The discovery of shortnosed sturgeon in the Penobscot River for the first time in nearly three decades may be a good indicator that environmental conditions on the river have vastly improved. That would be good news for sturgeon and other fish, including Atlantic salmon.

University of Maine researchers last week announced that they had caught two dozen shortnosed sturgeon, which have been listed as an endangered species since 1967, in a cove in Winterport. There are documented populations of shortnosed sturgeon in the Kennebec and St. John rivers, but the UMaine find is the first confirmed sighting of the fish in the Penobscot since 1978. Finding so many fish rules out the possibility that the sturgeon strayed from other rivers.

Unlike its relative the larger and better-known Atlantic sturgeon, which splits its time between river and ocean water, the shortnosed sturgeon spends the majority of its life in its home river. They can live for more than 30 years and weigh in excess of 25 pounds. The reclusive fish are little changed from the era of dinosaurs. They are covered with bony plates and have a mouth on the underside of their head to allow feeding along river bottoms.

The Penobscot sturgeon were tagged and the information gathered will be very helpful in learning about the fish’s life cycle and habitat. Data gathered next spring, during spawning season, will be especially helpful.

Sturgeon eggs are prized for caviar, leading to overharvesting of the fish. Dams and pollution are also suspected in their demise. While scientists say it is too early to know why the sturgeon appear to have returned (or even if their presence is new or just the result of better surveillance), the dramatic reduction in pollution from paper mills along the river during the shortnosed sturgeon’s lifetime likely is a large factor. This could be good news for Atlantic salmon, also an endangered species in seven Maine rivers and a tributary of the Penobscot but not the river itself.

The Atlantic Salmon Federation recently called for more study of why salmon aren’t returning to rivers in the eastern United States and Canada in large numbers. U.S. and Canadian fisheries experts are studying the problem, but ASF, which pointed to pollution and global warming as the leading likely causes for the salmon decline, is right that progress is slow.

The recent sturgeon discovery adds another piece to the fisheries puzzle, but it is still unclear what the final picture will look like.