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The addition of fish habitat to aquatic systems has been an integral part of fisheries management – both in fresh and saltwater – for years. Habitat structures have been deployed to increase angler catch rates, make up for the lack of quality fish habitat, create nursery areas for young fish and create holding/feeding areas for adult fish. Work of this nature also is important in fostering stewardship among resource constituents. The need for additional habitat is especially strong in large southeastern reservoirs created primarily for flood control and power generation. Frequently these systems were "scraped clean" and, over time, lost what little cover remained. Fishing clubs, fisheries managers, concerned anglers and others have attempted to remedy this situation with the addition of artificial habitat structures. These structures have run the gamut of materials (from tires to trees) and sizes. VDGIF biologists evaluated some of these more recent efforts with SCUBA gear at Lake Anna.

Three types of habitat structures in 9600-acre Lake Anna, Virginia were evaluated in 2000-2002. Dives were made from May-September downstream of Route 208 (due to visibility constraints), and each dive lasted about 20 minutes. Two divers descended to the structures and slowly worked around each recording observations (species and size categories) on slates. Structures were located in water depths of 12-22’, and (at the time of writing) all were marked with indicator buoys. Structure types included synthetic Berkley "fish habs"® and "dumbos" (an arrangement of 6-inch diameter corrugated drainpipe) and a conglomerate of cedar trees, block and dumbos (dubbed "combos"). The long-standing controversy regarding synthetic vs. natural structures was about to heat up! (Natural materials have been demonstrated to have superior fish holding ability initially, but their utility is lost after a few years).

Over three years, 26 dives were made on eight structures (four fish hab, two dumbo and two combo). Fish habs were aligned with the slats either on a horizontal or vertical plane and zip tied together in bunches of 7-20 units. Data analysis indicated some significant differences: fish hab and combo structures held more quality largemouth bass, but black crappie and bluegill were more abundant on combo structures. Whether this was due to the presence of natural materials or the nature of the mixture (heterogeneity) is unknown. Bass, crappie, redear, white catfish and channel catfish selected horizontal slat alignment on fish habs exclusively, while bluegill selected horizontal and vertical alignments equally. Thus, the horizontal arrangement is recommended.

The abundance of some species around the structures was affected by water temperature and depth. Crappie and quality-size bass became more abundant around the structures as water temperature dropped, and vice versa. Bluegill and small bass were more common around structures in shallower water, whereas channel catfish seemed to prefer deeper structures.

This study suggests that fish habs are a viable alternative to natural materials, but a larger sample size of all structure types and more rigorous statistical analysis are needed.

Copyright 2003 John Odenkirk All Rights Reserved
jodenkirk@dgif.state.va.us

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