STOCK AND RECRUITMENT RELATIONSHIPS IN 



PANULIRUS CYGNUS,* THE COMMERCIAL 



ROCK (SPINY) LOBSTER OF WESTERN AUSTRALIA 



G. R. Morgan, 2 B. F. Phillips, 3 and L. M. Joll* 



ABSTRACT 



r 



Abundance of the breeding stock, level of settlement of the puerulus stage, juvenile densities and 

 recruits to the fishery for Panulirus cygnus from 1969 to 1979 are examined. 



A dome-shaped relationship between the index of abundance of the breeding stock and subsequent 

 puerulus settlement indicates that stock-dependent effects during the planktonic larval stages 

 apparently control the level of puerulus settlement. However, density-dependent relationships 

 (characterized by more asymptotic relationships between the various life history stages) dominate 

 after settlement of the puerulus on the coastal reefs and control the level of recruitment to the fishery 

 and eventually to the breeding stock. The relationship between the settlement of the puerulus stage 

 and the catch rates of the recruits entering the fishery 4 years later is adequately described by a 

 Ricker's stock-recruitment curve as is the level of puerulus settlement to the subsequent abundance 

 of the breeding stock. The relationship between the level of puerulus settlement and the later abun- 

 dance of juveniles at various ages is not clear and possible reasons for this are suggested. 



The significance of the stock-dependent relationship between breeding stock and puerulus and the 

 density-dependent relationship between puerulus and breeding stock in maintaining recruitment to 

 the fishery is discussed. 



The importance of understanding the stock-re- 

 cruitment relationship in exploited fish popula- 

 tions has been recognized for many years and has 

 been the subject of several workshops and sym- 

 posia (e.g., Parrish 1973), as well as a great deal 

 of research. While the importance of such rela- 

 tionships in exploited invertebrate stocks has 

 been equally recognized, quantitative data, par- 

 ticularly for crustaceans, has been virtually non- 

 existent (Hancock 1973). 



Like many fish species, crustaceans in general 

 and spiny (rock) lobsters in particular, pass 

 through several distinct stages in their life his- 

 tory and, as Hancock (1973) pointed out, a proper 

 understanding of the overall stock-recruitment 

 relationship can be gained only by considering 

 the relationship between successive stages over a 

 number of years. Hancock's belief is reinforced 

 by the studies of Larkin et al. (1964) and Paulik 

 (1973) who, having considered the theoretical 



'The western rock lobster is referred to as P. longipes or P. 

 longipes cygnus in some of the literature quoted; these are 

 synonymous with P. cygnus. 



department of Fisheries and Wildlife, 108 Adelaide Ter- 

 race, Perth, 6000, Western Australia. 



3 CSIRO, Division of Fisheries Research, P.O. Box 21, Cro- 

 nulla, N.S.W. 2230 Australia. 



4 CSIRO, Division of Fisheries Research, P.O. Box 20, North 

 Beach, W.A. 6020 Australia. 



Manuscript accepted January 1982. 

 FISHERY BULLETIN: VOL. 80. NO. 3, 1982. 



forms of a stock-recruitment relationship in- 

 volving such multistage life histories, showed 

 that several stable equilibrium points can exist 

 in the overall spawning stock-recruitment curve, 

 depending on the relationships existing between 

 the various life history stages. 



The western rock lobster, Panulirus cygnus 

 George, the object of an important fishery in 

 Western Australia (Morgan and Barker 1979) 

 passes through several major stages during its 

 life history. These include a series of phyllosoma 

 larvae, a puerulus stage, and juvenile and adult 

 stages. After a planktonic life of 9-11 mo (Chittle- 

 borough and Thomas 1969; Phillips et al. 1979), 

 the surviving phyllosoma larvae metamorphose 

 into a puerulus stage and settle between Septem- 

 ber and January each year in shallow coastal 

 areas. The younger juveniles concentrate on 

 shallow limestone reefs to depths of 10 m, with 

 some larger juveniles to 20 m. At about 4 or 5 yr 

 of age (i.e., 4 or 5 yr from hatching) juveniles mi- 

 grate from the shallow reef areas onto the conti- 

 nental shelf into depths of 30-150 m where ma- 

 turity is reached, mating takes place, and the life 

 cycle is completed. 



Chittleborough and Phillips (1975) reported 

 that, based on the data available at that time, in- 

 dices of year-class strengths obtained from the 



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W- HYU. 



