The inflated heelsplitter, Potamilus inflatus, a federally listed freshwater bivalve, has been eradicated from northern portions of its range in the Amite River in Louisiana, USA. We hypothesized that the remaining populations of Potamilus inflatus in the southern part of the Amite River are being affected by increased urbanization of the watershed caused by growth of the surrounding Baton Rouge metropolitan area. Comparison of catch per unit effort in 2007 with a study conducted in 1994 indicated a significant drop in CPUE from 1.76 heelsplitters per site to 0.87. The size distribution of heelsplitters also had decreased in mean shell length from 116 to 97 mm, owing either to dislodgement of larger individuals in spates, or die-offs of larger males. Logistic regression suggested that site variables like substrate type and current velocity were not as important as landscape scale variables in predicting heelsplitter presence at a site. Heelsplitter presence was positively related to the amount of wetland riparian forest, and negatively related to the amount of residential development at the reach (1 km upstream) scale. Our results are significant because we show (1) that statistical models of GIS-based land use can predict the distribution of threatened mussel species, and that (2) conservation of endangered freshwater mussels will require more emphasis on the integrity of the riparian corridor.

Oyster reefs (Crassostrea virginica) supply important ecosystem services to estuarine habitats in the northern Gulf of Mexico, but little is known of the role of fish predators in controlling their structure or areal cover on soft sediments. At two sites and during fall and spring, we employed gill nets and trot lines to remove black drum (Pogonias cromis) from experimental reefs, and assessed oyster survival in comparison to control reefs. Numbers and biomass of black drum removed from reefs varied seasonally, among sites, and among removal methods. In the fall, black drum were rare at one site and abundant at the other, but did not significantly lower oyster survival on control reefs at either site. In the spring, black drum were common at both sites, and significantly lowered oyster survival on control reefs. Oysters and epizoic hooked mussels comprised roughly a third of the fishes' diet, and oyster mortality was closely related to the percentage of drum feeding on oysters. There was little evidence of mortality from other predators of seed oysters like stone crabs or Southern oyster drills, and a repeated measures analysis of variance indicated black drum biomass was significantly depressed on experimental reefs during the experiments. Black drum thus appear to be potentially important predators on oyster reefs, but more work needs to be done on what factors explain the temporal and spatial variation in their abundance and oyster consumption.

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Black drum Pogonias cromis are large, molluscivorous fish that severely limit the abundance of eastern oysters Crassostrea virginica in the northern Gulf of Mexico. In field experiments, we tested two fish removal methods—baited trot lines and gill nets—near commercial oyster leases to determine whether the removal of black drum would increase eastern oyster survival. Both methods removed fish and increased oyster survival in the spring but not in the fall, when little mortality occurred. The numbers and biomass of black drum caught varied with gear type: 10‐cm (bar mesh) gill nets landed the most fish, while trot lines and 10‐cm gill nets were equally effective in landing the greatest biomass. Eastern oysters were more common in the diet of black drum in the spring than in the fall and increased in importance with fish size. Fish of 70–75 cm (standard length) had the greatest impact on oyster production. These fish can be removed most effectively with 12.5‐cm gill nets, though trot lines are preferable because they require less effort and produce less bycatch. The removal techniques used here may also be successful in aiding other bivalve fisheries suffering from predation.

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