Modified hooks reduce incidental mortality of snapper (Pagrus auratus: Sparidae) in the New Zealand commercial longline fishery

Published source details Willis T.J. & Millar R.B. (2001) Modified hooks reduce incidental mortality of snapper (Pagrus auratus: Sparidae) in the New Zealand commercial longline fishery. ICES Journal of Marine Science, 58, 830-841.
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This study is summarised as evidence for the following.

	Action	Category
	Use a different bait type Action Link
	Use a different hook type Action Link

Use a different bait type

A replicated study in 1999 in a coastal gulf in the South Pacific Ocean off New Zealand (Willis & Millar 2001) found that using different types of bait in a longline fishery did not alter the incidence of hooking injury (related to higher post-release mortality) in unwanted undersized snapper Pagrus auratus. Proportional catches of undersized snapper hooked by the lip were similar for each bait type (squid Notodarus sloanii: 0.02, pilchard Sardinops neopilchardus: 0.02, mackerel Scomber australasicus: 0.02), and undersized snapper caught by the gut (squid: 0.016, pilchard: 0.011, mackerel: 0.015). In addition, the proportion of all sizes of snapper hooked by the gut was similar (squid: 0.2, pilchard: 0.1, mackerel: 0.1). Data were collected onboard a fishing vessel in the Hauraki Gulf in 1999, from 13 (January) and 12 (June) longline deployments. Each longline had 1,350 hooks, baited with equal numbers of the three bait types. Lines were left in the sea for one hour. Arrow squid, pilchard and blue mackerel were used as bait. All catch was counted and measured. Location of hook (lip or gut) was recorded.

(Summarised by: Rosslyn McIntyre)
Use a different hook type

A replicated, controlled study in 1999 in an area of seabed in the Hauraki Gulf, Pacific Ocean, off New Zealand (Willis & Millar 2001) found that hooks modified with additional wire appendages reduced the amount of discarded snapper Pagrus auratus caught by the gut (associated with post-release mortality), compared to standard hooks in a longline fishery. Overall snapper catch rates were reduced with modified hooks relative to the standard hook (20 mm appendage: 22% less, 40 mm appendage: 33% less). Relative to catches with a standard hook, the relative likelihood of under-sized (<26 cm) snapper being captured by the gut was reduced with both types of modified hook (20 mm appendage: 78% less, 40 mm appendage: 96% less), and decreased with increasing length of hook appendage. Thirteen longline deployments were made from a fishing vessel in January and 12 in June 1999. Each longline had 1,350 hooks, with equal numbers of standard hooks, and two types of hooks modified with wire appendages (20- and 40-mm length). Lines were deployed for one hour. Arrow squid Notodarus sloanii, pilchard Sardinops neopilchardus and blue mackerel Scomber australasicus were used as bait. All catch was counted and fish length measured, and location of hook was recorded.

(Summarised by: Rosslyn McIntyre)