Lake Superior Benthic Fish Community Structure By Michael H. Hoff U.S. Geological Survey

1. Lake Superior Benthic Fish Community Structure By Michael H. Hoff U.S. Geological Survey Great Lakes Science Center

2. Lake Superior Fish Community Objectives and Joint Strategic Plan for Management of Great Lakes Fisheries “The Parties must…meet the biological, chemical, and physical needs of desired fish communities.” Lake Whitefish

3. Background • Great Lakes fishery managers agreed to change from fish species to community management approaches • in 1987. • The Lake Superior Committee developed the • Fish Community Objectives to manage • Lake Superior fish communities Lake herring

4. Background • A community is an ecological unit that is structured • with unique, quantifiable attributes. • Statistical analysis has been used • in community ecology to; • Discover community data structure • Graph community data • Test for differences in communities Rainbow smelt

5. Background • Dynamics of fish communities can be used to • evaluate effects of management changes and • ecosystem perturbations (e.g. invasions) Deepwater sculpin Slimy sculpin Spoonhead sculpin

6. Background • Using statistical analyses, only two fish communities • have been described from Lake Superior- • both reside in Chequamegon Bay. • Fish communities have not been described from • Lake Superior’s main basin. Burbot

7. Report Objective To quantitatively describe the summer, benthic fish community structure and habitat associations in Lake Superior by examining the on-contour, bottom-trawl data set. On-contour trawl tows Cross-contour trawls Lake Superior

8. Fishing with a bottom trawl. Ship Trawl

9. Mouth of bottom trawl – side view.

10. Methods • Sampling • 22 locations sampled during • mid-June to mid-September • 937 bottom-trawl tows were taken • Fish densities (no./hectare) computed from catches • and the area swept by trawls

12. Methods • Data Analysis • 4 statistical procedures • 3 multivariate (many variables used) • 1 univariate (one variable used) Kiyi

13. Why all of those statistics? • No single test exists that examines community • structure • An integrated set of procedures was needed for a • thorough exploration, examination, and portrayal of the • existence and structure of communities. Round whitefish

14. Results • 937 on-contour bottom trawl tows at 22 stations • captured 396,390 fish from • 26 taxa • 23 species and • stocked lake trout, • wild lake trout, • siscowet lake trout • splake Lake trout Siscowet lake trout

15. Only four or less shortjaw ciscoes, splake, pink salmon, white suckers, spottail shiners, and yellow perch were caught in all tows. • 15 taxa were represented by at least 300 specimens. Shortjaw cisco

16. Sample sizes of bottom-trawl tows, by depth group. 300 250 200 150 No. of tows 100 50 0 5-9.9 10-19.9 20-29.9 30-39.9 40-49.9 50-59.9 60-69.9 70-79.9 80-89.9 90-99.9 100-109.9 110-119.9 120-141 Depth (meters)

17. Analysis of densities of 26 taxa accounted for • only 30% of the data variation, • Analysis of densities of 9 taxa • accounted for 65% of the variation. • Densities of 9 taxa used in further statistical analyses Ninespine stickleback

18. Trawl tows classified to depth groups • Highest overall correct classification rate (80%) was to • 5.0-39.9 meters (82% correct) • 40.0-79.9 meters (77% correct) • > 80.0 meters (56% correct) • All depth groups classified at rates greater than • were possible by chance Bloater

19. Differences of 9 taxa densities across depths • Multivariate analysis showed that • densities of the 9 taxa were different across • shallow (5.0-39.9 meters), • intermediate (40.0-79.9 meters), and • deep (80.0-141 meters) trawl depths. • Therefore, 3 communities existed • and habitats were their depth ranges. Pygmy whitefish

20. Comparison of densities of 9 fish taxa across depths. Significance test rainbow smelt shallow > intermediate > deep trout-perch shallow > intermediate, deep shallow, intermediate > deep ninesp. stickleback shallow, intermediate > deep slimy sculpin intermediate > deep lake whitefish deep > shallow, intermediate siscowet trout deep > intermediate > shallow bloater deep > shallow, intermediate kiyi deep > intermediate > shallow deepw. sculpin 0 10 20 30 40 50 No./hectare Shallow (5.0-39.9 m) Intermediate (40.0-79.9) Deep (80.0-141 m)

21. Significant Depth Associations of Other 17 Taxa None found – 10 taxa alewife splake pink salmon lake chub spottail shiner white sucker longnose sucker burbot yellow perch spoonhead sculpin Sample sizes small (< 216) of all but alewife and spoonhead sculpin

22. Densities, by depth, of 16 taxa in Lake Superior. Density (no./hectare) Depth (meters) 5.0-39.9 40.0-79.9 80.0-141.0 6 5 4 3 2 1 0 Kiyi Bloater Trout-perch Slimy sculpin Lake herring Wild lake trout Johnny darter Deepwater sculpin Lake whitefish Shortjaw cisco Rainbow smelt Siscowet lake trout Round whitefish Pygmy whitefish Ninesp. stickleback Stocked lake trout Shallow & Intermed. Shallow Intermediate Deep

23. Conclusions • Lake Superior contained 3 summer, • benthic fish communities. • Their habitats were described by depth ranges • Shallow (5.0-39.9 meters) • Intermediate (40.0-79.9 meters) • Deep (80.0-141 meters) Trout-perch

24. Lake Superior bays, and main basin depth zones. Bays > 80 m < 80 m Bays

25. Although a gradient of densities occurred across all depths for some taxa, • densities changed abruptly with depth for: • wild lake trout siscowet lake trout round whitefish pygmy whitefish bloater kiyi slimy sculpin deepwater sculpin trout-perch ninespine stickleback johnny darter Johnny darter

26. Recommendations • Lake Superior fish populations have changed • since much of the data were collected • A study of the present structure of benthic • fish communities is needed.

27. Recommendations • Agencies need to consider fish communities when implementing management strategies to achieve Fish Community Objectives.

28. Recommendations • Fish community structures should be documented in; • bays harbors estuaries tributaries • Areas of Concern, • and pelagia (above bottom) of main basin. • Except pelagia, all those habitats are • highly vulnerable to pollution and habitat degradation.

29. Recommendations 4. Need to construct models that relate fish population & community data to habitat measures Model outputs will better enable management to rehabilitate damaged ecosystems (Remember: Ecosystem = community + its habitat).

30. Recommendations • Areas of Concern (AOC) • 7 of the 8 have degraded fish populations and habitats. • Comparisons of community structures in AOCs, • with similar areas not damaged, • will help managers refine AOC • fish community and habitat objectives.

31. Recommendations • Areas of Concern (continued) • Monitoring structures of communities in AOCs will track progress in rehabilitating their degraded populations, communities, and habitats.

32. Acknowledgements Thanks to G. Cholwek, M. Burnham-Curtis, and J. Lyons for some of the photographs.

33. Densities, by depth group, of 16 taxa in Lake Superior. Density (no./hectare) Depth (meters) 5.0-39.9 40.0-79.9 80.0-141.0 6 5 4 3 2 1 0 Kiyi Bloater Trout-perch Slimy sculpin Lake herring Wild lake trout Johnny darter Deepwater sculpin Lake whitefish Shortjaw cisco Rainbow smelt Siscowet lake trout Round whitefish Pygmy whitefish Ninesp. stickleback Stocked lake trout Shallow & Intermed. Intermediate Shallow Deep