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Fishery Bulletin 108(4) 
ment plans for conserving their populations (Frisk et 
al., 2001; Stobutzki et al., 2002; Walker, 2005b). 
Most of the species in Australia’s rich diversity of 
elasmobranchs are endemic and occupy demersal habi- 
tats on the continental shelf or slope (Last and Ste- 
vens, 2009) and are thus potentially prone to depletion 
by demersal fishing methods such as trawling, gill- 
netting, and longlining (Stobutzki et al., 2001, 2002; 
Coelho et al., 2003; Perez and Wahrlich, 2005, Walker 
et al., 2005). Analyses of fisheries data for 1994 to 
1999 showed that the bycatch species Heterodontus 
poi'tusjacksoni (Heterodontidae) and Myliobatis australis 
(Myliobatidae) are abundant in catches of the temperate 
demersal gillnet and longline fisheries of southwestern 
Australia (McAuley and Simpfendorfer, 2003). These 
two species and the rhinobatid Aptychotrema vincentia- 
na and the squatinid Squatina australis, which are also 
caught as bycatch by commercial fisheries, collectively 
contributed as much as 17% to the total biomass of the 
172 species of fish caught during extensive trawling 
along the lower west coast of Australia (Hyndes et al., 
1999). It has been estimated that approximately half 
of the elasmobranchs taken as bycatch by commercial 
trawlers in this region are likely to die during or after 
capture (Laurenson et al. 1 ). Despite the potentially det- 
rimental effects of commercial fishing on the above four 
elasmobranch species and their ecological importance in 
the temperate waters of southern Australia, sound bio- 
logical data have been collected only for H. portusjack- 
soni (McLaughlin and O’Gower, 1971; Tovar-Avila et al., 
2007; Jones et al., 2008; Powter and Gladstone, 2008). 
The families to which the above four species belong 
are represented elsewhere in the world by species that 
are taken in substantial numbers as bycatch. For ex- 
ample, in the eastern Pacific, up to a thousand individu- 
als of the heterodontid shark Heterodontus mexicanus 
may be caught in a single gillnet set, many of which die 
(Garayzar, 2006). In some parts of the world, the popu- 
lations of several species of rhinobatid and squatinid 
have been so drastically depleted from overfishing that 
they have been listed as critically endangered (Morey 
et al., 2006; Lessa and Vooren, 2007). In eastern Aus- 
tralia, the commercial landings of Myliobatis australis 
have been steadily increasing to the point where their 
stocks now need to be monitored (White et al., 2006). 
The first aim of the present study was to determine 
the numbers, and thereby the percent contributions, of 
the females and males of each shark and ray species in 
samples of commercial catches taken in southwestern 
Australian waters by demersal trawling for prawns and 
scallops and by demersal gillnetting and longlining for 
sharks. These data enabled the percent contributions 
made by the bycatch and byproduct to the total elasmo- 
1 Laurenson, L. J. B., P. Unsworth, J. W. Penn, and R. C. J. 
Lenanton. 1993. The impact of trawling for saucer scallops 
and western king prawns on the benthic communities in 
coastal waters off south-western Australia, 93 p. Fisheries 
Res. Report, Department of Fisheries, no. 100 (part 1), Western 
Australia. 
branch catch to be estimated for each fishing method. 
The percent contributions of each species to the catches 
obtained by trawling, gillnetting, and longlining were 
then used to compare statistically the species composi- 
tions of the elasmobranchs in the catches taken by each 
of these fishing methods. 
Emphasis was next placed on determining the length 
compositions of the bycatch species H. portusjacksoni, 
A. vincentiana, S. australis , and M. australis in samples 
collected by trawling, gillnetting, and longlining and 
on estimating the lengths at maturity of the last three 
of these ecologically important species. The lengths of 
both the females and males at which 50% are mature 
(L 50 ) were first determined by using gonadal data as the 
criterion for determining maturity and then, in the case 
of males, by employing full clasper calcification as that 
criterion. The L 50 calculated for the males of each species 
by using the two maturity criteria were then compared 
to ascertain whether the L 50 derived by using clasper cal- 
cification as the index of maturity is a reasonable proxy 
for that derived using gonadal stage as that criterion. 
The L 50 at maturity of A. vincentiana, S. australis, and 
M. australis and of H. portusjacksoni (Jones et al., 2008) 
were then employed to determine the proportions of both 
sexes of each of these four species that were caught by 
each fishing method before they had the opportunity to 
reproduce. Finally, the management and conservation 
implications of our data are considered. 
Materials and methods 
Sampling regime 
The elasmobranchs were examined in commercial catches 
from 69 demersal trawls, 24 demersal gillnets, and 19 
longline sets of fishing vessels operating in southwestern 
Australian waters southwards of 32° S lat. on the west 
coast and then eastwards to 118° E long, on the south 
coast (Fig. 1). Trawling targets the western king prawn 
(Melicertus latisulcatus) and the Ballot’s saucer scallop 
(Amusium balloti), whereas demersal gillnetting and 
longlining target mainly the gummy shark (Mustelus 
antarcticus ), the dusky shark ( Carcharhinus obscurus), 
and the whiskery shark ( Furgaleus macki) (McAuley 
and Simpfendorfer, 2003). Sampling, which was under- 
taken between November 2002 and November 2008, 
was designed to ensure that the catches of each fishing 
method were sampled at least once, and generally on 
at least three occasions, in each season of the calendar 
year. The trawl, gillnet, and longline fishermen, whose 
catches were selected for sampling, were those that 
fished regularly and readily allowed us onboard, and 
whose methods were representative of those used in the 
area that is fished. The numbers of each elasmobranch 
species caught by each fishing method on each sampling 
occasion were recorded, as also were the sexes of all 
individuals except for those of a few species in a small 
number of trawl samples when the catches of those spe- 
cies were particularly large, in which case the sexes of 
