Clark and Tracey: Population changes of Hoplostethus atlanticus on the Challenger Plateau 



251 



years when the results of that year's spawning re- 

 cruit to the fishery. Hence, until that time the fish- 

 ery will be removing only accumulated adult stock 

 and low levels of virgin stock recruitment. A third 

 important feature of adaptive management is the 

 understanding that it can involve high risk to a 

 species like orange roughy. Changes in biomass 

 could occur rapidly and any quota system and in- 

 dustry response must be flexible, so catch levels can 

 be reduced rapidly. 



The recovery of orange roughy from heavy fish- 

 ing may be slow. Their fecundity is low at 20,000- 

 30,000 eggskg -1 body weight (Pankhurst and 

 Conroy, 1987; Clark and Tracey, 1991). There is no 

 evidence of a marked change in fecundity of Chal- 

 lenger Plateau fish over the period 1987-90 (au- 

 thors' unpubl. data), but Leaman (1991) reported 

 reduced fecundity in exploited stocks of Sebastes 

 alutus, rather than an increase which might have 

 been expected. In addition, Leaman and Beamish 

 (1984) suggested a possible correlation between lon- 

 gevity of a species and the period between strong 

 year classes. Brown et al. ( 1983) noted that a reduc- 

 tion in population size of several species in the 

 Georges Bank region to low levels ( 10-20% of peak 

 abundance) was followed by less frequent occurrence 

 of strong year classes. 



High vulnerability to fishing and possible slow 

 recovery from over-fishing are important for man- 

 agement of orange roughy fisheries. Data over a 

 comparatively long time period are required to pro- 

 vide a basis for sound management of long-lived 

 species (Leaman, 1991). It is clear with orange 

 roughy on the Challenger Plateau that such species 

 can be overfished in a much shorter time than that 

 required for the desired data collection. Hence, de- 

 velopment of an orange roughy fishery needs care- 

 ful control from the outset. It is important that re- 

 search occurs in advance of substantial fishing, so 

 that baseline data on distribution, abundance, and 

 biology are collected. The most commonly used tech- 

 niques for stock assessment of orange roughy (trawl 

 survey, acoustic survey, CPUE analysis) provide 

 relative abundance indices, and therefore require 

 several surveys before absolute biomass can be de- 

 termined. Results of surveys in other areas, where 

 the relation between survey indices and true biom- 

 ass has been established, may be useful, but only if 

 gear, bottom type, and fish distribution are similar. 

 Egg production surveys have been carried out in 

 both New Zealand and Australia, and may enable 

 more rapid assessment in some localized areas. 

 'Adaptive management,' as discussed above, may be 

 appropriate as an aid to estimate biomass by stock 

 reduction methods, but it must be carried out with 



flexibility in order to change catch levels quickly. If 

 development of the fishery is carefully regulated in 

 the first few years while such data are collected, 

 later management problems such as too many ves- 

 sels involved in the fishery and the need to quickly 

 and substantially decrease quota levels could be 

 avoided. 



Acknowledgments 



The authors thank those too numerous to name, who 

 have participated in research cruises over the years 

 which provided the basic data for this study. We also 

 thank Chris Francis and Ian Doonan for statistical 

 advice, Ralph Coburn for some of the commercial 

 data extracts, and Kevin Sullivan and John Annala 

 (all MAF Fisheries) as well as two anonymous jour- 

 nal referees for constructive comments on the manu- 

 script. 



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