Worthington et al.: Alternative size limits for Haliotis rubra in New South Wales, Australia 



557 



where their average growth was slower (Fig. 

 6). The residuals of the general growth model 

 were significantly higher at sites such as those 

 at Broughton Island, Sydney II, and Eden II 

 than at Eden I, which was, in turn, significantly 

 higher than Merrys Beach and Sydney I, or 

 Bittangabee Bay Otests, P<0.05; Fig. 6). This 

 ranking corresponds closely with the estimates 

 of average growth rates in Table 1. The residu- 

 als of the relation between length and the inde- 

 pendent variables width, weight, and ridge were 

 generally higher at sites where growth was also 

 high (Fig. 6). That is, given their width, weight, 

 and ridge, abalone at sites where they grew 

 quickly were longer than those where they grew 

 slowly. Alternatively, shells of abalone of a given 

 length at sites where they grew quickly were 

 thinner, lighter, and had a smaller ridge than 

 those at sites where they grew slowly. 



Discussion 



Patterns in growth 



The intense spatial variation in growth that we 

 observed for Haliotis rubra in NSW appears to 

 be characteristic of abalone populations world- 

 wide (Day and Fleming, 1992). At the smallest 

 spatial scale, there was significant variation in 

 the growth rate of abalone within sites. At a 

 larger scale, both average rates of growth and 

 the magnitude of within-site variation differed 

 among sites separated by only 1—20 km. Per- 

 haps the most likely explanation for variation 

 in growth over these smaller spatial scales in- 

 volves variation in the supply of food, related 

 to local habitat and hydrographic conditions 

 (Day and Fleming, 1992). At the largest spatial 

 scale, average growth rates at the two sites on 

 Broughton Island were significantly higher 

 than all others. Broughton Island is approxi- 

 mately 300 km farther north than any of the 

 other sites, and abalone around the island are 

 likely to be exposed to higher water tempera- 

 tures than abalone farther south. Water tem- 

 perature is known to affect the growth rate of 

 abalone (Day and Fleming, 1992), but the trend 

 in NSW stands in contrast to that found for H. rubra 

 in Tasmania, where abalone grow more slowly in the 

 warmer, northern areas (Nash, 1992). 



Several previous studies have found a relation be- 

 tween the rate of growth and maximum size of aba- 

 lone at a site (Shepherd and Hearn, 1983; McShane 

 et al., 1988; Sloan and Breen, 1988; Nash, 1992). In 



120 



B 4.50 



£ 4.251 



Merrys Beach 



C » 



Sydney II 



r = 0.44 



90 



100 110 



Length (mm) 



120 



Figure 5 



Relationship between shell length and (A) shell width, (B) shell 

 weight, and (C) shell ridge for blacklip abalone, Haliotis rubra, 

 recaptured from two sites. Filled circles and arabic numerals 

 denote abalone from Sydney II, and open squares and roman 

 numerals denote abalone from Merrys Beach. Numerals denote 

 the number of coincident points, and the lines were fitted by least- 

 squares. 



general, abalone at sites where they grow quickly 

 reach larger sizes than those at sites where they grow 

 slowly. A similar situation appears to exist in NSW 

 where abalone from the two sites on Broughton Is- 

 land had the fastest average growth rates and 

 reached the largest shell lengths (i.e. >150 mm, Table 

 1). In comparison, the slowest average growth rates 



