predator-prey tests, changes in prey escape success serve to indicate changes in 

 ecological fitness, which can affect natural mortaUty rates in localized 

 populations. 



MATERIALS AND METHODS 



For this study, larval prey species were restricted to those available from 

 laboratory culture. Wild ichthyoplankton were not considered because of the 

 potential for damage due to capture methods, and the difficulty in acquiring 

 adequate numbers of a single species of the same age. The cultured larval prey 

 species used were Menidia menidia and Paralichthys dentatus. Six hatched lots 

 {"^ 500/lot) of M. menidia were reared to six weeks of age and tested during 

 this period. Studies with P. dentatus were Umited to newly hatched larve only, 

 as this species experiences high mortahty at time of first feeding. All larvae 

 were reared at the prevailing Narragansett Bay water temperature {M. menidia, 

 summer-20.5 ± 0.7°C;P. dentatus, late fall- 15.1 ± 0.8°C). 



An attempt was made to correlate prey and predator species. Fundulus 

 majalis, a carnivorous near-shore predator, was chosen as a spatially coexisting 

 predator of estuarine larval fish (6). Larvae of P. dentatus are not highly 

 correlated with near-shore predators since they are usually found offshore at 

 hatching. However, this species was utilized to provide a larval fish with 

 different swimming abilities. Paralichthys dentatus rehes on high fecundity for 

 successful development and eventual recruitment. Larvae of this reproductive 

 strategy are usually weak-swimming relative to larvae of a species such as M 

 menidia, which has a lower fecundity, but relies on advanced morphological 

 development and strong swimming capabilities at hatching. 



Biological variables controlled for this study include: reproductive condition 

 of predator (a L:D 10:14 photoperiod was used to minimize reproductive 

 development interference); nutritive condition (all predators were fed a mixed 

 daily diet of Tetramarin flake food and adult frozen Artemia salina until 48 

 hours prior to a test); predator size in relation to prey size (preliminary tests 

 indicated selection of a predator size of 6-8 cm total length (TL)); feeding 

 periodicity (all tests were performed at the same time of day); and hunger state 

 (all predators were starved 48 hours prior to a test). 



Forty-eight hours prior to a test, each predator was placed into an 

 experimental predation tank, which consisted of a polypropylene tub 30 cm 

 diameter x 12.5 cm deep, with a clear Plexiglas bottom (Figure 19-1). Test 

 tanks received a continuous flow of filtered seawater ('v 400 ml/min.) pumped 

 directly from Narragansett Bay. All predation tests occurred between 1300 and 

 1 500 hours at ambient bay water temperatures. 



291 



