VERTICAL MIGRATION AND ITS EFFECT ON DISPERSAL OF 

 PENAEID SHRIMP LARVAE IN THE GULF OF CARPENTARIA, 



AUSTRALIA 



Peter C. Rothlisberg 1 



ABSTRACT 



i 



Penaeid shrimp larvae in the Gulf of Carpentaria, Australia, sampled over discrete depths and time 

 intervals showed a day-night pattern of vertical distribution. The magnitude of the migrations in- 

 creased with larval development. The patterns of vertical distribution were variable and depended 

 strongly on light penetration. Vertical migratory behavior of larvae was linked to currents at var- 

 ious depths. Daily and fortnightly extrapolations of larval displacement showed that vertical migra- 

 tion generally enhanced horizontal advection but the distances and directions were dependent on the 

 current regime and the vertical distribution pattern. It was estimated that larvae could beadvected 

 from 70 to 100 km, far enough to traverse the distance from the known spawning grounds to estuar- 

 ine nursery grounds. Results of this short-term study indicate that differential advection on a 

 seasonal scale may be responsible for the temporal and spatial recruitment patterns of postlarvae 

 observed in the Gulf of Carpentaria. 



Vertical migration is widespread among marine 

 and freshwater Crustacea (Russell 1925; Bain- 

 bridge 1961). The migration is often periodic and 

 can vary from diurnal and tidal through to sea- 

 sonal and ontogenetic periodicity. Almost as 

 diverse as the organisms involved are the prob- 

 able environmental cues that elicit the response 

 and adaptive advantages attributed to this be- 

 havior (Bainbridge 1961; Enright 1977; Pearre 

 1979). Undoubtedly animals have adopted verti- 

 cal migratory behavior for a variety of immedi- 

 ate and long-term biological advantages (Vino- 

 gradov 1968). 



Most of the adaptive advantages of vertical mi- 

 gration that have been suggested usually apply 

 to animals that live in relatively deep water with 

 temperature, pressure, light, food, and predator 

 abundance gradients. Shallow-water holoplank- 

 tonic and meroplanktonic animals also undergo 

 vertical migrations, however. Because the verti- 

 cally migrating animal is exposed to different 

 current regimes at different depths (Hardy 

 1936, 1953), the behavior has been invoked to aid 

 maintenance of position within estuaries (Bous- 

 field 1955; Graham 1972; Weinstein et al. 1980; 

 Wooldridge and Erasmus 1980) and on continen- 

 tal shelves (Walford 1938). It has also been sug- 

 gested that timed vertical migration enhances 



■Division of Fisheries Research, CSIRO Marine Laborator- 

 ies, P.O. Box 120, Cleveland, Qld. 4163, Australia. 



Manuscript accepted January 1982. 

 FISHERY BULLETIN: VOL. 80, NO. 3. 1982. 



horizontal displacement up an estuary (Carriker 

 1951; Wood and Hargis 1971; Sandifer 1975; Big- 

 ford 1979; Sulkin et al. 1980), alongshore (Long- 

 hurst 1968; Efford 1970), or onshore (Woodman- 

 see 1966; Penn 1975; Rimmer and Phillips 1979), 

 often against the prevailing currents. In no in- 

 stance, however, have these mechanisms been 

 demonstrated by monitoring both the vertical 

 behavior and the in situ current regimes simul- 

 taneously. 



Dispersal, during the pelagic larval phase, is 

 the most likely mechanism that brings postlar- 

 val and juvenile penaeid shrimp into shallow- 

 water coastal and estuarine nursery areas from 

 their offshore spawning grounds (Kirkegaard 

 1975). Evidence of vertical migration of penaeid 

 larvae, which might enhance the onshore move- 

 ment, is mixed and inconclusive. In the study by 

 Eldred et al. (1965) the larval vertical distribu- 

 tion patterns were variable between species, but 

 appeared to be consistent in the study by Temple 

 and Fischer (1965). A change in behavior from 

 photopositive to photonegative with develop- 

 ment was reported by Racek (1959), while a 

 gradual increase in vertical migratory ability, 

 without a phase change, has been seen in other 

 studies (Temple and Fischer 1965; Jones et al. 

 1970). Most noticeable have been the variable pat- 

 terns in vertical distribution with varying envi- 

 ronmental conditions in studies with repeated 

 sampling (Temple and Fischer 1965; Jones et al. 

 1970). Nevertheless, based on an idealized larval 



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