FISHERY BULLETIN: VOL. 80, NO. 3 



puerulus at settlement and those derived from 

 measurements of density of juveniles of P. cygnus 

 aged 2 or 3 yr were consistent. However, they 

 found survival to recruitment into the fishery did 

 not mirror the pattern of year-class strength at 

 or soon after settlement. The purpose of this 

 paper is to examine the changes that take place 

 in the abundance of the various stages in the life 

 history of P. cygnus including data on puerulus 

 settlement and juvenile density and to investi- 

 gate their interrelationships. 



METHODS 



The abundance of the several stages in the life 

 history of P. cygnus has been measured by vari- 

 ous methods over a number of years. The meth- 

 ods used have reflected the practical problems of 

 sampling the different stages and have included 

 catch and fishing effort data from the commer- 

 cial fishery for the adult stage, collectors com- 

 posed of artificial seaweed to catch the puerulus 

 stage, and mark and recapture studies of the 

 juveniles using baited traps. All ages and year 

 classes referred to in this paper relate to the year 

 of hatching and so include the 9-11 mo larval 

 phase. For example, the 1969 year class was 

 hatched in January-February 1969 and settled 

 as puerulus larvae between September 1969 and 

 January 1970. 



Abundance of the Breeding Stock 



The western rock lobster is confined to the 

 western coast of Australia from approximately 

 North West Cape to Cape Naturaliste (Fig. 1). 

 The majority of the commercial catch is taken 

 between lat. 28° and 32°S (Sheard 1962). The 

 coastal fishery operates from 15 November to 30 

 June of the following year although prior to 1978 

 the coastal season concluded on 14 August each 

 year. The Abrolhos Islands fishing season which 

 extended from 15 March to 14 August prior to 

 1978, now also ends on 30 June. 



The abundance of the breeding stock (i.e., 

 those females carrying external eggs) has been 

 measured since 1966 from research logbook data 

 supplied on a voluntary basis from about 200 

 boats or 25% of the commercial rock lobster fleet. 

 In addition to catch, fishing effort, and fishing 

 locality information separated into four depth 

 categories, i.e., 0-10, 10-20, 20-30, and over 30 

 fathoms, each fisherman records his daily catch 

 of numbers of spawning female rock lobsters. 



20° S 



2V 



28' 



32' 



36' 



North West Cape 



Indian Ocean 



Abrolhos Islands':. 

 Rat Is/* 



Rottnest /s. 

 Garden Is. 



Cape Naturaliste 



108° E 



112' 



116' 



720° 



FIGURE 1.— Location of the sites mentioned in the text. 



However, these data are not available from the 

 Abrolhos Islands for December, January, and 

 February since this area is closed to commercial 

 fishing at this time each year. Consequently, 

 comparable data on the breeding stock had to be 

 obtained from research vessel cruises to each of 

 the four island groups of the Abrolhos during 

 January and February 1979. Sixty commercial 

 wire beehive pots without escape gaps were set 

 each day for a total of 20 d on the fishing grounds 

 where the greatest concentration of spawning 

 females is to be found. The pots had previously 

 been calibrated in the Garden Island area (Fig. 

 1) by comparison with commercial catch rates of 

 spawning females. During the comparison, 

 catch rates of spawning females were low (mean 

 of 0.05 animals/pot) and the variances relatively 

 large so it is not surprising that no significant 

 difference (at the 5% level) could be detected be- 

 tween the catch per pot lift of spawning females 

 by the research vessel's pots and the catch per 

 pot lift of spawning females by commercial fish- 

 ermen's pots. However, additional calibration of 

 the research vessel's pots would add confidence 

 to this conclusion. 



476 



