The effects of dams and impoundments on downstream fish assemblages have been well documented, but changes in fish assemblages in upstream tributaries have received little attention. We compared changes in abundance and composition in fish assemblages in streams fragmented by impoundments with those found in nearby unfragmented streams by sampling fish, in‐stream habitat, physicochemical factors, and drainage features in 22 agriculturally dominated streams during the summers of 2002 and 2003. Eleven sampling sites were tributaries upstream of impoundments, while 11 were tributaries of free‐flowing rivers. We tested the hypothesis that fish assemblages upstream of impoundments would differ from those found in streams without impoundments. Using multiple regression and canonical correspondence analysis, we partitioned the variation in species distributions into that explained by in‐stream habitat, reach‐level factors, drainage features, and temporal variation. Spatial patterns of species distributions indicated significant upstream effects of impoundment, fragmentation being the single largest predictor of species distributions. Mean fluvial specialist richness was significantly greater in unfragmented (6 species/reach) than in fragmented streams (3 species/reach), whereas mean fluvial generalist richness was significantly greater in fragmented (12 species/reach) than unfragmented streams (8 species/reach). A shift in piscivore abundance and composition was also observed, with smallmouth bass Micropterus dolomieu and redfin pickerel Esox americanus replaced by largemouth bass M. salmoides and white bass Morone chrysops in the streams fragmented by impoundments. Additionally, greater total richness and piscivore abundance was observed in tributaries upstream of impoundments. Unfragmented streams showed a significantly lower total abundance of piscivores (7 fish/reach) than upstream tributaries of impoundments (14 fish/reach). The downstream presence of an impoundment led to significant homogenization of fish assemblages through a significant increase in generalist richness and abundance in fragmented streams and a shift in the abundance and type of piscivores.

We developed a conceptual model of reproductive resilience based on spatio-temporal diversity in spawning activity and the 'big old fat fecund female fish' effect, i.e., trends in reproductive traits with size and age. We chose red snapper Lutjanus campechanus as our case study, as this species is highly fecund, currently overfished, and long-lived (50+ yr). The intrinsic reproductive resilience of red snapper was assessed in terms of spawning site distribution, variability in time of spawning, and potential reproductive lifespan. To assess how age truncation might erode reproductive resilience, we evaluated the strength of the relationship between size and age and the following traits: spawning habitat, reproductive timing, batch fecundity, and egg quality. Few fish were older than 7 yr. Although younger fish occurred in a more restricted range of depths, there was no trend between size or age and depth. Spawning activity was well distributed over space and time, with actively spawning females collected at 92 of 195 sampling sites over an extended spawning season. Larger, older females exhibited longer spawning periods and higher batch fecundities, but neither greater spawning frequency nor egg dry weight. The ratio of the effective to predicted reproductive lifespan at maximum sustainable yield was 31%. Many parameters estimated in this study are common to fish reproductive studies, but we hope that integrating them into a reproductive resilience framework will help focus the need for research on the underlying relationships between reproductive traits and stock productivity.

Quantitative estimates of relative abundance, spatial and temporal distribution, and habitat preference of common snook Centropomus undecimalis along shoreline habitats in four Florida estuarine areas were determined. Significant differences in the relative abundance of common snook among the estuarine areas suggested marked variation in common snook population abundance and densities on a regional scale. The highest adjusted mean relative abundance of common snook occurred in the southern Indian River Lagoon (4.68 fish/haul; SE = 0.08), followed by Tampa Bay (3.36 fish/haul; SE = 0.11), Charlotte Harbor (2.13 fish/haul; SE = 0.10), and the northern Indian River Lagoon (0.76 fish/haul; SE = 0.21). Several common factors (e.g., mangrove and seagrass habitat, salinity, and water temperature) among the estuarine areas were linked with common snook relative abundance and distributions, allowing us to better understand how these fish interact with their environment in different regions of Florida.

Blue crabs (Callinectes sapidus (Rathbun)) are commercially important and are an integral part of the estuarine ecosystem as both predators and prey. Although adult blue crabs have been the focus of many studies, there is little published information on immature blue crab abundances, especially on the west Florida coast. The objectives of this study were to analyze the distributions and abundances of immature and adult blue crabs in the Tampa Bay estuary, specifically as they relate to 1) monthly and yearly trends in abundance and size, 2) timing of recruitment to the estuary, 3) sex-and sizedetermined distribution patterns, and 4) the influence of environmental factors, such as freshwater input. Catch rates, length frequencies, and indices of abundance were calculated for recruiting [#20-mm carapace widths (CW)], juvenile (21-80-mm CW), and adult (.80-mm CW) blue crabs caught during 1996 and 1997. Abundances of all size classes of blue crabs differed by region and month; juvenile and adult abundances were also significantly related to salinity. Immature crabs were collected in all months, confirming an extended spawning season, but there were elevated catches of recruiting blue crabs in February and September. Adults were caught year-round, with males generally being more abundant than females. Geographical regions close to the mouth of the bay had the highest densities of recruits, perhaps because of the supply of larvae being delivered to that area from offshore. With the use of monthly seine and river trawl data from an extended time period (1996-2004), annual variations in the abundance of immature and adult blue crabs were examined. A decline in the abundance of immature crabs collected in 21.3-m seines began after 1998, with a significant low occurring in 2002. A similar pattern was observed for adults collected in river trawls and by commercial fisheries. Unfavorable salinity regimes during this time period may have contributed to these abundance trends.

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