Relative Abundance, Growth, and Mortality of Five Age‐0 Estuarine Fishes in Relation to Discharge of the Suwannee River, Florida

Abstract

Understanding the relationships between river discharge and recruitment of estuarine fishes is important because of hydrological alterations caused by anthropogenic water withdrawals. Varying river discharge alters salinity, turbidity, nutrient levels, and detrital concentrations, all of which affect estuarine biota. The lower Suwannee River, Florida, is one of the few remaining large-river systems in the United States that has no major impoundments. We assessed the relationship between seasonal river discharge and relative abundance, growth, and mortality of estuary-dependent age-0 fish of five species in the Suwannee River estuary. We analyzed 9 years of data (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) collected as part of a long-term, fishery-independent monitoring program. The results showed a positive relationship between relative abundance and river discharge for age-0 spotted seatrout Cynoscion nebulosus, sand seatrout C. arenarius, and red drum Sciaenops ocellatus. The pinfish Lagodon rhomboides was the only species for which relative abundance was negatively related to river discharge; the relative abundance of spot Leiostomus xanthurus was not significantly related to changes in discharge. Instantaneous daily growth (G) estimates were positively related to river discharge for all species except spotted seatrout, for which a negative correlation was found. Instantaneous daily mortality (Z) estimates were positively correlated with river discharge for sand seatrout, pinfish, and red drum. The G : Z ratios for pinfish and early recruiting sand seatrout were negatively related to river discharge, indicating that recruitment potential declined with higher discharge. Changes in freshwater discharge affected the abundance, growth, and survival of these juvenile fishes, stressing the importance of water allocation decisions that affect estuarine fishes and the fisheries they support.

Fish Assemblages in the Oligohaline Stretch of a Southwest Florida River during Periods of Extreme Freshwater Inflow Variation

“…As noted by Estevez (2002), single-species analyses have tended to be more common than community-or assemblage-level assessments in estuarine inflow studies; the present study integrated both methods. Changes in habitat extent of the oligohaline zone and associated biota form an important component in the determination of appropriate freshwater inflows to estuaries, along with other factors such as secondary production (e.g., abundance and growth of fish; Purtlebaugh and Allen 2010). In studies that aim to track fish distributions in relation to changing isohalines, we recommend sampling much farther upriver than mean conditions indicate would be necessary, to capture the effects of events such as drought or the long-term effects of water withdrawal.…”

Environmental change drives long-term recruitment and growth variation in an estuarine fish

“…Attributing population dynamics to particular causal mechanisms is, however, difficult because biomass or abundance indices are an integration of demographic and behavioural processes that operate at different temporal and spatial scales (Robins et al, 2005). Repeated observations of recruitment (Staunton-Smith et al, 2004;Jenkins et al, 2010), growth (Robins et al, 2006;Purtlebaugh & Allen, 2010;Stocks et al, 2011;Glover et al, 2013) and behaviour (Crook et al, 2010;Walsh et al, 2013) provide the finer resolution needed to understand population dynamics and individual responses to environmental variability in estuaries. Better still, concomitant measures of these processes facilitate a more complete, in-depth understanding of a species' response to environmental change.…”

Top-Down and Bottom-Up Interactions Influence Fledging Success at North America’s Largest Colony of Caspian Terns (Hydroprogne caspia)

“…Increased freshwater input can affect the recruitment, residence time, and location of fishes in an estuary, as well as altering fish assemblages and abundance, especially of marine forage fishes (Jassby et al 1995;Loneragan and Bunn 1999;Purtlebaugh and Allen 2010). Weitkamp et al (2012) found reduced fish abundance and altered species representation in 2008, 2010, and 2011, years of unusually high discharge for the Columbia River, and reported that these Bnatural experiments for the influence of flow^resulted in both a decrease in numbers of marine forage fishes, especially northern anchovy and Pacific herring, and a decrease in residence time for juvenile salmonids.…”