Clark and Tracey: Population changes of Hoplostethus atlanticus on the Challenger Plateau 



245 



1984 



nfm) 5020 

 n(t)68 



I II II I I i r i i i i i i i i \ i frr ft 



ttfl ll II 



01 



fcl 20 



01 



1985 



n(m) 2609 

 n(t) 18 



& 



1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 r n 1 1 Fri 



rfl i n i 



1987 



n(m) 18 981 

 n(t) 124 



J 



1 1 1 1 1 1 1 1 1 ii 1 1 1 1 1 1 n 1 1 1 T n 1 1 1 



: krrr 



1989 



n(m)20 148 

 n(t) 158 



l l 1 1 1 ll 1 1 1 1 1 1 I r ftf I I - 



trh 1 1 1 1 



i m 1 1 1 1 1 1 



5 10 15 20 25 30 35 40 45 



Standard length (cm) 



5 10 15 20 25 30 35 40 45 



Standard length (cm) 



Figure 4 



Length-frequency distribution of the orange roughy {Hoplostethus atlanticus) popu- 

 lation by year (stipple=male, clear=female, dashed line=weighted length frequency 

 for all years combined, n(m)=number offish measured, nU)=number of trawls from 

 which samples were taken, data are scaled by stratum areas to represent total popu- 

 lation-size distribution). 



July; ripe fish dominated through mid-July; and the 

 proportion of spent fish increased progressively from 

 low levels during the first two weeks in July to peak 

 in the third or fourth week. 



Data are insufficient to examine regional varia- 

 tion in this pattern, but there may be some differ- 

 ences between areas; fish appear to spawn slightly 

 later on the Westpac Bank than those on the Central 



