Coastal Estuaries as Habitat for a Freshwater Fish Species: Exploring Population-Level Effects of Salinity on Largemouth Bass

Transactions of the American Fisheries Society
Norris, A;DeVries, Dennis;Wright, Russell A.
Pub ID:
Abstract.—Estuaries are systems where marine and freshwaters interface. The largemouth bass Micropterus
salmoides is a freshwater predator commonly found in the oligohaline portions of estuaries in coastal North
America. As a popular recreational sport fish in estuaries, largemouth bass are caught in large numbers, but
large (2.3-kg) individuals are rarer than in inland (freshwater) systems. A pervasive factor affecting
estuarine inhabitants is variation in salinity, which we hypothesized would represent a stress influencing
largemouth bass performance. To test this, we sampled fish monthly (2002–2004) across an upstream–
downstream gradient in the Mobile–Tensaw Delta of Alabama. Salinity remained negligible upstream but
increased seasonally downstream. Catch per effort did not differ predictably across the upstream–downstream
gradient, as would be expected if salinity influences abundance. Largemouth bass diets included more fish
than invertebrates both upstream and downstream, but fish were more abundant in the diet upstream. Marine
invertebrates remained an important diet component at all sites. Condition was generally high for all
largemouth bass but was consistently greater downstream than upstream. Length at age 1 was greater
downstream than upstream, but there were no differences for older fish. Few largemouth bass age-4 and older
were present, and survival was generally low (,57%). Although growth was greater for a population of
largemouth bass from the Mobile–Tensaw Delta established into a freshwater impoundment, survival
remained low in the absence of coastal influences. Our results suggest that the largemouth bass in the coastal
Mobile–Tensaw Delta have different growth patterns and perhaps different life history strategies than those in
freshwater, which may be the result of adaptation and could have important implications for management.
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