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Fishery Bulletin 89(1), 1991 



of the Fall 79 cohort as actually being part of that 

 cohort; the lower mode first became distinct in Feb- 

 ruary 1980 when those fish were primarily 55-75 mm 

 long and about 4 months of age, which would suggest 

 early October to early November hatching. 



Recruitment, movements, and nurseries 



Fall cohorts of P. burti seemingly recruit in abundance 

 at an older age (4-5 months) than Winter fish (2-4 

 months) off Texas. Winter fish formed abundant, 

 distinct groups soon after first appearing mid-April to 

 early June at 30-75 mm in length when 1.5-4.5 months 

 old (Fig. 4). Fall fish did not form abundant, distinct 

 groups until winter to early spring, although they first 

 appeared mid-November to early December when 

 30-75 mm and 1.5-4.5 months old. 



Young P. burti recruit to the bottom off Texas 

 primarily in 5-27 m depths when 2-5 months old. 

 Winter 79 fish 2-4 months old and 35-70 mm were cap- 

 tured only at 22 m in May 1979 (Figs. 4, 6). They oc- 

 curred from 16-55 m during the period June through 

 August 1979 (primarily June) but were most abundant 

 at 22-27 m; few were shallower than 22 m or deeper 

 than 36 m. Recently hatched Fall 79 fish 25-70 mm long 

 were captured only at 5-9 m in mid-November 1979 

 (Figs. 4, 6). Fall 79 fish occurred only at 5-27 m (pri- 

 marily 22-27 m) December 1979 through February 

 1980 when 3-5 months old. Similarly, Fall 78 fish were 

 abundant at 5-27 m March through May when 7-9 

 months old, but few occurred in deeper water. 



Juvenile P. burti disperse offshore as they mature 

 and approach age I. Winter 79 fish were most abundant 

 at 13-27m depths September through November 1979 

 when 6-8 months old (Fig. 6). However, none occurred 

 shallower than 22 m December 1979 through February 

 1980, when they were 9-11 months old; most were at 

 36- 100 m. The largest Fall 79 individuals occurred in 

 the deepest water December 1979 through February 

 1980, the size gradient suggesting gradual movement 

 offshore. Fall 78 fish were almost exclusively at 5-27 m 

 from March through May 1979 when 7-9 months old, 

 but they were at 36-100 m from June through August 

 when 10-12 months old. 



Age determination using otoliths 



Whole otoliths of P. burti apparently cannot be read- 

 ily aged. Only 984 of 2461 whole otoliths examined had 

 apparent internal features. Many were entirely opaque 

 or lacked a distinct boundary between opaque and 

 hyaline zones, possibly due to initial preservation or 

 storage fluids, though fresh otoliths showed similar 

 features. Only 11 of the 984 legible otoliths had an ap- 

 parent annulus. These 11 fish were 120- 160 mm in 



length and could have been about age I by length- 

 frequency analysis. Annuli frequently were not ap- 

 parent for fish that were age I by length frequencies. 



Growth and age determination 

 by length frequency 



Length frequencies could be used to determine age of 

 P. burti through at least 13-16 months of age in the 

 northwestern Gulf and apparently 20-27 months of age 

 in the northcentral Gulf. No more than two cohorts oc- 

 curred off Texas in any one month, except in March 

 and December 1978, November 1979 through January 

 1980, and May through June 1980 when a few members 

 of a third group were present (Fig. 4). Each cohort was 

 followed easily until it disappeared when 13-16 months 

 old. In contrast, in the northcentral Gulf in April 1980 

 there were three cohorts west of the Mississippi River 

 and four to the east (Fig. 7). Fish were abundant at 

 20 months of age west of the Mississippi and were as 

 old as 27 months to the east (Table 3). 



Early sizes for P. burti average 25mm in length at 

 1 month of age, 42 mm at 2 months, 57 mm at 3 months, 

 72mm at 4 months, and 84mm at 5 months. These 

 values are predicted from quadratic regressions of 

 length-on-age in days pooling all Winter and Fall 

 cohorts (Table 2). Similar size-age combinations may 

 be predicted from quadratic regressions for individual 

 cohorts, and for pooled Winter groups and pooled Fall 

 groups. 



Peprilus burti average about 65- 100 mm in length 

 at 6 months, 120-145 at age I, and about 170mm at 

 age II, but fish in the northcentral Gulf were smaller 

 at age than off Texas. Quadratic and von Bertalanffy 

 growth equations both fit observed data from off Texas 

 well, and they predict similar sizes-at-age over most 

 of the observed size range (Fig. 8). For Winter fish 

 quadratic and von Bertalanffy equations predicted 

 lengths of 99 and 100 mm at 6 months, respectively, 

 and 146 and 141 mm at age I (Fig. 8). Observed lengths 

 show many Winter fish were as large as 120mm at 6 

 months and 155 mm at age I (Fig. 4; Murphy 1981, 

 Table 1). For Fall fish, quadratic and von Bertalanffy 

 equations predict lengths of 93 and 97 mm at 6 months, 

 respectively, and 131 and 130 mm at age I. Observed 

 lengths show many Fall fish were as large as 105 mm 

 at 6 months and 145 mm at age I. Winter-spawned fish 

 from the northcentral Gulf averaged 120-124 mm at 



Figure 6 (facing page) 



Length frequencies of Peprilun burti by depth: March-May 

 1979, June-August 1979, September-November 1979, 

 December 1979-February 1980. 



