Study

The effects of hook and bait sizes on size selectivity and capture efficiency in Icelandic longline fisheries

  • Published source details Ingólfsson O.A., Einarsson H.A. & Løkkeborg S. (2017) The effects of hook and bait sizes on size selectivity and capture efficiency in Icelandic longline fisheries. Fisheries Research, 191, 10-16.

Actions

This study is summarised as evidence for the following.

Action Category

Use a different bait type

Action Link
Marine Fish Conservation

Use a different hook type

Action Link
Marine Fish Conservation
  1. Use a different bait type

    A replicated study in 2008–2009 in six areas of deep water in the North Atlantic Ocean, off Iceland (Ingólfsson et al. 2017) found that increasing the bait size reduced the capture of unwanted small fish compared to using a smaller bait size. The average length of hooked fish was greater with larger bait size than smaller bait for: cod Gadus morhua (large: 55–72 cm, small: 46–70), haddock Melanogrammus aeglefinus (large: 47–53 cm, small: 45–52,), tusk Brosme brosme (large: 47 cm, small: 43 cm), ling Molva molva (large: 65 cm, small: 63 cm) and wolffish Anarhichas lupus (large: 48–64 cm, small: 45 cm). Six fishing trials were conducted from commercial longliners between November 2008 and December 2009 (five trials off the northwest coast of Iceland, one trial off the southwest) at depths of 50–140 m. Large (30 g) and small (10 g) sizes of bait made of Pacific saury Cololabis saira were alternated every 100 hooks (up to 4,800 hooks/set) and gear fished for one hour. Hooked fish were recorded and their lengths measured.

    (Summarised by: Chris Barrett)

  2. Use a different hook type

    A replicated study in 2008–2009 in six areas of deep water in the North Atlantic Ocean, off Iceland (Ingólfsson et al. 2017) found that changing the hook size on longlines improved size selectivity for only two of five commercially targeted fish species, but reduced catch numbers of all species, and was also affected by bait size. Across both areas, hook size affected fish size selectivity only for wolffish Anarhichas lupus and cod Gadus morhua in the northern area, but not haddock Melanogrammus aeglefinus, tusk Brosme brosme or ling Molva molva (data reported as statistical results). The average length of wolffish caught increased by 1.3 cm for each increase in hook size, irrespective of bait size. However, for cod in the northern area, hook size improved size selectivity only when the small bait size was used, and average length increased by 1.4 cm with every increase in hook size. In addition, catch numbers decreased with increasing hook size for all species (data reported graphically). Six fishing trials were conducted on commercial longliners between November 2008 and December 2009 (five trials north of Iceland, one trial in the south) at depths of 50–140 m. Five hook sizes (EZ-Baiter hooks, sizes 10–14) and two sizes (10 and 30g) of Pacific saury Cololabis saira bait were tested (see original paper for dimensions). The two bait types were alternated in 100-hook blocks, each divided into five 20-hook blocks rigged with one of the five hook sizes. A total of 4,800 hooks were set each trip (except one trip of 2,400 hooks). Lines were hauled after one hour and fish species, number and length recorded.

    (Summarised by: Chris Barrett/Natasha Taylor)

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