eMOLT Phase VI: Bottom Currents

Given the recent issue associated with potential whale entanglements in lobster gear and the uncertainty of whether sinking groundline is actually needed in some regions, we had proposed in 2007 to develop a low-cost method of monitoring the bottom currents from lobster gear. As many lobstermen have suggested, the existing groundlines may often lay down on the seafloor given strong currents in certain areas. While some work is currently underway to examine the degree to which groundline is dragged down, little is known about the spatial and temporal variability of bottom currents in these areas. Since conventional means of monitoring bottom currents with commercially available instrumentation is cost prohibitive, we proposed to design and evaluate a simple concept of inferring bottom currents using locally-made $69 ONSET 3-d-accelerometers tethered above the ocean bottom. As of this writing, we have tested and validated this idea and compared the results with traditional current meters. It has worked exceedingly well.


Beginning in the early summer of 2008, initial deployments were made by Vitalii Sheremet (lead developer) within the Woods Hole Oceanographic Institute’s instrument test-well where tidal currents provide sufficiently-detectable observations.Deployments of more traditional instrumentation were also be made (alongside for comparisons) including two current meters: the Sontek Aquadopp owned by URI and the Nortek Vector owned by NEFSC (see comparison in figure above).

After these initial multi-day deployments in Woods Hole, we transferred the equipment to 10 local lobstermen working along the New England coast.These individuals have tested eMOLT equipment for us in the past. This deployment was conducted over multiple weeks in an attempt to detect variations due to storms and lunar periods. While the analysis of these records are under way, an example result is pictured below and links to other plots (as they are generated) are linked from Table 1 below.

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Given the recent advances towards a nation-wide ocean observing system, the idea is ripe. New England lobstermen now have an opportunity to make a significant contribution to the integrated system on the Northeast Continental Shelf by securing an unprecedented array of relatively inexpensive sensors on the seafloor. In the past few years, there has been some effort in developing ocean observing systems in the region. Both the National Science Foundation’s Ocean Observertory Initiative and NOAA’s IOOS project have funded several organizational meetings of potential partners but very little has resulted in the form of concrete governing structure.While all involved seem optimistic and hope for a large-scale coordinated system, a significant sum of money is needed to build such a network. So, until that money is available, we are forced to take small steps with low-cost alternatives. These small steps will, at least, provide some form of background data in the intervening years and provide a system to gradually build in the future. Much of our previous eMOLT work involved developing a network of participants. While this outreach work (building relationships with fishermen) will certainly continue, we hope to now focus the majority of our effort in providing useful products in the form of web-served information.


Table 1. First lobster-trap-SeaHorse deployment Log w/links to plots.

sn1 sn2

("major-axis" velocity)

 fname

(zoomed-in plot)

 lname

("minor-axis" velocity)

 Location

(zoomed-in plot)

 lat

(model comparison)

 lon

(direction)

 loran1 loran2 w_depth(m) deployed (GMT) endtime (or recovered) Other haul dates comments
2 2039122 Alex Brown Truro, Ma bayside 4202.56 7011.29

4.6 24-Sep-2008:013:00 03-Nov-2008:16:30 10/7,10/14,10/21,10/28 no temp
3 2039123 Dave Casoni North of Cape Cod Canal 4146.44 7028.86

11.0 24-Sep-2008:011:00 27-Oct-2008 02:33:17
Broke but good record w/temp; noted difficulty aligning bolts
4 2039124 Bob Marcella off Hull, Ma 4218.18 7048.00 13973.4 44253.6 23.7 09-Oct-2008 18:20:54 27-Oct-2008 02:33:17
MASS DMF coordinated study
5 2039028 Bill Doherty outside Boston Harbor 4219.88 7052.41

19.8 27-Sep-2008 00:41:48 27-Oct-2008 02:33:17

6 2223026 Brad Parady off York Maine 4304.25
 7036.82
 13652.0
 25964.0
 24.9 06-Oct-2008 14:28:38 27-Oct-2008 02:33:17
low velocity; most damage to tubing
7 2230127 Brian Tarbox Casco Bay 4339.07 7013.42

7.0 26-Sep-2008 23:36:46 03-Oct-2008 04:06:11
Undisturbed for 1 month. Probably, the cage landed on its side, after 6 days it apparently flipped upside-down such that the instrument stuck under the lobster pot.
8 2223018 Elliot Thomas Casco Bay 4342.19 7009.94

21.9 26-Sep-2008 23:36:46 17-Oct-2008 13:51:29

9 2223019 Jason Day off Vinalhaven Maine 4401.66 6851.33

9.1 02-Oct-2008:013:00 02-Nov-2008:013:40
he noted seiche on 27 Oct +/- 1 day but instrument was apparently lying on its side (failed?)
10 2223020
 Mike Dassatt Penobscot Bay 4422.10
 6849.17


???? 27-Oct-2008 01:28:15
11 2039121
 Jim/Reaz Manning/Kahn NEFSC Dock 4132.0
 7041.4


31-Jul-2009 10:00:00 05-Aug-2009 08:05:00
Included all three: Nortek, Onset, and StarOddi deployments