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DISCUSSION 



J. G. Skellam: In your equation (p. 57) you use FjK in a manner which 

 suggests that F is constant, yet elsewhere treat it as a function of t. Was F 

 assumed as a constant for simphcity, or was it determined from studies of 

 catches in relation to mesh size and the integral evaluated numerically? 



S. J. Holt: No integrals were actually evaluated; they were written 

 out only to demonstrate the parameters. F and M were assumed constant 

 for the purpose of brief exposition. The assumptions depend on the type of 

 prediction to be made, praticularly whether of an effect of change in selec- 

 tivity or of fishing intensity. The equation is equally relevant to the crustacean 

 growth problems discussed by Hancock. If one carries out a tagging experi- 

 ment and can obtain the increment at moulting, and from the same data 

 the inter-moult survival rate, it may not be necessary to know the frequency 

 of moulting. 



A. C. Simpson: This approach may be of great value in population 

 studies in Crustacea where the shedding of the cuticle at each moult renders 

 age determination impossible. Our data on the relation between moult 

 increment and total length, if extrapolated to the base line, do give a value 

 close to the largest known lobster size, i.e. to L^o- 



S. J. Holt: This might give a reasonable estimate of L^o, if not of iC, 

 and thus without knowledge of maturity size could permit use of length 

 frequency data for assessment purposes. 



B. B. Parrish: K might be obtained from aquarium studies on starved 

 fish for which changes in weight will be a function of K. 



