Can a fish serve as an environmental bellwether?
Rainbow smelt are important bait fish and vital to the health of New Hampshire's coastal ecosystem. (Photo: Tim Briggs)
Rainbow smelt, an important part of the coastal ecosystem but seldom studied, are now the focus of UNH research for a crucial reason: they may represent a bellwether for a coast challenged by warming waters and other stressors. If the conditions become more detrimental to smelt populations, a key food source for many other species, the ripple effects could be substantial for the marine ecosystem of coastal New Hampshire and beyond.
The research, led by Nathan Furey, associate professor of biological sciences, seeks to establish a current baseline for rainbow smelt movement and spawning behavior. The findings will allow researchers to track any future differences, which is increasingly important as conditions in New Hampshire’s coastal waters change.
“The rainbow smelt population has fallen since the 1970s,” says Furey. “Still, relatively little is known about their biology, knowledge that will be vital for conservation efforts in the face of increasing environmental pressures.”
A New Hampshire issue
Rainbow smelt were caught using a netting system in streams. (Photo: Brian Yurasits)
Rainbow smelt — like salmon — spend much of their lives in the ocean but migrate into fresh water to spawn. Adult smelt tend to spawn just past the transition zone from salt to freshwater and, soon after hatching, young smelt drift downstream to the estuary to grow before heading out to sea. They spend the warmer months in the ocean and return to estuaries and rivers in the late fall.
Furey is investigating whether adult smelt, like salmon, always return to the stream where they hatched to spawn. He is also measuring how long they stay in New Hampshire’s Great Bay Estuary. Longer stays would underscore the importance of the estuarine environment for them. Resolving these unknowns is crucial for determining rainbow smelt conservation efforts.
“There are already some concerning signs,” says Furey. “We’ve seen as many as 10 males for every female — producing eggs requires a lot of energy so it’s not uncommon to see more males, but that much skew is concerning.”
Transmit and receive
To track rainbow smelt movements, the team has had to employ some high-tech tools. Until recently, tracking fish depended on externally tagging them and noting where — and if — they were ever re-caught. Now Furey and his team are able to implant electronic transmitters in the smelt whose signal can be picked up by receivers placed in strategic locations, using two transmitter technologies.
"The better we understand rainbow smelt biology and ecology, the better we can manage coastal waterways to help maintain their populations."
Acoustic telemetry tags produce a unique sound that is inaudible to humans but, when picked up by a receiver, provides a location for the fish. They can transmit over long distances, but implanting them is labor intensive, and they require battery power to function. The team is also experimenting with passive integrative technology, better known as microchips like the ones pet owners use. They are smaller, cheaper, and easier to implant than acoustic tags, but their transmitting range is quite limited. So far none of the more than 1,000 microchipped smelt have been recaptured by hand beyond a few recaptured in the days following tagging, but the team recently tried placing a new receiver array directly across the Winnicut River and detected 25 fish tagged the prior year in one night.
“That was very exciting,” says Furey. “It provides the opportunity for more discovery, at least within the river systems.”
Small fish, large effort
Furey and his team work closely with the New Hampshire Fish and Game Department and its efforts to monitor rainbow smelt spawning grounds. NH Fish and Game capture fish to identify their sex, measure their size and determine their age from scale samples. Some of them are then passed on to the researchers to receive an implanted acoustic telemetry tag or microchip. The team is also aided by volunteers through New Hampshire Sea Grant’s Coastal Research Volunteer program.
The nearly 100 acoustic tags, including 50 implanted this year, have already yielded important data on how long the smelt stay in the estuary and river systems, where they go while there, and when they head back out to sea. And each year adds knowledge and technology that helps the research team gather more and better data in subsequent seasons. The ultimate goal is to generate a comprehensive picture of where rainbow smelt go when, and what affects their movement patterns.
“The better we understand rainbow smelt biology and ecology, the better we can manage coastal waterways to help maintain their populations,” says Furey.