BOWERINC: DISTRIBUTION OF WITCH FLOUNDER 



26 



28 



SO 



—I — 



LENGTH (CM) 

 12 



— I— 



X 



AGC (YRSI 



6 T 



T- 



MALE 



-t 5K (ST»-e3) 



-t JK it9TO-7e) 



3L (1979-83) •- 



14 49 



-I 5L (I9«e-TB) 



UAU 



» < 3K (1979-83) 



I t I 3K (1970-781 



-559 



-I 3L (1979-83) 



I I 1 iL (1968-78) 



fiMAL£ 



f£MM£ 



I ) 2J (1979 - 83) 



-»- 



2J (1973-78) I I I 



■»— I 3K (1979 -83) 



I 3K (1970-78) 



( ( 2 J (1979-83) 



2J (1973-78) I t ) 



I ( ( 3« (1979-83) 



I 1 \ 3K (1970-78) 



> < 3L (1979-83) 



I ( 1 JL (19*8-78) 



( ( 3L (1979-83) 



3L (1968-78) ' I ' 



_!_ 



_l_ 



_!_ 



_1_ 



_l_ 



_l_ 



38 



40 



42 44 



LENGTH (CM) 



46 



48 



8 9 



»C€ (YRS) 



10 



Figure 14. — A comparison of lengths (cm) and ages (years) at which 50';f of male and female witch flounder are mature from NAFO 



Div. 2J, 3K, and 3L from earlier and later time periods. 



range of its distribution (T. K. Pitt-^), although the 

 size-depth distribution is not as well defined as 

 presented here for witch flounder. Walsh (1984) 

 concluded, on the other hand, that juvenile plaice 

 occupy the same depth ranges as the adult plaice 

 on the Grand Bank. It should be noted that the 

 results presented in the present paper reflect the 

 depth and temperature preference of young ver- 

 sus old adult witch flounder and not juveniles 

 versus adults as in the studies mentioned. 



Age and Growth 



The age compositions of witch flounder have 

 changed substantially for all three NAFO Divi- 

 sions over the study period, with a much shorter 

 life span experienced in recent years. The impact 

 of the reduced life span appears to be greatest on 

 the Div. 2J stock. This may very well be the result 

 of heavy exploitation on prespawning concentra- 

 tions in the late 1960's when catches were double 

 recent levels of estimated biomass (Bowering 



3T. K. Pitt, Section Head, Flatfish Research, Department of 

 Fisheries and Oceans, P.O. Box 5667, St. John's, Newfoundland 

 AlC 5X1, Canada, pers. commun. 1986. 



1985). Bowering and Brodie (1984) showed a sim- 

 ilar reduction in the life span of witch flounder in 

 the Gulf of St. Lawrence. However, that reduction 

 was more dramatic because it occurred over a 

 shorter time. In 1976, the commercial catches in 

 the Gulf of St. Lawrence comprised fish up to 26 

 years old compared with a maximum age of 16 

 years old by 1981. Bowering and Brodie (1984) 

 attributed the sudden change in the population 

 age structure to the fact that almost the entire 

 fishable stock is located in a small area during the 

 winter months when the fishery is most intense. 

 This is particularly true for small stocks such as 

 that in Div. 2J, where it may not be economical to 

 direct effort when the fish are not densely concen- 

 trated. In Div. 3K, where the stock biomass is 

 relatively high in comparison to that of Div. 2J 

 and 3L, the fishery is spread more through the 

 year, although the main effort is still directed 

 towards prespawning concentrations. Therefore, 

 the reduction in age groups could be over a longer 

 time period and therefore less dramatic, which 

 seems to be the case here. However, this argu- 

 ment can only be true if, because of such a pattern 

 of fishing, the fishing mortality exerted in areas 

 such as Div. 2J is much higher than for areas such 



627 



