Hazell et al.: Somatic growth rale of Jasus lalandn 



515 



AMJJASONDJF 



Time (months) 



^ — I B 



17.5 22.5 27.5 32,5 37 5 

 Carapace length (mm) 



Figure 3 



Site-specific patterns of the proportions of sampled 

 juvenile rock lobster that were considered to be molt- 

 ing with respect to (A) sample month and (B) 5-mm-CL 

 size classes. MP = Mouille Point; HW = harbor wall. 



the proportion of lobsters in the molt state fluctuates over 

 time. In both cases, the proportion of lobsters in the molt 

 state was consistently lower at the harbor wall than at 

 Mouille Point (with the exception of the sample taken in 

 October 1996). This apparent dependence of molt state on 

 each of the factors site, size-category, and sample date is 

 confirmed by the corresponding significant second-order 

 interactions (Table 5). 



Together with the molt-increment data, these results 

 give reason to reject the hypothesis that current juvenile 

 growth rates on the harbor wall are no different from 

 those on the nearby natural nursery reef in Mouille Point; 

 growth is significantly faster at the latter. 



Discussion 



The significance of puerulus and postpuerulus ecology to 

 the management of rock lobster fisheries is now widely 

 accepted (Herrnkind et al., 1994). In the South African 

 J. lalandii resource, the current controversy surrounding 

 the question of whether or not temporal trends in juvenile 

 growth rates reflect those of adults provides a good exam- 

 ple of why so much emphasis should be placed on early life 



history stages. For this species, adult somatic growth rates 

 have declined substantially since the mid-1980s (Melville- 

 Smith et al., 1995; Cockcroft, 1997, Cockcroft and Payne, 

 1999). Although the causes of this phenomenon are not 

 yet clearly understood, its widespread nature is indica- 

 tive of a large-scale environmental perturbation. This has 

 prompted hypotheses that the anomalous El Nino years 

 of 1990-93 may have resulted in dramatic changes in 

 the productivity of the southern Benguela Current (Pol- 

 lock et al., 1997; Pollock et al., 2000). Alternatively, it is 

 plausible that heavy, size-selective fishing of this resource 

 may have caused a decline in growth rates by removing 

 individuals genetically predisposed to more rapid growth 

 (see for example Stokes and Law 12000]). Notwithstand- 

 ing the causes, if it is incorrectly assumed that juvenile 

 growth rates mirror the trends of the regularly monitored 

 adults, overly conservative estimates of recruitment into 

 the fishery might result, whereas assuming the converse 

 could lead to a higher risk of overfishing. 



Results from our re-examination of the growth rates of 

 juvenile J. lalandii provided some evidence that temporal 

 trends in their growth rates are consistent with those 

 of the adults of the species. Specifically, juvenile molt 

 increments at the Cape Town harbor wall were smaller in 



