Atlantic croaker Micropogonias undulates (Linnaeus, 1766) larvae < 6 mm showed a distinct pattern of vertical stratification in inner-shelf waters (< 25 m depth) of the northcentral Gulf of Mexico. Discrete-depth plankton collections were taken at night, early morning after
daylight, and at mid-day or early afternoon at 1, 5, and 11–16 m. No consistent pattern among cruises was evident in the vertical stratification of Atlantic croaker larvae found in mid-day and afternoon collections, but at night the highest abundances were observed at the deepest depths
sampled. Atlantic croaker larvae were least abundant in surface waters (1 m) at night. Of the 66,913 Atlantic croaker larvae collected, only 346 specimens (< 1%) were found in 1 m collections at night, and 266 of these larvae were from a single collection of large specimens (mean = 6.7
mm). By morning the vertical distribution of larvae suggested that Atlantic croaker had moved up in the water column, and highest abundances were usually found at 5 m. There was no indication that patterns of larval distribution reflected hydrographic stratification within the water column,
prey availability, size of larvae, or moonlight intensity.
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