BROWN and CAPUTI: FACTORS AFFECTING GROWTH OF ROCK LOBSTER 



Results 



In the January 1979 exposure experiment (Group 

 I), all eight undersize animals exposed for 60 min 

 died before the second molt after exposure, while one 

 animal died from each of 0-, 15-, and 30-min exposure 

 categories leaving 7, 10, and 7 animals respectively. 



An analysis of variance on growth increment at 

 the first molt after exposure showed that exposure 

 was significant {P < 0.01) after other factors (&g., 

 sex, damage, initial size), which may have affected 

 growth, were taken into account. However, at the sec- 

 ond molt after exposure, the effect of exposure on 

 growth increment was not significant (P > 0.05). An 

 analysis of variance on the time taken (days) between 

 the last molt before exposure and first molt after 

 exposure (intern lolt period) resulted in exposure 

 being not significant. Exposure was also not signifi- 

 cant for the following intermolt period. 



In the December 1979 exposure experiment 

 (Group II), one animal died in the 0-, 15-, 30-, and 

 120-min exposure categories and two died from the 

 60-min exposure before the second molt after ex- 

 posure In this experiment, exposure had a signifi- 

 cant effect on the growth increment for both the first 

 (P < 0.001) and the second (P < 0.01) molts after ex- 

 posure. An analysis on the intermolt period for the 

 first molt after exposure showed no significant ef- 

 fect due to exposure, but exposure was significant 

 (P < 0.05) for the following intermolt period, main- 

 ly due to the low number of days between molts for 

 animals in the 120-min exposure category. 



TAGGING TRIALS 



Materials and Methods 



There are two main events in the commercial 

 fishery for P eygnus which follow molting by a large 

 proportion of the population. The first event is in 

 November-December when maturing 4-5 yr old pale- 

 shelled animals known locally as "whites" move off- 

 shore into deeper water, where the breeding stock 

 is generally situated. During the "whites" fishery, 

 about 40% of the total catch is taken (Morgan 

 1980b). The second event is in March-April when 

 postmolt, dark-shelled, sedentary animals called 

 "reds" are captured (George 1958; Morgan 1977). As 

 already mentioned in Brown and Caputi (1983), ac- 

 count had to be taken of these two periods when 

 planning tagging trials as the migratory "whites" 

 could be more mobile and in a physiologically dif- 

 ferent state than nonmigratory "reds" and hence 



their growth could be affected differently by 

 handling practices (i.e., causing exposure, displace- 

 ment, and damage). With these possible differences 

 in mind, three tagging trials were conducted at Two 

 Rocks, Western Australia (lat. 31°29.7'S, long. 

 115°3rE), avoiding the period of the full moon, when 

 catches are at their lowest (Morgan 1974, 1977): 1) 

 migratory "whites" phase— 26 November to 10 

 December 1978; 2) nonmigratory "reds" phase— 19 

 February to 10 March 1979; and 3) migratory 

 "whites" phase— 16 November to 9 December 1979. 

 An area consisting of shallow limestone reefs (6-18 

 m depth) within 6 km of shore and stretching from 

 Two Rocks Marina to the mouth of Moore River was 

 fished with standard wire beehive pots without 

 escape gaps (Bowen 1971; Morgan and Barker 1974). 

 Pots were baited daily with a variety of fresh fish; 

 heads of Australian salmon, Arripis trutta; and 

 bullock hocks. 



Tagging Trial A 



An experimental area was established, consisting 

 of a grid on which pots were set and undersize 

 lobsters could be displaced distances of 0, 230, 460, 

 910, 1,370, and 1,830 m from a base Hne of ex- 

 perimental pots where they were captured (Brown 

 and Caputi 1983). Pots were pulled each morning 

 during the trial, weather permitting. Undersize (66 

 to <76 mm) lobsters were tagged with a numbered 

 western rock lobster tag (Chittleborough 1974b) and 

 their carapaces measured to the nearest 0.1 mm. 

 Also recorded was the animal's damage, sex, and the 

 depth and bottom type where it was caught and 

 released. Grid areas were generally fished only once 

 to avoid recapturing previously tagged animals. 

 Recaptures of tagged animals were made by com- 

 mercial fishermen who were paid a reward for the 

 tag and market value for the animal if it had molted 

 to legal size See Brown and Caputi (1983) for com- 

 plete details of experimental procedures. Number of 

 releases for this trial was about 1,500. 



Tagging Trial B 



Procedure for trial B was the same as trial A ex- 

 cept that the 1,370 m transect was not set and ex- 

 posure categories of 0, 30, 60, 120, and 180 min were 

 also examined. Exposed undersize lobster were 

 placed in plastic prawn baskets (lug baskets; com- 

 monly used by fishermen to sort their catch) and ex- 

 posed to air for the desired period before release at 

 one of the displacement transects. About 2,300 tag- 

 ged animals were released. 



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