89 



Abstract — Many modern stock assess- 

 ment methods provide the machinery 

 for determining the status of a stock 

 in relation to certain reference points 

 and for estimating how quickly a 

 stock can be rebuilt. However, these 

 methods typically require catch data, 

 which are not always available. We 

 introduce a model-based framework 

 for estimating reference points, stock 

 status, and recovery times in situ- 

 ations where catch data and other 

 measures of absolute abundance are 

 unavailable. The specific estima- 

 tor developed is essentially an age- 

 structured production model recast 

 in terms relative to pre-exploitation 

 levels. A Bayesian estimation scheme 

 is adopted to allow the incorpora- 

 tion of pertinent auxiliary informa- 

 tion such as might be obtained from 

 meta-analyses of similar stocks or 

 anecdotal observations. The approach 

 is applied to the population of goli- 

 ath grouper \Epinephelus itajara) off 

 southern Florida, for which there 

 are three indices of relative abun- 

 dance but no reliable catch data. The 

 results confirm anecdotal accounts of 

 a marked decline in abundance during 

 the 1980s followed by a substantial 

 increase after the harvest of goliath 

 grouper was banned in 1990. The ban 

 appears to have reduced fishing pres- 

 sure to between 10% and 50% of the 

 levels observed during the 1980s. 

 Nevertheless, the predicted fishing 

 mortality rate under the ban appears 

 to remain substantial, perhaps owing 

 to illegal harvest and depth-related 

 release mortality. As a result, the 

 base model predicts that there is less 

 than a 40% chance that the spawn- 

 ing biomass will recover to a level 

 that would produce a 50% spawning 

 potential ratio. 



A catch-free stock assessment model 

 with application to goliath grouper 

 iEpinephe/us itajara) off southern Florida 



Clay E. Porch 



Anne-Marie Ekiund 



Gerald P. Scott 



Southeast Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 75 Virginia Beach Drive 

 Miami, Florida 33149-1099 

 E-mail address clay porchiSnoaa. gov 



Manuscript submitted 30 April 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 14 July 2005 by the Scientific Editor. 



Fish. Bull. 104:89-101 (2006). 



The last decade has witnessed con- 

 siderable interest in the so-called 

 precautionary approach to resource 

 management, where human activities 

 are curtailed to prevent further envi- 

 ronmental degradation without the 

 burden of proving that these activities 

 are to blame. Fisheries applications 

 of the precautionary approach typi- 

 cally hinge on the notion that fishing 

 pressure should be reduced in a pre- 

 determined fashion as certain "limit" 

 reference points are approached (FAO, 

 1995; Caddy, 1998; Restrepo et al., 

 1998). In the United States, the Mag- 

 nuson-Stevens Fishery Conservation 

 and Management Act (Public Law 

 94-265) mandates the development 

 of fishery management plans (FMPs) 

 that specify criteria for determin- 

 ing when a stock is overfished and 

 the remedial measures necessary to 

 ensure a timely recovery. The National 

 Standard Guidelines developed by the 

 National Marine Fisheries Service to 

 implement the Act require each FMP 

 to include an "MSY control rule" that 

 comprises two reference points, known 

 as the maximum fishing mortality 

 threshold (MFMT) and the minimum 

 stock size threshold (MSST). When 

 the abundance of the stock dips below 

 the MSST, special provisions must be 

 made to rebuild the stock to the level 

 that would support the maximum sus- 

 tainable yield within a time frame 

 that is as short as possible and that is 

 commensurate with the intrinsic pro- 

 ductivity of the stock and the needs of 

 the fishing community. 



Many modern stock assessment 

 methods provide the machinery for 

 determining limit reference points 

 as well as for appraising where the 

 stock is in relation to them and how 

 quickly it can be rebuilt. However, 

 these methods typically require data 

 on total catch or absolute abundance, 

 which are not always available. In the 

 case of goliath grouper (Epinephelus 

 itajara), for example, a recent review 

 panel concluded that the catch sta- 

 tistics were unreliable and not use- 

 ful for assessment purposes (Anon.'). 

 Several ad hoc control rules have 

 been developed to accommodate such 

 "data-poor" situations. One of the 

 more common is simply to define the 

 MSST in terms of historical indices of 

 abundance that supposedly represent 

 a desirable stock condition (Annala, 

 1993; Cadrin et al., 2004). An advan- 

 tage of this type of approach is that it 

 is model-free, and nothing is assumed 

 concerning the recovery rate of the 

 stock. Being model-free, however, is a 

 disadvantage with respect to the re- 

 quirements of the Magnuson-Stevens 

 Act, inasmuch as the recovery time 

 cannot be estimated. Moreover, there 

 may be other types of information 

 that could influence the perception of 

 the status of the stock, and it would 

 be useful to integrate that informa- 

 tion formally into the assessment. 



Anon. 2003. Goliath grouper data 

 workshop report. SEDAR3-DW-1, 11 p. 

 South Atlantic fishery Management 

 Council, 1 Southpark Circle, Charles- 

 ton SC 29406. 



