MEPS 128:279-285 (1995)  -  doi:10.3354/meps128279

We investigated the effects of variations in the abundance of microzooplankton (Artemia sp. nauplii) and the size of larval fish on the latter's vulnerability to predation by a vertebrate, the threespine stickleback Gasterosteus aculeatus. We used capelin Mallotus villosus, cod Gadus morhua and winter flounder Pleuronectes americanus larvae as our prey species. Analysis of covariance indicated a highly significant effect on mortality rates due to predation caused by the presence of alternate prey (F_3,148 = 10.8, p < 0.001), but a close examination of the results indicates that only levels of alternate prey exceeding 250 nauplii l^-1 caused a reduction in the impact of sticklebacks on larval fish. Furthermore, the size of the fish larvae also had a significant impact on mortality rates (F_1,148 = 6.9, p < 0.001) in a comparison among species, however, this relationship was not apparent within species. Overall, as the size of larvae increased, mortality rates increased. As the size of the larvae decreased, the ingestion rate of larvae by the predator at low levels of alternate prey (<=25 nauplii l^-1) showed a substantial increase relative to the ingestion rate of larvae at high levels of alternate prey (250 nauplii l^-1). Results indicate that as the size of larvae approaches the size of the more abundant alternate prey, the likelihood of an attack may decrease due to the presence of alternate prey. Whether the impact of increased microplankton abundance in the field would be greater through enhanced feeding of the larvae or reduced impact of the predator is unclear.

Fish larvae . Body size . Predation