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Fishery Bulletin 103(1) 



of a species as a function of age. The parameters com- 

 mon to the von Bertalanffy growth function (VBGF) 

 are used in stock assessment models such as empiri- 

 cal derivatives of natural mortality (Pauly, 1980) and 

 assessments of yield per recruit and spawning stock 

 biomass (Beverton and Holt, 1957). Despite the von 

 Bertalanffy growth parameters being well established 

 as cornerstones of many stock assessment models, sev- 

 eral authors have highlighted limitations of the original 

 derivation of the growth function to adequately repre- 

 sent growth of a population (Knight, 1968; Sainsbury, 

 1979; Roff, 1980; Schnute, 1981; Bayliff, et al, 1991; 

 Hearn and Polacheck, 2003). This limitation becomes 

 especially evident with limited or patchy data. The 

 limitations of the von Bertalanffy growth function have 

 created three scenarios: 1) use the VBGF and retain the 

 use of the parameters to derive per-recruit estimates 

 at the possible expense of physiological integrity; 2) 

 derive or employ a model that is not based on the von 

 Bertalanffy parameters (such as a linear or logistic 

 model) or another polynomial function (for instance, 

 the Gompertz equation [Schnute, 1981]) and in doing 

 so the expediency of the von Bertalanffy parameters 

 in stock assessments is compromised; 3), use or develop 

 an extension of the von Bertalanffy equation with the 

 caveat that, by introducing additional parameters, the 

 problem of reduced parsimony by over parameterisation 

 would need to be considered. 



While investigating the life history characteristics of 

 striped trumpeter, we became aware that the original 

 description of the VBGF would not adequately represent 

 growth of this species, in part because of the patchy 

 data available for analysis. 



This study aims to describe the age and growth of 

 striped trumpeter from Tasmania. Seasonal growth 

 oscillations are considered for the first four years by 

 using actual length-at-age data from a strong cohort. 

 We then employ and evaluate an extension of the VB- 

 GF that offers a better fit to the sample population of 

 aged individuals and allows the flexibility of assigning 

 representative growth and mortality parameters to 

 different life phases of the population. Growth param- 

 eters derived from both the standard von Bertalanffy 

 and extended von Bertalanffy models are used in our 

 catch curve analyses, and the empirical models of Pauly 

 (1980) and Hoenig (1983) are used to allow comparison 

 of mortality estimates. 



Materials and methods 



Striped trumpeter were collected opportunistically from 

 various sites off the east and southeast coasts of Tasma- 

 nia from a variety of fisheries dependent and indepen- 

 dent sources spanning the period 1990-2002 (Table 1). 

 Inshore catches were predominately taken with gill nets 

 ranging in mesh sizes from 64 to 150 mm. Offshore 

 catches were taken by hook-and-line methods. Samples 

 ranged from intact specimens, for which the full range of 

 biological information was collected, to processed frames 



from which length and, depending on condition of the 

 body, sex and gonad weight were recorded. All specimens 

 were measured for fork length (±1 mm) and, where pos- 

 sible, total weight was recorded (±1 gram). Otoliths were 

 collected when possible. This ad hoc sampling approach 

 created a temporally irregular data set. 



Kolmogorov-Smirnov tests (o=0.05) were used to de- 

 termine whether significant differences existed between 

 male and female length-frequency distributions or be- 

 tween length-frequency distributions by depth strata. 



Analysis of residual sums of squares (Chen, 1992) 

 was used to determine whether a significant difference 

 existed between the sex-specific length-weight rela- 

 tionships that were fitted by minimizing the sum of 

 square residuals and that are described by the power 

 function 



W=aL b , (1) 



where W = whole weight (g); 



L = fork length (mm); and 

 a and b = constants. 



Sex ratios were compared for significant deviation from 

 1:1 by chi-square tests. 



Aging technique 



Sagittal otoliths were removed from 873 individuals and 

 a subsample of 295 otoliths were individually weighed 

 to the nearest milligram. One randomly selected oto- 

 lith from each fish was embedded in clear polyester 

 casting resin. A transverse section was taken through 



