Over the last two decades, scientists have found the abundance of American eel (Anguilla rostrata) in the northwest Atlantic in serious decline. Many factors contribute to the decline but, to what degree?

Information about eel behavior passing down-stream through dams has been limited. However, in 2003, Leah Sullivan, then a graduate student at the University of Massachusetts, used acoustic telemetry to investigate their behavior along the Connecticut River, at one of the numerous north eastern hydro-electric facilities.

Fifty eels were surgically implanted with HTI's Model 795 Acoustic Tags and their movement was monitored in 3D in the forebay (the first 100 m of area located directly upstream of the project). The study helped shed light on how the eels were choosing to pass the dam. Each eel’s 3D location was revealed every 3 seconds. Resulting tag positions were plotted in 3D revealing the fine-scale movement of each eel.
It was discovered that the eels occupied a variety of depths throughout the forebay; however, most their of time was spent near the bottom. The eels occupied the middle and upper water column more frequently and displayed an increase in turning movement immediately upstream of the trash racks. The increase in surface orientation and elevated turning angle was the result of the eel’s vertical and horizontal searching behavior in this area.

Most frequent behaviors included quick, upstream movements after eels encountered the trash racks, vertical and horizontal changes in position at or near the trash racks. Eels appeared to be volitionally choosing the turbines as their preferred downstream passage route based on dominant flow. To view a few clips from the 3D tracks, please see tracks above right.