Do rare-earth metals deter spiny dogfish? A feasibility study on the use of electropositive “mischmetal” to reduce the bycatch of Squalus acanthias by hook gear in the Gulf of Maine

Tallack, S. M. L., and Mandelman, J. W. 2009. Do rare-earth metals deter spiny dogfish? A feasibility study on the use of electropositive “mischmetal” to reduce the bycatch of Squalus acanthias by hook gear in the Gulf of Maine. – ICES Journal of Marine Science, 66. Catches of spiny dogfish (Squalus acanthias) are considered by commercial and recreational fishers to be unacceptably high during summer and autumn in the Gulf of Maine off the northeast coast of the USA. Consequently, there is interest in finding a dogfish deterrent for application in various fishing gears. Field studies tested triangular slices of the rare-earth metal cerium/lanthanide alloy (“mischmetal”) incorporated into longlines and rod-and-reel gear to assess its effectiveness in reducing dogfish catches. Treatment catches (mischmetal present) were compared with control (no mischmetal) catches. Laboratory studies provided video-taped, behavioural observations on the effects of alloys under variable levels of food deprivation and dogfish density. No significant reductions in dogfish catch were recorded for either rod and reel or longline, and in situ video footage verified persistent dogfish feeding behaviour, regardless of mischmetal presence. The laboratory trials found some evidence of avoidance behaviour in dogfish approaching treatment baits, but only with dogfish fed to satiation; no aversion to the material was observed after 2 and 4 d of food deprivation. Dogfish density had no effect on feeding behaviour in the laboratory. Overall, there is little evidence to suggest that mischmetal can significantly reduce catches of dogfish in hook gears in the Gulf of Maine.