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National Oceanic and Atmospheric Administration National Marine Fisheries Service

166 Water Street Woods Hole, MA 02543

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20 March 2002


NOAA Fisheries Research Vessel DELAWARE II Cruise DE 01-09 (Parts I – IV)

Atlantic Herring Hydroacoustic Survey


The 2001 Fall Atlantic Herring Hydroacoustic Survey was conducted during four parts between 4 September and 12 October 2001. Scientific operations were conducted in the Gulf of Maine and Georges Bank regions, including the Canadian Exclusive Economic Zone on eastern Georges Bank.


Cruise objectives were to (1) calibrate the transducers of the EK500 scientific echosounder, (2) conduct acoustic surveys of Atlantic herring (Clupea harengus) spawning stocks in the Gulf of Maine and Georges Bank regions to provide fisheries independent abundance estimates, (3) repeat the Georges Bank survey using varies survey designs, (4) collect in-situ multi- frequency target strength (TS) measurements on herring, and (5) test and evaluate advanced technologies (e.g., broad-band acoustics) for improving fisheries acoustics estimates.


EK500 Calibrations:

The multifrequency Simrad EK500 Scientific Sounder must be calibrated before each survey to ensure precise and accurate backscatter measurements required for species-specific population estimates. Standard sphere calibrations were conducted for each frequency before the survey to ensure that the system was operating properly with high accuracy and precision in the measurements. The FRV Delaware’s EK500 operated three downward looking hull-mounted transducers (one 12 kHz single-beam transducer, and two split-beam transducers at 38 and 120 kHz). During the first day (4 September), the 38 and 120 kHz split-beam transducers were successfully calibrated alongside the pier of the Woods Hole Oceanographic Institute. For each frequency, a calibration sphere of known target strength was suspended under each transducer. The sphere was moved throughout the beam pattern using three remotely controlled downriggers. Gain and angle offset parameters for the 38 and 120 kHz transducers were derived using the Simrad Lobe (v.95-01-17) program. The TS and Sv gain for the 38 kHz was modified to 23.28 and 23.10 dB, respectively. The TS and Sv gain settings for the 120 kHz remained unchanged from the last survey (26.20 and 26.10 dB, respectively). The single-beam 12 kHz transducer was calibrated in the Gulf of Maine during 7 September, and its previous gain settings of 18.3 dB were not changed. Ambient noise tests were conducted to ensure there was no cross- interference between acoustic instrumentation. The amplitude from the EK500 test/transceiver menu was routinely checked during and at the end of the survey to ensure the EK500 system was working properly.

Hydroacoustic Survey Operations:

Atlantic Herring Hydroacoustic Surveys have been conducted by the Northeast Fisheries Science Center (NEFSC) during the autumns since 1998, in which standardized NEFSC hydroacoustic survey procedures have been implemented.

Systematic surveys were conducted on selected historical spawning grounds of Atlantic herring in the Gulf of Maine and Georges Bank regions. Standardized NEFSC hydroacoustic operations included continuous EK500 and SCS data collection throughout the cruise track and during gear deployments. Midwater trawling, underwater video, and CTD deployments were routinely conducted to identify acoustic backscatter, and obtain biological and oceanographic data. Biological samples were collected and processed according to standard NEFSC procedures. EK500 acoustic data were routinely processed at sea using the Echoview post-processor. Continuous and deployment data were linked and managed using the SCS Event Logger program. During this year’s survey, the northern Georges Bank region was surveyed several times using various survey designs to determine the optimum design to adopt for future NEFSC fisheries acoustic surveys.

EK500 Survey Operations:

The multifrequency Simrad EK500 (v.5.30) Scientific Sounder was the primary instrumentation used to obtain acoustic measurements for conversion to herring population estimates. The EK500 was operated continuously throughout the cruise during the systematic transects and gear deployments. Survey transects were defined as a course of constant heading and survey speed (ranging 8-11 knots), and were sequentially numbered throughout the cruise. All gear deployments were also sequentially numbered. After a deployment, the current transect number was assigned when resuming the same course heading and survey speed. EK500 data were collected simultaneously from three frequencies (12, 38, and 120 kHz) at a ping rate of 2 seconds throughout the cruise track. The EK500 echo-integrator vertically integrated volume backscatter (Sv in units of m2/m3 ) into 0.5 m depth increments. Data between the surface and the bubble layer were not included in the analysis to eliminate scattering by surface bubbles and noise. The bubble layer was set to 10 m for the 38 and 120 kHz data, 32 m for the 12 kHz data. Volume backscatter were converted to cross- sectional backscatter (Sa in units of m2/nmi2) as a relative index of abundance along the cruise track. Individual target strength (TS) measurements were also collected by the EK500, and are used to scale acoustic indices to abundance. EK500 data were logged with the Echoview software (release 2.20.5) via TCP/IP ETHERNET line. The EK500 received its navigational input from the vessel’s Scientific Computer System (SCS) differential GPS output. Preliminary post-processing of the EK500 data was conducted at sea using Echoview. Post-processing included removal of unwanted noise and bottom backscatter, and partitioning of the herring acoustic backscatter.

High Speed Midwater Rope Trawl Sampling Operations:

The High Speed Midwater Rope Trawl (HSMRT, Gourock design R2028825A) was the primary sampling gear used to verify fish backscatter and collect biological data. The four seam HSMRT pelagic trawl was designed with 53.1 m headrope, footrope, and breastlines to provide a 350 m2 net opening (averaging 13 ± 3 m vertical and 27 ± 5 m horizontal). The HSMRT was rigged to 1.8 m2 double-foiled Suberkrub-type doors with 62.4 m of upper and lower bridles/legs. The optimum tow configuration (2.5 m setback, 272 kg tomweights, intermediate door spread with two shoe weights per door) was used during survey operations (refer to Cruise Results DE 98-09 for further details). The HSMRT was towed at 4-5 knots typically for 30 minutes in duration. However, tow duration often varied between 10 to 60 minutes depending on acoustic fish signals observed during the tow. Tow duration was defined as the time between setting the doors and when doors were hauled out of the water. The tow profile of the trawl was typically dropped incrementally through the water column to the desired depth of the scattering layer or when the footrope was about 10 m from the bottom, and held at the targeted backscatter layer for the duration depending on the fish targets observed passing into the trawl by the trawl monitoring system.

HSMRT deployments were targeted on selected fish backscatter along the cruise track, and generally conducted about once per 6 hour watch. Deployments served to verify species composition for partitioning of backscatter and obtaining biological catch data. Trawl duration, tow depths, and tow speeds were not standardized or consistent between trawls, therefore trawl catch data should not be used for abundance estimates.

Midwater Trawl Monitoring:

The HSMRT trawl tow profile and performance were monitored using a Simrad FS903 and ITI systems. The Simrad FS903 Trawl Monitoring System via third- wire constant tension winch provided real-time sonar images of the trawl opening and performance. The FS903 sonar display also showed acoustical signals of fish passing through or around the trawl opening, thus allowed the tow duration to be minimized for capturing only the necessary amount of herring required for scientific samples. The Simrad ITI wireless trawl sensors were used to obtain point measurements of the trawl depth, wing spread, and door spread. Vemco Minilog depth-temperature probes were attached to the trawl headrope and footrope to provide continuous depth-temperature and trawl performance profile data for each deployment.

Biological Sampling:

The catch from each trawl was sorted by species, weighed, and measured (fork length to the nearest cm) according to standard NEFSC procedures. Additional biological sampling for Atlantic herring included individual weights (to nearest 0.1 g), fork lengths (nearest mm), stomach content analyses, and otolith samples for aging.

Furuno CSH-5 Omni-directional Sonar:

A 64 kHz Furuno CSH-5 Omni-directional Sonar was used intermittently during survey for locating fish aggregations and documenting the horizontal spatial patterns of herring schools. The CSH-5 sonar simultaneously scanned a full 3600 with a cone-shaped receiving beam, and its beam was usually angled 7-100 from the surface to eliminate surface noise. The 100 tilt angle and 150 vertical width of the receiving beam generally resulted in a horizontal search radius of 800 m when bottom depths were around 200 m. In shallow waters of less than 80 m depth, the search radius of the cone-shaped beam was reduced to 250 m. The external trigger of the sonar was wired as a slave to the EK500 in order to synchronize its ping for eliminating acoustical interference. Analog images from the omni-directional sonar were obtained every 30 seconds using a video capture-board, and these files were merged with the SCS navigational data and archived.

Multi-purpose Underwater Video System:

The Multi-purpose Underwater Video System (MUVS) was configured for this cruise to directly verify and obtain stereo imagery of acoustic targets alongside the EK500 acoustical beam. The MUVS was deployed midship from the forward A-frame alongside the acoustic beam of the EK500 while the FRV Delaware drifted over selected backscatter aggregations. A pair of matched underwater low-light CCD video cameras (DSP&L Super SeaCam 5000) were mounted in the MUVS to obtain stereo imagery of targets. The stereo imagery was calibrated with a plexiglass cube having equal sides of 30 cm. The cameras have a low light (0.001 lux) auto adjusting iris with a 970 horizontal and 770 vertical view field. Two DSP&L Multi-SeaLites provided illumination that were dimmed remotely using a 120 v voltage regulator. The SeaLites were fitted with stainless collars which allowed for easy installation of various light filters in an effort to minimize avoidance reaction of organisms. The real- time depth profile, temperature, compass bearing, and three-dimensional orientation of the camera system were recorded every 10 seconds using the JASCO Attitude Sensor. Real-time dual video and environmental data were recorded from the MUVS through a 300 m multi-conductor cable to a PC computer and digital video recorders. Stereo recordings were synchronized using a Horita time-code generator.

Fisheries Scientific Computer System (FSCS):

The FRV Delaware’s Scientific Computer System (SCS) was recently upgraded with the newly developed Fisheries Scientific Computer System (FSCS). The SCS system continuously collected navigational, oceanographic, and meteorological data, while the FSCS provided onboard entry of trawl station and catch data.

Further improvements were also made to the SCS Event Logger program which provided an effective system for logging and managing operational events throughout the cruise. For example, all start and end data for deployments and acoustical transects were logged using the SCS Eventlog. The Eventlog also contained operational and observational comments. The Eventlog was critical for managing and linking our continuous and deployment type data by time. All computers, instrumentation, acoustic data collection, and data recording were synchronized in GMT time using the SCS master clock.

CTD Deployments:

Conductivity-Temperature-Depth (CTD) casts were conducted at the waypoints of each transect and before each deployment. CTD were deployed while drifting to obtain vertical hydrographic profile data from surface to bottom. Water bottle samples were typically taken once a day for salinity calibrations.

Survey Design Experiment:

Three type of surveys (i.e., evenly spaced parallel, randomly spaced parallel, and zig-zag transects) were completed on Georges Bank to investigation the effects of survey designs on the variability of the acoustic populations estimates. An adaptive approach was implemented to ensure that the length of the transects included the herring aggregation (i.e., a transect did not end in an area of high fish concentration). Transects (lengths and distances between transects) were chosen to cover the bathymetric features (generally between 50-300 m) which delineated each historic spawning area. Survey speed was designated at 10 knots, while actual survey speeds ranged from 8-11 knots depending on weather conditions and currents.

In-situ TS Measurements:

Given the extensive cruise track, some of the preselected transects had to be dropped, and minimal time was allocated for collecting in-situ target strength (TS) measurements for herring.

Other Data:

Conductivity-temperature-depth (CTD) were conducted throughout the cruise, generally at the transect nodes and locations of gear deployment. During part II of the cruise, Gerald Denny of Scientific Fisheries Incorporated (Anchorage, Alaska), conducted acoustic measurements with a broadband acoustic system. His towbody was suspended from the forward A-frame while the FR/V Delaware was drifting and during trawl operations. Acoustic data from the broadband system was collected and analyzed using a Scientific Fisheries software package. Also during part II, Dr. Redwood Nero and Mr. Charles Thompson of the Naval Research Laboratory, Stennis Space Center (Stennis, Mississippi) conducted acoustic measurements with a low-frequency broadband system. Two deployment methods were used. The first method was to deploy a raft and hydrophone array off the stern, and to collect data while the ship steamed at 2-4 knots along a transect. The second deployment method was to suspend an omni-directional transducer and hydrophone off the forward A-frame and collect data while drifting. The transducer and hydrophone were set at a variety of depths.


During the first day (4 September), the FRV Delaware’s EK500 split-beam transducers (38 and 120 kHz) were successfully calibrated alongside the Woods Hole pier. The FRV Delaware departed on 5 September and completed systematic surveys on selected offshore banks in the Gulf of Maine (Jeffery’s Ledge, Platts Bank, Cashes Ledge, and Fippennies Ledge) during 6-14 September (Figure 1). The single-beam 12 kHz transducer was calibrated in the Gulf of Maine during 7 September. An overnight portcall in Portland, Maine was made during 8-9 September to exchange scientific staff. The last few days of the first leg (9-14 September) was devoted to experimental work on using the EK500, broadband acoustics, and low-frequency acoustics. During part II, Atlantic herring aggregations were surveyed on Georges Bank using the two broadband acoustic systems (SciFish, Inc. and NRL) and the EK500. The systems were operated simultaneously during four deployments to collect data over a wide frequency spectrum (0.5-10 kHz, 12, 38 and 120 kHz, and 100-200 kHz). Data from these experiments are currently being analyzed.

During the second leg, the northern Georges Bank region was survey twice using an evenly spaced parallel transect design on 18-22 September and randomly selected parallel transect design on 23-27 September (Figures 2 and 3). For the third leg, a zig-zag survey design was completed on northern Georges Bank during 2-8 October. Given the extensive cruise track, some of the preselected transects were not completed and the number of trawl deployments was limited. Atlantic herring was the predominant pelagic species observed and captured during the surveys.

The remaining four days (9-12 October) of the cruise was dedicated to inter-vessel comparisons between the FRV Delaware’s EK500 and Canadian RV Alfred Needler’s SM2000 multibeam system.

In-situ TS measurements and video observations were made on spawning aggregations of herring on 11 October. Preliminary field tests using blue, green, red, and infrared light filters suggested that green filters might reduce avoidance reactions and provide adequate light penetration unlike the infrared light. Video observations were obtained during the spawning event, which was verified by the deposition of herring eggs on the MUVS camera array.


All data and results are archived at the Northeast Fisheries Science Center. Results will be presented and data distribution on CD-ROM at an annual Northwest Atlantic Herring Acoustic Workshop in conjunction with scientists from the Canadian Department of Fisheries and Oceans.


National Marine Fisheries Service, NEFSC, Woods Hole, MA

William Michaels

Chief Scientist

Parts III, IV

Michael Jech

Research Fisheries Biologist

Parts I, II, III, IV

(Chief Scientist - Parts I, II)

William Overholtz

Research Fisheries Biologist

Part III

PTSI Contractors, NEFSC, Woods Hole, MA

Peter Chase

Bioacoustical Technician

Parts I, II, III, IV

Elizabeth Pratt

Bioacoustical Technician

Parts I, II, III, IV

Naval Research Laboratory, Stennis, MS

Woody Nero

Acoustical Engineer

Parts I, II

Charles Thompson

Acoustical Engineer

Parts I, II

Scientific Fisheries Incorporated, Anchorage, AK

Gerald Denny

Acoustical Engineer

Part II

Maine Dep. Marine Resources, W. Boothbay, ME

Matthew Cieri

Fisheries Biologist

Part III

Worcester Polytechnical Institute, Worcester, MA

Anna Sellars

Student Volunteer

Parts I, II, III, IV

Julie Cequera

Student Volunteer

Parts I, II

David Chevier

Student Volunteer

Part IV

Part I September 4-8, 2001

Part II September 9-14, 2001

Part III September 17-28, 2001

Part IV October 1-12, 2001


For further information contact: William Michaels at the National Marine Fisheries Service,

Northeast Fisheries Service Center, Woods Hole, Massachusetts 02543-1097.

Telephone (508) 495-2000, Fax (508) 495-2258



Graphic showing cruise tracks for Part I of Atlantic Herring Acoustic Survey DE 01-09.

Figure 1. Cruise track for Part I of the Fall 2001 Atlantic Herring Hydroacoustic Survey cruise DE 01-09 during 6 - 14 September 2001. Systematic surveys were conducted on selected offshore banks in the Gulf of Maine and experimental operations were conducted along northern Georges Bank.

Graphic showing systematic parallel transects for Part II of Atlantic Herring Acoustic Survey DE 01-09.

Figure 2. Systematic parallel transect survey for Part II of the Fall 2001 Atlantic Herring Hydroacoustic Survey cruise DE 01-09 during 18-22 September 2001.

Graphic showing random parallel transects for Part II of Atlantic Herring Acoustic Survey DE 01-09.

Figure 3. Random parallel transect survey for Part II of the Fall 2001 Atlantic Herring Hydroacoustic Survey cruise DE 01-09 during 23 - 27 September 2001.

Graphic showing cruise tracks for Part III of Atlantic Herring Acoustic Survey DE 01-09.

Figure 4. Cruise track for Part III of the Fall 2001 Atlantic Herring Hydroacoustic Survey cruise DE 01-09 during 2 - 12 October 2001. Zig-zag survey was conducted along northern Georges Bank. The FRV Delaware II conducted acoustic comparisons with the Canadian FRV Alfred Needler’s SM2000 multibeam operations 7 - 11 October 2001.
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