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According to University of Maine student Chris Holbrook, the Penobscot River’s salmon population is low, and it is important for us to know why.
Wednesday, Holbrook, a graduate student in the department of biological sciences, presented a seminar entitled, “Migration of Penobscot River Salmon Smolts and Adults,” to a small audience in Norman Smith Hall.
During his presentation, Holbrook revealed the results of a seven-month analysis that traced the migration patterns of Atlantic salmon along the Penobscot.
Last year, Holbrook and two faculty members of the graduate program in ecology and environmental science, Mike Kinnison and Joe Zydlewski, conducted a series of experiments that tested systemwide passage success of salmon going upstream and downstream the Penobscot during April through October.
The experiments assessed the proportion of salmon using the Stillwater River, the effects of dams on salmon population and the overall salmon mortality rate on the Penobscot.
Currently, the Penobscot River remains New England’s second largest river system. It drains an area of 8,750 square miles, and its main stem drains into Penobscot Bay near Bucksport.
The Penobscot is best known for being the largest Atlantic salmon run remaining in the United States, with 1,000-4,000 adult salmon returning in recent decades.
However, the salmon population has been dwindling during the last few years, provoking Holbrook and his team to seek answers.
The experiment kicked off with the release of more than 3,000 smolt salmon at the northern end of the Penobscot.
A smolt is a young salmon at the stage of intermediate growth, when it becomes covered with silvery scales and is ready to migrate from freshwater to the sea.
Acoustic tags acting as tracking devices were surgically implanted inside each fish, while an array of acoustic receivers planted periodically along the Penobscot would indicate the location of each smolt and its varying paths down the river.
Holbrook and his team then analyzed all behavioral, environmental and physiological changes that occurred during the migration downstream.
Holbrook’s findings concluded that dams may in fact act as a serious impediment during migration and may be responsible for high smolt mortality rates.
Conversely, the experiment attempted to track the voyage up river as well, as adult salmon were released at the southern end of the river.
Once again, high numbers of delays were found because of dams, with failure rates highest near the Veazie dam.
Currently, the Penobscot River restoration project hopes to improve fish passage by removing all dam barriers, including the dismantling of the Veazie and Great Works dams.
The hydropower generation created by these dams may pose a serious threat to the Penobscot salmon population, and according to Holbrook, the restoration project would be a step in the right direction.
“With the effect the restoration project will have on dams, there is great potential to increase salmon population and survival after it’s through,” said Holbrook.
Holbrook’s project was funded by the university, along with various environmental science organizations, including the U.S. Fish and Wildlife Service.
In 2006, Holbrook will replicate his smolt study along the Penobscot River. No decision has been made to repeat the adult salmon study.
Holbrook’s presentation was part of a spring seminar series focusing on Penobscot River research, sponsored by the Senator George J. Mitchell Center for Environmental and Watershed Research, and the program in ecology and environmental science.
Bangor Daily News