Je. Serafy et al., MECHANICAL REMOVAL OF HYDRILLA IN THE POTOMAC RIVER, MARYLAND - LOCALIMPACTS ON VEGETATION AND ASSOCIATED FISHES, Journal of freshwater ecology, 9(2), 1994, pp. 135-143
Tidal freshwater fish assemblages were sampled quantitatively from bed
s of Hydrilla verticillata in the Potomac River, Maryland, to assess l
ocal impacts of mechanical plant harvesting. Seasonal and diel estimat
es of fish density, biomass and species richness were compared at an u
ndisturbed site and an adjacent mechanically harvested site. Harvestin
g had a ''pruning'' effect on Hydrilla: plant biomass levels at the ha
rvested site exceeded those at the undisturbed site after periods > 23
d. Fish species composition at the two sites was very similar and spe
cies richness differences were minor. Significantly lower (P<0.05) mea
n fish density and biomass values were found at the harvested versus t
he undisturbed site < 23 d after plant removal. However, 43 d after pl
ant removal, fish density was significantly higher (P<0.05) at the har
vested site, while biomass differences were minor. Species-specific di
fferences suggested that harvesting improved habitat for pelagic speci
es (e.g., Menidia beryllina) but negatively affected cover-oriented sp
ecies (e.g., Fundulus diaphanus). Results suggest impacts of mechanica
l harvesting on the fish assemblages investigated were short-term and
minor at the local, community level. However, ten species were killed
in the mechanical harvesting process. We estimated that this immediate
loss represented 11-22% of fish numbers and 4-23% of biomass. Mechani
cal harvesting, when macrophyte beds are in short supply, may not be p
rudent.