440 
Fishery Bulletin 96(3), 1 998 
plied breathing apparatus (SSBA) with an umbilical 
length of 100 m. 
Prior to a dive, each diver was randomly allocated 
three or four compass bearings. On the bottom, each 
diver oriented himself towards the appropriate com- 
pass bearing and tucked the floating transect-line 
under his arm. Each diver was instructed to use a 
plastic laboratory tally counter to count, or an aba- 
lone iron to collect (depending on the study), emer- 
gent abalone larger than 50-mm shell length within 
an approximately 1-m wide strip from the 5-m mark 
laterally along the transect line. Abalone smaller 
than 50 mm were ignored because previous experi- 
ence had shown that these juveniles were difficult to 
locate and were likely to be subject to large sampling 
errors among divers. Where estimates of the abun- 
dance of juvenile abalone were required, cryptic habi- 
tat within the transect was searched thoroughly by 
overturning boulders and examining crevices. These 
searches for juveniles were relatively time consum- 
ing. The width of the transect was constrained by 
the distance from the transect line under the diver’s 
armpit to the hand of the outstretched arm on the 
opposite side of the diver’s body. When abalone were 
not collected, separate counts of prerecruit abalone, 
i.e. those individuals smaller than the legal mini- 
mum length (LML), and of postrecruited abalone 
(larger than the LML) were made with a simple mea- 
suring gauge for discrimination. Each diver covered 
a linear distance of 30 m to survey an area of about 
30 m 2 per transect. Any part of an aggregation of 
abalone falling outside the designated 1-m width was 
not included in the count. Underwater counts were 
made in instances where the removal of abalone 
would have interfered with further surveys of the 
study sites. However, during routine stock monitor- 
ing, abalone were collected and taken aboard the 
research vessel to obtain length-frequency data. 
Each diver made additional collections in differ- 
ent directions radiating from the same point before 
surfacing. Total bottom time for each dive was usu- 
ally between 30 and 60 minutes. 
Timed searches The timed search method was the 
same as that described by McShane (1994), where 
each diver made timed searches at randomly selected 
subsites within each site previously surveyed by ra- 
dial transects. Commencing at the research vessel’s 
anchor, a pair of divers independently collected as 
many abalone as possible within a subsite in 10 min- 
utes, using a nylon mesh catch bag and an abalone 
iron for removing the abalone off rocky substrata. 
Divers were free to search as much area as their sur- 
face air supply hose would allow (about a 100-m ra- 
dius from the research vessel). 
Operator effects on methods 
Diver effects on radial transects Variation among 
divers and each diver’s precision with radial transects 
were investigated at Gabo Island near Mallacoota 
(Fig. 1). Precision was defined as the level of congru- 
ency among an individual diver’s repeated counts of 
the same transect. A team of four scientific divers, 
each experienced in radial transects, completed two 
experiments at a fixed site. The objective of the first 
experiment was to estimate the precision of abalone 
counts by each diver. This was done by randomly 
assigning three transects from a set of twelve to each 
diver and by having them repeat abalone counts along 
the three allocated transects four times. Precision esti- 
mates for each diver were obtained as the quotients of 
the standard errors of the four counts for each transect 
divided by their mean count and were compared be- 
tween divers by a one-way analysis of variance. 
The second experiment compared differences 
among divers’ abundance estimates. Each of the four 
divers completed counts along each of the twelve 
transects used in the first experiment. An analysis 
of variance was performed to test the hypothesis that 
differences among divers’ mean abalone counts were 
not significantly different. 
During both experiments, the reference shot-line 
remained undisturbed. Sea conditions were consis- 
tent throughout the day. Surge was slight and hori- 
zontal underwater visibility was about 10 m. The 
study site provided bottom topography that ranged 
from high relief with deep crevices to open ground 
with scattered boulders. 
Comparison of diver effects on radial transect and 
timed search survey methods Timed search and 
radial transect methods were compared during aba- 
lone abundance surveys conducted on reefs at Cape 
Schanck, Point Cook, and Williamstown (Fig. 1). 
These reefs were selected to provide variety in to- 
pography, sea conditions, and abalone population 
structure. One site was selected at random on each 
of the three reefs. We tested the hypothesis that there 
were no significant differences in abalone abundance 
estimates between research divers for either sam- 
pling method. Sea conditions at each site were con- 
sistent between sampling methods but varied be- 
tween the sites. In Port Phillip Bay (Point Cook and 
Williamstown) wind was slight, swell height was 
negligible, there was no surge, and horizontal under- 
water visibility was less than 3 m, whereas at Cape 
Schanck there was considerable surge (swell height 
1-2 m) and underwater visibility was about 6 m. 
Two experienced scientific divers, each expert in 
one of the techniques (>300 dives) but neither hav- 
