2.5 m. at station II. Salinities at both stations 

 ranged from 4 to 31 p.p.t. and averaged 23 p.p.t. 

 at station I and 24 p.p.t. at station II. Water tem- 

 peratures were similar at both stations, ranging 

 from 9° to 30° C. and avei^aging 23° C. 



Two locations in the upper estuary were selected 

 for study of Atlantic croakers — station III, off the 

 eastern shore of Escambia Bay, near Trout Bayou, 

 and station IV, oft' the western shore of the bay. 

 The bottom at both is predominantly mud; at- 

 tached vegetation is lacking, but station III has 

 isolated oyster reefs. Average depth at mean low 

 water is 2.5 m. at station III and 2.0 m. at station 

 IV. Salinities ranged from to 29 p.p.t., average 15 

 p.p.t., at station III and from to 27 p.p.t., average 

 12 p.p.t., at station IV. 



MATERIALS AND METHODS 



Collections were made with a 5-m. otter trawl of 

 12-mm. bar mesh. This trawl is the standard "try 

 net" used by commercial shrimj^rs in Pensacola 

 Bay to find commercial quantities of shrimp. The 

 trawl was pulled behind the ll-in. research vessel 

 Dolphin at about 2.5 knots. 



All stations were visited 22 times from August 

 1963 to December 1965; usually 10 trawl hauls (30 

 minutes) were made at each Atlantic croaker sta- 

 tion and 30 hauls (15 minutes) at each pinfish 

 station. Trawling usually began in the middle of 

 the montli and lasted 7 days (not necessarily con- 

 secutive). The number and duration of hauls were 

 selected to give a reliable estimate of fish abun- 

 dance. In periods when fish were not abundant the 

 number of trawl samples was reduced to less than 

 half that during periods of abundance. 



Treatment of both species after capture was simi- 

 lar. On the boat they were counted, measured to the 

 nearest millimeter of standard length, and when- 

 ever possible 50 fisli from each 25-mm. size group 

 were preserved in a mixture of 4 jDercent formalde- 

 liyde and sea water of 16 p.p.t. salinity. Fish were 

 slit open to presence innards (including stomach 

 and gonads). At the laboratory, preserved fish 

 were measured for length and weight (to the near- 

 est millimeter and 0.01 gram) and stomachs and 

 scale samples were removed. 



Confidence intervals were computed for the num- 

 ber of fisli cauglit per trawl-haul and on the 

 average length of the fish. Mention of significant 

 differences indicates that confidence intervals, 95 

 percent confidence coefficient, do not overlap. 



Stomach contents of fish captured at the same 

 time were combined by length of the fish — 14 to 75 

 mm. or >75 mm. — and stored in 70 pei'cent 

 ethanol. After identifying and sorting the contents, 

 I blotted them dry and determined their liquid 

 displacement. 



Discussion of tlie volume of stomach contents 

 includes all of the contents but discussion of the 

 composition excludes unidentifiable material; 

 which represented 8.8 percent of the 205.8 ml. of 

 food from 3,577 pinfish stomachs and 25.2 percent 

 of the 58.4 ml. of food from 2,520 Atlantic croaker 

 stomachs. The unidentifiable component of the 

 stomach contents included small particles of 

 inorganic and organic detritus and food digested 

 beyond recognition. Reid (1954) also found large 

 amounts of unidentifiable material in croaker 

 stomachs. 



Ages were determined from length- frequency 

 distributions and by examination of scales. The 

 scales were predominantly from fish at the size 

 range where length-frequency distributions indi- 

 cated a change in age. The scales were taken from 

 the area above the lateral line behind the opercu- 

 lum, stored between sheets of paper, and examined 

 under a monocular microscope. The distances from 

 focus of the scale to the annulus and to the margin 

 of the scale were measured to the neare.st 0.1 mm. 

 witli an ocular micrometer. 



Tlie spawning season extends throughout the 

 winter (about November to March for pinfisli and 

 November to February for croakers) . In assigning 

 ages to these fish, I used January 1 of the year 

 following the winter of hatching as the first 

 birthday. 



I used two methods to study the growth. First, 

 I used tlie differences in average lengths between 

 consecutive trawling periods to compute the aver- 

 age daily increases in length. Second, I used 

 measurements of scales from yearling pinfish io 

 compute growth increments; increases in length 

 after annulus formation were determined for eaeh 

 sampling date and used to derive daily growth for 

 each season. 



To discover movements before spawning, I 

 clipped fins of 26,980 pinfish and 5,269 Atlantic 

 croakers. Fish from different localities were 

 marked differently by removal of either one or 

 both pelvic fins. After the marking, the fish were 

 kept in a tank of circulating water on the boat 



LIFE HISTORIES OF PINFISH AND ATLANTIC CROAKER 



137 



