178 



Fishery Bulletin 103(1) 



A likelihood ratio test (LRT) identified a slight sig- 

 nificant difference between male and female VBGF S 

 growth curves (/ 2 =13.20 df=3 P=0.04), but there was 

 no significant difference when the VBGF TP was tested 

 (X 2 =10.83 df=6P=0.09). 



Mortality estimation 



Ages 9-23 and 7-25 were included in the LCCCA regres- 

 sions of the VBGF S and the VBGF TP , respectively, to 



n = 776 



100 



10 



15 



20 25 



Age (yrs) 



30 



35 



40 



Figure 7 



Pooled length-at-age data for striped trumpeter (Latris lineata). 

 The black line represents the optimal two-phase von Bertalanffy 

 growth function (VBGF TP ), with a mean age at transference of 4.4 

 years and a standard deviation equal to 1; the gray line represents 

 the optimal standard von Bertalanffy growth function (VBGF S ). 



estimate Z (Fig. 9). Individuals below these ranges were 

 assumed, by their respective model, not to have fully 

 recruited to the offshore fishery, and individuals over 

 the age of 25 were excluded due to poor sample size. 

 These age ranges effectively excluded the strong 1993 

 recruitment pulse from the regression, thereby avoiding 

 the complication of including a known strong year class 

 in the analysis. 



Application of the VBGF TP model resulted in lower 

 estimates of Z and M (based on the Pauly equation), 

 compared with those calculated by using the 

 VBGF S parameters (Table 4). The estimate 

 of Z based on the Hoenig (1983) equation 

 was assumed to be close to M because F is 

 low for this species. The Hoenig M was very 

 similar to the Pauly estimate when VBGF TP 

 parameters were used. In this case M was 

 just below 0.1, indicating an annual natural 

 mortality rate of about 9%. The VBGF TP 

 estimates indicate that F was slightly higher 

 than M in the offshore fishery. By contrast, 

 the standard VBFG S parameters produced 

 a substantially higher estimate of M (0.15) 

 based on the Pauly equation than predicted 

 by the Hoenig approximation, indicating an 

 annual natural mortality rate of about 14%. 

 Derived estimates of F with the VBGF TP 

 were slightly higher than M, whereas F in 

 relation to M was variable for the VBGF S , 

 depending on the equation used to derive M. 



45 



2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18 19 

 Age at transference 



Figure 8 



Negative log-likelihood profile plot of increasing age-at-transference 

 values for striped trumpeter iLatris lineata). 



Discussion 



The present study represents the first report 

 of age and growth of striped trumpeter. 

 Despite having available a patchy data set, 

 we were able to validate age and overcome 

 the limitations of the von Bertalanffy equa- 

 tion to represent these data by the use of a 

 robust growth model. Striped trumpeter are 

 long lived, have a maximum age in excess of 

 40 years, and growth is particularly rapid up 

 to age five, after which it slows dramatically. 



The species has a complex early life his- 

 tory involving a long planktonic larval phase 

 of around nine months (Morehead 1 ), an in- 

 shore juvenile phase, and then movement 

 offshore into deepwater. 



Gear selectivity (gill nets in the shallow 

 and hook catches in the deeper waters) may 

 have influenced the fish-size structure of our 

 samples, especially when grouped by depth, 

 although it is highly unlikely that the size 

 differences could be completely attributed 

 to gear type alone. For instance, small indi- 

 viduals (<400 mm) were occasionally taken 

 by hooks in the deeper strata and individu- 

 als over 500 mm were taken by gill nets in 

 less than 50 m. The commercial hook fishery 



