Seasonal Variation in Fish Assemblages Within the Estuarine Portions of the Myakka and Peace Rivers, Southwest Florida

Abstract

Juvenile and small adult fish were sampled monthly from 1996 to 2002 in the estuarine portions of the Myakka and Peace rivers, at the northern end of Charlotte Harbor (a relatively pristine estuarine system in southwest Florida). We provide a detailed description of the fish faunas in these areas, including seasonal assemblage structure. Seasonal cycles in assemblage structure were evident. Nearshore (to ~5 m) fish assemblages sampled by seine were separated into three main seasonal groups by cluster analysis (January-April, May-September, September-January). The ichthyofauna collected from deeper (≥1.8 m) areas by otter trawl formed two seasonal groups (June-October and November-March). Small schooling taxa such as Anchoa mitchilli, Menidia spp. and Eucinostomus spp. dominated seine catches, and variations in their abundances contributed greatly to dissimilarities between seasons, as did seasonal recruitment of young-of-the-year (YOY) estuary-dependent species such as Mugil cephalus, Lagodon rhomboides, Leiostomus xanthurus, and Bairdiella chrysoura. Estuarine residents (e.g., A. mitchilli and Trinectes maculatus) and YOY estuary-dependent species (e.g., Cynoscion arenarius and Menticirrhus americanus) were important in defining seasonal dissimilarities in fish assemblages from the trawled areas. Correlations between biotic patterns and environmental factors (water temperature, salinity, dissolved oxygen, precipitation, and river discharge) were relatively low, perhaps reflecting the euryhaline nature of the fish present and their intrinsic spawning periods. The present study provides a detailed description of temporal ichthyofaunal patterns in the estuarine portions of two tidal rivers in southwest Florida and provides a baseline with which future fish populations in this area can be compared.