436 



Fishery Bulletin 102(3) 



Southern zone 



-i — i — i — i — i — i 

 1995 1999 



octopus 



1983 

 li, dead lobster 



- 1 — i — i — i — i — i — 

 1987 1991 



— i — r — i — i — r- 

 1983 1987 



1991 



-MFA 51 

 -MFA 56 



1995 



-MFA 55 

 MFA 58 



1999 



B lobster Northern zone 

 600 

 500 

 400 - 

 300 

 200 

 100 







1983 1987 



D octopus 



-1 — I — I — 

 1991 



1995 



-T 1 1 1 1 1 1 1 T 



1983 1987 1991 1995 



>_MFA 15 g MFA 28 a MFA 39 

 MFA 40 _*_MFA 49 



Figure 5 



Annual catch rates of the major MFAs in each fishing zone for lobsters (CPUE L ) (A and Bi. 

 octopus (CPUE i i C and D), and dead lobsters (M L l (E andF). 



by other predators. The mean CL of dead male lobsters 

 was greater than live males (120 ±21.1(SD) vs. 110 ±18.3 

 (SD) mm, P<0.001). There was no significant difference 

 in the mean size of live and dead female lobsters. For 

 both sexes the probability of mortality increased with 

 size according to the following relationships: 



P (M L , males) = i/i +e -(-5.04+o.02CL) 

 P <M L , females) = m+ e -l-*.i&+o.oiCL) m 



Above 100 mm CL, the probability of mortality increased 

 more sharply for male lobsters than for female lobsters 

 (Fig. 8). 



Discussion 



Logbook data from the SARLF show that over the last 

 five years approximately 240,000 lobsters have been 



killed in traps each year. Although there are numerous 

 predators of trapped lobsters — such as seals, conger eels, 

 and several species of finfish — the impacts of these taxa 

 appear to be minor compared to the effects of predation 

 by O. maorum. The field-sampling program conducted in 

 the SZ in 2001-02 suggested that over 98% of within- 

 trap mortality was attributable to O. maorum. Although 

 the sampling program was spatially and temporally 

 restricted, this finding, in conjunction with the strong 

 correlations between annual, seasonal and spatial trends 

 in the CPUE and M, , clearly demonstrates that O. 

 maorum is the major predator of lobsters in SARLF 

 traps. 



The results of this study suggest that about 4</r of the 

 total annual catch of the SARLF is lost to predation 

 by O. maorum in traps. Mortality rates attributable to 

 octopuses in other Australian lobster fisheries range 

 from \% in the Western Australian fishery for Panulirus 

 cygnus 1 (O. tetricus) to 5% in the Tasmania!) fishery for 



