Symposium Abstract: A Before-After-Control-Impact Study of the Sea Scallop Fishing Grounds of Georges Bank
K. D. E. Stokesbury and B. Harris
A Before-After-Control-Impact (BACI) study is the optimal environmental impact experimental design. The null hypothesis is “an impact resulted in no biological damage”. Fisheries management often relies on time series of data but unless there is a control all before-after comparisons must assume homogeneity over time, an assumption that has been found invalid time and again. We surveyed the historic scallop fishing grounds of Georges Bank that have been closed to mobile gear since 1994. We employed a BACI design with a 1-year set of baseline observations, two experimental areas that were exposed to intense fishing pressure, two control areas with no fishing, and one control with constant fishing. Within each experimental area we conducted a high-resolution video survey using a multistage design with stations separated by 0.85 nautical miles. The video survey was based on sea scallop densities to obtain a 5% to 15% level of precision for the normal and negative binomial distributions, respectively. Mounted on the pyramid were two video cameras and several lights. Four quadrat images (2.8 m2 ) of the sea floor including counts and sizes of scallops, other macroinvertebrates and benthic fishes and sediment types, were relayed in real time to the surface. These images were video taped and the exact position (latitude and longitude from differential GPS) depth, and time. During all surveys the same stations were sampled. Changes in species composition, density and distribution macroinvertebrates and groundfish, and in sediment structure will be compared.