Live Transport of Crustaceans in Air - Prolonging the Survival of Crabs

Abstract

We studied the live transport of crustaceans in air, using the spanner crab Ranina ranina as an example, and developed guidelines for handling live spanner crabs which we presented to an industry workshop. Our findings were also of general relevance to the live shipment of other oceanic crab species.
The spanner crab fishery has burgeoned over the last couple of years through interest in the live market. The choice of spanner crabs as a topic of study was therefore timely . The handling practices used on boats in this fishery, (storing crab s out of water), were appropriate for handling "live" crabs destined for cooking but we found that more careful handling was required for the live export market.
While spanner crabs appeared to tolerate being stored in air, our studies showed that this tolerance was misleading. The crabs stressed quickly when they arrived on deck and became quiescent . Their blood pH fell rapidly, a symptom called acidosis . Quiescence was their only means of dealing with acidosis.
In practical terms, any time that a spanner crab was out of water was too long. Spanner crabs are stored in air twice after harvest, first while on the boat and again when actually exported . The conditions experienced by the crabs stored in air at ambient temperature on boats were much worse than those of crabs cooled for export. At the very least, the crabs should be cooled down or sprayed with cold seawater when stored in air on boats. The best way to store crabs on boats would be submerged in live wells but there are problems with this because the unrestrained crabs can injure each other.
We also tested other methods of alleviating stress. Spanner crabs cannot buffer low pH in the blood, unlike many other commercially harvested crustaceans. We sought to correct this using a dip treatment . However, this did not improve their survival. For an animal that cannot correct acidosis, spanner crabs survive for an extraordinary period in air. The stressed crabs may linger on because they "shut down" and keep the acidosis from reaching fatal levels.
Using the results of our research, we presented guidelines for handling spanner crabs at an industry workshop on December 9-1Oth 1993. This workshop attracted favourable comment from the industry and copies of several papers were published in the May edition of Queensland Fisherman.
We concluded that the way the crabs are currently being handled on boats is too stressful.
Physiological studies show that spanner crabs, like other oceanic crabs, are not well equipped to survive in air . Yet even if you store them cold on the boat they still die after a few days in tanks on shore. This mortality is an impediment to the maturity of the industry. The crabs may be succumbing to bacterial infections caused by injury and we recommend that their claws are immobilised by banding after capture.