Critter of the Month: Lake sturgeon
Known as the living dinosaur of the fish world, the Lake Sturgeon, or Rock Sturgeon, is the oldest and largest fish in the Great Lakes region, so large, in fact, that the Ojibwe used to call it “nahmay” or ”namé” meaning “king of fish.”
What does this fish look like
Lake sturgeon are large fish which can grow to 6 ½ feet in length and up to 200 pounds. They are gray or brown with many varying shades in between. They have flat spade-like heads, four feelers under their snout, and a bottom facing sucker-like mouth. Lake sturgeon has fleshy lips but no teeth. The top of the tail is longer than the bottom, giving them a shark-like appearance.
The most distinguishing features, however, are the bony plates covering the head and shield-like plates covering the body. It is these features that give the lake sturgeon its characteristic prehistoric look.
Lake sturgeon are known to perform a peculiar act called porposing, meaning jumping out of the water. The lake sturgeon can completely leave the water by jumping into the air. Scientists think this may be a way to help prevent lamprey from adhering to the lake sturgeon as most of these fish are found to have several lamprey attached to them at any given time.
Where do lake sturgeon live
Contrary to their name, these fish live not only in lakes but also in rivers. Their distribution is solely in North America from Hudson Bay to the Mississippi River; however, they are no longer that widespread and are now mostly found in the drainage basins of the Mississippi River, Lake Superior and Lake Michigan.
What do they eat
Lake sturgeon feed on large invertebrates and small fish as well as freshwater mussels, clams and other crustaceans. Their food selection is due to the fact they that do not have teeth. They are bottom feeders, using the feelers on the bottom side of the snout to help locate food. When food is present, they suck in water, sand and muck from the bottom of the lake or river. They then expel the inedible things like the sand out through their gills and ingest the food. Though not overly fussy about what they eat, they will not eat dead or decaying organisms.
What is the life cycle of the lake sturgeon
In late April through early June, when the water flow is high and the water temperatures have reached 52 to 58 degrees, lake sturgeon will spawn. Like salmon, lake sturgeon return to the place of their birth for spawning, migrating as far as 300 miles. In groups of one female and two males, the female will lay thousands of eggs over the course of one or two days. The males then fertilize the eggs.
The eggs are sticky and cling to the rocks or gravel at the bottom of the river or stream. The eggs hatch in five to eight days and larvae with an attached yolk sac emerge. The larvae fall into the cracks and crevices between the rocks and feed off their yolk sac for 10 more days, at which point they are large enough to swim upstream. The fish grow fast at this point, becoming 5-7 inches long by five months of age.
At five years of age, the lake sturgeon are about 20 inches long and will move into large rivers and lakes. Their growing slows at this point. By the time they reach reproductive maturity (15 years of age for males and 25 years of age for females), males are around 45 inches long, while females are around 55 inches long. Once reaching reproductive maturity, males will spawn every one to two years, while females will only spawn every four to eight years. Lake sturgeon can live to be quite old. Males can live anywhere from 65 to 90 years, while females can live to 150 years or more.
There are few predators for these large fish. While in egg or larvae stage, they can be eaten by other fish or birds, once they reach a larger size, however, their main predators are humans.
What threats do lake sturgeon face
In the 1800s, commercial fishermen found the lake sturgeon to be a nuisance fish. They would tear their nets and damage equipment, mostly due to their size, so fishermen were known to simply toss the lake sturgeon on the bank to die. Once their roe, or eggs, were discovered as a popular caviar, lake sturgeon were fished heavily until numbers were extremely depleted by the early 1900s.
In the early part of the twentieth century, lake sturgeon numbered about 15 million; today there is less than 1% of that historic number. There is currently no federally designated status regarding this fish, but in 19 of the 20 states in which they are found, they are listed as endangered, threatened or of special concern.
In Wisconsin, lake sturgeon are listed as a special concern. They can still be fished, but the season and limits are very strict, and fishermen are asked to consider catch-and-release for these fish. Poaching is a big problem, but the selling of lake sturgeon flesh or roe is illegal in Wisconsin.
While previous overfishing and now poaching is one of the reasons for the decline of the lake sturgeon, the creation of many dams along rivers is another. Not being able to return to the spawning grounds of their birth keep the fish from reproducing. Add to that, the length of time until the fish are old enough to reproduce and the time between spawnings, and it is easy to see why their numbers have depleted.Work, however, is currently being done to get the lake sturgeon on the federally protected species list.