1122 North American Journal of Fisheries Management 25:1122–1129, 2005 [Managment Brief]  Copyright by the American Fisheries Society 2005 DOI: 10.1577/M04-111.1 Index-Removal Estimates of Dredge Efficiency for Sea Scallops on Georges Bank TODD GEDAMKE,* WILLIAM D. DUPAUL, AND JOHN M. HOENIG Virginia Institute of Marine Science, College of William and Mary, Post Office Box 1346, Route 1208 Greate Road, Gloucester Point, Virginia 23062, USA Abstract.—In June of 1999, fishermen were allowed access to the southern section of Georges Bank Closed Area II in the North Atlantic to harvest the large biomass of sea scallops Placopecten magellanicus that had ac- cumulated during a 5-year multispecies fishing ban. Pri- or to the opening, managers conducted a fine-scale sur- vey of the area and a catch quota was established as a fixed percentage of the estimated biomass. The estimate of biomass was uncertain because it was based on es- timates of dredge efficiency that ranged from 16% to 40%. Because survey stations were reoccupied at the end of the fishery and significant removals had occurred, it was possible to use the index-removal method to ob- tain an estimate of gear efficiency. The estimate was 54% and ranged from 41% to 54% depending on model inputs. The 54% efficiency is believed to represent a maximal efficiency estimate. In 1998, the fishery for sea scallops Placopecten magellanicus began lobbying for access to the Georges Bank closed areas in the North Atlantic to harvest the large biomass that had accumulated during a 5-year multispecies fishing ban. An industry–government partnership was initiated to provide a more detailed description of sea scallop abundance in the closed areas. As part of this co- operative program, a fine-scale grid survey of Georges Bank Closed Area II (GBCAII) (Figure 1) was conducted to quantify resource abundance and distribution during the summer of 1998. The results of this survey provided managers with enough information to develop Framework Adjustment 11 to the Scallop Fishery Management Plan (FMP) and Framework Adjustment 29 to the Northeast Multispecies FMP. These frameworkad- justments allowed sea scallop fishermen access to the southern section (south of 41°30'N) of GBCAII as part of an experimental fishery program begin- ning on June 15, 1999. Prior to the opening, indices of biomass were generated from both the 1998 cooperative survey and the annual sea scallop survey conducted by * Corresponding author: gedamke@vims.edu Received July 12, 2004; accepted December 6, 2004 Published online July 22, 2005 the National Marine Fisheries Service (NMFS) RV Albatross. However, the conversion of this infor- mation into absolute values was difficult. Three different models estimated 16–40% dredge effi- ciency and left managers with absolute biomass estimates that ranged from 25 million to 63 million lb and sea scallop total allowable catch (TAC) es- timates that ranged from 6 million to 15 million lb. A sea scallop TAC was set at approximately 10 million lb based on an assumed gear efficiency of 25%, and a bycatch TAC for yellowtail flounder Limanda ferruginea was set at 850,000 lb. In 5 months, nearly 6 million lb of large sea scallop meats were harvested before the yellowtail floun- der TAC was reached on November 12, 1999. A study we conducted during the opening (Gedamke et al. 2004) and a review of data from the opening (NEFMC 2000) indicated that the 25% efficiency chosen in the final framework adjustment signifi- cantly overestimated stock size. In this study, preseason survey stations were reoccupied during the last few weeks of the com- mercial fishery. Since total catch is known and a postfishing survey index is available, the gear ef- ficiency can be estimated with the index-removal method (see Hoenig and Pollock 1998). Methods Study site and data collection.—The GBCAII is located along the Hague line in the easternmost U.S. portion of Georges Bank (Figure 1). It is ap- proximately 200 nautical miles (nm) off the coast of Cape Cod, Massachusetts, and encompasses an area of 2,020 nm 2 . Three different sources of in- formation from GBCAII were used for this study: a 1998 cooperative fine-scale grid survey, vessel monitoring system (VMS) reports, and survey data collected onboard commercial vessels during the last few weeks of the opening. The 1998 cooperative survey involved partici- pants from the Center for Marine Science and Technology of the University of Massachusetts– Dartmouth, the Virginia Institute of Marine Sci- ence (VIMS) of the College of William and Mary,