Gorfine et al.: Two methods for estimating abundance of Haliotis rubra 
449 
agement zone against a background of increases and 
decreases at different sites within that zone. Al- 
though the Monte Carlo simulations predict that, 
with the use of transects, such overall changes should 
become detectable within several years, it is obvious 
that a much longer time series than three years is 
required to determine if significant interannual 
changes form part of a trend in abundance. In addi- 
tion to the temporal scale required for effective moni- 
toring of abalone stocks, there is also the issue of 
selecting an appropriate spatial scale over which to 
sample. Many abalone fisheries are managed in spa- 
tial units involving several hundreds of kilometres 
of coastline, and the relatively high cost of fishery- 
independent surveys ensures that compromises must 
be made to maximize the benefits from stock assess- 
ment programs. Consequently, the biologist investi- 
gating abalone is faced with selecting between a lim- 
ited number of intensive surveys of substocks over 
small spatial scales and extensive surveys that are 
less detailed but at the scale over which the fishery 
is managed (McShane et al., 1994). In their discus- 
sion of the design of surveys for abundance indices, 
Hilborn and Walters (1992) favored extensive sur- 
veys with low sampling intensities that cover the 
entire fishing grounds. Their preference for many 
sampling stations and minimal effort per station has 
recently been supported by Van der Meer’s ( 1997 ) study. 
This is the approach we are currently using to survey 
abalone stocks in Victoria, although we maintain rela- 
tively high within-site replication to allow greater pre- 
cision for site means. Whether power is traded off 
against precision depends on the extent to which infer- 
ences are to be drawn regarding individual sites. 
Acknowledgments 
We would like to thank staff at MAFRI who provided 
assistance to the Abalone Stock Assessment Program 
Team in the development and implementation of 
abalone stock assessment surveys. In particular, we 
thank Mike Callan, Cameron Dixon, Mark Ferrier, 
Steve Frlan, and Bruce Waters who performed much 
of the scientific diving for this study. Nik Dow as- 
sisted with experimental design and statistical analy- 
sis. Miriana Sporcic provided statistical advice on 
the final version of the manuscript. We also thank 
Dave Allen and Murray Smith, who provided their 
expertise and experience in conducting abalone dive 
surveys, and the Abalone Fishermen’s Co-operative 
Ltd. (Mallacoota), who provided vessel support for 
investigations in the eastern zone. Cameron Dixon 
assisted with data manipulation, Monte Carlo simu- 
lations, and the production of figures. Rob Day, An- 
thony Hart, and David Smith provided many valu- 
able suggestions for improving this manuscript. Fi- 
nally, three anonymous reviewers provided construc- 
tive comments on a previous draft. 
Literature cited 
Breen, P. A. 
1992. A review of models used for stock assessment in aba- 
lone fisheries. In S. A. Shepherd, M. J. Tegner, and S. A. 
Guzman del Proo (eds.), Abalone of the world: biology, fish- 
eries and culture, p. 253-275. Blackwells, Oxford. 
Day, R. W., and G. P. Quinn. 
1989. Comparisons of treatments after an analysis of vari- 
ance in ecology. Ecol. Mono. 59:433-463. 
Hart, A. M., and H. K. Gorfine. 
1997. Abundance estimation of blacklip abalone (Haliotis 
rubra ) II. A comparative evaluation of catch-effort, change- 
in-ratio, mark-recapture and diver-survey methods. Fish. 
Res. 29:171-183. 
Hilborn, R., and C. J. Walters. 
1992. Quantitative fisheries stock assessment: choice, dy- 
namics and uncertainty. Chapman and Hall, New York, 
NY, 570 p. 
Keppel, G. 
1991. Design and analysis: a researcher’s handbook, 3rd 
ed. Prentice-Hall, Englewood Cliffs, NJ, 594 p. 
Marks, A. D., and T. L. Fallowfield. 
1994. A retrospective study of decompression illness in rec- 
reational SCUBA divers and SCUBA instructors in 
Queensland. In Queensland diving industry workplace 
health and safety committee, proceedings of safe limits: 
an international dive symposium, Cairns, October 1994, 
p. 52-59. Worksafe, Australia. 
McShane, P. E. 
1994. Estimating the abundance of abalone ( Haliotis spp. ) 
stocks — examples from Victoria and southern New Zea- 
land. Fish. Res. 19: 379-94. 
1995. Estimating the abundance of abalone: the importance 
of patch size. Mar. Freshwater Res. 46:657-62. 
McShane, P. E,, K. H. H. Beimssen, and S. Foley. 
1986. Abalone reefs in Victoria: a resource atlas. Victorian 
Department of Conservation, Forests and Lands, Marine 
Science Laboratories Technical Report Series 47, 50 p. 
McShane, P. E., S. F. Mercer, and J. R. Naylor. 
1994. Spatial variation and commercial fishing of New 
Zealand abalone (Haliotis iris and H. australis). N. Z. J. 
Mar. Freshwater Res. 28:345-55. 
McShane, P. E., and M. G. Smith. 
1989. Direct measurement of fishing mortality in abalone 
(Haliotis rubra Leach) off southeastern Australia. Fish. 
Res. 8:93-102. 
1990. Victorian abalone monitoring: first review August 
1990. Victorian Department of Conservation, Forests and 
Lands, Marine Science Laboratories, Program Review Se- 
ries 100, 47 p. 
1992. Shell growth checks are unreliable indicators of age 
of the abalone Haliotis rubra (Mollusca: Gastropoda). 
Aust. J. Mar. Freshwater Res. 43:1215-19. 
Nash, W. J., T. L. Sellers, S. R. Talbot, A. J. Cawthorn, and 
W. B. Ford. 
1994. The population biology of abalone ( Haliotis species) 
in Tasmania. I. Blacklip abalone (H. rubra) from the north 
