Does Classic Stock Assessment Have a Role in a Failed Case of Reconciliation of Fisheries with Conservation?

摘要

Benthic shellfish populations worldwide are under heavy pressure given the inherent characteristics of these resources coupled with the typically high value of the product. The South African abalone Haliotis midae fishery is faced with ever-increasingproblems from illegal fishing and recent ecosystem change in the form of a movement of West Coast rock lobsters Jasus lalandii into much of the range of the abalone. It seems that the lobsters have dramatically reduced sea urchin Parechinus angulosus populations, thereby indirectly negatively impacting juvenile abalone, which rely on urchins for shelter. Total allowable catches (TACs) for commercially valuable abalone are set separately for each of seven fishing zones, with the typical historical overall TAG of some 600 metric tons (mt) (wet mass) per annum having been reduced recently to some 400 mt or less. A spatial and age-structured production model has provided the basis for management advice for this resource over recent years by projecting abundance trends under alternative future catch levels. The model estimates the reduction in juvenile abalone survival due to the ecosystem change and estimates the illegal take using a novel fisheries index - confiscations per unit of policing effort. As aconsequence of the recent explosion of poaching activities, the combined zones A-D model-predicted 2003 poaching estimate of 933 mt (corresponding to the assumption that, on average, 36% of all poached abalone are confiscated) is more than seven times the legal 2003 commercial TAG for these zones. This begs the question of whether a reasonably sound stock assessment exercise as applied in these circumstances has played any role other than that of accurately documenting the decline of the resource. It is argued that despite being associated with a management regime that has failed to achieve conservation, there have been clear advantages to having continued these exercises. The extent to which legal commercial fishers should be penalized because of theactions of illegal fishers is discussed. Results point to the need for caution in crying wolf in such circumstances because this may exacerbate problems by resulting in scientific credibility being questioned because of unsubstantiated claims by concerned scientists. A new system of comanagement based upon the Territorial User Rights in Fisheries concept has been introduced in this fishery in an attempt to address the threat of illegal harvesting.