Illinois Natural History Survey - University of Illinois

drum_lkMi.jpg Artificial reefs are often added to aquatic environments to attract desirable fish species, increase angler effort and success, or provide spawning habitat for fish species. Use of artificial reefs in larger freshwater bodies, such as the Great Lakes, was limited until the 1980s, and research on the ecology and success of freshwater artificial reefs is sparse. We evaluated an artificial reef constructed in southwestern Lake Michigan near Chicago, Illinois to determine if it was effective at attracting smallmouth bass and other fish and providing additional angling opportunities.

In November 1999, the artificial reef was constructed 2.8 km offshore in 7.5 m of water, using approximately 4,500 tons of granite rock of various sizes (0.25 m to >1.5 m diameter). The completed reef was 256 m long, with a mean height of 2.1 m and mean width of 15.5 m; total bottom area covered by the artificial reef was 5,440 m2 (S. Anderson, Applied Marine Acoustics Inc.). A reference site, approximately 3.3 km south of the reef site, with comparable biological characteristics, depth, and distance from shore also was sampled for comparisons between sites before (1999) and after (2000-present) reef construction. We sample using SCUBA transect surveys and gill nets to determine what fish are present at both the artificial reef and reference sites during May through October.

Total number of fish observed during SCUBA dive transects was higher at the artificial reef than at the reference site during 2000-2006. Smallmouth bass, rock bass, round goby, and yellow perch were most commonly observed by divers at the artificial reef site. Freshwater drum, alewife, common carp, and juvenile largemouth bass have also been observed at the reef. Numbers of fish species observed at the reference site were lower than at the reef. Round goby was the most prevalent species, while smallmouth bass were seen on only two dives at the reference site. When looking at SCUBA data, the artificial reef did attract both smallmouth bass and rock bass compared to the reference site. These two species strongly prefer structure, and numerous studies recognize that centrarchids in general are very attracted to artificial habitat (Prince et al. 1985; Bohnsack et al. 1991; Kelch et al. 1999). Smallmouth bass association with the reef was seasonal and correlated with temperature. The first sighting of adult smallmouth bass has consistently been on the first sampling date when surface water temperatures exceed 22ºC. Smallmouth bass remain at the reef until early October when temperatures decline to 14 - 17ºC.

The artificial reef in southern Lake Michigan was constructed to attract smallmouth bass and increase angling opportunities. However, angler use of the Lake Michigan reef has been minimal. Although anglers were aware of the artificial reef, fishing effort and success were low, in part because few anglers targeted bass. The majority of Illinois’ Lake Michigan anglers target salmonines and yellow perch, which were not attracted to the reef in large numbers or for long periods of time.

We will continue to monitor both sites on a less frequent basis to see if there are any deviations from the pattern observed thus far. It is also important to monitor the maturation of the artificial reef in relation to the entire aquatic community to improve our understanding of artificial reef dynamics in large freshwater systems.

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