MORGAN ET AL.: STOCK AND RECRUITMENT RELATIONSHIPS IN PANUURUS CYGNUS 



Abundance of the Puerulus Stage 



Phillips (1972) showed that the last larval 

 stage, the puerulus, of P. cygnus could be cap- 

 tured using collectors composed of artificial sea- 

 weed moored at the surface within the protection 

 of the coastal reefs. Subsequent studies by Phil- 

 lips and Hall (1978) have shown that the catches 

 from these collectors provide a measure of the 

 relative strength of settlement from year to 

 year. 



All collectors used in this study were as de- 

 scribed by Phillips (1972). The collectors were 

 checked monthly after each new moon period 

 when most puerulus settled. All settlement took 

 place at the puerulus stage. The western rock 

 lobsters were removed from the collectors either 

 as puerulus or after they had molted into very 

 small postpuerulus juveniles. Since the plank- 

 tonic period is 9-11 mo, settlement occurs be- 

 tween September of the year of hatching and the 

 following January. 



Abundance of Juveniles 



Density of age groups (ages 2-7 yr) has been 

 measured on shallow test reefs at Garden Island 

 (since 1965) and Seven Mile Beach (since 1970), 

 using the single census trap-mark-recapture 

 method described by Chittleborough (1970). 

 These test reefs are adjacent to the collectors 

 used to catch the puerulus stage. 



Abundance of Recruits to 

 the Fishery 



During late November of each year, large 

 numbers of immature, newly molted, pale col- 

 ored rock lobsters migrate into deeper water 

 from the shallow water inshore reefs (which are 

 generally inaccessible to fishermen) where they 

 have spent the previous 4 or 5 yr. This offshore 

 movement normally lasts through December 

 and in all lasts about 6 wk. Since they are newly 

 molted, their food requirements are high (Chit- 

 tleborough 1975) and consequently their catch- 

 ability by baited pots is high (Morgan 1974). 

 During this migration the fishermen catch large 

 quantities of these animals which are locally 

 known as the "whites" (George 1958). Although a 

 small number of animals undergo two or per- 

 haps three "white" phases in their life cycle, the 

 "white" phase generally occurs only once during 

 an individual's lifetime (George 1958), and this 



enables the migrating "whites" to be equated 

 with the recruits to the fishery. 



Estimates of the abundance of the potential 

 emigrants from the shallow reefs have been 

 made by Chittleborough (1970), although a better 

 measure of their abundance is available from the 

 catch rate (measured as the catch per pot lift) of 

 the commercial fishery during November and 

 December when practically all of the commer- 

 cial catch consists of "white" rock lobsters. Infor- 

 mation on catch and fishing effort for November 

 and December each year has been taken from the 

 fishermen's monthly returns, which are com- 

 pleted as a condition of the fishing license by all 

 fishermen. 



RESULTS 



Since there have been several customs adopted 

 in the designation of year classes in P. cygnus 

 (e.g., Chittleborough 1970; Morgan 1977) a sum- 

 mary of the convention used in this paper will 

 enable the various relationships presented below 

 to be followed more easily. The convention used 

 and the major events in the life history of P. 

 cygnus are as follows: 



Hatching of eggs 



Settlement of 

 puerulus larvae 



Juveniles on 

 inshore reefs 



Migration of 

 "whites" to 

 offshore areas 



Maturity and 

 first breeding 



November, December year 

 x — 1, January, February, 

 and March year x, with 

 midpoint taken as 1 Janu- 

 ary of year x. 



September year x to Janu- 

 ary year x + 1. 



Year x + 1 to x + 4 and x+5 

 (ages 1 to 4 or 5). 



November and December 

 year x + 4 and x + 5, with 

 the majority being x + 4. 



January and February year 

 x + 6 and x + 7, with the 

 majority being x + 6. 



Stock Definition 



Based on similarities in catch rates from the 

 commercial fishery, Morgan (1977) concluded 

 that although some population parameters such 

 as growth rates, size at first maturity, etc. varied 

 between localities, the western rock lobster 

 could, as a first approximation, be considered as 

 a single, genetically coherent, unit stock. This 

 view is reinforced by the studies of Phillips et al. 

 (1979) who demonstrated the wide dispersal of 



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