The world's large rivers have proven to be important assets to human populations, allowing for the rise of civilizations—think of the Nile—as well as the emergence of modern industrial economies, such as the auto-dominated industries of the Detroit region. In the process, however, large rivers have often been degraded, profoundly altering fish communities. Siltation and removal of fish spawning habitats, altered hydrological conditions disconnecting floodplains from river channels, and water pollution have been common forms of river and stream degradation. Fortunately, efforts to abate these disturbances and restore functional fish habitat are underway.
The St. Clair-Detroit River system
Since 1970, water quality has improved in river systems of the United States due to legislation that reduced “point-source pollution,” that is to say, pollution emerging from an easily identifiable point, such as the end of an industrial pipe. As a result, this improved water quality provided opportunities to restore spawning habitat in many large rivers, including the St. Clair-Detroit River system (SCDRS).
The SCDRS is an economically and ecologically important system connecting lakes Huron and Erie and is composed of the St. Clair River, Lake St. Clair, and the Detroit River. Both rivers have been degraded ecologically through pollution, overharvest of fish, and loss of fish and wildlife habitat. The 1978 Great Lakes Water Quality Agreement between Canada and the U.S. designated the region as an Area of Concern (AOC). In particular, construction of shipping channels removed spawning areas and coarse rocky substrates required by many commercially and recreationally important fish species, including lake sturgeon, walleye, and lake whitefish. These species are called “lithophilic broadcast spawners” because they spawn on rocky substrates (lithophilic) by broadcasting their eggs among the rock rubble. These fishes and other native species that reproduced in and migrate through the SCDRS provided valuable sport and commercial fishing opportunities in the rivers as well as in the adjoining Great Lakes.
The USGS Great Lakes Science Center (GLSC) has worked with a number of different partners to restore spawning habitat in the SCDRS. The team has constructed seven artificial spawning reefs in the system since 2004, and an eighth and final reef should be completed in 2017.
Lake sturgeon and other lithophilic broadcast spawning fishes have been documented to use the artificial reefs for spawning. During construction of one of the artificial reefs, lake sturgeon were seen spawning on the reef even during construction! Viable eggs have been collected on and adjacent to nearly all the constructed reefs, and larval fish originating from the reefs have been collected in both rivers.
The USGS research team has garnered international recognition for developing innovative techniques for sampling fish eggs and larval fish and for implementing an adaptive management approach to developing each additional reef. In December 2016, scientists from GLSC and the USGS Geomorphology and Sediment Transport Laboratory in Golden, Colorado, were invited to participate in a fish habitat restoration workshop in Helsinki, Finland. The USGS staff discussed their approach to developing the habitat restoration programs in the SCDRS and their methods for assessing the effectiveness of the projects. The Natural Resources Institute Finland and their collaborators in the Baltic region are adapting the same adaptive management approach for their fish habitat and population restoration program.
Lake sturgeon in the Lake Ontario and St. Lawrence River tributaries
Lake sturgeon are native to New York State and the only sturgeon species endemic to the Laurentian Great Lakes. Presently, lake sturgeon are found in 20 U.S. states and seven Canadian provinces at only a fraction of their historic abundance. Prior to the mid-1800s, lake sturgeon were commonly found in New York waters of Lake Ontario, Lake Erie and the St. Lawrence River and its tributaries. The vast number of lake sturgeon supported a commercial fishery that utilized their eggs for caviar and flesh for a variety of purposes including consumption and leather. Lake sturgeon populations were vulnerable to overharvesting due to their long maturation process, irregular spawning cycles, and extremely long life span. By the 1960’s, lake sturgeon populations in New York were greatly reduced and the fishery was closed in 1976. Other factors contributed to their decline as well, including reduced water quality, degraded habitat, and dams on tributaries that restricted access to critical habitat.
Scientists at GLSC study lake sturgeon restoration in Lake Ontario and the St. Lawrence River tributaries. The goal of this research is to support the efforts of the New York cooperative lake sturgeon restoration program. The primary activities of the restoration program include stocking and habitat improvement in targeted rivers.
The team has marked important milestones in recent years through stocking activities. Over 90% of young sturgeon are surviving past two years, stocked males are reaching maturity by 11 years, and some of the earliest stocked females are now reaching maturity at 17 years. Scientists from the USGS have been monitoring and evaluating use of spawning habitats, both natural and constructed. Large, ripe females are present at the spawning reefs with anywhere between 124,000 and 561,000 eggs per female. In fact, evidence for natural recruitment was possibly found in the Oswegatchie River in 2013. A 25-inch, five-year-old sturgeon was captured—the first small wild sturgeon caught in the river for over 30 years. Assessment of other New York rivers will continue into the future.
The USGS and New York partners are using the monitoring results from restoration activities in an adaptive management process to improve restoration methods for this key native Great Lakes species.