Field investigation of rare-earth metal as a deterrent to spiny dogfish in the Pacific halibut fishery

  • Published source details Kaimmer S. & Stoner A.W. (2008) Field investigation of rare-earth metal as a deterrent to spiny dogfish in the Pacific halibut fishery. Fisheries Research, 94, 43-47.


This study is summarised as evidence for the following.

Action Category

Attach an electropositive deterrent to fishing gear

Action Link
Marine Fish Conservation
  1. Attach an electropositive deterrent to fishing gear

    A replicated, randomized, controlled study in 2007 of an area of fished seabed in in the Gulf of Alaska, USA (Kaimmer & Stoner 2008) found that longline hooks with electropositive metal attached reduced the catches of unwanted spiny dogfish Squalus acanthias, longnose skate Raja rhina and undersized commercially targeted Pacific halibut Hippoglossus stenolepis, compared to standard hooks, and in most cases compared to hooks with non-electropositive metal attached. Catch rates were lower on electropositive hooks than standard and steel-fitted hooks for spiny dogfish (positive: 17, standard: 21, steel: 19 ind./50 hooks) and longnose skate (positive: 13, standard: 24, steel: 23 ind./50 hooks). Undersized (<82 cm) halibut catch rates were lower on electropositive hooks (1 ind./50 hooks) than standard hooks (2 ind./50 hooks) but similar to steel-equipped hooks (1 ind./50 hooks). Overall catch rates of halibut (all sizes) were similar between all hook types (3 ind./50 hooks). In September and October 2007, thirty-six longline sets were deployed in Kachemak Bay at 16–58 m depths of three hook types: circle hooks equipped with electropositive cerium mischmetal (a nonmagnetic metal alloy), standard circle hooks, and circle hooks equipped with inert steel that mimicked the mischmetal. All hooks were baited with 110–150 g of chum salmon Oncorhynchus keta. Hooks were fixed to a groundline in randomized blocks of 150 for each type (450 hooks/set) using 31 cm nylon lines attached to the groundline every 5.5 m. Gear was hauled after a minimum soak time of 90 min (average 192 min).

    (Summarised by: Leo Clarke)

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