Jim Manning
Woods Hole, Ma. 02543


Troy Hartley
Northeast Consortium
University of New Hampshire
142 Morse Hall
39 College Road
Durham, NH 03824

19 April 2003

Dear Northeast Consortium,

What are  the physical processes governing the transport/fate of  lobster larvae and other planktonic particles along the coast of  Maine, New Hampshire, and Massachusetts? Can we accurately simulate these processes with state-of-the-art numerical circulation models?   We propose to address these questions with a truly collaborative effort that could potentially involve hundreds of lobstermen along the entire western edge of the Gulf of Maine.  By seeding the Maine Coastal Current with a few dozen low-cost drifters at selected transects on a monthly basis during the summer of 2004  (with the help of lobstermen to assemble, deploy, and report these units), we propose  to provide the first  summer-long,  coast-wide, description of the synoptic flow fields.   These surface current velocity observations will be used to validate a set of numerical simulations conducted by a suite of circulation models currently under development at local state, federal , and academic facilities.

In order to understand the interannual variability of stock recruitment processes, it is necessary to both monitor and model the underlying physical environment.  Are there large changes in the conditions and pathways of  drift during critical stages of  larval development?   The three most-important variables in describing  the physical oceanography of the Gulf of Maine are temperature, salinity, and  current velocity.  Having setup an infrastructure for measurement and management of the first two data streams (temperature and salinity) in earlier phases of eMOLT, plans are now underway to obtain observations of the third (current velocity).    While each of these variables are dependent on the other,  all three are required in a complete description of the physical system.  As in the case of atmospheric weather models,  in order to generate realistic output for the entire  three-dimensional field,  it is necessary to repeatedly assimilate data at key locations throughout the geographic domain.
 

As in the case of temperature and salinity, we propose a low cost solution.  Recognizing the complexity of the Gulf of Maine circulation and the Maine Coastal Current in particular,  it is necessary to maximize the geographic coverage of observations.  A few  expensive current meter moorings and/or satellite-tracked drifters provide very little information with respect to the entire system. The cost of these state-of-the-art measurement platforms far outweighs the benefits in this case.  Hence,  we propose, with the help of local fishermen, to deploy dozens of low-cost expendable drifters at selected depths off the coast of Maine.   While this method had been used decades ago  (Bigelow, Bumpus, etc.),  the  recent increase in the quantity of lobstermen working in this area and their use of both GPS and cell phone technology should provide  far more successful return rates.   Lobstermen  would deploy a series of surface drifters on a monthly basis along selected transects  perpendicular to the coast and other lobstermen will report each drifter as sighted downstream.   The surface configuration of each drifter, similar to that shown in the figure above, will have a small section of PVC pipe denoting an id number and phone number (to call in the fix) replacing the satellite antennae.

Each drifter will be  tracked on the web along with a model projection.   Model runs will be conducted prior and after each deployment to investigate the tracks expected given climatologic forcing and those actually experienced over the course of the drift.  The figure below, for example, portrays a particular run forced by historical collection of temperature, salinity, and wind.  How does this flow compare to that observed in 2004?  What are the limitations of these models and can they be used to examine, for example, the exchange mechanisms between the coastal current and the estuaries?

Discussions and coordination of this project with other ongoing observational efforts by  GoMOOS,  MERHAB, and NEC-funded projects are critical,  but, in addition to coordinating our efforts with all these ocean observing initiatives,  we  intend to foster closest relationships with the various modeling efforts throughout the Gulf of Maine area.  We expect to draw interest from numerical modeling groups such as those at Dartmouth College,  UMASS Dartmouth,  UMass Boston, UMaine Orono, and the Woods Hole Oceanographic Institute.    Any modeling group, for that matter,  generally  interested in simulating subtidal, wind driven, baroclinic flow in a coastal current system should welcome the potential source of observed particle tracks for test and evaluation purposes.

In order to document the thermal  structure associated with each transect of drifters,  we propose to have lobstermen sample the entire water column with the "fast-response temperature probe" (purchased with eMOLT Phase I funding).  The intention  is to examine the placement of drifters with respect to frontal features that often govern their displacements.  While satellite imagery may often be used for this purpose,  there is no guarantee they will be available from the time of each deployment and there is enough day-to-day variability in the position of the fronts to warrant better depiction.   Given a cross-sectional picture of the coastal current extent,  questions related to frontal convergence and entrainment can be addressed   With the large quantity of drifters to deploy,  particular processes in specific regions can be examined in detail.   The  hypothesized bi-furcation of the Eastern Maine Coastal Current just south of Penobscot Bay, for example, can be a focus of investigation.  Investigators such as Lew Incze and Carl Wilson have expressed interest in this oceanographic phenomenon and may want to participate, when the time comes, in deciding on exact placement of drifters with respect to satellite inferred position of the frontal system.


 

In order to test the idea and the drifter designs before submitting the full proposal,  a pilot deployment of several drifters will be conducted  this May-June 2003.   We will release two sets of these low-cost drifters (separated a few days apart) on a transect perpendicular to the coastline just south of the Penobscot Bay.  This test deployment will be in coordination with the MERHAB project cruise scheduled on the R/V Oceanus 28 May through 7 June 2003.   Lobstermen working in this area will be notified about the project and protocol through  various means  (association newsletters,  phone calls, and  radio broadcast).  Results of this pilot study will be summarized in the full proposal.

As in the past three phases of eMOLT,  all four of the major lobster associations will be involved.  Atlantic Offshore Lobster Association  will  not be directly involved with the drifter deployments but will be requesting more temperature probes to better resolve the very dynamic, less coherent, temperature distributions along the shelf edge.  The inshore associations (Mass Lobstermen, Maine Lobstermen, and the Downeast Lobstermen) will be funded for coordinating the lobstermen and maintaining the database associated with phoned-in fixes.  The distribution of funds will be similar to previous years with the Gulf of Maine Lobster Foundation coordinating the budget and general organization.

In order to involve local students in the project,  we have begun discussions with  the  Marine Biology Department of the Southern Maine Community College in So. Portland. Students will help design, construct, and assemble the hundred or more drifters needed.  Given  surplus funds and  drifter-making  materials from previous projects (SeaGrant and GLOBEC),  the pilot study drifters will be constructed by SMCC students after they graduate on 19 May 2003.

Finally,  this is a natural extension of the eMOLT project.  The observational network of temperature and salinity monitors provide the necessary bottom waters conditions below the very dynamic 3-d structure of the Gulf of Maine's coastal current.  The temperature sensors, in particular, now in their third year of operation have documented a large degree of interannual temperature change (4-5 degF).   What do these variations in water mass conditions mean in terms of the current velocity and the ultimate fate of lobster larvae into and out of the Maine Coastal Current?
 

Sincerely,
Jim Manning


For further information contact: James.Manning@noaa.gov

Return to main eMOLT page

Return to main Oceanography Page

Link disclaimer | Email webmaster | Privacy policy |     File Modified Jun 21, 2006