510 



Abstract-Catch rates in the South Af- 

 rican rock lobster iJasus lalandii) fish- 

 ery declined after 1989 in response to 

 reduced adult somatic growth rates 

 and a consequent reduction in recruit- 

 ment to the fishable population. Al- 

 though spatial and temporal trends in 

 adult growth are well described, little 

 is known about how juvenile growth 

 rates have been affected. In our study, 

 growth rates of juvenile rock lobster 

 on Cape Town harbor wall were com- 

 pared with those recorded at the same 

 site more than 25 years prior to our 

 study, and with those on a nearby 

 natural nursery reef We found that 

 indices of somatic growth measured 

 during 1996-97 at the harbor wall had 

 declined significantly since 1971-72. 

 Furthermore, growth was slower among 

 juvenile J. lalandii at the harbor wall 

 than those at the natural nursery reef 

 These results suggest that growth rates 

 of juvenile and adult J. lalandii exhibit 

 similar types of spatiotemporal pat- 

 terns. Thus, the recent coastwide decline 

 in adult somatic growth rates might also 

 encompass smaller size classes. 



Do fluctuations in the somatic growth rate of rock 

 lobster Uasus lalandii) encompass all size classes? 

 A re-assessment of juvenile growth 



R. W. Anthony Hazell 



Department ol Zoology 

 University ol the Western Cape 

 Private Bag X17 

 Bellville, 7535, South Africa 



David S. Schoeman 



Department ol Zoology 



University of Port Elizabeth 



PO Box 1600 



Port Elizabeth, 6000, South Africa 



E-mail address (for D S Schoeman, coniacl aultior) zladssiSzooupeacza 



Mark N. Noffke 



Marine and Coastal Management 



Private Bag X2 



Rogge Bay 8012 South Africa 



Manuscript accepted 2 May 2001. 

 Fish. Bull. 100:510-518 (2002). 



The South African fishery for rock 

 lobster (Jasus lalandii) began in the 

 late nineteenth century and expanded 

 rapidly so that catches peaked at 

 approximately 10,000 metric tons (t) 

 per annum between 1950 and 1965 

 (Pollock, 1986). However, subsequent 

 deterioration in catches in the 1960s 

 and 1970s was arrested only in the 

 mid-1980s by the implementation of 

 a management approach centered 

 on an annual total allowable catch 

 (TAC). Over the following five years, 

 catches were maintained at apparently 

 sustainable levels of 3500-4000 t per 

 annum (Cockcroft and Payne, 1999), 

 still representing the largest yield of 

 any Jasus species at that time (Pollock, 

 1986). However, the period of stability 

 ended after 1989, when catch rates 

 declined in response to reduced adult 

 somatic growth rates and a concomi- 

 tant reduction in recruitment to that 

 part of the population larger than the 

 minimum legal size (Melville-Smith et 

 al., 1995; Goosen and Cockcroft, 1995; 

 Cockcroft, 1997). 



Adult somatic growth rates for this 

 resource are assessed by means of a tag- 

 recapture program. This is relatively 

 simple because mature individuals 



molt only once a year, just prior to 

 the start of the commercial fishing 

 season, and samples of these animals 

 can be tagged shortly before they 

 molt. Annual gi'owth increments can 

 therefore be calculated from postmolt- 

 tagged animals recaptured during the 

 subsequent commercial fishing season. 

 This type of tag-recapture data is 

 routinely collected from most of the 

 fishing grounds that are important 

 to the South African commercial fish- 

 ery (Fig. 1, inset). This tagging pro- 

 gram has yielded one of the most com- 

 prehensive rock lobster tagging-for- 

 growth databases in the world; it con- 

 tains continuous time-series for most 

 areas since 1986 and broken time- 

 series for some sites dating back to the 

 1969-70 season (Goosen and Cockcroft, 

 1995). Consequently, temporal and 

 spatial trends in adult growth are well 

 described (Melville-Smith et al, 1995; 

 Goosen and Cockcroft, 1995; Cockcroft, 

 1997; Cruywagen, 1997; Pollock et al., 

 1997). By contrast, little is known about 

 what may affect juvenile growth rates. 

 Of particular concern is the lack 

 of information regarding the way in 

 which juvenile growth rates might 

 have been affected by factors that 



