Jones et al.: Species compositions of elasmobranchs caught by three commercial fishing methods 
377 
Compositions of the catches taken by the three 
fishing methods 
Our results indicate that the elasmobranch component of 
the catches taken by demersal trawlers on the lower west 
coast of Australia is dominated by rays, which comprise 
10 of the 14 elasmobranch species caught by this method. 
Furthermore, these batoids were either small species, 
e.g., stingarees, or represented by smaller individuals, 
e.g ., Aptychotrema vincentiana and M. australis. Indeed, 
the four small species of stingaree (Urolophidae) caught 
by trawling contributed as much as two-thirds to the 
total trawl catch of elasmobranchs and were so abun- 
dant in samples collected during an extensive trawling 
study along the lower west coast of Australia that they 
collectively contributed 17.5% to the total biomass of 
the 172 fish species caught during that study (Hyndes 
et al., 1999). The large number of small batoids caught 
paralleled the situation recorded for other trawl fisher- 
ies, including the multispecies bottom trawl fishery off 
Argentina (Tamini et al., 2006). As with the large ray 
species, the only two shark species taken in appreciable 
numbers in our study, H. portusjacksoni and S. australis, 
were represented predominantly by small individuals. 
The large number of elasmobranchs taken by prawn 
and scallop trawling emphasizes the lack of selectivity 
of this fishing method for its targeted species. Indeed, 
Bonfil 2 has stated that towed nets are the most indis- 
criminant of all fishing gears because they are designed 
to capture everything in their path and thus inevitably 
encounter a large number of nontarget species. The 
susceptibility of small demersal elasmobranchs to cap- 
ture by trawling is due to their limited mobility and 
benthic lifestyle (see also Stobutzki et al., 2001, 2002; 
Walker, 2005a; Tamini et al., 2006) and to the trawlers 
often operating in nearshore waters, which typically 
act as nursery areas for several elasmobranch species, 
including H. portusjacksoni (White and Potter, 2004; 
Jones et al., 2008; Kinney and Simpfendorfer, 2009). 
The catches of elasmobranchs taken by trawls in our 
study comprised only six individuals that were retained 
as byproduct compared with the 2980 individuals dis- 
carded as bycatch. 
Although the three species targeted by gillnetting, 
C. obscurus, M. antarcticus, and Furgaleus macki, col- 
lectively accounted for just over half of the total number 
of elasmobranchs caught by this method, the contri- 
bution of all retained species (i.e. including byprod- 
uct), accounted for three quarters of the total. This 
is very similar to the situation recorded for a gillnet 
fishery in southeastern Australia (Walker et al., 2005). 
The remainder of the catch (i.e., the bycatch) was still 
substantial, however, emphasizing that a considerable 
number of the sharks and rays caught by gillnet were 
2 Bonfil, R. 2000. The problem of incidental catches of sharks 
and rays, its likely consequences, and some possible solu- 
tions. Shark Conference 2000 online documents, 8 p. (Pacific 
Fisheries Coalition, http://www.pacfish.org/sharkcon/docu- 
ments/bonfil.html, accessed May 2010). 
discarded, as has been reported in gillnet fisheries else- 
where in the world (e.g., Perez and Warhlich, 2005). 
The mesh sizes of the gillnets (165 and 178 mm) were 
selected to catch the three targeted species, C. obscu- 
rus, M. antarcticus, and F. macki, at a marketable size 
which, depending on the species, typically corresponded 
to modal fork lengths of between 800 and 1200 mm 
(McAuley and Simpfendorfer, 2003). This mesh selec- 
tivity accounts for the fact that the TL of the majority 
of A. vincentiana and S. australis in our gillnet catch- 
es fell within a relatively narrow range of 700-1000 
mm, with the latter length closely approximating the 
maximum length recorded for these two species dur- 
ing the present study (Table 5). However, the TL for 
H. portusjacksoni, the second most abundant species 
in the gillnet catches, spanned the full range of this 
species in southwestern Australian waters (Jones et al., 
2008). The capture by gillnet of a substantial number 
of H. portusjacksoni with lengths less than 700 mm is 
attributable to the tendency for all sizes of H. portus- 
jacksoni to become entangled in gillnets as a result of 
their possessing prominent dorsal fin spines (Walker, 
2005a). In the case of the ray M. australis, the larger 
individuals were proportionately less in gillnet than 
longline catches because this wide disc-shaped species 
becomes increasingly deflected from the net as it grows 
larger (Walker, 2005a). 
Longlining was so successful at targeting M. ant- 
arcticus that this shark contributed nearly two thirds 
to the total elasmobranch catch taken by this method 
and, together with the other two targeted species, C. 
obscurus and F. macki, represented nearly 70% of that 
total catch. However, those last two species were not 
abundant in these catches. In fact, the second to fifth 
most abundant species were bycatch species. Although 
11 of the 19 nontargeted elasmobranch species were 
typically retained as byproduct, none of those species 
was numerous and collectively accounted for only ~7% 
of the elasmobranch catch. From the above, it follows 
that the contribution of bycatch to the longline catches 
(-26%) was similar to that in the gillnet catches. How- 
ever, unlike the situation with gillnetting, the bycatch 
species S. australis was never caught on longline hooks, 
presumably because this squatinid is an ambush preda- 
tor that targets mobile prey such as teleosts and cepha- 
lopods (E. Sommerville, personal commun. 3 ). 
Although the use of nMDS ordination and associ- 
ated tests emphasized that the species compositions of 
the elasmobranchs caught by trawling, gillnetting, and 
longlining differed markedly, SIMPER showed that H. 
portusjacksoni was a major typifying species for the 
elasmobranchs taken by trawling in relatively shal- 
low waters and by gillnetting and longlining in deeper 
and more offshore waters. This bycatch species is thus 
clearly abundant and widely distributed throughout the 
inshore and more offshore coastal waters of southwest- 
3 Sommerville, Emma. 2007. Centre for Fish and Fisher- 
ies Research, Murdoch Univ., Murdoch, Western Australia, 
6150. 
