GEOGHEGAN and CHITTENDEN: REPRODUCTION. MOVEMENTS OF LONGSPINE PORGY 



growth between October and December 1977 is 

 high when compared with the same period in 

 other years; and 3) size at age I is comparatively 

 large for the 1977 year class. The 1977 and 1978 

 year classes were difficult to distinguish after 

 December 1978, so that the 1977 year class there- 

 after may include fast growing members of the 

 1978 year class. 



Stenotomus caprinus growth varied between 

 year classes, but sizes averaged 110-135 mm TL 

 at age 1, 130-155 mm at age II, and 160 mm at age 

 III. Observed mean sizes at age I, based on pooled 

 data from February and March (Table 2), were 

 134.2 mm TL for the 1977 year class (range 113- 

 157 mm), 120.8 mm for the 1978 year class (range 

 96-145 mm), and 107.5 mm for the 1979 year 

 class (range 91-119 mm). These sizes at age I 

 agree with regression predictions (Fig. 5) of 

 114.8 mm TL for the 1978 year class and 110.0 

 mm for the 1979 year class. Observed mean size 

 at age II was 132.5 mm TL for the 1978 year class 

 (range 116-155) (Table 2), which closely agrees 

 with a regression prediction of 128.6 mm (Fig. 5). 

 The few survivors of the 1977 year class aver- 

 aged 155.8 mm TL (range 146-182) at age II and 

 160.8 mm at age III (range 154-175 mm) (Table 

 2). Many fish approached the maxima in the size 

 ranges at age cited for each year class, and the 

 ranges at age appeared constant between collec- 

 tions indicating uniform growth (Table 2). 



Possible error in assigned hatching dates 

 would have little effect on our estimates for mean 

 sizes at age because 99% confidence intervals of 

 observations were constant within the following 

 periods (Table 2): December 1977-April 1978 for 

 the 1977 year class; December 1978-June 1979 

 for the 1978 year class; and December 1979- 

 March 1980 for the 1979 year class. 



Stenotomus caprinus grow rapidly in their 

 first 8 mo, but growth slows greatly as they ma- 

 ture and appears negligible after maturity. The 

 1978 and 1979 year classes showed a rapid, 

 almost linear decline in monthly growth incre- 

 ments during their first 8 mo (Fig. 3). Growth of 

 the 1978 year class averaged 13.62 mm TL/30 d 

 from 15 February through early October 1978, 

 and the 1979 year class averaged 12.66 mm/30 d 

 from 15 March to early November 1979, ignor- 

 ing the regression effect. In contrast, the 1978 

 year class grew only 13 mm TL in its second year; 

 and the 1977 year class grew only 23 mm in its 

 second year and 4 mm in its third year. This 

 growth pattern may result in gradual merging 

 of year class size compositions after age I as indi- 



cated by the 1978 and 1979 year classes (P^ig. 2). 

 The small amount of growth after maturity 

 seems to occur primarily during the late spring- 

 early fall interim between reproductive activi- 

 ties (Fig. 3). Very little growth occurred in the 

 January-April spawning period when the 1978 

 year class averaged 0.83 mm TL/30 d in that pe- 

 riod in 1979 and 0.80 mm/30 d in 1980. 



Size at age I varies between S. caprinus year 

 classes, but growth is not obviously density de- 

 pendent. No simple relationship was apparent 

 for the 1977-79 year classes (Fig. 10) between 

 mean size at age I and their index of year class 

 strength, calculated as tcJXfi where 5/,- is the 

 total number of tows and Sc, is the total catch at 

 age I for each year class at depths of 27-47 m. 

 Fish of the weak 1979 year class averaged 

 smaller at age I (107.5 mm TL) than the strong 

 1978 year class (120.8 mm), a pattern not consis- 

 tent with density dependent growth. Growth of 

 the 1979 year class might have been depressed by 

 interaction with the strong 1978 year class, but 

 no density dependent relationship was apparent 

 even when a pooled index of population strength 

 was substituted for the 1979 year class strength 

 index. 



140 



100 



1977 



* 



1978 



* 



25 50 75 100 



INDEX OF YEAR CLASS STRENGTH 



Figure 10.— Relationship between mean sizes at age I and 

 year class strength for Stenotomus caprinus off Freeport, Tex. 

 Indices of individual year class strength are indicated by stars 

 and the pooled index by solid circle. 



Discussion 



Our findings on growth are largely new be- 

 cause the growth of S. caprinus has not been 

 described previously. Sizes at age I agree with 

 Chittenden and McEachran's (1976) suggestion 



535 



