Largemouth Bass in Coastal Estuaries: A Comprehensive Study from the Mobile-Tensaw River Delta, Alabama
Dennis R. DeVries, Russell A. Wright, David C. Glover, Troy M. Farmer, Michael R. Lowe, Alicia J. Norris, and Adam C. Peer
Abstract.—Largemouth Bass Micropterus salmoides is typically thought of as a freshwater species, but populations occur in oligohaline portions of estuaries throughout the U.S. Atlantic and Gulf of Mexico coasts, often with popular fisheries. These coastal populations must deal with the physiological stresses associated with salinity variation and may be isolated from inland freshwater populations, increasing the potential for differentiation. To understand factors important to the ecology and management of these coastal populations, we quantified individual- and population-level parameters for Largemouth Bass across a natural salinity gradient in the Mobile-Tensaw River delta in southwestern Alabama during 2002–2009 (including population demographics, feeding ecology, movement, recruitment, and bioenergetics processes). Combining traditional mark–recapture and telemetry techniques with otolith microchemical analyses, we demonstrated that Largemouth Bass of all ages moved very little, even in response to increasing salinity (up to 15‰) in downstream areas. Large individuals were rare in our sampling across both fresh and brackish habitats (only 7 out of 9,530 individuals were >2.27 kg), and fish body condition increased downstream with increasing marine influence. Growth responses for fish across the estuary were more complex, varying with both fish age and salinity. Faster growth was observed in the brackish, downstream areas for fish ≤age 2, while growth of older fish was faster in freshwater upstream sites. Using bioenergetics modeling, we demonstrated that a complex combination of spatial variation in water temperature, prey energetic content, and metabolic cost of salinity was responsible for age-specific spatial variation in growth. Preliminary genetic analysis suggests that these coastal Largemouth Bass may differ genetically from inland fish. Coastal Largemouth Bass populations face a number of potential conservation concerns, and their management will require different approaches compared to their inland counterparts, including different goals and expectations, likely even requiring consideration as unique stocks.