Purdue News

August 21, 2006

Sturgeon's general warning: Stable for now, but beware

WEST LAFAYETTE, Ind. — They take a long time before they mate and, once old enough, don't mate every year. Even so, sturgeons are heavily sought after for their eggs, which are made into caviar.

Trent Sutton and Kendall Huffer
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For these and other reasons, many sturgeons — a variety of ancient, bottom-feeding fish — are in trouble.

Trent Sutton, a fisheries biologist at Purdue University, has helped to ensure that a local variety of sturgeon, the shovelnose, does not become endangered or threatened like many of its relatives.

"The problem with sturgeons in general is that they are a long-lived fish that take a long time to reach sexual maturity," Sutton said.

He has completed a series of studies on the shovelnose sturgeon in Indiana waterways, particularly the Wabash River. His findings have become the basis for size and catch limits on the fish that will be put into place next summer, said Bill James, chief of fisheries for the Indiana Department of Natural Resources (DNR). There are currently no fishing regulations for the shovelnose.

Sutton's research identifies many of the fish's habits that were previously unknown. Importantly, he found that the Wabash River population appears to be stable. Nevertheless, his sampling uncovered very few young fish in the river.

"This raises a few red flags," Sutton said. "This means that either the females aren't laying eggs or that they aren't spawning at all — both of which would have serious ramifications."

Another possibility, he said, is that the researchers' sampling may not have been in the right place and most of the young were somewhere else.

"This is an issue that needs to be resolved," he said.

The shovelnose, the smallest of sturgeons, reaches sexual maturity between ages 6 and 9 and spawns about every other year. This is relatively quick growth compared to the lake sturgeon, now endangered in much of North America, that doesn't reach sexual maturity until 20-25 years of age and only spawns every three to five years. The shovelnose, like others sturgeons, is particularly vulnerable to overfishing because of the long time they require to breed and regenerate their numbers.

Caviar, considered by many to be a delicacy, consists of brined sturgeon roe, or eggs. Until recently, larger species of sturgeon in central Asian waters, particularly the Caspian Sea, provided the world with most of its caviar. Habitat degradation, pollution and overfishing have taken a toll on these populations, and smaller sturgeons, like the shovelnose, are now targeted for their roe. The shovelnose, for example, is currently harvested throughout much of the Mississippi River basin for this reason.

While shovelnose populations have declined in the Missouri and Mississippi rivers, James considers the Wabash River population to be among the healthiest remaining in the entire Mississippi River basin, a large area including 28 states.

"We have a healthy, stable population, and we intend to keep it that way," James said. "Professor Sutton's work will help us do that."

Sutton's work appears in three articles, one of which was published in the June-July issue of the Journal of Applied Ichthyology, with the remaining two to follow in separate journals by year's end. Tony Kennedy, one of Sutton's former graduate students, was a co-author in each of the three articles.

Sturgeons, whose fossil record dates back 100 million years, are covered with bony plates and have a distinctive wedge-shaped snout with sensitive barbels, or tactile whiskers, to detect food in river-bottom sediment.

Sutton's research shows that when a shovelnose sturgeon (Scaphirhynchus platorynchus) reaches reproductive age, it moves north up the Wabash River to spawn (shovelnose are found in fewer numbers in Indiana's White River). The fish is a broadcast spawner, meaning its eggs are fertilized in the water. After fertilization, the embryos develop on the river bottom and, once they absorb their yolk sac left over from the egg, drift downstream with the current. This may help explain why Sutton found few young fish.

Last year, the United States banned all imports of caviar from the beluga sturgeon, one of the largest and most endangered fish. Beluga caviar is considered to be the best and sells for high prices — one online company sells it for $1,600 a pound. In 2006 the United Nations imposed a temporary ban for the remainder of the year on the international trade of most varieties of caviar harvested from wild fish.

The proposed Indiana DNR regulations would allow for an open season on the shovelnose from Oct. 1 through May 31 and mandates a minimum fork length of 25 inches (fork length, as opposed to total length, is the measurement from the tip of a fish's mouth to the point at which the tailfin forks).

James said the Illinois Department of Natural Resources has the same regulations pending, based in part on Sutton's research. Sturgeon are typically harvested solely for their roe; they are not considered good as flesh fish and are not commonly sought for catch and release.

The DNR regulation process is under way. A public hearing will be scheduled and announced, then a final recommendation meeting will take place before the proposed limits are finalized.

The research was funded by Purdue's College of Agriculture and the Indiana DNR. Sutton plans to continue his research on the shovelnose at some point in the future.

Writer: Douglas M Main, (765) 496-2050, dmain@purdue.edu

Sources: Trent Sutton, (765) 496-6266, tsutton@purdue.edu

Bill James, (317) 232-4092, bjames@dnr.in.gov

Ag Communications: (765) 494-2722;
Beth Forbes, forbes@purdue.edu
Agriculture News Page

In this 2005 photo, Trent Sutton and student intern Kendall Huffer of Lafayette weigh, measure and tag shovelnose sturgeon in the Wabash River as part of Sutton's research. (Purdue Agricultural Communication photo/Tom Campbell.)

A publication-quality photo is available at https://news.uns.purdue.edu/images/+2006/sutton-sturgeon.jpg



Reproductive biology of female shovelnose sturgeon in the upper Wabash River, Indiana

A.J. Kennedy, T. M. Sutton and B.E. Fisher

Shovelnose sturgeon (Scaphirhynchus platorynchus) are commercially important, supporting a viable roe fishery throughout much of the Mississippi River drainage. We examined the reproductive attributes of stage-5 female shovelnose sturgeon captured from the upper Wabash River, Indiana, from March to June 2004. Shovelnose sturgeon were collected using boat electrofishing and experimental gill nets, measured for fork length (FL) and wet weight, and sexed externally if possible. Size- and age-at-maturity, absolute and relative fecundity, relative egg size, and gonadosomatic index (GSI) were determined for 49 female shovelnose sturgeon (range, 601- to 858-mm FL). Female shovelnose sturgeon reached sexual maturity at approximately 600 mm and age-at-maturity ranged from ages 6 to 12 (median age = 9). Relative fecundity ranged from 11 220 to 23 956 eggs kg1 (mean = 18 156 eggs kg1). Absolute fecundity ranged from 14 294 to 65 490 eggs female1 (mean = 30 397 eggs female1) and was positively related to FL (r2 = 0.76) and wet weight (r2 = 0.82). The number of eggs g1 of ovary weight ranged from 72 to 170 (mean = 98 eggs g1) and was negatively correlated with GSI. GSI values ranged from 9.4 to 27.2 (mean = 19.3) and were positively correlated to FL (r2 = 0.18). Our results increase our understanding of shovelnose sturgeon reproductive biology and recruitment dynamics and provide input for models to evaluate the effects of harvest on this species.


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