that starved larvae tended to be neutrally buoyant because of a relative increase 

 in body water. They speculated that under starvation conditions larvae would 

 be relatively inactive, suspended in midwater, and thus more susceptible to 

 plankton net sampling than well nourished larvae. Blaxter and Ehrlich's (20) 

 results differ somewhat from Wyatt's (100), partly because of the different 

 criteria used to define activity. 



Behavior of northern anchovy larvae in dense patches of prey, 

 Gymnodinium splendens and Brachionus plicatilis, was investigated by Hunter 

 and Thomas (49). In dense patches larvae swam slower and covered smaller 

 areas. Reversals in swimming direction occurred more frequently in patches of 

 food than in non-patch situations. The evidence strongly suggested that 

 northern anchovy larvae were able to maintain themselves in suitable patches 

 of prey, and that such an adaptation would allow larvae to take advantage of 

 prey patchiness in the sea. 



PREDATION 



Predation almost certainly is the greatest direct cause of mortahty to marine 

 fish larvae, but there have been few attempts to evaluate its impact in 

 laboratory studies. The food supply of larval fishes and other environmental 

 factors can modify the predation mortaUty experienced by a cohort. As 

 Gushing (29) noted, larvae that have an adequate food supply grow fast and 

 swim well. Thus, they presumably avoid predation by growing quickly through 

 the larval phase, when they are most vulnerable to a variety of planktonic 

 predators. Similarly, pollutants or toxicants that retard larval growth or modify 

 behavior could lead indirectly to increased predation mortality. 



Four recent laboratory investigations have examined the potential impact of 

 predators on larvae. Three species of pontellid copepods could more than meet 

 their metabolic requirements by preying upon yolk-sac larvae of northern 

 anchovy (62). Predation in 3500 ml beakers increased as anchovy larvae 

 concentration was raised. Two of the copepods, Labidocera jollae and L. 

 trispinosa, were only efficient as predators on yolk-sac larvae, but a third 

 species, Pontellopsis occidentalis , also was able to prey on more developed, 

 faster swimming larvae. The presence of alternate prey {Artemia salina nauplii) 

 reduced larval mortality caused by Labidocera spp.in direct proportion to the 

 numbers oi Artemia that were present. In similar experiments, but using the 

 euphausiid Euphausia pacifica, as an anchovy larva predator, Theilacker and 

 Lasker (94) demonstrated that larval, juvenile and adult stages of the 

 euphausiid could meet their daily carbon requirements by preying upon 

 northern anchovy yolk-sac larvae. There was no strong evidence that anchovy 

 concentration, when above 10 per 3500 ml, or the presence of alternate prey 

 (Artemia nauplii) significantly influenced the predation rate on anchovies, at 



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