FISHERY BULLETIN: VOL. 80, NO. 3 



correlation between total density of juveniles on 

 the test reefs and annual mortality rate. 



Puerulus Settlement/Juvenile Densities and 

 Recruitment to the Fishery 



Chittleborough and Phillips (1975) examined 

 the relationship between the density of larger 

 juveniles on the coastal reefs during the latter 

 part of the year and the success of the commer- 

 cial white fishery in adjacent waters. They found 

 that, although density-dependent mortality dur- 

 ing the juvenile phase ensures reasonably con- 

 stant recruitment to the fishery over a wide 

 range of initial year-class strengths, in some 

 years the level of puerulus settlement may be in- 

 adequate (i.e., below the holding capacity of the 

 shallow-water reefs), and poor recruitment to the 

 fishery may result. They reported that from the 

 data available at that time only the incidence of 

 particularly poor year classes could be used to 

 predict the relative success of the "white" fishery, 

 i.e., to forecast poor future recruitment to the 

 fishery. 



Thus, as reported by Hancock (1971), follow- 

 ing the low settlement of puerulus larvae on the 

 collectors in 1969-70 (the hatchings of January- 

 March 1969) and low density of early juveniles, it 

 was predicted by Chittleborough and Phillips in 

 1971 (Anonymous 1974) that low catch levels 

 would be likely in 1972-73 and even lower levels 

 likely at the opening of the 1973-74 season (i.e., 

 the "whites" of November and December 1973). 

 This prediction was borne out by the catches of 

 these 2 years (Anonymous 1974), the white sea- 

 son of 1973 being the poorest on record, particu- 

 larly in the Fremantle area (reflecting trends 

 observed in the Garden Island research area). 



It was pointed out by Chittleborough and Phil- 

 lips (1975) that the appearance of a very strong 

 settlement, such as that resulting from the hatch- 

 ings of 1974 at Seven Mile Beach, did not neces- 

 sarily mean that a high level of recruitment to 

 the fishery could be predicted for the 1977-78 

 and 1978-79 seasons. The preceding year classes 

 were relatively strong so that the year class of 

 1974 faced intense competition and high mortal- 

 ity while on the "nursery" reefs. Nevertheless, 

 the 1978 "white" catch rate was the second high- 

 est on record. 



Figure 3 shows that in fact a good relationship 

 does exist between the level of settlement of the 

 puerulus and the subsequent catch rate (mea- 

 sured as the catch per pot lift) of the "whites" 4 yr 



later. (Proportion of sum of squares accounted 

 for is 0.574.) The relationship is well described 

 by a Ricker (1958) stock-recruitment curve, fitted 

 by the method of Cushing and Harris (1973). 

 Parameter estimates and their standard errors 

 (SE) are A = 0.048, SE = 0.0066 and B = 0.012, 

 SE = 0.0018. A similarly good relationship is 

 achieved by using the puerulus settlement data 

 from Seven Mile Beach only; this is to be expected 

 because of their close correlation with the annual 

 index of settlement (r = 0.966, P<0.01). 



Since the "whites" catch contributes about 40% 

 of the total catch of any one season, it follows 

 from Figure 3 that there should also be a good 

 relationship between the level of puerulus settle- 

 ment in year x and the total commercial catch 

 rate of the season beginning in November, year 

 x + 4, despite the inevitable confusion of year 

 classes in catches taken after December (i.e., af- 

 ter the "whites") each season. The total commer- 

 cial catches for 1965-66 to 1978-79 are shown in 

 Table 6. The influence of the poor white catch 

 rate of 1973 and the high white catch rate of 1978 

 on total catches of these years can be clearly seen. 



Puerulus Settlement and 

 Subsequent Spawning Stock 



Whereas the relationships between the other 

 stages in the life history of P. cygnus are not influ- 

 enced by the effects of fishing mortality, the rela- 



PUERULUS SETTLEMENT 



Figure 3.— The Ricker (1958) stock-recruitment model, to- 

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

 on the index of the annual level of puerulus settlement and sub- 

 sequent catch rates of Pa nut iriis cygnus at recruitment into the 

 fishery 4 yr later. The year shown is the season of hatching of 

 the larvae. 



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