Archive of Spotlight Feature Articles

Fish, Biodiversity, and Fishing Gear Impacts

by Marcia R. Collie and Julie Z. Russo

Studying fishes of the deep waters of the Gulf of Maine, like ecologists study animals on land, is an exercise that requires more than binoculars and a notebook. Using occupied submersibles and remotely operated vehicles to go to work, scientists supported by the National Undersea Research Program venture beneath the cold and turbid waters of the Gulf to understand how fish interact with a myriad of other seafloor species and geological structures which can enhance their survival.

...fishing gears such as trawls and dredges impact seafloor habitats by reducing complexity and altering communities of animals that live on and in the seafloor.

The Gulf of Maine and Georges Bank have supported fishing for over 400 years. From the time that Basque fishermen ventured far beyond their European shores, the waters of this region have been known as some of the most productive in the world. To all who saw the bounty of this part of the ocean, there seemed to be an endless supply of fish. It was not until the last half of the 20th century that the limitations of the ocean became obvious. While there have been extensive efforts to study responses of overexploitation on fish populations, relatively little work has addressed the role that habitat plays in enhancing the survival of individual animals in outer continental shelf environments. Further, while we struggle to understand how habitat features affect fish populations and communities, fishing gears such as trawls and dredges impact seafloor habitats by reducing complexity and altering communities or animals that live on and in the seafloor.

Fish such as Atlantic cod, haddock, Acadian redfish, and spiny dogfish are at very low population levels. Species like redfish have not fully recovered from overexploitation in the 1960s. Their recovery may, in part, be impeded because their habitats have been destroyed by fishing gear. Just as some animals take refuge in the African prairie grass to shelter from lions, some marine fish take refuge in places like boulder reefs, anenome forests, worm tube mats, sponge-covered gravel, and complex mud burrows to hide from bigger fish.

Peter Auster, Science Director for the National Undersea Research Center at the University of Connecticut, has been studying the ecology of fishes, primarily those of the outer continental shelf and beyond, for over 15 years.

He and his colleagues have used submersibles and ROVs to collect data on the distribution, abundance, and behavior of fishes in relation to the underwater landscape. Underwater video is the primary way data are collected.

Using parallel laser systems to continuously calibrate the area viewed by the video camera and as a way to measure fishes, what was once a qualitative way of recording what scientists see is now a quantitative tool. "Submersibles and ROVs allow us to conduct the same types of studies on fishes that my colleagues who study terrestrial animals have been able to do by walking out into meadows, forests, and deserts," said Auster.

However, the field studies are only part of the picture. "The field work gives us information on the patterns of habitat use by the animals of interest," said Auster, "but the story does not end there." The researchers then take the results of the fieldwork to design laboratory studies and computer models which apply their research results at the geographic scales of fish populations and communities. "Laboratory experiments allow us to study how differences in habitat features affect rates of survival and escape behaviors", said James Lindholm, a Post-Doctoral Fellow in Auster's lab. For example, their studies of juvenile cod link survival of young fish to patterns in the types of invertebrates that grow on the seafloor.

Survival was greatest when "sponge" habitats were present, in contrast to bare cobble and sand. The data from both field and laboratory are then used to construct computer models that demonstrate how fish populations are affected by habitat change. The results of studies on cod showed that when adult populations are high, habitat changes had little effect on juvenile survival and overall population dynamics. However, when adult populations are low, habitat changes had a large effect on the survival of juveniles and overall population structure. The results suggest that managing seafloor habitats, as well as populations of fishes, may be the path towards sustainability. Further, the work suggests a direct link between biological diversity and the sustained production of species we want to exploit by fishing. "Everywhere we look", said Auster, "we see relationships of fishes with various types of habitats which are composed in part by other organisms such as sponges and anenomes." "We need to take lessons from those managing wildlife on land - we need to be worried about all of the parts of the environment that support the species we want to exploit as well as conserve."

[8/28/00]

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