Abstract. Growth of the blacklip 



abalone, Haliotis rubra, was estimated 

 from 1,464 individuals that were tagged 

 and left at large for up to five years at 

 seven sites in New South Wales, Aus- 

 tralia. Both the shape of the fitted 

 growth curves and the average growth 

 rates differed significantly among sites, 

 separated by only 1-20 km. There was 

 also significant variation in the growth 

 of individual abalone within sites and 

 this variation differed among sites. 

 Abalone at sites where they grew 

 quickly reached larger lengths and 

 were morphologically different from 

 those at sites where they grew slowly. 

 For example, the shells of abalone from 

 sites where they grew slowly were 

 wider and heavier at a given length 

 than those from sites where they grew 

 quickly. The implication that rates of 

 growth in width are less variable than 

 growth in length suggests that a mini- 

 mum legal width limit may be more 

 appropriate than the present size limit 

 that is based on length. A minimum 

 legal width limit would redistribute 

 fishing effort away from sites where 

 abalone grow in length quickly towards 

 sites where they grow slowly, including 

 sites which are presently unfished be- 

 cause few individuals reach the mini- 

 mum legal length. If this were possible, 

 it would reduce the differences in exploi- 

 tation among sites which, at present, 

 have the potential to seriously deplete 

 populations at sites where individuals 

 grow quickly. 



Covariation between growth and 

 morphology suggests alternative 

 size limits for the blacklip abalone, 

 Haliotis rubra, 

 in New South Wales, Australia 



Duncan G. Worthington 

 Neil L. Andrew 

 Gary Hamer 



NSW Fisheries Research Institute 



RO. Box 21. Cronulla NSW 2230 Australia 



Manuscript accepted 24 January 1995. 

 Fishery Bulletin 93:551-561 (1995). 



Legal restrictions on the minimum 

 size of individuals allowed to be 

 harvested are used to manage many 

 fisheries. The theory behind their 

 use asserts that by delaying the 

 harvest of individuals until they 

 have grown to a certain size, both 

 yield and egg production can be in- 

 creased (Beverton and Holt, 1957). 

 Appropriate minimum size limits 

 have traditionally been estimated 

 by considering average rates of 

 growth, mortality, and reproduction 

 (Goodyear, 1993). Spatial variation 

 in demography can complicate the 

 use of a single size limit for a stock 

 by making different size limits ap- 

 propriate in different areas. En- 

 forcement of different size limits 

 over large spatial scales is possible 

 (e.g. Guzman del Proo, 1992), but if 

 demography varies over small dis- 

 tances, appropriate size limits are 

 difficult to enforce. 



A common finding of studies on 

 the growth of abalone has been that 

 individuals at different sites can 

 grow at markedly different rates 

 (Sainsbury, 1982; Breen, 1986; 

 Tegner et al., 1989). Despite this, 

 there have been few systematic at- 

 tempts to determine the spatial 

 scale over which differences in 

 growth occur (see Day and Fleming, 

 1992, for a review). Nonetheless, it 



is apparent that growth can vary 

 among regions separated by hun- 

 dreds of kilometers (Nash, 1992) 

 and among sites separated by tens 

 of kilometers (Breen, 1986). As well 

 as differing in their rate of growth, 

 abalone that grow quickly will, in 

 general, reach larger sizes than aba- 

 lone that grow slowly (e.g. McShane, 

 1992; Nash, 1992). Consequently, 

 many abalone fisheries contain 

 populations with individuals that 

 grow very slowly to only small sizes 

 (Sloan and Breen, 1988; Tegner et 

 al., 1989; Nash, 1992). Because 

 minimum legal sizes are, in general, 

 enforced over areas larger than 

 those over which such variation in 

 growth can occur, these sites often 

 remain unfished. 



Commercial fishing of abalone 

 Haliotis rubra in New South Wales 

 (NSW), Australia began in the early 

 1960's. Initially, divers harvested 

 abalone of any size, but in 1973 a 

 minimum legal length limit of 100 

 mm was introduced. This length 

 limit was chosen to ensure that aba- 

 lone recruiting to the fishery had 

 reproduced at least once after 

 reaching sexual maturity at ap- 

 proximately 80-90 mm. As fishing 

 pressure increased through the 

 1970's and 1980's, it became appar- 

 ent that the length limit of 100 mm 



551 



