Invasive Scpices Conclusion

There is still considerable room for improving current baiting practices. By applying the findings of chemoreception research, the effectiveness of conventional fish baits could be almost doubled with the simple addition of small sections of sugarcane. The selectivity potential of the bait was also demonstrated by adding sugar to the fish mince teabags, which maintained the catches of P. pelagicus but reduced those of other crab species. In the future, determining the taste preferences of the target organisms can help design species-specific bait, and this will have serious applications in eradication programs. This new "designer" bait would considerably reduce the number of non-target organisms in the catch, and the handling damage and stress they are subjected to while they are in the traps.

Live decoys seem to be an attractive alternative to common fish bait because they only attract crab conspecifics and greatly reduce the non-target catch. In the past pheromone baited traps have been used for the removal of insect pests, and such technology may also be applied in the future to eradicate invasive crustacean species. Recent work on crab pheromones and their isolation might be used to develop pheromone bait by binding these substances in a gel matrix that can be used instead of live decoys (Behrens Yamada et al. 2006).

Trap design profoundly affected the number of crabs found in the catch. Round or oval based traps enhanced crab exploration around their perimeter, and consequently increased the probability of crabs encountering an entrance that would lead them to the bait found inside. Entrance design was crucial as well; tight slit entrances prevented escape but at the same time hindered entry into the traps. The netting material forming the slits tangled with the spines on the carapace and appendages of the crabs, and restricted their forward movement into the traps. Open funnel entrances performed much better because they do not obstruct crab passage and facilitated access towards the bait. This entrance type allowed for easy entry but also permitted escape. Escape has been blamed for decreasing a trap's performance, but recently, as the negative consequences of lost traps by ghost fishing have been documented, the need for escape mechanisms has been recognized. Traps containing sufficient bait quantity will keep the catch inside satisfied until they are hauled, and escape will not be a problem until a considerable time has passed.

The dome trap with open funnel entrances proved to be the best design for both commercial exploitation and for eradication purposes. This trap is ideal for removing crabs of all sizes when fitted with smaller mesh netting to also retain smaller ones. In the future, other ways to improve its design might be to increase its size and volume, so that more space is available and larger crabs do not exclude smaller ones from entering the trap. Increasing the number of entrances would also facilitate entry and increase the probability of the bait odor trail coinciding with one of the entrances and thus effectively guide the crabs into the trap. In extreme cases, fitting the entrances with escape preventing devices could be applied to improve crab retention; soft-eyed entrances or triggers may be installed. In large-scale eradication programs the loss of some trapping gear is inevitable, for this reason fitting all traps with "ghost fishing" prevention biodegradable panels that disintegrate with time, or installing time releases that open some part to make the trap non-operational should be mandatory.

Investigating the possible application of alternative fishing gear like liftnets or tangle nets should be considered for eradicating crustacean pests. In several countries the use of this gear is considered "illegal" and is favored by poachers because they are operated quickly and are very effective. Crustacean fisheries employing tangle nets are found in some countries, and a good example is the spanner crab Ranina ranina fishery in Australia, where this gear has proved much more efficient than using conventional traps (Kennelly and Craig 1989). Preliminary trials using liftnets to capture swimming crabs confirmed their superiority to traps, and caught five times more crabs in one hour than dome traps in one day. Liftnets are fished much shorter times, from 30-60 minutes and consume half the amount of bait. When considering the expense of bait, lift nets caught 20 crabs per kilogram of bait, while traps caught only 2.8 (Vazquez Archdale, unpublished results). Liftnets can also be deployed from land, small dinghies and even canoes. They are easily constructed and the materials employed are cheap, so sport fishers and volunteers can easily join eradication campaigns. Funds and manpower to educate the public should be given priority, involving the local community and fishing cooperatives on fishing campaigns and even teaching them how to prepare dishes, consume and market these novel delicious crabs. Even restaurants serving "alien crabs" on their menu may be surprised at the demand their dishes may have among educated customers, who are willing to contribute their part to help reduce the numbers of these invasive pests.

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