FISH PREDATION ON JUVENILE BROWN SHRIMP, 



PENAEUS AZTECUS IVES: EFFECTS OF TURBIDITY AND 



SUBSTRATUM ON PREDATION RATES 



Thomas J. Minello, Roger J. Zimmerman, and 

 Eduardo X. Martinez! 



ABSTRACT 



Predation on juvenile brown shrimp, Penaeus aztecus, by three species of estuarine fishes was examined 

 in a series of laboratory experiments to determine the effect of turbid water and the presence of a suitable 

 substratum for burrowing. Regardless of the type of substratum, turbid water increased predation by 

 southern flounder, Paralichthys lethostigrm, and decreased predation by Atlantic croaker, Micropogonias 

 undulatus. In both clear and turbid water, the presence of sand, which allowed shrimp to burrow, 

 decreased predation by southern flounder but had no significant effect on feeding rates of Atlantic croaker. 

 There was a significant interaction between the effects of turbidity and substratum on predation by pin- 

 fish, Lagodon rhomboides. Turbid water decreased predation in tanks with hard substrata but had no 

 significant effect in tanks with sand. The presence of sand reduced predation only in clear-water tanks. 

 Burrowing by brown shrimp was reduced in turbid water which may explain this interaction. Overall, 

 the data indicate that both turbid water and a suitable substratum for burrowing may reduce predation 

 on brown shrimp, but the value of these refugia is highly dependent upon the species of predator. 



Predation by fishes appears to be a major source of 

 mortality of juvenile brown shrimp, Penaeus aztecus 

 Ives, in estuarine nurseries. Brown shrimp spend 

 several months as juveniles in estuaries, and anal- 

 yses of the stomach contents of some estuarine 

 fishes indicate a high incidence of predation on 

 penaeid shrimp (see Minello and Zimmerman 1983 

 for review). The presence of salt marsh vegetation 

 apparently offers shrimp protection from some of 

 these predators (Minello and Zimmerman 1983; 

 Zimmerman and Minello 1984), but other habitat 

 characteristics that modify or control the extent of 

 predator-related mortality have not been examined. 

 Estuarine systems in the northern Gulf of Mexico 

 are generally characterized by high turbidity and 

 fine-grained sediments owing to an abundant supply 

 of suspended sediment from rivers and a relatively 

 low-energy environment (Chapman 1968; Linton 

 1968; Folger 1972). Production of penaeid shrimp 

 in these estuaries is high, and the presence of tur- 

 bid water together with suitable substrata for bur- 

 rowing may contribute to productivity by reducing 

 predation. 



The effect of turbidity on predator-prey inter- 

 actions varies with the organisms examined. In 

 laboratory experiments with the flounder, Platich- 



'Southeast Fisheries Center Galveston Laboratory, National 

 Marine Fisheries Service, NOAA, Galveston, TX 77550. 



thys flesus, Moore and Moore (1976) found that 

 turbid water reduced the ability of the fish to see 

 epibenthic prey and increased the ability of prey to 

 avoid capture. The degree of this effect varied with 

 prey species. Gardner (1981) also found that turbid- 

 ity reduced predation by bluegill, Lepomis macro- 

 chirus, on Daphnia in laboratory aquaria. Boehlert 

 and Morgan (1985), however, found that predation 

 rates of larval Pacific herring, Clupea harengus 

 pallasi, apparently increased up to a point in turbid 

 water. Other work in the laboratory and in fresh- 

 water lakes and streams has shown that turbidity 

 can interact with the activity, behavior, and distri- 

 bution of both predators and prey (Heimstra et al. 

 1969; Swensen and Matson 1976; DeVore et al. 

 1980; Gradall and Swenson 1982; Matthews 1984; 

 Sigler et al. 1984), and predation rates in turbid 

 water may be reduced or enhanced (Swenson 

 1978). 



Burrowing by prey in the substratum may also af- 

 fect predation rates, and burrowing by the crayfish, 

 Orconectes propinquus, has been shown to reduce 

 predation by smallmouth bass, Micropterus dolo- 

 mieui (Stein and Magnuson 1976). Although experi- 

 mental evidence is lacking, it has frequently been 

 suggested that burrowing by penaeid shrimp func- 

 tions in a similar manner (Williams 1958; Fuss and 

 Ogren 1966; Hughes 1966, 1968a). Diel periodicity 

 in the burrowing behavior of brown shrimp has been 



Manuscript accepted August 1986. 



FISHERY BULLETIN: VOL. 85, NO. 1, 1987. 



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