Dataset: groundlines_current
Deployment: NEC-LL2006-1

Determining the effect of Eastern Maine bottom currents on lobster gear groundlines

Principal Investigator:

Ms Laura Ludwig (Gulf of Maine Lobster Foundation, GoM-LF)

BCO-DMO Data Manager:

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

Project:

Northeast Consortium: Project Development (NEC_ProjDev)

Version Date:

2010-12-14

Data URL:

https://www.bco-dmo.org/dataset-deployment/453440/data

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Description

"Determining the Effect of Eastern Maine Bottom Currents on Groundlines"

This project sought to examine the effect of bottom currents on lobster gear in nearshore eastern Maine waters, to establish whether bottom currents there are strong enough to significantly reduce the profile of floating rope used as groundline between traps, thus reducing the risk of whale entanglements in lobster gear.

Assessment of the current meter data indicates that the current off Jonesport, Maine, where all the equipment was deployed, measured at the bottom of the ocean on level with the traps (1-2m off bottom), is often over 30 cm/sec and has little to no 'slack' period between tides. Analysis of the sensor data showed the floating groundlines at or below 2m (one fathom) of arc height over a 20 fathom length, and overall the measurements suggest that the flow of current is significantly stronger near the ocean bottom than anticipated, which would tend to depress the floating line more than would be estimated assuming much lower flows.

See final report

Associated dataset: Groundline rope height (m) above seafloor between lobster traps

Methods & Sampling

Dataset acquisition description

Datasets from three measuring devices were collected during five months of field-work. Depth and groundline height data was extrapolated from Star-Oddi pressure sensors deployed on a 20-trap trawl each month; current velocity and directional data was recorded by a Sensor Data 6000 current meter deployed near the lobster trawl; and three months' worth of data from acoustic Doppler current profilers (ADCP), rigged in a customized 3' lobster trap directly into the trawl, gave more detailed information about the velocity and direction of current acting on the groundline.

Data Processing Description

Dataset Processing Description

All data were processed by staff from the three organizations (GOMLF, MER, and Maine Oceanographic Services) with expertise in the standard preparation and data processing procedures recommended by the instrumentation manufacturers and by established practice.

More information about this dataset deployment

Funding

Award Number	Funding Source
07-090	NorthEast Consortium

Instruments

Acoustic Doppler Current Profiler

Supplied Description:

Instrument Type

Generic Name: Acoustic Doppler Current Profiler

Acronym: ADCP

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/115/

Generic Description:

The ADCP measures water currents with sound, using a principle of sound waves called the Doppler effect. A sound wave has a higher frequency, or pitch, when it moves to you than when it moves away. You hear the Doppler effect in action when a car speeds past with a characteristic building of sound that fades when the car passes. The ADCP works by transmitting "pings" of sound at a constant frequency into the water. (The pings are so highly pitched that humans and even dolphins can't hear them.) As the sound waves travel, they ricochet off particles suspended in the moving water, and reflect back to the instrument. Due to the Doppler effect, sound waves bounced back from a particle moving away from the profiler have a slightly lowered frequency when they return. Particles moving toward the instrument send back higher frequency waves. The difference in frequency between the waves the profiler sends out and the waves it receives is called the Doppler shift. The instrument uses this shift to calculate how fast the particle and the water around it are moving. Sound waves that hit particles far from the profiler take longer to come back than waves that strike close by. By measuring the time it takes for the waves to bounce back and the Doppler shift, the profiler can measure current speed at many different depths with each series of pings. (More from WHOI instruments listing).

Pressure Sensor

Supplied Description:

Star-Oddi pressure sensors

Instrument Type

Generic Name: Pressure Sensor

Generic Description:

A pressure sensor is a device used to measure absolute, differential, or gauge pressures. It is used only when detailed instrument documentation is not available.

Sensor Data 6000 Current Meter

Supplied Description:

A vector averaging field current meter.

Instrument Type

Generic Name: Sensor Data 6000 Current Meter

Acronym: SD-6000

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/114/

Generic Description:

The Model SD-6000 MINI current meter is a vector averaging field current meter with recording capacity for up to 6,000 measurements of current speed, direction and temperature. The instrument can be programmed to carry out measurements at given intervals from each minute to each 3 hour via PC or by holding a magnet outside marked points on the instrument.Information is communicated to and from SD-6000 via an infra-red emitter/photodiode pair mounted inside the instrument's transparent top cap. An optoconverter (SD-40) which is positioned over the instrument top cap during communication with a PC converts optosignals to standard RS-232. Download of data to a PC takes a maximum 30 seconds after which data can be immediately processed and displayed. SD-6000 can also be used as a remote monitoring instrument supplying data in real time via a cable.

Parameters

Supplied Name	Supplied description	Supplied Units	Standard Name
curr_dir_abs	direction of current, averaged over a 5 minute interval	degrees magnetic	curr_dir_abs
curr_speed_abs	absolute current speed, averaged over a 5 minute interval	cm/sec	curr_speed_abs
date_local	local date	mm/dd/yyyy	date_local
day_local	day of month, local time	1 to 31	day_local
month_local	month in local time	1 to 12	month_local
temp	temperature	degrees Celsius	temp
time_local	local time: 24 hour clock	HHmm	time_local
year	year of sampling	YYYY	year
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
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

Database

Contribute Data

Dataset: groundlines_current
Deployment: NEC-LL2006-1

Dataset acquisition description

Dataset Processing Description

Database

Contribute Data

Dataset: groundlines_currentDeployment: NEC-LL2006-1

Dataset acquisition description

Dataset Processing Description

Dataset: groundlines_current
Deployment: NEC-LL2006-1