Dataset: doggrate_catch
Deployment: NEC-MP2007-1

DOGGRATE: Development of a Spiny Dogfish Excluder in a Raised Footrope Whiting Trawl: catch data

Principal Investigator:

Michael Pol (Massachusetts Division of Marine Fisheries)

Scientist:

David Chosid (Massachusetts Division of Marine Fisheries)

Contact:

David Chosid (Massachusetts Division of Marine Fisheries)

BCO-DMO Data Manager:

Nancy Copley (Woods Hole Oceanographic Institution, WHOI BCO-DMO)

Project:

Northeast Consortium: Project Development (NEC_ProjDev)

Current State:

Cruise complete

Version:

20101019

Version Date:

2010-10-19

Data URL:

https://www.bco-dmo.org/dataset-deployment/453400/data

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Description

See final report

A spiny dogfish Squalus acanthias excluder grate (grid) within the extension of a silver hake (whiting) Merluccius bilinearis trawl net was designed and tested in Massachusetts Bay. We collected evidence between October 2008 and August 2009 using live-fed underwater video footage around the grate to support the proof of concept. Grates with 50 mm (2 in) spacing were investigated for effects from color (white or black), angles of placement, and direction (leading to a top or bottom escape vent). Spiny dogfish numbers were greatly reduced for all gear configurations based on video observations and data collected from the codend. Catches of target species were sizeable. Four tows (of various gear configurations) resulted in spiny dogfish blockages in front of the grate. The reduction of spiny dogfish led to apparent increases in the quality of marketable catches, reductions in non-target species mortality, and decreases in the codend catch handling times.

Study location: northwest of Cape Cod

Methods & Sampling

Dataset acquisition description

Different nets and grates were used in each phase. Testing locations also differed between trials. In Phase 1, grate angles were investigated using an initial white prototype grate with a bottom escape opening. In Phase 2, we refined the grate design and explored grate color effects and leading fish towards a top or bottom escape vent. Please see final report for detailed information.

Tows were conducted during Phase 1 to investigate the general performance (catching and exclusion properties) of the grate at two different angles (set with the lower portion of the grate tilted to the aft of the net at approximately 45 degrees and 35 degrees on land). Tows one through six were conducted with the grate set at approximately 45 degrees (arrangement 1); tows seven through nine had the grate set at approximately 35 degrees (arrangement 2). All used an upward guiding panel, a white grate with a forward-leaning top portion, and a bottom escape vent. An underwater camera (Remote Ocean Systems Navigator) was attached either on the guiding panel pointing aft or on the grate itself viewing towards the escape vent.Net mensuration sensors were used to obtain door spreads, wing spreads, headrope heights, and net openings. Additionally, an angle sensor was borrowed from Notus Electronics Ltd. to record the grate's angle while towing; this sensor was attached to the grate.

Phase 2
The following tows and gear configurations (continuing sequentially from Phase 1) were completed:
- Arrangement 3, Tows 10-15: Black grate, top of grate forward-leaning 45 degree angle, upward guiding panel, and bottom escape vent.
- Arrangement 4, Tows 16-21: Black grate, top of grate aft-leaning 45 degree angle, downward guiding panel, and top escape vent.
- Arrangement 5, Tows 22-28: White grate, top of grate aft-leaning 45 degree angle, downward guiding panel, and top escape vent.
- Arrangement 6, Tows 29-33: White grate, top of grate forward-leaning 45 degree angle, upward guiding panel, and bottom escape vent.
The underwater camera was attached forward of the grate looking aft. as in Phase 1, net mensuration data were collected for exploratory analyses (without an angle sensor); some data were also collected on the square height and footrope height while towing. Temperature data were collected using an Onset Tidbit logger also for exploratory purposes.

Gear Letter	Net_Name	Grate_Material	grate angle (degrees)	grate spacing (inches)	Grate_Color	Escape_Vent
A	Phase 1 net	HDPE	45	2	white	bottom
B	Phase 1 net	HDPE	35	2	white	bottom
C	Phase 2 net	HDPE	45	2	black	bottom
D	Phase 2 net	HDPE	45	2	black	top
E	Phase 2 net	HDPE	45	2	white	top
F	Phase 2 net	HDPE	45	2	white	bottom

Deployment-specific acquisition description

A spiny dogfish Squalus acanthias excluder grate (grid) within the extension of a silver hake (whiting) Merluccius bilinearis trawl net was designed and tested in Massachusetts Bay. We collected evidence between October 2008 and August 2009 using live-fed underwater video footage around the grate to support the proof of concept. Grates with 50 mm (2 in) spacing were investigated for effects from color (white or black), angles of placement, and direction (leading to a top or bottom escape vent). Spiny dogfish numbers were greatly reduced for all gear configurations based on video observations and data collected from the codend. Catches of target species were sizeable. Four tows (of various gear configurations) resulted in spiny dogfish blockages in front of the grate. The reduction of spiny dogfish led to apparent increases in the quality of marketable catches, reductions in non-target species mortality, and decreases in the codend catch handling times.

Data Processing Description

Dataset Processing Description

Video clips were examined to determine the number of dogfish entering the field of view. Dogfish behaviors from the video clips were individually categorized until they were lost off the camera, lost from view, escaped, or were captured (through the grate). Once spiny dogfish became impinged or twisted on the grate, or escaped through the vent, we then recorded the area of the body where the dogfish contacted the grate and the head orientation (when possible). The final body position and facing were recorded only after the dogfish settled into those movements. Video, acoustic sensor data, and other measurements were reviewed following the field work to determine if the nets performed appropriately.

All tows were conducted during daylight hours following typical fishing practices for silver hake. Vessel speed-over ground was kept at around 1.5 m/s (~3.0 kt) when possible but was affected by water current directions. Operational data (location, weather, time, duration, etc.) were recorded for each haul. Catch composition and weights (using a motion-compensated Marel M1100 floor scale) were determined for all species retained. Mid-line lengths were recorded for spiny dogfish, silver hake, red hake Urophycis chuss, managed species (Atlantic cod Gadus morhua, yellowtail flounder Limanda ferruginea, winter flounder Pseudopleuronectes americanus, etc), and other selected catch. Sub-samples were taken as time required.

Catch weights per unit effort was measured; length frequency distributions were analyzed within the gear configurations using box and whisker plots. Catch comparisons were considered a secondary priority, and the study was not designed to allow rigorous comparisons using statistical methods.

Deployment-specific processing description

More information about this dataset deployment

Funding

Award Number	Funding Source
09-047	NorthEast Consortium

Instruments

Raised footrope whiting trawl

Supplied Description:

Raised footrope whiting trawl with a spiny dogfish Squalus acanthias excluder grate (grid) within the extension trawl net.

Grates with 50 mm (2 in) spacing were investigated for effects from color (white or black), angles of placement, and direction (leading to a top or bottom escape vent).

Instrument Type

Generic Name: Raised footrope whiting trawl

Acronym: Trawl Raised footrope

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/61/

Generic Description:

The raised footrope whiting (or hake) trawl is a trawl with a specially designed spiny dogfish excluder grate within the extension of a silver hake (whiting) trawl net.

Parameters

Supplied Name	Supplied description	Supplied Units	Standard Name
year	year of sampling	YYYY	year
haul	haul number	integer	haul_id
gear_code	see table, above	A to F	no_bcodmo_term
lat	latitude in decimal degrees: North is positive and negative denotes South	decimal degrees	lat
lon	longitude in decimal degrees: East is positive and negative denotes West	decimal degrees	lon
day_local	day of month, local time	1 to 31	day_local
month_local	month, local time	1 to 12	month_local
yrday_local	local day and decimal time, as 326.5 for the 326th day of the year, or November 22 at 1200 hours (noon)	1 to 365	yrday_local
time_local	local time	24 hour clock	time_local
date_local	local date	number	date_local
species	genus and species name	text	species
name_common	common name	text	no_bcodmo_term
weight_lb	weight of catch	pounds	weight
CPUE	catch per unit effort	pounds per hour	CPUE
trip	trip or cruise number		no_bcodmo_term
valid_tow	whether the haul was valid or not	TRUE/FALSE	no_bcodmo_term
haul_duratn	length of time that the haul sampled the water	decimal hours	no_bcodmo_term
length_collected	whether a length was measured on the specimen: TRUE = yes	TRUE/FALSE	no_bcodmo_term

Database

Contribute Data

Dataset: doggrate_catch
Deployment: NEC-MP2007-1

Dataset acquisition description

Deployment-specific acquisition description

Dataset Processing Description

Deployment-specific processing description

Database

Contribute Data

Dataset: doggrate_catchDeployment: NEC-MP2007-1

Dataset acquisition description

Deployment-specific acquisition description

Dataset Processing Description

Deployment-specific processing description

Dataset: doggrate_catch
Deployment: NEC-MP2007-1