Introduction

Increases in ocean traffic, construction of manmade canals, and release of live animals and plants into new environments are responsible for the introduction of numerous marine organisms around the world. Among them, crustaceans account for a large proportion of this total amount, and have been transported attached to the hulls of ships and in ballast water, intentionally released into new environments to enrich fisheries resources, or made their own way by swimming across new canals connecting water bodies that were geographically isolated in the past. These species, finding a new habitat devoid of ecological checks, such as predators, diseases or parasites, occasionally proliferate and become a nuisance by competing with local organisms for space and resources. They can potentially damage important fisheries and aquaculture industries by targeting local species as food prey or by transmitting new pathogens to which the local species have no natural resistance.

Humans have dealt with invading organisms in the past by adopting several strategies to contain their spread, but all attempts to eradicate them must begin with a detailed study of their ecology and life cycle, in order to determine the weakest points where pressure can be applied (Burdick 2005). Simple approaches have been to introduce a specific predator or parasite of the invading species hoping to limit its growth or hinder its reproduction, to attempt to remove or kill it using traps or poisons, or by encouraging hunters and fishers to catch them for a small reward. The latter may offer possibilities with some decapod crustaceans because they are already fished and represent a valuable fisheries resource. Humans consume crabs for food; consequently, sometimes developing a new fishery can be applied to reduce their numbers and enrich the local diet, particularly if there is one already in their country of origin. In some cases the invading crab species may have been studied in its place of origin; in that case, searching for literature and interviewing fishers or researchers may highlight some possible solutions.

The target swimming crabs used as models in this chapter, the Japanese shore swimming crab Charybdis japonica and the blue swimming crab Portunus pelagicus, are commercially exploited in Japanese waters, which are part of their natural habitat (Fig. 1). These crabs are also considered invasive, C. japonica in the coastal waters of Australia and New Zealand, and P. pelagicus in the eastern Mediterranean Sea. For this reason, studying commercial fishing gear that is currently being employed to capture them can help determine the most efficient trap type, and improvements in its design can serve to create a new eradication trap. Furthermore, because of the possibility of losing traps in the area where they are deployed, ways to minimize the negative impact they could have if lost in the fishing ground should be incorporated into the new design.

Figure 1. Japanese shore swimming crab Charybdis japĆ³nica (top) and blue swimming crab Portunus pelagicus (bottom).

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