ences among numbers of species inhabiting sections 

 of the Bay appeared to be of little or no con- 

 sequence. This appraisal, however, is exclusive of 

 those species not considered to be of commercial 

 importance in this report. 



Catch per unit of effort data made it possible to 

 determine whether immature animals had a prefer- 

 ence of habitat among areas of the Tampa Bay 

 system (table 6). An overwhelming preference 

 was apparent for Old Tampa Bay (Area III) 

 where there were three times as many total animals 

 as in either Lower or Central Tampa Bay (Areas I 

 and II) and seven times as many as in Hillsbor- 

 ough Bay (Area IV). Abundance in Area III 

 exceeded that of Areas I, II, and IV during 9 

 months out of 12. Although peak abundance 

 varied between areas and time periods, March and 

 April produced the greatest number of specimens 

 per unit of effort from the collective areas. 



Data on abundance of individual species by 

 area and season also indicate an areal preference 

 (fig. 3). Seven species were taken in numbers 

 greater than 100 during at least one season (three 

 units of effort) in Area III, five in Area II, four in 

 Area I, and two in Area IV. The data indicate, 

 therefore, that Area III (Old Tampa Bay) pro- 

 duces or develops more individuals during a greater 

 portion of the year than any other area of the 

 Tampa Bay system, and that Hillsborough Bay is 

 the least productive of commercially important 

 species. 



Based on the known salinity preference of many 

 euryhaline animals, it was expected that the 

 greatest abundance of important species would be 

 found in the low salinities of Old Tampa and Hills- 

 borough Bays. Pearson (1929) and Gunter 

 (1945, 1950) showed that a cycle of spawning, 

 growth, and movement bore a distinct relation to 

 salinity for many valuable fishes and invertebrates 

 on the Gulf of Mexico coast. Salinity lower than 

 that which is characteristic of the ocean is one of 

 the requisites in early development of these ani- 

 mals. Abundance in Hillsborough Bay, however, 

 was not nearly as great as in Old Tampa Bay. 

 Because annual salinity patterns of Hillsborough 

 Bay and Old Tampa Bay are similar, the difference 

 in abundance of valuable species between the two 

 areas must result from other environmental 

 factors. 



The introduction of industrial and domestic 

 sewage is common in Hillsborough Bay. Natural 



flushing has not kept pace with the deposition of 

 the effluents and has resulted in the accumulation 

 of silt-size sediments throughout the Bay. Nox- 

 ious compounds in solution, unstable and un- 

 inhabitable sediments, and insufficient dissolved 

 oxygen appear to have contributed to a decline in 

 Hillsborough Bay fisheries within a relatively short 

 period of time. 



As a nursery area for fish and crustaceans, Hills- 

 borough Bay is no longer productive. Com- 

 mensurate with alterations in bottom type and 

 water quality, littoral areas which once supported 

 a luxuriant growth of marine grasses are now 

 barren except for the seasonal appearance of some 

 red and blue-green algae. 



In contrast, Old Tampa Bay remains in a 

 relatively undisturbed state supporting blue crab, 

 bait shrimp, and oyster fisheries, and serving as a 

 nursery area for estuarine dependent fauna. Al- 

 though industrial and residential interests con- 

 tinually threaten this area, it is vegetated with 

 turtle grass (Thalassia testudinum), shoal grass 

 {Diplanthera wrightii), cord or manatee grass 

 (Syringodium Jiliforme), the red mangrove (Rhiz- 

 ophora mangle) , and the black mangrove (Avicennia 

 nitida) (Springer and Woodburn, 1960). The 

 emergent vegetation aids in controlling the intro- 

 duction of particulate detritus in surface water 

 run-off before it enters the Bay. 



Biologically, the water quality is good, and the 

 predominantly firm sediment pattern creates a 

 substrate suitable for the habitation of dense ag- 

 gregations of benthic invertebrates. The sta- 

 bility of the bottom also promotes water clarity 

 necessary for the existence of dense stands of 

 marine algae and sea grasses which extend around 

 the entire periphery of the area. The^ algae- 

 sea grass ecosystem appears to be absolutely 

 essential for survival and growth of juvenile stages 

 of many commercially important species. 



We conclude that the relatively undisturbed 

 conditions of Old Tampa Bay and the fact that its 

 salinity distribution is ideally suited to the de- 

 velopment of many euryhaline fishes are responsi- 

 ble for its comparatively good productivity. 



Many species recorded as inhabiting the estuary 

 were omitted from our lists in this report. Some 

 of these contribute indirectly but significantly to 

 commercial fisheries by serving as food for market- 

 able species. An example of an outstanding forage 

 species is the scaled sardine (Harengula pensa- 



IMMATURE SPECIES IN TAMPA BAY 

 774-711 O — 66 6 



377 



