Invasive Swimming Crabs Development of Eradicating Trapping Gear and Methods

Miguel Vazquez Archdale*

Field of Fisheries Engineering, Faculty of Fisheries, Kagoshima University, Shimoarata 4-50-20, Kagoshima City 890-0056, Japan

Making simple improvements on traditional fishing gear and methods can be applied to develop effective eradicating tools that can be integrated with other strategies used to combat invasive aquatic species. Swimming crabs are the target choice; they travel widely by swimming, attached to the hulls of ships or as larvae suspended in ballast water. They represent a valuable fisheries resource and are consumed as food. They are however also carriers of pathogens that may damage fisheries and aquaculture industries, which results in the need of effective eradication methods.

Traps make good eradicating gear because they are light, inexpensive, small, easily stacked onboard, keep the catch alive, and permit the release of non-target organisms undamaged. They are passive gear, so the target organism has to be lured into the traps with the promise of food, shelter, company or even a mating partner.

Improving luring methods, such as common baits or pheromone emitting decoys, is just as important as research on new trap design for increasing the catch. Determining the taste preferences of the target crab, and making bait combinations of fish plus sugarcane have demonstrated a synergistic effect that doubled the catch. Alternative bait made from fish mince inside teabags was as effective as ordinary bait, and allowed enrichment of the bait with attractants and the use of fish byproducts as raw material, which reduces cost and conserves valuable food resources. Pheromones offer attracting potential, have been found in swimming crabs and are emitted by the live decoys employed in their trap fishery. This fishing method eliminates the non-target catch by attracting only crab conspecifics. Specially designed traps containing live decoy crabs were more effective than baited traps, and eliminated unwanted organisms that feed on bait.

When designing eradicating gear, the quantity of the catch is more important than its size or quality; consequently, traps must be fitted with smaller meshed netting to

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