Fate and Potential Significance of Postspawning Anadromous Fish Carcasses in an Atlantic Coastal River

Large numbers of spawning, anadromous clupeid fish (Alosa spp.) ascend North American coastal rivers and streams annually. In many regions, post-spawning mortality is high, resulting in potentially significant inputs of marine-derived animal detritus to tidal and nontidal freshwater systems. I estimated retention of carcasses and assessed the mechanism(s) of biological processing for carcasses of migratory blueback herring Alosa aestivalis in the James River, Virginia. In a first experiment, 418 tagged and weighed carcasses placed in the river were transported downstream at an average rate of 986 m/h. In a second experiment, 72 carcasses were fixed in the river as artificial substrates and recovered over the next 192 h. Instantaneous decomposition rates averaged 0.015/h, and the predicted mean time to complete decay was more than 240 h. An aquatic saprolegniale fungus (Saprolegnia sp.) heavily colonized most carcasses after 48 h. No aquatic macroinvertebrates were associated with any recovered ca...