Brian J. Todd

Stock evaluation of giant scallop (Placopecten magellanicus) using high-resolution acoustics for seabed mapping

Abstract Survey designs in use for the evaluation of sea scallop stocks do not consider the variability of sediment type, despite strong evidence of its importance for the recruitment and survival of scallops on the sea floor. This study examines the distribution of scallops on Browns Bank, Scotian Shelf, at two test sites, in comparison to sea floor sediment distribution, with particular attention to the effects of small-scale sediment variability on the abundance of the commercially exploited scallop. Important links between scallop abundance, sediment type and habitat structure are described. Scallops are strongly associated with gravel lag deposits, which are readily distinguishable from sand-covered terrain through the use of multibeam backscatter data. There exists a highly significant correlation between scallop survey catch rates and backscatter intensity which can be used for the prediction of scallop stock abundance. Developments in underwater acoustics enable for more precise sea floor mapping and contribute to better estimates of scallop abundance.

Quaternary geology and surficial sediment processes, Browns Bank, Scotian Shelf, based on multibeam bathymetry

Abstract Browns Bank is located on the glaciated continental shelf off southern Nova Scotia. Geological mapping of Browns Bank is based on interpretation of multibeam bathymetric and backscatter data, in conjunction with 220 line km of seismic reflection profiles and sidescan sonograms, sea-floor sediment samples and bottom photographs. The Fundian Moraine, part of the previously identified end moraine system on the continental shelf off Nova Scotia, is a prominent west–east, flat-topped, multi-lobate ridge identifiable in the multibeam bathymetric data and in geophysical records. The Fundian Moraine was subjected to erosion in the surf zone during sea-level rise in depths less than 100 m. A series of north–south, roughly parallel till ridges, continuous in the subsurface with the Fundian Moraine, is interpreted as interlobate moraines suggesting formation by a tidewater glacier. The Browns Bank Moraine, connected to the Fundian Moraine, is evidence of a newly identified grounded ice position farther seaward than the latter. Bedforms, including obstacle marks, comet marks, sand waves and megaripples, are evidence of a vigorous anticyclonic current pattern on Browns Bank. The combination of multibeam bathymetric imagery with high-resolution geoscientific information represents a powerful technique for sea-floor geological investigations.

The multiple roles of acoustic mapping in integrated ocean management, Canadian Atlantic continental margin

Coastal and ocean environments worldwide are coming under increasing pressure from resource development. In some cases, integrated coastal zone management programs have been successfully adopted. However, with the collapse of offshore fisheries and competition among industries for use of the seabed, many maritime countries are recognizing that more data are needed to support the sustainable management of offshore resources. Developments in multibeam mapping technology, in concert with traditional geoscience survey techniques, now provide the capability to image the sea floor in high resolution. Examples from the Canadian Atlantic continental margin are used to demonstrate the application of high-resolution sea floor mapping techniques to develop data bases and maps; these maps are fundamental information for the future management of offshore resources.

Chapter 2 Continental shelves of Atlantic Canada

Abstract The wide continental shelves of Atlantic Canada are characterized by a series of banks separated by transverse troughs. These shelves have been imprinted by repeated Quaternary glaciations, so that fluvial valleys have been deepened into fjords and shelf-crossing troughs, and a suite of glacigenic sediments has been deposited. In shallow areas the seafloor is shaped by waves and currents, including the strong tidal currents of the macrotidal Bay of Fundy. Glacigenic sediments have been reworked by modern processes to yield thick muds in basins, and thinner deposits of sand and gravel on wave-dominated banks and the littoral zone. As a result of a cold climate and the Labrador Current, seasonal sea ice occurs to varying degrees across the region, and iceberg impact continues on much of the Newfoundland and Labrador shelves. For the purpose of description, we divide Atlantic continental shelves into four regions and focus on advances in understanding over the past several decades relating to: (1) processes on upper continental slopes; (2) glacial history in the last glacial cycle; (3) glacial land systems; (4) geographical changes caused by glacio-isostasy; and (5) sediment mobility on the offshore banks. We conclude with a brief overview of the biota.