Coral reef crustacean fisheries options for management, stock enhancement, habitat enhancement and aquaculture

 

Richard G. Hartnoll

 

Port Erin Marine Laboratory, University of Liverpool,

Isle of Man IM9 6JA, British Isles

 

 

ABSTRACT

In coral reefs the only exploited crustaceans of any substantial importance are palinurid lobsters. Some shrimps are fished for the aquarium trade, but these are of minor significance. Penaeid prawns are important in associated ecosystems such as mangroves and sea grass beds, but not in coral reefs themselves. This analysis will be restricted to lobsters.

Species of commercial interest in the Indo-West Pacific include Panulirus longipes, P. ornatus, P. penicillatus and P. versicolor. All species are heavily exploited throughout most of their range, and generally must be considered as seriously overexploited. This is based on the evidence of reduced catches and smaller landing size. There is a need for formal data on stock size and CPUE to confirm this presumption.

This presumed overexploitation has serious economic repercussions, since reef lobsters are a high-value catch which supports almost entirely artisanal fisheries which require low capital investment. They can thus be of substantial direct value to local coastal communities (unlike industrial fisheries where most of the benefit is exported). However the artisanal nature of the fishery, and the diversified marketing (often direct from fishermen to users) mitigates against collecting fisheries statistics, and also against effective legislation. Nevertheless, the potential direct economic benefits justify substantial efforts to manage and/or enhance these fisheries.

Management requires information on the biology of the lobsters, and the status of the stocks and fisheries, in order to frame effective regulations. All of these are currently limited, and effective protocols to collect data need to be established. The assessment of stock size, recruitment levels and growth rates are all difficult in reef environments, and little is known of stock boundaries and dispersal. Sound fisheries data are hard to obtain in an informal artisanal situation. To have any value regulations must be enforced, and this is again difficult in an artisanal mode: consideration must be given to the possibility of fishing rights which generate self regulation. Other strategies to improve the fisheries, besides better management of natural stock, are aquaculture, stock enhancement, and habitat enhancement.

Currently there is little potential for aquaculture, because of the problems of obtaining supplies of larval/postlarval lobsters. The larval cycle of palinurid lobsters involves a lengthy pelagic phase with up to 20 delicate phyllosoma instars with a total duration of up to a year. There is no prospect of rearing these in captivity on a commercial scale. An alternative approach is to capture the settling postlarvae, but this has never proved a dependable strategy. The only possible aquaculture initiative is to capture juveniles from the wild, and ongrow these in pounds. This approach deserves worth study.

Stock enhancement has been successful in homarid lobsters, but has been based on large scale rearing of larvae which are then released at an advanced postlarval stage. As discussed above, this is not an option for palinurid lobsters due to their quite different larval history.

Habitat enhancement is a more attractive proposition. The basic concept is to provide artificial shelters/reefs which will generate recruitment and growth of lobsters additional to those stocking the natural reefs. They are not intended to act as aggregation devices to concentrate existing stocks this would be counterproductive. There is considerable experience of artificial shelters in the Caribbean, and their value in the Indo-West Pacific merits examination.