--Exerpts taken from WDNR publication Lake Sturgeon (PUBL-FM-704 88)
A giant among Wisconsin's inland fresh water fishes, the
bottom-dwelling lake sturgeon is a living fossil - a relic from the
Middle Ages of fish evolution. This ancient species made its first appearance
about 100,000,000 years ago in the Upper Cretaceous period of the Mesozoic
era, just about the time that the dinosaurs made their abrupt exit from
the Earth. Today the lake sturgeon retains many primative characteristics
that have been lost or modified in other
modern-day fish.
The sturgeon is long lived and can reach ages over 150 years and can weigh in excess of 200 punds. It has a torpedo-shaped body with a shark-like turned up tail. As befits a representative of fishdom's midieval era, the lake sturgeon wears "armor" in the form of bony, shell-shaped plates arranged in five rows with each plate coming to a peak. Another ancient characteristic is a continous, flexible, cartilage-encased rod called a notochord running the length of the body instead of a backbone with seperate vertebrae.
Four barbels, or feelers, dangle in a row on the lower side of the snout just in front of the mouth. Sturgeon do not have teeth, instead they rely on suction to feed. Their diet is restricted to snails, insect larvae, leeches, small clams and other invertebrates. When it is searching for food they will drag its barbels lightly over the bottom. As soon as these sensitive feelers touch food, the fish protrudes its tubular mouth and sucks up the food.
A female sturgeon reaches sexual maturity when she is 24 to 26 years old and about 55 inches long, and will spawn once every four to six years thereafter. Males mature at about 15 years, when they are 45 inches long. Most males spawn every other year. They migrate to their annual spawning grounds between late April and early June, preferring to spawn in shallow, rocky areas along river banks. The fertilized eggs, each about one-eighth inch in diameter, are sticky and cling to rocks and other solid materials in the water until they hatch. Females can release 50,000 to 700,000 eggs in one season. The eggs hatch in five to eight days, depending on water temperature. In 12 to 14 days, the young fish are one inch long and have fully developed mouths and barbels.
Historically, the lake sturgeon was revered by native americans and considered a nuisance by early commercial fishermen. Once the fisherman realized the value of sturgeon roe (eggs) for caviar, the flesh was delicious, and a high quality gelatin could be extracted from their swim bladder, the great lakes sturgeon fishery exploded. The species was fished so intensively that lake sturgeon populations were reduced to a level from which they have never recovered. The lake sturgeon is listed as a rare species in the United States. Wisconsin, however, is fortunate to have a good, naturally reproducing population in several of our river systems.
The Wisconsin Department of Natural Resources (WDNR) is doing their part to help the lake sturgeon population here and abroad through egg collecting, rearing, and restocking.
During a warm week in May, WDNR staff set up nets across a section of the Yellow River in Burnett County. The nets were placed in a "V" shape with the apex pointing upstream. The migrating fish would swim along the edge of the nets to the middle catch area sporting "doors" that kept them from escaping.
The Department's goal was to collect eggs and milt (sperm) from 2 females and 3 males. Once a lake sturgeon was netted it was placed in a transport tank and moved to a holding pen in a safe location downstream. There is not a sure way of identifing the sex of the fish, but generally the females are larger than the males. Fish that were captured and not needed were released to continue their journey. The holding tank in the center picture holds a female that was about 54 inches long and if you look closely there is a smaller male also in the tank.
Eggs were "milked" from the females and mixed with milt collected from the males. Due the the size and strength of the fish it made quite a sight for spectators. The fish were then returned back to the river as quickly as possible.
The majority of the eggs collected went to the Wild Rose Fish Hatchery, located in the southeastern part of the state, who specializes in raising sturgeons. Some eggs were kept for the first time at the Gov. Tommy Thompson Fish Hatchery (TTFH) in Spooner . The picture on the left shows jars holding sturgeon eggs at TTFH. The middle picture is a closeup of the eggs and the photo on the right is about one week later. The newly hatched fry (young) already show some of the adults unique characteristics.
Most of the newly hatched fry at TTFH were release back into the Yellow River. The hatchery kept a few hundred that will be released when they are a few inches long. The photo on the right is a close up of the fry in the tank in the photo on the left. After only 2 weeks they are already 1-1/2 inch minuatures of the adults. They young are notorious as finicky eaters. Wild Rose staff are always working to develop an acceptable buffet. After hatchng they are fed a diet of live brine shrimp, and progress to zooplankton, chironomid larvae, and eventually fresh frozen krill (ocean plankton) shipped from Washington.
The photo on the right is a yearling raised at the Wild Rose hatchery. At about 8 inches long it will be released in the fall. Before it goes back to the river this strugeon and its siblings will be implanted with a PIT (passive integrated transponder) tag which is about the size of a grain of rice. The tag and injecter are shown on the right. A hand-held scanner, similar to those used in the grocery checkout, placed over a tagged fish displays identification information from the tag. On August 5, 2003 a truckload of young sturgeon returned home. Nearly 400 11-inch yearlings and 3,450 3-inch fingerlings made the trip from Wild Rose Hatchery to the St. Croix basin. The photo on the right is a few of the young of the year ready for release.
Both hatcheries had such a high hatch rate resulting in more fry than was needed for rearing, that the surplus made a trip to the upper Tennessee River of northern Georgia. Georgia as well as many other states have no viable native population left to work with. Wisconsin is a big player in efforts across the nation to restore sturgeon populations.
Photos courtesy of the WDNR