Water Column Sonar Data Collection (SH1601, EK60)

Scientists from the Fishery Resource Analysis and Monitoring (FRAM) division at the Northwest Fisheries Science Center (NWFSC) led the winter 2016 hake IAT survey aboard the NOAA Ship Bell M. Shimada, a 63.7-m (209-foot), acoustically quieted Fisheries Survey Vessel equipped for fisheries and oceanographic research. The survey was conducted between January 9 and February 9 (Table 1). The Shimada surveyed from 45.5°N to 31.3°N, beginning at Newport, Oregon, proceeding south to the U.S./Mexico border, and then heading north back to Newport (Figures 1 and 2). Pre-planned (“coarse”) zigzag transects were oriented east-west, with larger offshore diagonals connected via smaller nearshore diagonals. Offshore diagonals, spaced roughly 100 nmi apart at the inshore side, ranged from the 30-m isobath (or as close to shore as was safely navigable) to bottoms depths of roughly 3,500–4,500 m. Nearshore diagonals extended from the ≥30-m contour to roughly 2,000 m. If hake were detected at the offshore end of a transect, the vessel proceeded west to the end of the hake sign and then beyond for an additional 0.5 nmi to ensure that the end of the aggregation was located. When aggregations of spawning hake were detected along a pre-planned transect and confirmed by midwater trawling, adaptive transects, either parallel at a fine resolution (spaced either 0.5 or 1.0 nmi apart) or in a star pattern, were used to determine the spatial extent and size of the spawning aggregation(s). Additional acoustic data were collected to evaluate crepuscular migration (vertical and/or horizontal) of spawning hake aggregations by having the Shimada remain stationary one hour before sunrise to one hour after.