Aggregative patterns of pre-spawning Atlantic herring on Georges Bank from 1999-2010

Abstract

-Atlantic herring (Clupea harengus) in the offshore regions of the Gulf of Maine migrate each fall from their feeding grounds to the northern portion of Georges Bank to spawn. The Northeast Fisheries Science Center's (NEFSC) herring acoustic survey has taken advantage of this behavior by conducting systematic surveys of the prespawning fish each year since 1999. Multi-frequency acoustic and midwater trawl data were collected along transects oriented perpendicular to bathymetric contours. Acoustic backscatter was analyzed to describe the aggregative patterns (e.g., size, location in the water column, and spatial and temporal distribution) of Atlantic herring during these surveys and regression trees were used to examine the aggregation characteristics. The positional variables of distance to spawning grounds and vertical location in the water column were the primary characteristics for describing prespawning aggregations. Secondary to these were the temporal variables of diel and survey timing, and the morphological characteristic of aggregation area. Lower numbers of aggregations were observed close to the herring spawning grounds but with higher acoustic energy than larger numbers of aggregations observed further from the spawning grounds but smaller in size and lower in acoustic energy. Most aggregations were in the lower portion of the water column, but those that were in the upper portion of the water column had higher acoustic energy. Consistently throughout the decade, 90% or more of herring aggregations were located within 40 nautical miles of their spawning grounds. The regression tree method provided valuable insight to the data series where it highlighted spatial and temporal patterns and was an effective way to quantitatively summarize relationships.

Diel and Spatial Dependence of Humpback Song and Non-Song Vocalizations in Fish Spawning Ground

“…The herring comprise a keystone prey species, common in the diets of many marine mammals, piscivorous fish and seabirds of the region [38,41]. The spawning activity of Atlantic herring on the northern flank of Georges Bank during the Fall season each year has been observed and recorded [16,17,38,39,42] by the US National Marine Fisheries Services (NMFS) for over 30 years, coinciding their annual survey of the Georges Bank herring stock with this period each year. Acoustic recordings of whale vocalizations were acquired using a large-aperture densely-sampled coherent hydrophone array towed by a research vessel along designated tracks in Franklin Basin, north of Georges Bank [2].…”

“…The Atlantic herring instantaneous areal population densities over wide areas shown in Figures 7 and 8 were obtained from active OAWRS imaging after extensive calibration with tens of thousand instantaneous coincident conventional ultrasonic fisheries echosounding measurements [12,13,15] with fish species identification and physiological parameters extracted from trawl samples collected over the course of the experiment [16,49]. The Atlantic herring shoals were consistently observed to form when the population density reached a critical value of 0.2 fish per m 2 s [12].…”

“…The humpback song and non-song vocalization rate spatial distributions are overlain with the spatial distribution of their fish prey, the Atlantic herring. The fish distributions were instantaneously and simultaneously acquired over tens of thousands of square kilometer areas by ocean acoustic waveguide imaging (OAWRS) [12][13][14][15], combined with conventional fisheries ultrasonic echosounding [16] and fish trawl sampling [17] to obtain thousands of calibrations at statistically significant locations [13]. Here we examine the temporospatial correlation between the humpback song, non-song moan and cry vocalizations with the fish areal population densities.…”

Angular Resolution Enhancement Provided by Nonuniformly-Spaced Linear Hydrophone Arrays in Ocean Acoustic Waveguide Remote Sensing

“…The Gulf of Maine 2006 Experiment [1,2,7,8,[11][12][13]24,50] was conducted from 19 September to 6 October 2006, coinciding with the annual herring spawning period on the northern flank of Georges Bank [51][52][53]. During the experiment, acoustic recordings were acquired using the nonuniformly-spaced 160 hydrophone-element ONR-FORA towed horizontally behind a research vessel along designated tracks north of Georges Bank [2,12,13,50].…”

Vocalization Source Level Distributions and Pulse Compression Gains of Diverse Baleen Whale Species in the Gulf of Maine

“…The Atlantic herring comprises a keystone prey species, common in the diets of many marine mammals, piscivorous fish and seabirds of the region [52,55]. The spawning activity of Atlantic herring on the northern flank of Georges Bank during the fall season each year has been observed [52,53,[56][57][58] [16,17,60] with fish species identification and physiological parameters extracted from trawl samples collected over the course of the experiment [56,62]. The overall Georges Bank Atlantic herring stock estimate for autumn 2006 based on the OAWRS survey has been found to match well (with 80%-90% agreement) with independent NMFS stock estimates for 2006 and 2007 [61].…”