Grass Pond Eel Ramp: 2008 Summary Report
Project Partners: Massachusetts Division of Marine Fisheries, Harwich Conservation Trust, Town
of Harwich, John Sennott (cranberry bog operator).
Date: November 12, 2008
(Draft – Brad Chase)
Introduction
Grass pond is a small natural pond from which water flows through Cold Brook to meet Nantucket
Sound at Saquatucket Harbor in Harwich, Massachusetts. A maximum size of 24 acres has been
reported for Grass Pond, although historical flow manipulations for hydropower and cranberry
growing have likely reduced the size of Grass Pond. Presently there is high seasonal variability to
the wetted perimeter and outflow of the pond. The Harwich Conservation Trust (HCT) own 60
acres of former cranberry bog east of Bank Street, Harwich, in the Grass Pond watershed. They
share water rights with an adjacent cranberry bog operator (John Sennott) granted from license
No. 769 issued in 1927 by the MA Division of Waterways. The HCT has been considering options
for land-use and habitat restoration of their bog property. They contacted the MA Division of Fish
and Wildlife (MassWildlife) and Division of Marine Fisheries (MarineFisheries) for advice on fish
and wildlife restoration. They have also been working with the National Resource Conservation
Services (NRCS) on potential agriculture and habitat restoration options for the property.
Observation by HCT, MassWildlife, and MarineFisheries confirmed the presence of American eel
in the Grass Pond watershed. MarineFisheries determined that the recently rebuilt (2007) Bank
Street flume presented an impediment to eel passage into Grass Pond and recommended that an
eel passage restoration project be considered.
Following several site visits and consultations with property owners and the Town of Harwich,
plans were initiated during the winter of 2008 to install an experimental eel ramp at the Bank Street
flume to allow migrating eels to pass into Grass Pond. The HCT received funding from NRCS to
make improvements to culvert in their bogs and the grant included funds for improving eel
passage. For the 2008 spring migration, it was decided to build a temporary wood eel ramp with
MarineFisheries funds in order to assess the utility and performance of an eel pass at this location
during a monitored pilot project.
2008 Monitoring
Eel Ramp Construction. The eel ramp was constructed by Luis Carmo and Ed Clark of the
MarineFisheries fishway construction crew. The ramp was built of plywood in two 8’ sections
connected by hinges. The ramp sections were 12” wide, lined with Enkamat, and has ¼” aluminum
screening resting on 3” side walls. The lower section was set at water level in Cold Brook. The
upper section connected to an eel holding tank next to the flume in Grass Pond (photograph). A
battery (12V, 650 amp) powered bilge pump (Rule 360 gph) supplied water to attract eels to the
ramp and to maintain captured eels in the flow-through holding tank. The battery could not keep
pace with the bilge pump despite frequent charges. Following this experience, a series of
experiments were conducted on maintaining power to the pump with AC power and a Sunsei SE1500 solar panel.
Monitoring Methods. Efforts were made to inspect the ramp holding tank each day except
Sunday when the pump was operating. With each visit, the time of day and number of eels in
holder tank were recorded to allow the calculation of catch-per-day or catch-per-hour. Eels were
counted in the following three size groups: glass eel (young-of-the-year, YOY), age-1 eel (fully
pigmented with minor length gain over YOY), and age-1+ (approx. >10 cm with length/weight
separation from age-1). Notes were recorded on by-catch and ramp operations. The following
water chemistry parameters were measured next to the ramp tank with a YSI 6-Series sonde on a
monthly basis: water temperature (C), DO (mg/l), DO saturation (%), specific conductivity
(mS/cm), pH, and turbidity (NTU)
Monitoring Results. The monitoring period to capture the typical YOY eel migration in
Massachusetts should be April 1st through June. The ramp was not ready for installation until May
16th; about the mid-point of the migration season. The ramp passed 78 age-1 and age-1+ eels
during the first night of operation. The pump operated for seven of the next 10 days catching low
numbers of age-1 or age-1+ eels with the first appearance of YOY eels on May 24th. On May 27th,
many YOY eels were observed in Cold Brook immediately downstream of the flume. With this
observation, a board was added to the flume, causing no flow to exit Grass Pond except pumped
flow down the ramp. On this day, we also converted to AC power from the neighbor’s house. On
May 28th catches of both YOY and larger eels increased dramatically, beginning a 10-day period
where catches peaked for the season with over 100 eels counted each day. The eel count for the
season was 6,414. Overall catches were dominated by YOY eels (4,521, 70%) with evidence of
an earlier peak and shorter run duration for age-1 eels (1,518, 24%) and age-1+ eels (375, 6%).
By-catch was not anticipated for this specialized eel pass, yet 15 crayfish, two recently hatched
snapping turtles and many freshwater beetles made the trip up the ramp and into the holding tank.
Ramp Operation. The eel ramp performed well as evident by catches the first night of operation,
large catches during a short season, and no tank mortality. Frequent troubleshooting was needed
for the bilge pump power supply. Richard Cooper, an electrical engineer who volunteered for HCT,
conducted detailed tests of the ramp’s power system. It was clear that the bilge pump load was too
much for the battery on a charging schedule or connected to solar panels. The solar panels were
rated for a maximum current output of 1.5A yet under testing both panels achieved only 1.1 A. The
best performance was achieved when two solar panels were connected with a 25 W rheostat timer
set to turn the pump off between 8 am and 6 pm and to limit the pump to 80% capacity while
pumping. This configuration kept the pump running continuously (8-day experiment) under
conditions of ample summer sun. It is apparent that the panels do not meet their advertised
performance and cannot handle a steady load without a timer.
Outlook for 2009 Season. The HCT will use funds received from NRCS to construct a more
durable eel ramp with a properly sized solar panel for the 2009 season. The MarineFisheries
fishway crew will construct a custom aluminum ramp with the same dimensions as the wood ramp.
The aluminum ramp will not degrade in the wet environment and provide many years of service.
Richard Cooper’s recommendations will be used to outfit the ramp with a low-maintenance, solar
power source. The ramp will be installed on or near April 1st, and operate through all of April, May,
and June and removed when eel catches approach zero in early July. This seasonality covers the
migratory period of glass eels from the ocean and upstream movements of older eels. It is also
consistent with other eel monitoring projects in Massachusetts. The partners will also meet to
discuss other potential eel habitat improvements in the watershed and operational considerations
for the Bank Street flume related to the silver eel emigration in the fall. Mature silver eels exit freshwater habitats on a spawning run to marine waters between September and November each fall.
Acknowledgements
Pump-supplied eel ramps are a new restoration tool in Massachusetts. The first ramp in a MA
coastal river was installed in Saugus in 2007 and the Grass Pond ramp is the second. The large
catches in a small, altered brook were surprising and encouraging. The project was dependent on
the ideas and cooperation from the bog owners, adjacent home owners, the Town of Harwich,
volunteers, and the MarineFisheries fishway crew. From this list we appreciate and recognize the
efforts of Ben Wright, John Sennott, Shirley Fletcher, John Pashanyan, Tom Leach, Richard
Cooper, Christin Marshall, Luis Carmo and Ed Clark.
2
Luis Carmo of MarineFisheries installing eel ramp at Grass Pond, Harwich.
Figure1. American eel count at Grass Pond eel ramp, 2008.
800
YOY eels
Age-1+
Eels
600
400
200
0
5/17
5/24
5/31
6/7
6/14
Date
3
6/21
6/28
7/5