Sturgeon

From Great Lakes Wiki

The Lake Sturgeon (Acipenser fulvescens) courtesy of the New York State Department of Environmental Conservation.

Great Lakes Sturgeon

Lake Sturgeon are superior benthic feeders which have 4 feeling barbels in front of a protrusible anterior mouth with prehensile lips used to eat small invertebrate insect larvae, leeches, crustaceans, bivalves and small fish. They also come equipped with 5 distinct rows of bony defensive scutes that grow dull as the fish grows older and larger. In every lake system they exist, sturgeon grow to be the largest and oldest fish (MI Sea Grant).

In addition to its prolonged life, lake sturgeon also have an extended maturation period that lasts 24-26 years in females and 8-12 years in males. Once sexually mature the females only swim upstream to spawn once every 4-9 years, the males every 2-7. They like to spawn in fast, warm, shallow gravel shoals (GLLS). Much like sea turtles, the sturgeon of the Detroit River are frequently prevented from mating after a long coming-of-age, and are considered a threatened species in 19 of 20 states in its original range (Caswell, Hill). When they try and migrate to their original spawn site in the Detroit River, or one of its tributaries they often find that it has been dredged, developed or polluted. All three discourage sturgeon spawning and all three exist in and along the Detroit River.

Background

The history of the Detroit River lake sturgeon is a turbid one; one that lead the EPA to declare the sturgeon an important indicator species of river health. From 1880 to 1920 sturgeon suffered from overfishing for their precious caviar and isinglass, and were unable to recover (MI Sea Grant). As a result, Canada and the US Fish and Wildlife Service closed sturgeon seasons, and tightened size limits, creel limits, and gear restrictions (GLLS). But, the surviving fish were simultaneously hassled by a series of river alteration projects for nearly 80 years between 1876 and 1959 that included dredging, coastal wharf construction, channel girth improvements and river spanning structures like dikes and concrete bridges (Army Corps of Engineers). Reproducing under these ever-changing and stressful conditions was apparently highly unsuccessful for sturgeon. A 1974 report for the MDNR by W.H. Tody estimated that a mere 1% of the original average sturgeon population remained in the Detroit River at the time of the study (Tody).

There have been many other potential barriers to sturgeon survival that were not studied until more recently. These include the effects of industrial and agricultural waste discharge, sturgeon behavior in the presence and treatment of invasive species, and changing habitats and diets throughout the sturgeon life cycle.

Current Status

To identify whether sturgeon were recovering since Tody’s publication, a 1998 study was put on by the US Fish and Wildlife Service and the Great Lakes Science Center (GLSC), who utilized Detroit River anglers to assess the sturgeon population. The GLSC study found that the sampled fish were sub-adult and too young to spawn, but were healthy and growing logarithmically from year class to year class (Hill). This led to another study to take place in 2003 by Nathan Caswell, of the USFWS, which aimed to locate sturgeon spawning sites, old and new. Using information on historical spawning sites and radio telemetry Caswell confirmed 3 active sturgeon spawning sites, as well as a sturgeon “home area.” (Caswell).

Following the evidence provided by Caswell and the USFWS, three separate habitat restoration efforts began between 2003 and 2006. All three aimed to restore historical sturgeon spawning areas by constructing off shore, underwater shoals made of crushed limestone, coal cinders and coarse gravel (USGS). Fortunately, researchers have found that the three restored sites have been used by spawning sturgeon and other fish, but are in need of more funding to continue spawn monitoring (EPA).

All sturgeon caught in the studies were tagged in various ways. Two of the recent monitoring strategies implemented by Great Lakes Fish Commission are a sturgeon tag database and an interactive GIS map designed to reflect sturgeon feeding, running and spawning populations. The websites are intended to facilitate communication between “those who tag and those who recapture” sturgeon, so that a firm background on sturgeon activity can be established around the Great Lakes (GLFC, GLLS).

Tracy Hill’s Evaluation of Lake Sturgeon in the Detroit River by Sports Anglers reported that “foods vomited by captured lake sturgeon in decreasing order of occurrence included whole and crushed zebra mussel Dreissena polymorpha shells, snail shells, and fish remains,” and that “Zebra mussels appear to be a common food of lake sturgeon in the Detroit River.” The only other known fish and water fowl that predate on the invasive zebra mussels are casual ones at best (DePolo). In 2002, Dr. Robert Werner and the EPA studied sturgeon diets and habitat substrates by year class in the St. Lawrence Seaway, and demonstrated that a majority of the stomach contents of adult sturgeon was zebra mussels. It also demonstrated that two very different substrates must be maintained to allow sturgeon to grow to a size that allows the digestion of the bivalves. By making zebra mussels a majority of their diet as adults, the long-living sturgeon show themselves to be a keystone species, as well as an EPA bioindicator.

Also in Hill’s Evaluation was a mention of how many of the young sturgeon appeared to have been attacked by sea lamprey. There has not been any research on how much of lamprey diets consist of young sturgeon and only recently has there been research on how lampricides affect the growth of juvenile sturgeon. Young fish can withstand as much chemical lampricide that it takes to kill larval lamprey, but higher doses would kill the sturgeon too.

References

Caswell, Nathan M., D L. Peterson, and B A. Manny. REPORT: "Spawning by Lake Sturgeon (Acipenser Fulvescens) in the Detroit River." Environmental Protection Agency Web Site. 19 May 2003. GLSC, USGS, EPA. 17 Nov. 2007 <http://www.epa.gov/glnpo/ecopage/aquatic/lkstrugeon/rpt.PDF>.

Depolo, Jamie. "Go Fish." Futures (2007). 18 Nov. 2007 <www.maes.msu.edu/publications/futures/springsum2007/fish_springsum2007.pdf ->. "Detroit River." US Army Corps of Engineers. 27 July 2006. US Army Corps of Engineers. 29 Nov. 2007 <http://www.lre.usace.army.mil/greatlakes/hh/outflows/discharge_measurements/detroit_river/>.

Hill, Tracy, comp. REPORT: Evaluation of Lake Sturgeon in the Detroit River as Reported by Sport Anglers. Mar. 1999. US Fish and Wildlife Service - Fish Resource Office, Alpena, MI. 18 Nov. 2007 <http://www.fws.gov/midwest/Alpena/rpt-detriv98.html>.

Kavetsky, Bob. "USFWS Coastal Program Funded Lake Sturgeon Projects." Great Lakes Lake Stugeon Web Site. 25 Oct. 2007. U.S. Fisheries and Wildlife Service. 17 Nov. 2007 <http://www.fws.gov/midwest/sturgeon/usfws.htm>.

"Lake Sturgeon, Dinosaur of the Great Lakes." Great Lakes Science Center Web Site. 12 Apr. 2006. United States Geological Survey, US Department of the Interior. 16 Nov. 2007 <http://www.glsc.usgs.gov/main.php?content=research_sturgeon&title=Fish%20at%20Risk0&menu=research_risk_fish>.

Manny, Bruce A., and James Boase. REPORT: "INDICATOR: Lake Sturgeon Population." Environmental Protection Agency. 3 May 2007. EPA, USGS, GLSC, USFWS. 16 Nov. 2007 <http://www.epa.gov/medatwrk/grosseile_site/indicators/sturgeon.html>.

"Sturgeon Habitat Restoration, Monitoring and Education." Michigan Sea Grant. 01 Nov. 2007. 17 Nov. 2007 <http://www.miseagrant.umich.edu/sturgeon/index.html>.

Tody, W.H. 1974. REPORT: “Whitefish, sturgeon, and the early Michigan commercial fishery.” Michigan Fisheries Centennial Report 1873-1973. Pp. 45-60. Michigan Department of Natural Resources, Lansing, MI.