MORGAN ET AL.: STOCK AND RECRUITMENT RELATIONSHIPS IN PANULIRUS CYCNUS 



Table 5.— Catch (kg) per pot lift of rock lobsters 

 taken by the commercial fishery during November 

 and December for the years 1964-79. 



Table 6.— Total catch for the western rock lobster fishery. 



INDEX OF SPAWNING STOCK 



Figure 2.— The Flicker (1958) stock-recruitment model, to- 

 gether with 95% confidence limits. The model is fitted to data 

 on the index of abundance of spawning Panulirus cygnus and 

 the resultant level of settlement of the puerulus stage. The year 

 shown is the season of hatching of the larvae. 



lus in year x (plus January of year x + 1) may be 

 compared directly with the index of abundance 

 of the spawning stock (I.A.S.) in year x. 



The Ricker (1958) stock-recruitment relation- 

 ship of R - AS exp(-BS), where R = recruit- 

 ment, S = stock size, A = coefficient of density- 

 dependent survival, and B = coefficient of den- 

 sity-independent mortality, was fitted using the 

 method of Cushing and Harris (1973). The rela- 

 tionship is shown in Figure 2 and provides a good 

 fit to the observed data (proportion of sum of 

 squares explained is 0.775). Estimates of A and B 

 with their standard errors (SE) are A = 7.645, 

 SE = 2.193 and B = 0.026, SE = 0.004. 



Puerulus and Juvenile Densities 



The relationship between puerulus and juve- 

 nile densities is not clear. In contrast to the state- 



ment of Chittleborough and Phillips (1975) that 

 puerulus settlement is a good indicator of subse- 

 quent juvenile density, the additional data avail- 

 able for Seven Mile Beach (Table 7) indicate that 

 the correlation between puerulus settlement and 

 the subsequent density of 2-yr-old juveniles is 

 poor ( r = 0.359, P>0.05). Neither do the data give 

 an acceptable fit to a Ricker ( 1958) stock-recruit- 

 ment curve. The same conclusion is reached from 

 examination of Garden Island data (Tables 3, 4) 

 ( r = 0.528, F>0.05). For example, relatively high 

 settlement of puerulus at Seven Mile Beach in 

 1974 and 1977 (Table 7) when total juvenile den- 

 sity was also high gave rise to very poor and very 

 high densities, respectively, of 2-yr-olds. Beyond 

 2 yr of age, however, density-dependent mortal- 

 ity is evident. At both Garden Island and Seven 

 Mile Beach there was a significant (P<0.001) 



Table 7. — Level of puerulus and subsequent juvenile densities of Panulirus cygnus in January and mortality 

 rates at Seven Mile Beach, Western Australia. — = not measured; NA = not yet available; arrows connect 

 individual year classes. 



Year of 

 hatching 



Puerulus 

 mean no 

 settling/ 

 collector 



Age in years of juveniles arising from puerulus 



2 



No /ha 



3 

 No. /ha 



4 

 No. /ha 



5 

 No. /ha 



Juveniles present on 



reef at time of 

 puerulus settlement 

 Total no. /ha 2-5 yr 



Mortality rate/yr 

 of animals 

 aged > 3 yr 



1969 

 1970 

 1971 

 1972 

 1973 

 1974 

 1975 

 1976 

 1977 

 1978 

 1979 



10.231 

 15.829 

 21.310 

 39.472 

 15.566 

 13.032 

 46.716 

 36.478 

 NA 



0863 

 0466 

 0768 

 1 934 

 686 



657 



1 879 

 1 780 



NA 



481 



