddock below the legal size (44 cm) as normal mackerel bait (restructured: 17–19%, normal: 18%) and catch rates were also similar (restructured: 57–76 fish/100 hooks, normal: 74 fish/100 hooks). Two trials were carried out in June/July 1996 by two commercial longliners fishing in two areas using different hooks/rigging configurations (see paper for specifications). Four bait types and sizes (twice the normal size) were tested against a standard bait of 2 cm-thick slices of mackerel. Restructured baits were based on minced fish and algal binding agent. Baits were tested on longline fleets consisting of groups of 50 hooks with test baits (400–4,566 hooks) alternated with groups of 50 hooks with standard baits (7,250–15,323 hooks). Numbers and lengths of haddock captured were recorded.

(Summarised by: Natasha Taylor)
Use a different hook type

A replicated, controlled study in 1995–1996 of two pelagic areas in the Barents Sea, off north Norway (Huse & Soldal 2000) found that a modified hook design (plastic bodies attached) on pelagic longlines caught fewer undersized haddock Melanogrammus aeglefinus, but also reduced the total catch compared to standard hooks. In two of two trials of hooks with inedible plastic bodies attached, the proportions of haddock below legal size (44 cm) were lower than for hooks without plastic bodies (with: 12–31%, without: 15–34%), but overall haddock catch rates were also reduced (with: 43–68 fish/100 hooks, without: 52–77 fish/100 hooks). In one trial of unbaited hooks modified with nylon bristles, catch rates were lower compared to baited hooks without bristles (with: 3 fish/100 hooks, without: 74 fish/100 hooks), and so low that no further trials were done. Trials were carried out in July 1995 and June/July 1996 by two commercial longliners (see paper for full fishing specifications). Modified hooks had either inedible plastic bodies or coloured nylon bristles attached to the hook shank. Hooks were tested on longline fleets of lengths of 50 modified hooks alternated with 50 standard hooks. For trials with plastic bodies, a total of 4,845 modified hooks and 5,000 standard hooks were fished. In the nylon bristle trial, a total of 786 modified and 15,323 standard hooks were fished. Numbers and lengths of captured haddock were recorded.

(Summarised by: Natasha Taylor)