558 



Fishery Bulletin 93(3). 1995 



1 SI 



MB 





HI 



+ 



[SII 



[SII 



Bn 1 



-113 5 



Residual (growth) 



Figure 6 



Average residual from growth and morphological relation- 

 ships for blacklip abalone, Haliotis rubra, recaptured from 

 eight sites. Vertical and horizontal bars are standard er- 

 rors. Sites are abbrieviated as follows: BI and BII = Broughton 

 Island I and II; SI and SII = Sydney I and II; MB = Merrys 

 Beach; EI and EII = Eden I and II; BB = Bittangabee Bay. 



were recorded at Sydney I where the largest abalone 

 was smaller than those at all other sites (i.e. 124 mm, 

 Table 1). Despite this general relationship, slow rates 

 of growth were recorded at Eden I, but growth was 

 expected to continue until 140 mm, and many aba- 

 lone were found over 130 mm in length. 



Direct comparison of growth rates estimated by 

 different studies are complicated by the variety of 

 methods used for tagging and analysis. For example, 

 tags attached by wire through an abalone's respira- 

 tory pore can affect growth (McShane et al., 1988), 

 and growth parameters estimated from tagging and 

 age-length data need to be interpreted differently 

 (Francis, 1988a). Any comparison of growth rates 

 among studies can also be confounded by the growth 

 model used to fit the observed increments (e.g. com- 

 pare estimates of growth from the different models 

 used in Tables 1 and 2). When fitted with a similar 

 growth model to past studies, our estimates of the 

 growth of abalone in NSW span almost the entire 

 range of those from similar studies in other states of 

 Australia (Table 2). In addition, estimates of growth 

 at the two sites on Broughton Island are consistently 

 higher than any previously reported natural growth 

 rates for the species. 



Relation of growth to morphology 



Differences in the morphology of individuals among 

 populations have been reported for a range of gas- 

 tropod species including abalone (see review by 

 Vermeij, 1980). Despite the significance of variation 



in the morphology of Haliotis rubra in NSW, differ- 

 ences among sites were not large (e.g. compare with 

 those of Breen and Adkins, 1982). There was also 

 substantial variation in the morphology of individu- 

 als within sites. Despite little evidence, explanations 

 for the variation in morphology of abalone usually 

 concentrate on environmental rather than on genetic 

 factors (McShane et al., 1988). As for other gastro- 

 pods, it is likely that all aspects of shell growth that 

 result in morphological differences are influenced by 

 a variety of factors including exposure to wave ac- 

 tion, diet, and water temperature (Tissot, 1992; Belda 

 et al., 1993). Although we only present evidence to 

 suggest that differences in morphology of the shell 

 exist among populations of Haliotis rubra, there is 

 also evidence for related morphological variation in 

 the soft tissues (McShane et al., 1988). 



Differences in the morphology of Haliotis rubra 

 among sites were related to differences in growth. 

 At sites where they grew slowly, the shells of aba- 

 lone were wider, heavier, and had a broader ridge 

 than those at sites where they grew quickly. These 

 observations are similar to those made on other spe- 

 cies of abalone (e.g. Breen and Adkins, 1982; Shep- 

 herd and Hearn, 1983; Tissot, 1988) and perhaps are 

 not surprising considering that the processes pro- 

 posed to influence both growth and morphology are 

 similar. Inclusion of the slow-growing population at 

 Bittangabee Bay strengthened the relation between 

 growth and morphology that was evident among the 

 seven sites where extensive tagging was done. Ex- 

 tensive tagging was not done at Bittangabee Bay 

 because few animals grow above the present 115-mm 

 legal length limit and hence the site is rarely fished 

 by commercial divers. Because of the relationship be- 

 tween the maximum size reached by abalone at a 

 site and their growth rate, very slow growing sites are 

 rarely visited by commercial divers and, consequently, 

 were not chosen for tagging in this study. As a result, 

 our estimates of growth represent the higher end of 

 the range of growth rates for abalone in NSW. 



The increased width and weight of shells from aba- 

 lone that grew slowly in length imply that rates of 

 shell growth in width and weight are more consis- 

 tent among sites than growth in length. This might 

 be explained by increased synthesis of the organic 

 matrix of the shell when energy is plentiful (Palmer, 

 1992) and can be devoted to expansion of the mantle 

 at the growing edge and hence to rapid growth in 

 length (Belda et al., 1993). Alternatively, when less 

 energy is available, reduced synthesis of the organic 

 matrix may result in a slower expansion of the grow- 

 ing edge of the mantle, causing slower growth in 

 length and proportionally more growth in width and 

 weight (Vermeij, 1980). Such an explanation would 



