Fish Ecology, Evolution and Behavior

Ted Rogers for TEI

The ocean is a living organism. It warms, it cools. Fish stocks can migrate and sometimes disappear. With impending climate change and over-fishing running riot, Francis Juanes, Professor in the Department of Natural Resources Conservation, has his work cut out for him as he studies fish species along the Atlantic coast.

Juanes’ research focuses on the ecology, evolution, and behavior of fishes and benthic crustaceans. Particular areas of interest include understanding the mechanisms leading to recruitment variability of marine fishes, the evolution of life history strategies, and behavioral ecology as it applies to prey size selection and spatial distribution of species.

“Dolphin fish rarely used to be found off Cape Cod,” he starts, speaking of the Floridian game fish, “but fishermen have been pulling more and more up over the past decade; something that could be connected with global warming.” Juanes has worked on many projects dealing with fish stocks, and to see the subtropical dorado move into Georges Bank foretells of major changes. One of these is the dramatic decline of Atlantic salmon all along its range, often attributed to changes in their freshwater habitats. Juanes and his colleagues have found however, that marine conditions strongly affect both the size and timing of adult salmon returning to freshwater to spawn. Over the last one hundred years, changes in ocean temperature also correlate with the decline in salmon abundance suggesting that future ocean warming could be fatal for the species.

Like the ocean itself, fish populations within it are all connected. As the dolphin fish population moves further north, stocks of the once common bluefish are nearing the breaking point. Bluefish are a species of predatory fish that can often reach the size of an outstretched arm. And as Juanes will tell you, they are disappearing, fast.

“All along the coast, people will sit on the beach and pull the juveniles out of the water as sport. Near the Cape, large party boats full of people will spend a day out on the water taking the bigger specimens.” One of Juanes’ research projects is to understand how the decline of stocks of bluefish and other predatory fishes will affect the predator/prey dynamics on Georges Bank, a massive area of shallow sea on the American side of the North Atlantic. To do this, he and his students have used longterm databases collected by the National Marine Fisheries Service. One of the findings this work revealed was the increasing importance of squid in fish diets. Along with a grad student, Michelle Staudinger, and a collaborator, Dr. Roger Hanlon, of the Marine Biological Laboratory in Woods Hole, Juanes used large tanks full of both benthic (bottom dwelling) and pelagic (open sea) predators and squid and prey fishesto observe their interactions. Theresults of these experiments will help scientists and resource managers as they move from singles-epecies to multispecies and ecosystem management. In addition, Juanes studies predator and prey dynamics with the assistance of sport fishermen. After a fishing tournament concludes, Juanes will ask participating anglers for their catches’ stomach contents. These catches include species such as bluefin tuna, dolphin fish and various sharks. Most recently he has concluded a study, led by grads student Tony Wood at URI, of mako shark stomach contents collected from fishing tournaments along the east coast. A puzzling result of this study is that mako shark consumption of bluefish has increased over the last 30 years. Bluefish now contribute about 93% of the mako diet; an average mako consumes about 500 kg of bluefish per year.

Juanes has also enlisted commercial fishermen in another research project using passive acoustics, the science of listening to fish. People often are unaware that many fish species can vocalize. New technology in the field of underwater hydrophones has given Juanes a new look at these deep communications. Along with colleague Dr. Rodney Rountree and grad student Katie Anderson, Juanes has worked with fishermen to deploy underwater hydrophones both in coastal and deep sea waters. Most vocalizing is performed by males and thought to be related to spawning. Haddock vocalizing peaks at similar times as females are ready to produce eggs. Cusk eels sing in chorus throughout the summer off Cape Cod, a location where they had not been collected using conventional methods because of their cryptic nature, but we can now hear them using hydrophones.

Professor Juanes also uses technology that he developed with former graduate student Nikolai Klibansky, to figure out the breeding prowess of Atlantic cod. Using a scanner and computer freeware , Juanes and Klibansky were able to determine how many eggs can be produced and their sizes given a cod’s body size. This new technology will be a tremendous boon to fecundity studies, as the scanning method is quick, inexpensive, and easy to use. The scanner method has come not a moment too soon, because, as Juanes will tell you, “my favorite statistic is that the last time a fecundity and body size relationship in cod was figured out was in 1880.” Part of the reason for this lack of information, is that cod spawn in the middle of winter when scientific research vessels are not at sea. It was their collaboration with commercial fishermen that allowed enough fish to be collected for the project.

In another research project, Juanes is studying the Hudson River for clues as to why and how fish communities change including the collapse of the native shad population and the invasion of the freshwater drum. The shad population has been so low for the past few years that the state of New York has instituted a mandatory catch and release policy for the fish. Juanes along with a graduate student, Megan O’Connor, is using historical records and climate indices to study the shad decline. Juanes and Rountree hope to use passive acoustics to track the invasion of the freshwater drum as it moves south in the River. In another research project in Florida, Juanes and grad student John Murt, are examining the winter recruitment and growth of juvenile bluefish, something that he hopes will explain the decline in that fishery. Juanes makes sure to include his research in his teaching. “Most of the research I conduct ends up as lessons in the classroom,” he states. This reflects his philosophy that real-life examples of good research and involving graduate students in his work makes him a better teacher.