Diets and selective feeding by larvae of Atlantic mackerel Scomber scombrus on zooplankton

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Abstract
The diets of 201 larval S. scombrus L. collected from Long Island Sound, New York (USA) during May-June 1982 and 1983 are described. First-feeding larvae (3.5 mm in length) were phytophagous. The diets of larvae 45 mm were composed of the nauplii of Acartia hudsonica, Temora longicornis and Pseudocalanus sp. Larvae > 5 mm ate some copepodites of A. hudsonica and T. longicornis and smaller proportions of the phytoplankton and copepod nauplii. Mackerel .gtoreq. 6.5 mm were cannibalistic, eating larvae 3.5-4.5 mm in length. Weight in stomach contents averaged 1.8% of an individual''s body weight. In order to satisfy its daily energy requirement, a mackerel larva must consume 25 to 75% of its body weight/day. Larvae fed selectively, taking a greater proportion of T. longicornis and Pseudocalanus sp. nauplii and a lesser proportion of A. hudsonica nauplii than expected by chance alone. Ivlev index values for T. longicornis nauplii were +0.66, for Pseudocalanus sp., +0.25, and for A. hudsonica, -0.55. The Chesson index and Pearre''s ''C'' yielded the same result. Mackerel larvae probably select food primarily on the basis of prey visibility (both Pseudocalanus sp. and T. longicornis nauplii are more motile than A. hudsonica nauplii). Even though mackerel larvae consume large numbers of copepod nauplii per day and feed selectively on certain species, mackerel larvae are not sufficiently abundant in Long Island Sound to have an impact on copepod population dynamics.

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