Environmental influences on juvenile fish abundances in a river-dominated coastal system

We investigated the influence of climatic and environmental factors on interannual variations in juvenile abundances of marine fishes in a river-dominated coastal system of the north-central Gulf of Mexico, where an elevated primary productivity sustains fisheries of high economic importance. Fish were collected monthly with an otter trawl at three stations near Mobile Bay from 1982 to 2007. Fish sizes were used to isolate juvenile stages within the data set, and monthly patterns in juvenile fish abundance and size were then used to identify seasonal peaks for each species. The average numbers of juvenile fish collected during these seasonal peaks in each year were used as indices of annual juvenile abundances and were related to corresponding seasonal averages of selected environmental factors via a combination of principal components analysis and co-inertia analysis. Factors contributing the most to explain interannual variations in juvenile fish abundances were river discharge and water temperature during early spring-early summer, wind speed and North Atlantic Oscillation index during late fall-winter, and atmospheric pressure and wind speed during summer-fall. For example, juvenile abundances of southern kingfish Menticirrhus americanus during summer-fall were positively associated with atmospheric pressure and negatively associated with wind speed during this period. Southern kingfish juvenile abundances during late fall-winter were also negatively associated with wind speed during the same period and were positively associated with river discharge during early spring-early summer. Juvenile abundances of the Atlantic croaker Micropogonias undulatus during early spring-early summer were negatively associated with river discharge and North Atlantic Oscillation during late fall-winter. Overall, the importance of river discharge for many of the species examined emphasizes the major role of watershed processes for marine fisheries production in coastal waters of the north-central Gulf of Mexico.