Predation dynamics of mackerel on larval and juvenile anchovy: is capture success linked to prey condition?
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We tested whether the predation dynamics of chub mackerel Scomber japonicus and spotted mackerel S. australasicus on young anchovy Engraulis japonicus relates to individual growth characteristics of the prey and could account for the growth-selective survival predicted by recruitment hypotheses. Juvenile and adult mackerel were sampled along with their young anchovy prey field in 2004 (juvenile mackerel and larval anchovy) and 2005 (adult mackerel and juvenile anchovy) off the Pacific coast of Honshu, Japan. The recent 5-day mean growth rate of larval and juvenile survivors and prey found in the stomach of mackerel was estimated from the otolith microstructure. No significant difference was found between the recent growth of larval or juvenile survivors and that of preyed individuals. We conclude that despite a relatively small body size, the high activity level and predation skills displayed by mackerel prevent fast-growing larvae and early juveniles from benefitting in terms of the expected survival advantage over slow-growers. Hence, growth-selective predation mortality of larval fish would depend on the feeding ecology of the predator rather than predator size. Selection for fast growth is more likely to occur under predation pressure from invertebrate organisms and small pelagic fish specialized on zooplankton, such as herring and anchovy.
KeywordsGrowth rate Growth-selective predation Larval and juvenile anchovy Mackerel Otolith microstructure Predation mortality
We are grateful to the officers and crew of RVs Hokuho-maru, Kaiun-maru, and Soyo-maru and to M. Takahashi, A. Yatsu, and N. Yamashita for their support during the sampling at sea. We also thank S. Shindo and A. Matsuura for their help with otolith preparation, and M. Saito for otolith reading. DR was funded by a joint scholarship of the Japan Society for the Promotion of Science (JSPS) and the Natural Science and Engineering Research Council of Canada (NSERC).
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