The USGS Great Lakes Science Center (GLSC) is known for some of the longest-standing data sets surveying Great Lakes fishes. Some lake areas have been sampled continuously since the 1950s. These rich data archives are a critical resource for fishery management decisions and they clearly illustrate human impacts on Great Lakes fish communities. At the GLSC we understand it is paramount to maintain and expand these legacy datasets.
Responding to changing conditions and questions: the evolution of the Lake Ontario sculpin survey
The scientists at the GLSC’s Lake Ontario Biological Station (LOBS) in Oswego, New York, maintain various long term data sets including one on benthic prey fish (bottom-dwelling bait fish). The survey, which began in 1978, was designed to answer relevant management questions at that time. Lake Ontario managers needed to know the abundance of slimy sculpin. Sculpin were a critical food for stocked lake trout, the lake’s native top predator and the focus of an intense international restoration effort. The then titled “Sculpin Survey,” assessed the species at six transects along the southern Lake Ontario shore. As this historic dataset grew each year, it increased in value.
However, since the survey began, Lake Ontario has undergone remarkable changes which have brought about new questions the survey could not answer. The Clean Water Act drastically reduced nutrient inputs, which limited algal blooms, but also decreased the nutrients supporting the lake’s food web. Water temperatures have steadily climbed. Invasive zebra and quagga mussels, introduced in the 1980s, quickly dominated benthic habitats and their massive filter-feeding capacity increased water clarity. Finally, the round goby invasion in the 1990s coincided with sharp declines of native benthic prey fish populations, including the slimy sculpin.
Today, Lake Ontario managers are asking different questions than they were in the 1970s. Round goby have become an integral component of the food web. Zebra and quagga mussels are consumed by goby, which are then eaten by popular native sport fish like smallmouth bass and lake trout. The historic survey’s limited lake coverage could not provide answers about lake-wide distribution of round goby. Deepwater sculpin, a native benthic species that were thought to have been extirpated, have been miraculously increasing, but the survey did not sample their preferred deep habitats.
As Federal scientists, LOBS biologists must not only attend to these current concerns, but also anticipate the questions managers will be asking decades into the future. Will land use changes influence where nutrients enter the lake? How will changing water use affect lake levels and nearshore habitat? To answer current and future species and ecosystem-scale questions, LOBS scientists realized their limited-scale, single-species approach to assessing benthic fishes could be improved.
With the help of their colleagues, they gave the Lake Ontario benthic survey a new look. The survey was carefully redesigned to maintain consistency with the historic dataset while expanding sampling to answer new and broader-scale questions. The new survey fundamentally depends on collaboration with partners, such as the Ontario Ministry of Natural Resources and Forestry (OMNRF), the New York State Department of Environmental Conservation (NYSDEC), and the U.S. Fish and Wildlife Service. By including state and provincial research vessels, the survey efficiently samples all lake areas, including the northern shore, eastern basin, and deep habitats out to 225m (743 feet).
This partnership has created a collaborative culture with active data sharing among groups and holistic, lake-scale understanding of Lake Ontario fish populations. For instance, new trawls in deep habitats have revealed that the deepwater sculpin population has recovered. This information is currently being used by state and provincial agencies as they consider whether to reduce the species’ elevated conservation status.
Improving other Lake Ontario prey fish surveys
The benthic fish survey is not the only Lake Ontario data set being improved. Decades of well-managed bottom trawl data allowed researchers to illustrate how separate spring trawl surveys for alewife and rainbow smelt were providing duplicate information. Combining the surveys freed resources to collaboratively expand the previously U.S.-based survey into Canadian waters in 2016. The expanded, more efficient survey yielded immediate results for decision making. With increased confidence in alewife and smelt abundance data, fisheries managers decided to reduce predator stocking levels and protect the lake’s predator-prey balance.
Scientists from across the basin, both within and outside USGS, advised the LOBS team as they designed a new hydroacoustic/midwater-trawl survey, which is aimed at estimating the abundance of native prey fish like cisco and bloater. (For a description of GLSC hydroacoustic technology, see, “Sounding the depths of the Great Lakes food webs: GLSC hydroacoustics”). These species historically dominated the Lake Ontario fish community but their populations declined drastically in the early 1900s due to overfishing and interactions with nonnative species. From July 25 to August 5, 2016, the LOBS team joined the Lake Ontario Acoustic Survey, led by OMNRF and NYSDEC. The LOBS team captured over 360 cisco in their new midwater trawls. Interestingly, a few weeks prior, a traditional LOBS bottom trawl survey conducted in the same lake areas failed to collect any cisco. Because of the growing bi-national effort to restore these native species in Lake Ontario and across the Great Lakes basin, it is critical to identify efficient methods to sample cisco and other coregonids.
Improvement. Innovation. Insight. These are what drive USGS scientists studying the Lake Ontario fishery. By increasing efficiency, responding to emerging needs, and developing new, data-driven approaches, the USGS is not only delivering the best possible information on Lake Ontario, but also preparing for the challenges that lie ahead.