400 



Fishery Bulletin 97(2), 1999 



Table 3 



Chi-squared statistics for the constant model of misgraded 

 prawn size in each period of catch 1 1: July-December 1993, 

 2: January-June 1994, and 3: July-December 1994), for 

 both small and large packs. P< 0.0001 



Period 



Small pack 



Large pack 



45.088 

 45.916 

 32.915 



17.963 

 55.701 

 83.060 



Of the prawns misgraded, 92'^J were sized either 

 one grade larger or smaller. Of those misgraded in 

 the 16 to 20 grade, 11% were misgraded by as much 

 as two grades, whereas less than 2% were so 

 misgraded for the other size grades. 



The misgrading proportions can again be used in 

 Equation 5 to obtain the at-sea grade-size distribu- 

 tion for these large packs. Shown in Table 5 are these 

 corrected distributions compared with at-sea 

 gradings; here the adjustments can be seen to be 



more substantial than those for the small packs, par- 

 ticularly for the smaller grades 13 to 15 and 16 to 20 

 prawns per pound, owing to the tendency of the fish- 

 ermen to classify the prawns to smaller size grades. 



Discussion 



Our analysis indicates that small prawns are graded 

 less accurately than large ones. Given that the length 



