abundance, were similar from year to year, I as- 

 sume that average catch gives a reasonably good 

 estimate of general abundance. 



Pinfish young (0-group) and older migrants re- 

 turning to the estuary began to arrive on the grass 

 flats at both stations in late November and early 

 December. Trawling did not capture young fish 

 in numbers indicative of their actual abundance 

 but seining caught large numbers of them near 

 both stations. The migiation continued until the 

 population had reached a maximum by late June. 

 The month that young first appear seems to depend 

 on conditions offshore, because salinity and tem- 

 perature changes in the estuary show no relation to 

 the time of migration. Progressively fewer fish 

 were captured after June because of natural 

 mortality and emigration. 



Pinfish abundance changed from year to year. 

 If catch in August (a month fished in each of 3 

 years) is used as an indicator of yearly changes in 

 abundance, pinfish were significantly less plentiful 

 in 1964 than in 1963 or 1965. Pinfish were most 

 numerous at station I in 1963 and at station II in 

 196.5. Tlie number of fish caught in the winters of 

 1963-64 and 1964-65 did not differ from November 

 to February at station I and November through 

 April at station II. 



The numbers of fish caught at the two stations 

 at each sampling time were similar, differing sig- 

 nificantly only in August and September of each 

 of the 3 years. This period marks the start of mi- 

 gration out of the estuary ; significant changes in 

 abundance might, therefore, be expected if the fish 

 left one station earlier than the other. 



ATLANTIC CROAKER 



Atlantic croakers are one of the dominant fish 

 in the upper Pensacola Estuary. Therefore, I in- 

 A'estigated seasonal and annual change in the food, 

 growth, migration, reproduction, and abundance 

 at two locations from August 1963 to December 

 1965. 



FOOD 



Atlantic croakers are carnivorous (table 5) . The 

 animal food in the present collections included 

 five phyla and numerous species. Vegetation and 

 sediments in some stomachs were probably taken 

 incidentally while fish were capturing animal 

 food. 



142 



Table 5. — Percentage of total volume contributed by different 

 items in Atlantic croaker stomachs collected in the tipper 

 Pensacola Estuary at stations III and IV in different 

 seasons, 1963-66 



I Numbers of stomachs from both stations are shown in parentheses. 



Annelids were the major food except in large 

 fish in the spring, when fish were dominant. Pear- 

 son ( 1928) , who collected along the Gulf Coast, and 

 Roelofs (1954), on the Atlantic Coast, found that 

 annelids were dominant and that the other foods 

 listed in table 5 were present in the stomachs of 

 young croakers. 



Fish were most common in Atlantic croakers 

 over 75 mm. long. At station III, fish were most 

 plentiful in stomaclis in the spring and summer. 

 At station IV, fish were most abundant in the 

 winter in croakers less than 76 mm. long and in 

 tlie spring in croakers over 75 mm. 



Arthropods, chiefly crustaceans, were most plen- 

 tiful in small fish in the winter and spring and in 

 large fish in the spring and summer. The most 

 important crustaceans were copepods, amphipods, 

 isopods, mysids, shrimp, and crabs; larger forms 

 were most common in stomachs of large fish. In- 

 sects — mainly tendipedids. dytiscids, and anisop- 

 terans — made up 67 percent of the arthropods in 

 stomachs collected at station IV after heavy runoff 

 in the spring. 



Mollusks and nemerteans were minor constitu- 

 ents ill the stomachs of Atlantic croakers. Mollusks 

 were most plentiful in stomachs of large fish in the 

 spring and summer. 



The volume of food in croaker stomachs wixs 

 greatest in the winter and spring; average for 

 768 fish under 76 mm. long was 0.0-2 ml. and for 

 3-24 fish over 75 mm. long, 0.04 ml. Food volumes 

 decreased in the summer and fall ; for 285 fish less 

 than 76 mm. long the average volume was 0.01 ml. 

 in both summer and fall, and for fish longer than 



U.S. FISH AND WILDLIFE SERVICK 



