This study will be significant in that it will be a crucial first step at applying telemetry technology to determine migration dynamics of striped bass in the Saco River and adjacent coastal waters of the Gulf of Maine. The following is a description of the technological equipment that is being used in this study.

Acoustic Tags

Commercially available acoustic tags (Lotek Wireless Inc.) are coated with a biologically inert resin to prevent host rejection and are activated just prior to implantation by a magnetic reed switch.  If you would like to learn more about this surgical procedure please visit our Surgery Page.

Activated tags broadcast up to 212 individually coded acoustic pulses per frequency. Long-lived tags are 16 x 80 mm and weigh up to 18 grams in water. Tags include a battery with an expected life span of up to four years.

Acoustic tags will be surgically implanted inside of the peritoneum but outside of the stomach. Fishes will be secondarily tagged with external tags (Internal Anchor tags) identifying the fish as carrying a transducer and suggesting its release upon recapture by anglers. Release of tagged fish will be further encouraged as part of our education program.

Fish for tagging will be healthy specimens captured by circle hook and line, trawl, or electrofishing. Local recreational fishermen are participating in locating and landing a series of fish. Fish range in size to the largest available, but include a number of smaller specimens (<28 inches) to reduce recreational fishing-related mortality/removal.

Tagging and release is occurring throughout the Saco River and the adjacent coastal water. Tagging of fish in fall includes the participation of winter residents. Donations by recreational angler clubs is supporting additional tag releases through an Internet-based fish adoption campaign.

Hydrophones

Hydrophone units are suspended in the water column under a moored buoy. Each hydrophone unit has an expected life of 4 years, although D cell batteries in a field changeable pack need to be replaced every 4-6 months.

Ultrasonic signals detected underwater are relayed by VHF to a data logger/receiver. 
This map shows the Saco River as it empties into Saco Bay. The small red circles mark the placement of the hydrophones during the first year of the striped bass research project. The large red star shows the location of the University of New England.
Hydrophones can detect acoustic tags at a maximum range of about 500 m (1 km radius) depending on conditions. Therefore, a single hydrophone can effectively intercept all tagged fish moving along the river axis at its narrower points. It is not necessary that all hydrophone ranges overlap along this axis. The ability to confidently detect movement at certain points along the river, even if not continuously, will effectively divide the river into a course scale grid suitable for the testing of contingent and migration participation.

Hydrophone Placement

For the first year, three hydrophones will be deployed along the estuarine portion of the river beginning with a location near the salt front in the vicinity of Biddeford including shoal-foraging habitat and sharp drop-offs to deep water.

Farther downstream, placement of a fourth mooring just offshore from the University of New England’s Marine Science Education and Research Center will take advantage of natural constrictions as found at upstream locations, but in higher salinities.

A fifth mooring at the Wood Island intercepts fish arriving or leaving the entrance to the Saco river estuary. A sixth and seventh mooring will be located along the coast north and south of Wood Island to detect coastal migration in either direction from the Saco River estuary entrance and into Biddeford Pool.

Throughout, we will examine various configurations of the hydrophone array for sensitivity to placement and environment. For example, the effects of surf and boat noise, and the potential baffling of acoustics by bathymetry should be accounted for in optimizing the array towards both tag detection and spatial coverage.

In following years, the array will be extended to integrate with GoMOOS BUOYS to include two cross shelf transects off the Gulf of Maine.

Logger/Receivers

Each hydrophone mooring-buoy contains transmitting equipment that radios data to a logger/receiver to be installed at key locations along the river and adjacent coastal waters. These sites provide high altitude locations, providing line-of-site contact with the hydrophone array. The logger/receiver may simultaneously monitor up to 64 individually coded acoustic tags.

In the second project year, a data logger/receiver will be installed at additional sites to monitor the inlet hydrophone array and extensions into the Gulf of Maine. Additional logger/receivers with attached cell phones may be added to the system at later dates by deployment in lock boxes at strategic places, thus significantly expanding the potential range of deployment sites for hydrophones.

Directional Mobile Hydrophones

Movements of tagged striped bass initially located by fixed hydrophones will be monitored on several occasions at finer scale by following them with directional mobile hydrophones on small boats, from which physical environmental parameters will be consecutively measured using a CTD (conductivity, temperature, density), differential global positioning system (DGPS) and fathometer.