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: 315–322. 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.

Tallack, S. M. L. 2007. Escape ring selectivity, bycatch, and discard survivability in the New England fishery for deep-water red crab, Chaceon quinquedens. – ICES Journal of Marine Science, 64: 1579–1586. The trap fishery for red crab, Chaceon quinquedens, occurs at depths of 600–800 m along the continental slope of New England. The target product is a male crab with a carapace width of ∼105 mm or greater. Selectivity was tested at two discrete depths (600 and 800 m), for four different escape ring scenarios: control trap with no escape rings, and escape rings with internal diameters of 9, 10, and 11 cm. Proportions of non-marketable C. quinquedens were large (71–100%) at both depths for all traps, but were smallest in traps with escape rings. Discard mortality was estimated at ∼5% through caging experiments across three haul frequency conditions (every 24 h, every 4 d, and after 8 d), which represented the likely reality of multiple recaptures during a commercial trip. The impact of discarding techniques (low and high impact) was also assessed. If discard proportion estimates of >71% are realistic, and if an estimated ∼5% of these discards die, the recommendation must be made for fishery participants to improve gear selectivity, and thereby to minimize discard mortality rates. On the management side, stock assessments will be more accurate if estimates of discard mortality are incorporated.

Seasonality of the reproductive cycle for Cancer pagurus was determined using three biological indicators: extruding sperm plugs (mating period), extrusion of eggs (spawning period) and presence of empty egg capsules (hatching period). Sperm plugs were found only in recently moulted females, indicating that mating coincides with moulting periods. Cancer pagurus mating indicators were observed during the summer months and into autumn; spawning occurred in winter, and broods were hatching throughout the summer into early autumn. Size at maturity, was assessed using a variety of reproductive and morphometric criteria; estimates from reproductive criteria are generally larger than those from morphometric criteria and these differences are often indicative of 'functional' vs 'behavioural' maturity. In C. pagurus, size at maturity estimates ranged from 101.6-125.0 mm carapace width (CW) in males and 110.7-147.3 mm CW in females; the sizes at functional maturity proposed are larger than those from morphometric indicators.

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