Distribution and Abundance of Ommastrephid Squid Paralarvae off the Florida Keys in August 1989

Latitudinal and vertical distribution and abundance of paralarval ommastrephid squid were determined from 178 vertically stratified MOCNESS plankton samples taken at 35 stations. Ommastrephids were divided into three morphological types: Type A′ and Type B′, which may include the genera Ommastrephes, Ornithoteuthis, and Hyaloteuthis, and Type C′ which is Illex. The most abundant type was Type A′ with a mean catch of 3.51·10 m⁻² and a maximum catch of 16.2·10 m⁻². Ommastrephid paralarvae had peak latitudinal abundances at the Gulf Stream front. Types A′ and B′ differed in depth of peak concentration: Type A′ was most abundant between 25–50 m and Type B′ was most abundant between 75–100 m depth. This difference in depth distribution suggests differences in habitat utilization between the two types. Some evidence of diel vertical migration was found for Type A′. Paralarvae ranged in size from 0.7–7.5 mm mantle length. Large and small paralarvae coincided in samples along the Florida Keys indicating multiple spawning events upstream of the Keys. Only three Illex spp. paralarvae were collected in August but more have been found in subsequent winter cruises. Illex is considered a winter spawner north of the Florida Straits. Illex in our samples could reflect an extended spawning season in southern I. illecebrosus populations or advective losses from other species in the Gulf of Mexico and Caribbean Sea.