Benthic Resources Assessment Technique, a Method for Quantifying the Effects of Benthic Community Changes on Fish Resources

Abstract

Preoperational baseline characterizations and postoperational monitoring strategies associated with dredged material disposal in the coastal zone commonly document changes in sediment and benthic invertebrate communities inhabiting those sediments. The U.S. Army Engineer Waterways Experiment Station is developing and field-testing a technique that uses benthic invertebrate community data to make quantitative statements about the feeding habitat value to fish of natural bottoms and bottoms modified by dredged material disposal or other activities influencing substrate quality. The technique, called Benthic Resources Assessment Technique (BRAT), employs two different types of information from a project area. A list of the bottom-feeding fishes inhabiting a project area is used to select the benthic resources important to an impact assessment. As the first step, observations and measurements of the morphology of specimens of these species are carried through a data reduction and analysis sequence that assigns each fish to a feeding strategy class or guild that appears to correlate with potential prey size and a prey's location (depth) below the sediment surface. The second step involves the analysis of information from a benthic macroinfaunal invertebrate community survey. The BRAT then classifies the invertebrate taxa according to their size and the distribution of their biomass relative to the sediment surface. Estimates of standing crop complement this classification scheme. When combined, the two types of information provide an estimate of the potential prey biomss (grams/ meter squared) or energy (kilocalories/meter squared) available to the fish in a particular feeding guild. This technique facilitates the development of a quantitative impact statement using data on changes in the benthos related to project activities. Additionally it allows quantitative comparison to be made between areas being considered for disposal and/or other modification during project planning and uses a measure with social significance (i.e., the potential productivity of the demersal fishery).