Estimates of Sea Scallop (Placopecten magellanicus) Incidental Mortality from Photographic Multiple Before—After-Control—Impact Surveys

Abstract

After several decades of stock decline, the Atlantic sea scallop (Placopecten magellanicus) resource has rebounded to become one of the most valuable fisheries in the United States. The continued sustainability of this fishery is supported by catch limits determined by annual stock projection models. Incidental mortality is an important term in these projection models, but is historically difficult to measure. Current estimates are derived from field experiments that relied heavily on qualitative observations and as a result are based on limited data with low precision. To better quantify incidental mortality, a multiple before-after-control-impact experimental design was used to measure the effect of scallop dredging on the disposition of sea scallops that remain uncaptured on the seafloor following dredging. An autonomous underwater vehicle was used to collect color photographs and side-scan sonar images of the seafloor before and after controlled dredge treatments in the mid-Atlantic and Georges Bank regions. Approximately 170,000 photographs were annotated for instances of mortality. Dredge-induced incidental mortality of 2.5% and 8% was estimated for the mid-Atlantic Bight and Georges Bank sites, respectively, a difference that is likely attributable to the relatively harder substrate of the scallop habitat on Georges Bank that results in greater physical trauma to the uncaptured scallops. This study provides a quantitative estimate of incidental mortality using a noninvasive platform that offers precise mission navigation for repeated surveys. The spatial scale and distribution of the study sites are broad relative to past incidental mortality studies, and the substrate types at each are common in the sea scallop fishery. Estimated mortality rates are lower than the values currently used in fishery stock models and suggest the existing values are conservative, but likely appropriate estimates for management purposes.

Discard Mortality of Sea Scallops Placopecten magellanicus Following Capture and Handling in the U.S. Dredge Fishery

“…One process entails an individual encountering the gear but not being captured (i.e., incidental mortality). While often difficult to measure in the field, some studies have been able to estimate incidental mortality rates empirically (Medcof and Bourne 1964;Caddy 1973;Murawski and Serchuk 1989;McLoughlin et al 1991;Ferraro et al 2017;Patterson et al 2017). The other component of the nonharvest mortality process results from an animal being captured and subsequently discarded (i.e., discard mortality; Broadhurst et al 2006).…”

A Review of Unmanned System Technologies with Its Application to Aquaculture Farm Monitoring and Management

“…The images used as a dataset were captured by a downwardpointing digital camera installed in the nose of the AUV. In the work of Ferraro [170], UAV was also used to collect color photos and side-scan sonar images of the seafloor to perform a quantitative estimate of incidental mortality using a precise and non-invasive method for sea scallops. AUV was also used to capture a reliable image of the seafloor to determine the density and size of the scallops, thus providing an accurate set of data for site surveys.…”

“…Table 8 presents the different application of unmanned vehicles for aquaculture farm monitoring and management. GoPro camera and led lights [172] Assessment of the population/ stocks of wild scallops Gavia AUV Downward-pointing digital camera [169] Telegavia UAV a Point Grey Grasshopper 14S5C/M-C model with Sony ICZ285AL CCD [170] Teledyne Gavia AUV Nose cone camera, GeoSwath phase measuring bathymetric sonar, Marine Sonic side-scan sonar) [171] Monitoring of the growth environment at the farm site Customized ROV USB camera based on LIFI [165] Offshore kelp monitoring DJI Phantom 4 Pro 20 MP (1" CMOS sensor, 84 • FOV) color camera [168] Recognition of fish species Underwater drone (type not specified) 360-degree panoramic camera with two 235-degree fisheye lenses [174] Salmon protection Underwater laser drone Stereo camera system [177] Fish cage inspection BlueROV2 of BlueRobotics Camera [175] Observation of fish behavior Customized UAV Cameras with power LEDs and water quality sensors [56] Fish tracking AggieAir…”