SHORTNOSE STURGEON


Acipenser brevirostrum LeSueur 1818

For inquiries, contact Alan Richmond, Biology Department, Box 5810, Morrill Science Center, University of Massachusetts, Amherst, MA 01003-5810

There are two species of sturgeon found in the Connecticut River, the Shortnose sturgeon (Acipenser brevirostrum) and the Atlantic sturgeon (Acipenser oxyrhyncus). The Atlantic sturgeon is primarily a marine and estuarine animal. The Shortnose sturgeon is the only sturgeon found in the river north of Hartford.

Adult Shortnose Sturgeon

The Shortnose sturgeon is the only federally endangered freshwater fish in New England. Harming or harassing a Shortnose sturgeon is punishable by a $20,000 fine so don't hassle them, just look. Shortnose sturgeon are one of the largest species of fish found in the river: large adults may approach 4 feet in length. They are easily identified by their shark-like (heterocercal) tail, long nose with four sensory barbels on the ventral surface and ventral, protrusible mouth. Sturgeons lack scales but have five rows of bony plate-like scutes extending along the body. As adults, they are toothless; they suck in prey items (usually invertebrates such as worms and freshwater mussels) and grind them up in a gizzard-like organ in their digestive system.

The Shortnose sturgeon is found from the St. John River in New Brunswick, Canada, to the St. Johns River in Florida. Most populations are considered anadromous. In an anadromous species, adults typically live in the ocean, but leave the ocean and migrate upstream into fresh water where they spawn. Then the adults either die or migrate back to the sea. Upon hatching, young anadromous fish drift down stream, eventually reaching the ocean where they remain until adulthood. Connecticut River Shortnose sturgeons are more correctly termed amphidromous. Amphidromous fishes utilize discrete habitats within a freshwater system for feeding and spawning. That is, they may feed in a lake, then migrate to feeder streams to spawn or they may feed in one area of a river and then migrate to a different section of the river to spawn.

Historically a single population of Shortnose sturgeon existed in the Connecticut River. Adults most likely spawned in the late spring near the confluence of the Deerfield River then moved downstream to foraging areas, usually mussel beds or sand bars near islands. Occasionally adults would migrate to the estuary at Long Island Sound. Here they would forage until some environmental cue triggered their spawning behavior. Those fish in spawning condition would undertake the fall migration upstream from the estuary back to their natal spawning grounds near the Deerfield. These adults would remain in the upper reach of the river through the winter and spawn the following spring.

The construction of a permanent dam in Holyoke in 1848 effectively divided the Connecticut River population. Each year a few adults and juveniles from the Holyoke pool population (the reach of river that extends from the Holyoke dam to the Turners Fall dam) still follow this ancient genetically predisposed behavior as they try to migrate downstream from the Holyoke pool into the lower river. To accomplish this they must either spill over the Holyoke dam during periods of high flow or they follow the current of the river through the power turbines at the electric generating plant on the west side of the river. Also each year a few adults, driven by the genetic predisposition to return to their natal spawning area, migrate from the lower river and are lifted at the Holyoke fish lift and re-introduced into the Holyoke pool population. This keeps a flow of genes between the two populations and prevents the formation of a genetic "bottle-neck" in the upstream population.

Until very recently, it was believed that the fish above the dam and those below the dam formed essentially discrete populations. It was believed that the downstream population was comprised of about 1,000 adults. Evidence indicated that adults in spawning condition would attempt to migrate upstream to the historic spawning site near the confluence of the Deerfield. Unable to pass the dam at Holyoke, it was believed that these fish would aggregate and, out of desperation, spawn near the Holyoke dam.

It was believed the upstream population, consisting of about 450 adults, behaved much as the historic population did except that their downstream migration stopped at the Holyoke dam. Prespawning adults from the "Holyoke pool" population would migrate upstream in the fall, overwinter in the upper reach, then spawn in the historic spawning site near the confluence of the Deerfield the following spring.

Recent evidence indicates that this is untrue. No successful reproduction occurs int the population below the Holyoke dam. This downstream population is sustained by the influx of outmigrating sturgeon from the upstream group. Much successful reproduction occurs within the upstream population when they migrate downstream and are unable to return back up over the dam.

Juvenile Shortnose Sturgeon

Adults spawn in late spring. The eggs hatch in 1-2 weeks. The hatchlings swim under any available object on the bottom and remain there for approximately two weeks. During this period they resemble little tadpoles. These larval sturgeon do not feed but continue to live off nutrients provided by their yolk. After about two weeks the larval yolk supply is exhausted and the now juvenile sturgeon begin to forage. At this time the juveniles are only about an inch long and resemble tiny adults. They forage at night and are carried downstream by the current until they reach an area with low enough flow that they can feed in less turbulent water. The juveniles gradually continue their migration downstream until eventually they reach the foraging area of the adults.

See Seeking Shortnose Sturgeon Sightings for more information on this fish.