term changes in Florida Bay ecosystem processes remains unclear. Until additional 
information is obtained on the loss of adults, and subadult dispersal and recruitment 
rates to the breeding population, osprey population trends as Indicators of habitat 
change in Florida Bay could not be substantiated. 
1969 0 
Hughes, D. A. (1969) On the mechanisms underlying tide-associated movements of Penaeus 
duorarum. FAQ Fish. Rep. . 57(3):867-74. 
[DATE OF SAMPLING UNKNOWN OR NOT APPLICABLE.] Postlarval shrimp move inshore 
on flood tides while juveniles move offshore on ebb tides. The mechanism whereby this 
discrimination between the tides is effected appears to be based on the respective 
response of postlarvae and juveniles to changes in salinity. Juveniles are positively 
rheotactic within a current of water. However, when the salinity of that water is 
decreased downstream swimming ensues. This ensures that juveniles will, in nature, 
resist displacement in an inshore direction by the flood tide but will swim and be placed 
in an offshore direction by the ebb tide. When the salinity increases (flood tide), they 
become active in the water column and are displaced inshore. The apparent dependence 
of tide associated movements on changes in salinity points to an explanation for the 
positive correlations that have been found between the extent of rainfall in the vicinity 
of "nursery" areas and the commercial catch of the following year. 
1969 0 
Hughes, D. A. (1969) Evidence for the endogenous control of swimming in pink shrimp, 
Penaeus duorarum. Biol. Bull. . 136:398-404. 
[DATE OF SAMPLING UNKNOWN OR NOT APPLICABLE.] Evidence that the swimming of 
migrating juvenile pink shrimp is under some measure of endogenous control was 
derived from experiments which indicated (1) that the pattern of swimming exhibited 
by a group of shrimp, maintained under constant conditions within a current of water, 
was similar over each of the two nights following their collection from nature, and (2) 
that the swimming of two such groups, collected together, but maintained in separate 
current chambers within the laboratory, was similar during the night following their 
capture. Endogenous control over swimming extended to the sign of rheotaxis which, 
during certain nights, in the absence of change in external conditions, would reverse in 
all shrimp at approximately the same time. A predictable relationship occurred between 
the tide cycle to which shrimp were exposed prior to capture and their subsequent 
swimming in the laboratory. The adaptive nature of this relationship is suggested from 
the fact that downstream swimming, which in nature occurs only during ebb tides, and 
facilitates the offshore movements of juveniles, occurred in the laboratory only at the 
time of ebb tides in nature. It did not, however, occur at the time of all ebb tides but 
only during those occurring early in the evening. It is suggested that the cohesion of the 
aggregations of migrating shrimp may largely be maintained by means of the synchrony 
imposed on the activities of all individuals by endogenous timing mechanisms. 
1969 0 
Hughes, D. A. (1969) Responses to salinity change as the tidal transport mechanism of pink 
shrimp, Penaeus duorarum. Biol. Bull. . 136:43-53. 
[DATE OF SAMPLING UNKNOWN OR NOT APPLICABLE.] The inshore movements of 
postlarval pink shrimp and the subsequent offshore movements of the juveniles are 
facilitated by flood and ebb tides respectively. This investigation concerns the 
behavioral mechanisms involved in the selective use of one tide and the evasion of the 
other. Salinity changes, similar to those occurring with change in tide in the inshore 
environment usually occupied by pink shrimp, were imposed on both postlarvae and 
juveniles in a constant-current apparatus. Juvenile shrimp were almost invariably 
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