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Video: LSU scientists utilize active acoustics technology to capture a dolphin feeding on a school of fish. [WMV]

LSU Uses Sophisticated Acoustic Technology to Study Fishy Behavior

Cowan Lab uses DIDSON “acoustic cameras” to learn more about fish in their natural habitats

The Cowan Fisheries Science Labs, housed in LSU’s Department of Oceanography and Coastal Sciences, has made quite a name for itself – and for the university – by being among the first to employ unique acoustic methods to monitor fish in their natural environment.

“This equipment was developed prior to use for our purposes,” said Jim Cowan, professor of oceanography and leader of the Cowan Lab. “It was developed for military surveillance of harbors and ports. Also, the state of Alaska routinely uses it to count salmon, but we are among the first to use it for habitat and behavioral research.”

The utilization of sophisticated acoustic technology, which uses pulses of sound to form real-time, near-video quality images of objects underwater, is necessary for the advancement of fisheries science because researchers in the field start off with a heavy disadvantage – they can’t see what they’re studying.

“One of the biggest challenges in fisheries science is actually counting fish and observing behavior,” said Cowan. “Indirect estimation of stock size is a problem because we really have no accurate way to see what we’re doing. These techniques are direct and have begun to illustrate how well we are doing using indirect approaches.”

Cowan, along with post-doctoral researchers and doctoral candidates working in his lab, utilizes acoustic technology to find more specifics than researchers have ever been able to learn about fish, whales and other marine animals and their behavior in natural environments.

“How does a whale spend a typical day?” asked Kevin Boswell, post-doctoral researcher in LSU’s Department of Oceanography. “It may sound like a silly question, but until we understand what kind of pressures these animals exert on their forage base, i.e., basic predator-prey dynamics, we remain at a disadvantage in our understanding of fundamental marine life processes.”

Boswell studies fish use of estuarine and coastal habitats, integrating the development of acoustic technology. He has been working with Sound Metrics Corp.’s DIDSON, or Dual-Frequency Identification Sonar, technology to perfect the software he uses to track the effects of predation on a highly contentious herring species off the coast of Alaska.

“Using these ‘active acoustics’ provides us the opportunity to directly observe fish distribution and behavior – specifically relating to predation, and habitat use,” said Boswell. “This gives us vision where we would otherwise be blind.”

Using active acoustics gives Boswell the opportunity to actually see the activity going on beneath the water’s surface and to study predatory behavior and the response of intended prey [see accompanying visualization].

He is currently preparing for a research trip to Iceland, where he will utilize this technology to identify and track spawning aggregations of Icelandic cod. Jody Callihan, a doctoral candidate in Cowan’s Lab, studies something a little closer to home – and to the hearts of sport fishermen everywhere – spotted trout, or “specks,” in Calcasieu Lake, located in Southwestern Louisiana.

“I’m exploring how and to what extent fish use different habitat types, how they migrate seasonally and how they interact with their environment in general,” said Callihan. “The estuary is famous for large, 'trophy-sized' trout that are extremely popular with recreational fishermen.”

Callihan, with generous support from the Louisiana Department of Wildlife and Fisheries, or LDWF, has been able to tag 172 fish with acoustic transmitters, or “pingers,” over the past two years. He and Cowan have placed approximately 60 receivers throughout the estuary to listen for tagged fish. When a tagged fish pings while within a few hundred yards of a receiver, the instrument will record the date and time of the ping and also mark the identity of the individual fish. Some tags with special sensors go a step farther and record the water temperature and depth at which the fish was swimming.

“We can’t begin to express our gratitude to the folks at Wildlife and Fisheries,” said Cowan. “There’s no way we could be as thorough in our research as we have been without their support, both financially and through the assistance of their staff and volunteers.”

“We also are greatly appreciative of the volunteer efforts of local anglers from the Lake Charles Coastal Conservation Association, or CCA, chapter, who caught all the fish used in the study,” said Callihan. “I believe this study is a fine example of how collaborative efforts among the user group of the resource, or fishermen, governmental agencies in charge of managing the fishery, like LDWF, and academia, such as LSU-based researchers like our team, can glean important scientific information that can ultimately be used to promote the sustainable use of an important fishery resource.”

The acoustic telemetry data they are gathering has begun to answer some of the mysteries surrounding these spotted seatrout. Prior to employing this technology, it was extremely difficult to gather data on individual fish behavior, movements and habitat use throughout time and space. The integration of a newly available software package, Eonfusion, delivers the ability to project the acoustic and environmental data at unprecedented resolutions to include multiple dimensions.

“Using this technique and integrating the telemetry data with habitat and environmental information in Eonfusion, we’ve been able to determine some very interesting trends in tagged fish,” said Callihan. “For instance, we now know that not all fish stay in the estuary; some leave for the Gulf. Also, there appears to be a difference in salinity preferences for male and female trout, which could affect their accessibility and vulnerability to the fishery.”

This advancement in technology provides Cowan, Boswell and Callihan – and other researchers with whom they collaborate – the opportunity to study aspects of marine life that have only been guessed at previously.

“Until we more fully understand how fish interact with their natural habitat, we can’t really manage or predict the impact of big issues like global climate change or restoration efforts on fisheries resources,” said Cowan.

Eventually, the DIDSON data will be used for behavioral modeling, and is expected to corroborate data captured from the acoustic telemetry projects. “The acoustic work we’re doing will take us a long way toward solving the gap between practice and theory,” said Cowan. And it’s a win-win situation for the company, since Boswell continues to work with them, pushing the envelope of possibilities for its use and incorporating the data at various temporal and spatial scales.

“We can now see how fish interact with each other and their habitat from a biological standpoint,” said Boswell. “By integrating the high-resolution acoustic data, habitat maps and environmental information into this multi-dimensional framework, we now have a way to easily visualize and interrogate seemingly disparate data.”

“We are very fortunate to stay well ahead of the curve in applying technology to fisheries science,” said Jim Cowan. “I believe we’re at the technological forefront of our field right now, due to some forward thinking and the extensive support of Louisiana’s Department of Wildlife and Fisheries.”

Ashley Berthelot | Writer | Office of Communications & University Relations
April 2009