Developmental Taxonomy and Distribution of Paralarval Squid from the Florida Current
Adams, Carrie Leeonne
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Distribution patterns of paralarval squid across the continental shelf of Florida were examined based on five years of collections. Squid occurrence patterns were described in relation to coastal, intermediate, and Florida Current (Gulf Stream) water masses by comparing horizontal and vertical distribution patterns of squid species to physical-chemical distribution patterns Twenty-six squid taxa were collected in this study. Representative taxonomic descriptions and illustrations of all taxa were produced to serve as an identification aid for the paralarval squid from the Florida shelf. Patterns of species composition among stations were analyzed with cluster analysis based on four sampling approaches. Species distribution patterns were compared to the spatial patterns of hydrographic parameters determined by cluster analysis. The four methods of sampling utilized in this study were transect, discrete, drogue, and fixed site sampling. The cross-shelf transect sampling detected an association of species distribution with a particular water mass. Hydrographic properties indicated meandering of the Gulf Stream as it moves from a more inshore to more offshore location. The highest species diversity of all three water masses was associated with the Gulf Stream. The discrete sampling, which partitioned the water column into three vertical sections, found higher abundance and diversity of paralarval squids in the mid-depth regions. There was some evidence that paralarval squid exhibited vertical migration from mid-depth and bottom waters during the day to the surface waters at night, although sample numbers were low. The drogue sampling showed differences in squid abundance between years and even some differences in squid abundance and composition on successive tows on a single day. Differences in mean hydrographic conditions on successive tows suggest that a surface drogue may not adequately track subsurface water masses. The oblique sampling at a fixed site found a significant difference in total abundance over a three day period. While each of these sampling regimes are encouraged for future studies, the emphasis should be on the transect and discrete sampling approaches. Day-night sampling should be conducted over a longer time period to provide a more accurate determination of the paralarval squid species that exhibit vertical migration.