FISHERY BULLETIN: VOL, 71, NO. 1 



the surface. The stratification was even more 

 evident at canal stations where the difference 

 between surface and bottom values ranged be- 

 tween n.6%r (Station 6) and IS.O^r (Station 3). 

 In general, the most landward stations exhibited 

 the greatest differences between surface and bot- 

 tom salinities. 



OXYGEN 



Daytime concentrations of dissolved oxygen 

 at the surface and bottom for each station are 

 shown in Table 1. Only at the control station 

 were surface and bottom values similar, varying 

 linity at the control station was 9.0'/(< higher than 

 no more than 0.6 ml/liter at any one sampling 

 time throughout the year. At this station the 

 lowest observed concentration was 2.1 ml/liter 

 (August 1971). Surface oxygen values within 

 the canal system were comparable with those at 

 the control station throughout the year. How- 

 ever, bottom oxygen dropped in the canals in 

 February when less than 2.0 ml/liter was re- 

 corded at Stations 3 and 4. These values rose 

 above 3.0 ml/liter in March, but in April and 

 May dissolved oxygen near 2.0 ml/liter or less 

 was recorded at several canal stations. In July 

 less than 1.0 ml/liter was recorded at Stations 

 3, 4, and 5, and by August less than 1.0 ml/liter 

 of oxygen was recorded at the bottom at all 

 canal stations. 



To determine the diel changes in oxygen con- 

 centration during the July sampling period, a 

 24-hr sampling program was conducted at each 

 station. Results showed that surface and bottom 

 values were similar only at the control station 

 (Figure 4). Surface oxygen concentration in 

 the canals corresponded with values recorded at 

 the control station and never fell below 2.0 ml/ 

 liter. However, at all canal stations the bottom 

 was nearly anoxic throughout the 24-hr sam- 

 pling period. 



FISHES AND MACROINVERTEBRATES 



Thirty-six species and 10,497 individuals of 

 vertebrates and invertebrates were collected 

 within the canals during the year (Table 2). 

 Of the 36 species, 32 were finfish (23 of sport 

 or commercial value), 1 was the diamondback 



N 6 

 E . 



O 



>- 



X 



O 



O 2 



m 

 i/i 



5 



STATION 1 (control) 



STATION 2 



STATION 3 



STATION 4 



STATION 5 



-' 



STATION 6 



T*^ 



■^**-p 



I I I I I \ 1 1 r 



0800 1000 1200 1400 1600 1800 2000 2200 2400 0200 0400 0600 



HOURS 



Figure 4. — Results of 24-hr oxygen survey in July 1971 

 (surface • •; bottom • •)• 



terrapin, Malaclemys terra'pin, and 3 were com- 

 mercially important invertebrates (blue crab, 

 Callinectes sapidus; pink shrimp, Penaeus duo- 

 rarum; and brief squid, LolUguncula brevis). 



The four species of fish caught in greatest 

 abundance represented 92 Sr of the total number 

 of specimens. They were the bay anchovy {An- 

 choa mitchilli) , spotfin mojarra {Eucinostomus 

 argenteus) , spot {Leiostomus xanthurus), and 

 silver jenny (Eucinostomus gula). The bay an- 

 chovy alone made up nearly 72 9f of the total. 



The brief squid was by far the most abundant 

 invertebrate (84% of all invertebrates collected) 



158 



