49. Malcolm Clark provided a summary of his work to document relevant information on the common deepwater species harvested in the study area. He noted that uncertainty remained regarding certain issues, for example, productivity and recruitment of orange roughy. He felt that few orange roughy/alfonsino fisheries have been well managed from a sustainability perspective. Current sustainable biomass targets are 30 % Bo but many stocks had been depleted to levels of 10 - 20 % Bo. Despite attempts to be conservative, in such New Zealand fisheries there remained needs to limit serial depletion of resources.
50. Management target reference points for exploitation for orange roughy in Australia and New Zealand are approximately 30 % Bo (limit reference point 20 % Bo); in Namibia the target is 50 % Bo. The suite of species is considered to be ecologically unproductive with little potential for rapid replacement of reduced biomass. Estimates of natural mortality vary depending on region and the estimation method used; estimates of M were » 0.045 for orange roughy; 0.2 for alfonsinos; 0.3 - 0.4 for black cardinal and 0.06 for oreos. Sustainable catch rates for orange roughy are 2 % of Bo, which is much lower that for most shelf species. In New Zealand, there have been no strong signs of stock recovery though little information exists concerning their recruitment characteristics. In his view, use of judgement would be important in the management of this fishery and rates of exploitation should be set conservatively.
51. Reference was made to the New Zealand National Institute of Water and Atmospheric Research (NIWA) work on Seamount meta-analysis - a generalized linear analysis of relevant factors in relation to seamount productivity. The results indicate some predictive capability from variables including depth and topography. Results of the analysis indicate sustainable yields in the range of 10s - 100s of tonnes per seamount.
52. Reference was made to the episodic nature of recruitment of orange roughy stocks such that there may be long periods without recruitment - in such cases, conventional perspectives of “fishing down” the biomass and then taking a percentage of the Bo may not work. In Australia there has been no indication of the expected response, such as compensatory changes in growth rates as a consequence of exploitation. The target fisheries show little changes in length-frequencies stock structure.
53. Comment was made of the large area of the Chatham Rise fishery; almost an exception among deepwater fisheries in that » 30 000 tonnes/yr had been harvested for an extended period in the 1980s. However, this success had not been repeated in smaller orange roughy fisheries, which usually became depleted. Indeed the absence of other “Chatham Rise-type” fisheries (i.e. a moderate number of 40 - 60 tonnes/tows maintained over many years) indicates that they probably do not exist.
54. The difficulty in justifying funding for management and research on such reduced roughy and alfonsino populations was raised (but was not answered - Ed.).
