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> Spotlight on Sturgeon

The East Coast of North America supports two species of sturgeon, Atlantic (Acipenser oxyrinchus) and shortnose (Acipenser brevirostrum). Both species of sturgeon are primitive bony fishes with rows of armor-like plates on their sides. Sturgeon feed along the river or ocean bottom, disturbing the substrate with their mouths and ingesting small animals into their tube-like mouth. Large, slow-to-mature fish, Atlantic sturgeon can grow to 18 feet in length while shortnose sturgeon grow up to 4 feet in length. In Maine waters, the U.S. Endangered Species Act and state laws protect both Atlantic and shortnose sturgeon. 

Shortnose sturgeon and Atlantic sturgeon in the Penobscot River

University of Maine graduate student Stephen Fernandes with endangered shortnose sturgeon.

The Penobscot River historically supported spawning populations of both of these threatened sturgeon species. Research on sturgeon in the Penobscot River began in 2006 when University of Maine researchers confirmed the presence of both species, a surprising find given that shortnose sturgeon had not been recorded in the system for several decades.  Research has since expanded to include questions about how many sturgeon use the river and for what purpose. With the recent removal of the Veazie and Great Works dams, research is now concentrated on whether and how sturgeon will use the newly available habitat. Clearly it is an exciting time on the river for understanding and restoring sturgeon and other migratory fish species.

Current sturgeon research on the river builds on past research that formed the foundation of our knowledge. Telemetry is used to track the movement patterns of sturgeon tagged with acoustic tags. Each year in the late summer and early fall, researchers use gill-nets to collect adult sturgeon. Under NOAA-Fisheries Endangered Species permits (#16306 and #16526) all fish caught in gill nets receive numerically unique external and PIT tags that allow for later identification if the fish are recaptured. This netting contributes to a long-term mark-recapture dataset to estimate how many sturgeon are in the river. In addition, a subset of these individuals is implanted with acoustic tags to determine specific migratory patterns and habitat use. These tags are detected by approximately 30 receivers sitting on the river bottom. The receivers are attached to pink buoys that are visible while driving along the lower river and extend from Penobscot Bay up to just downstream of the Milford Dam.

Shortnose sturgeon

An interesting behavioral pattern that has been documented since 2007 is the movement of some individuals (both shortnose and Atlantic sturgeon) between the Penobscot River and the Kennebec River. This observation led to broader discovery that shortnose sturgeon in the Gulf of Maine undergo extensive marine migrations that are uncommon elsewhere. Indeed, shortnose sturgeon have long been studied and managed as a river-resident species. This migratory life history raises important questions about how best to quantify and manage shortnose sturgeon in the Gulf of Maine  

With a known spawning population in the Kennebec River, researchers want to know if there could be one in the Penobscot too. To date, researchers know that shortnose sturgeon use the Penobscot River throughout the year, moving to an upstream area of the river in the fall when water temperatures drop to spend the winter. In other rivers where spawning occurs, sturgeon have been documented moving to spawning grounds in the spring when water temperatures rise above about 7° Celsius. Each spring since 2007, during the expected spawning season, researchers have monitored for signs of spawning on the Penobscot. Researchers set special gear to potentially collect sturgeon eggs or larvae in an attempt to confirm whether sturgeon are spawning in the river. Spawning has not been discovered in the Penobscot River to date, but that could change given new opportunities for sturgeon to access restored habitat.  

The presence of a spawning population of shortnose sturgeon in the Penobscot River would have serious implications for recovery of the species in the Gulf of Maine, but spawning may depend on more than just increased access to habitat. Other factors also influence whether sturgeon will spawn, such as appropriate substrate and flow conditions. A baseline study of spawning habitat suitability, funded by the Penobscot River Restoration Trust, was completed below the Veazie and Great Works dam sites in the river in 2010 by University of Maine researchers. A hydrodynamic model based on depth and velocity was used to estimate and map suitable spawning habitat in anticipated habitat reaches after dam removal. Currently, bottom substrate data are being collected to incorporate with the velocity and depth model to provide a refined map of potential spawning habitat for improved future monitoring and restoration efforts. 

Atlantic sturgeon

Atlantic sturgeon have been less studied in the Penobscot River compared to shortnose sturgeon. However, valuable information on habitat use and movement patterns has been collected for Penobscot Atlantic sturgeon, also using acoustic telemetry. At the end of the 2014 field season, a total of twenty-seven Atlantic sturgeon were equipped with active acoustic tags.  Individuals of this species also move between the Penobscot and Kennebec River. However like Atlantic sturgeon elsewhere, they also make even longer marine migrations that can take them out of Maine waters. In fact, Atlantic sturgeon tagged in the Penobscot River have been detected as far north as Minas Basin in the Bay of Fundy and as far south as the Hudson River. In the Penobscot River, Atlantic sturgeon spend most of their time in the lower river around Winterport and Bucksport. This region is characterized by muddy bottom substrate that is rich in spionid worms and is considered a foraging ground for sturgeon. Tagged Atlantic sturgeon have been detected as far upstream in the Penobscot as Bangor and Brewer.

Telemetry studies are not restricted to the Penobscot and Kennebec River systems. Receivers are deployed at the mouths of other major rivers in Maine, including the Saco, Union, Narraguagus, Passagassawakeag, St. George, Medomak, and Damariscotta Rivers to learn more about what other rivers are being used by sturgeon. Other recent research regarding sturgeon on the Penobscot River has included the study of diet of Atlantic and shortnose sturgeon in the lower section of the river to identify important feeding habitat and prey. This research was conducted as part of a University of Maine undergraduate research project. Further work by graduate students at the University of Maine School of Marine Science includes a study of population dynamics of shortnose sturgeon throughout the Gulf of Maine, with an emphasis on determining how populations of different rivers may be related. 

Information Update provided by Catherine Johnston, University of Maine School of Marine Sciences

Photo by Christopher Holbrook.

Sturgeon Articles:

Article on modern methods of tracking fish migration in Working Waterfronts

Article on surprising route sturgeon take from Maine to Merrimack River in Boston Herald
Article on Leaping Living Fossils (7 Mb PDF) in On the Water magazine.


Scroll down for links to video and underwater sonar images

Researcher Kevin Lachapelle listens to radio signals from tagged shortnose sturgeon. Photo: Cheryl Daigle.

Researchers Phil Dionne and Kevin Lachapelle set up holding pens for shortnose sturgeon. Photo: Cheryl Daigle

Phil Dionne weighs a shortnose sturgeon while collecting data. Photo: Cheryl Daigle

Researcher Phil Dionne examines shortnose sturgeon while collecting data. Photo: Cheryl Daigle

Researchers scan a shortnose sturgeon to determine if it has been radio-tagged in the past. Photo: Cheryl Daigle

Research volunteer Cheryl Daigle with shortnose sturgeon before releasing the sturgeon into the Penobscot River. Photo: Kevin Lachapelle

WATCH UNDERWATER IMAGING SONAR OF STURGEON (Video images taken pursuant to ESA permit number 1595).

VIDEO OF RESEARCHERS COLLECTING DATA ON STURGEON (Video images taken pursuant to ESA permit number 1595-02).

December 2008 Bangor Daily News article


READ MORE: NOAA press release (2006) and original Bangor Daily News article

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