Tracey and Lyle: Age validation, growth modeling, and mortality estimates for Latns lineata 



181 



relationship between longevity (.t max ) and the magnitude 

 of the physiological growth parameters k and L r . As 

 such, it would be reasonable to assume that if a good 

 fit exists between length at age that the growth param- 

 eters, when employed in such an empirical model, would 

 yield a natural mortality estimate approximately equal 

 to that determined by a regression model that is based 

 on t max (Hoenig, 1983). The two-phase growth function 

 also provided a more conservative estimate of M than 

 the standard von Bertalanffy model. Overestimates of 

 M can lead to unrealistically high estimates of produc- 

 tivity and a potential yield that may in turn lead to 

 overexploitation of a stock. 



Protracted longevity, slow growth in later life, large 

 body size, recruitment variability, and relatively low 

 natural mortality once individuals reach adulthood are 

 all characteristics typical of a K-selected species (where 

 equilibrium is the biological strategy). Such species are 

 often regarded as being susceptible to growth over-fish- 

 ing and stock depletion (Booth and Buxton, 1997). For 

 instance, increased fishing effort on the inshore fishery, 

 as has been observed with the recruitment of strong 

 cohorts, will affect subsequent recruitment to the off- 

 shore fishery and spawning stock. The current analysis 

 indicates that fishing mortality is slightly higher than 

 natural mortality and, in the absence of further strong 

 recruitment, a decline in the stock size is likely if fish- 

 ing pressure is not reduced. 



Acknowledgments 



The authors gratefully acknowledge Ray Murphy and 

 Alan Jordan who collected many of the earlier samples 

 and undertook preliminary examination of the otoliths. 

 The assistance of the captain and crew of FRV Challenger 

 in collecting samples is also thankfully acknowledged. 

 Philippe Ziegler, Dirk Welsford, and Malcolm Haddon 

 provided constructive criticism and ideas in terms of the 

 analyses and reviewed the manuscript; Sarah Irvine and 

 an anonymous reviewer provided constructive feedback 

 on final versions of this manuscript. 



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