Effects of tethering on predatory escape by juvenile blue crabs Callinectes sapidus Rathbun were examined. Trials were conducted in a large flume to simulate the natural sedimentary and hydrodynamic properties of open sand flats in low-energy estuarine environments. Behavioral interactions between juvenile (prey) and adult (predator) blue crabs were video recorded, then quantified by cornputervideo motion analysis. Sig~uficantly more tethered juveniles (70%) were captured by adults than non-tethered juveniles (10%). Kinematics of the prey swimming escape response changed little as a result of the tether. Mean velocity, maximum velocity, and maximum acceleration did not differ significantly between tethered and non-tethered juveniles. But tethered juveniles traveled shorter distances during bursts of sw~rnrning to escape predatory adults, and they could not evade persistent attackers. Whereas tethering is used to assess relative rates of predation, it increases vulnerability of prey organisms to attack. Predation rates will be most inflated for highly mobile prey that effectively evade capture when they are not restrained. Investigators are strongly encouraged to quantify the impacts of tethering on prey escape and survivorship.
Meiofauna are known to be trophically integrated into estuarine food webs in temperate regions primarily as food for bottom-feeding juvenile fishes. In subtroplcal/tropical mangrovedominated estuaries there were few data indicating juvenile fish utilized meiofauna for food. After determining several fishes that ate meiofauna in southeastern Queensland, Australia,,juvenile winter whiting Sillago maculata were allowed to feed on natural mud-dwelling meiofaunal communities in microcosms. Six juvenile whiting (21 to 38 mm) significantly reduced both the nematode and copepod populations in the feeding microcosms and ate a mean of 177 nematodes and 65 copepods fish-' h -' This feeding rate, if continued 4 times a day, is sufficient to provide an adequate daily ration for the whiting [based on estimates from similarly feeding North American juvenile fish). Of the available copepods the whiting ate significantly more Brianola sp., Canuellidae sp. and Ectinosoma sp. than would have been expected by chance. They d~d not select Stenheha (D.) sp., probably because it burrowed beyond the bite depth of the whiting. Whiting are an economically important fish in the IndoPacific and they require meiofauna in their diet during the juvenile stages. They obtain this meiofauna from mangrove-derived detrital muds; in an aquaculture setting they would probably need to be fed meiofauna.
The female reproductive cycle is described in detail. The ovarian cycle passes
through seven stages of maturation, recognized by changes in macroscopic and microscopic
structure. The presence of ovigerous setae in females has been used to estimate
size at sexual maturity; these setae are developed fully only at the maturity moult.
No stages of development could be described for the testis from macroscopic or
microscopic examinations. The structure of the testis and the process of spermatogenesis
are described and compared with results obtained by Matthews (1951) for
Panulirus pencillatus (Oliver). No simple indication of sexual maturity was found for
males, but an estimate was made using other, indirect, evidence.
Observations made of stomach contents of the spiny lobster, Jasus lalandei (H. Milne-Edwards),indicated that it is an opportune feeder, calcareous food forming a large proportion of the natural diet. Laboratory experiments showed that J. lalandei feeds preferentially if given a choice, and selects baits of marine origin before those of terrestrial origin. Feeding is a rhythmic process, most feeding taking place during the early night. Feeding records made in the laboratory under constant conditions of light and dark indicated some persistence of this feeding rhythm in constant darkness, but no persistence in constant light. However, the feeding rhythm observed under normal diurnal conditions of light and dark was altered by abnormal day lengths. J. lalandei is stimulated to feed by the change from light to dark. An initial correlation was made between feeding and locomotor activity.
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