Francis et al.: Age and growth estimates for Polyprion oxygeneios 



237 



40n 



TAN9301 

 n = 434 



30 40 50 60 70 80 90 100 110 120 130 

 Total length (cm) 



Figure 9 



Hapuku length-frequency distributions (both sexes combined) ob- 

 tained from four Tangaroa trawl surveys off Southland in Febru- 

 ary-March 1993-1996. n = sample size. 



errors and were deleted from the data set, leaving 

 138 fish. 



A simple linear model, with a single growth-rate 

 parameter, produced an estimated gi-owth rate of 4.26 

 cm/yr (Table 3, model 1). A model with two growth- 

 rate parameters produced no improvement in fit 

 (Table 3, model 2). The addition of parameters for 

 outlier contamination, measurement bias, and sea- 

 sonal growth did not significantly improve the log- 

 likelihood (Table 3, models 3-5), nor did subdivision 

 of the data into three geographical areas (Table 3, 

 model 6). For the Cook Strait data subset, inclusion 

 of separate growth parameters for male and female 



hapuku did not significantly improve the model fit 

 (Table 4). However, sample sizes were small, statis- 

 tical power was low, and only large differences could 

 have been detected. 



Therefore the best GROTAG model (Table 3; model 

 1) consisted of simple linear growth over the length 

 range 55-85 cm. It had no apparent pattern or trend 

 in the residuals. GROTAG was then run in simula- 

 tion mode (Francis, 1988) by using parameter esti- 

 mates from model 1 to determine the accuracy and 

 precision of the growth-rate estimate. The mean an- 

 nual growth rate was estimated to be 4.25 cm/yr with 

 a standard error of 0.017 cm/yr. 



