1. Status of lake trout in Lake Superior 1993-2000 Shawn Sitar, MIDNR; Chuck Bronte, USFWS; Mark Ebener, CORA; Tom Fratt, RCFD; Ken Gebhardt, BMIC; Ted Halpern, MNDNR; Bill Mattes, GLIFWC; Gene Mensch, KBIC; Mike Petzold, OMNR; Steve Schram, WIDNR; Don Schreiner, MNDNR.

2. Fish Community Objective lake trout Achieve and maintain genetically diverse self- sustaining populations of lake trout that are similar to those found in the lake prior to 1940, with lean lake trout being the dominant form in near-shore waters, siscowet lake trout the dominant form in offshore waters, and humper lake trout a common form in eastern waters and around Isle Royale.

3. Lake trout management units in Lake Superior

4. 195019601970198019902000 Year 0 1 2 3 4 Millions stocked Lake trout stocking in Lake Superior

5. Relative abundance of lake trout in Lake Superior, 1993-2000

6. Relative abundance of wild lake trout in Lake Superior, 1993-2000 GM CPUE (fish/km/night) 153.1

7. Relative abundance of hatchery lake trout in Lake Superior, 1993-2000 Management Unit GM CPUE (fish/km/night)

8. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 ON-1 ON-14 MN-1MN-2MN-3 WI-1WI-2MI-2MI-3MI-4MI-5MI-6MI-7 ON-24ON-28ON-31ON-33 Management Unit Total Annual Mortality Total annual mortality for lake trout in Lake Superior 1993-2000 (catch curves)

9. 0 0.5 1 1.5 2 2.5 3 3.5 4 18671877188718971907191719271937194719571967197719871997 Year Canada U.S. Yield (million kg) Lean lake trout commercial yield in Lake Superior, 1867-2000

10. Recent commercial harvest of lake trout in Lake Superior Avg. 1983-92

11. Recreational harvest of lake trout in Lake Superior, 1970-1999

12. Sea Lamprey Marking of Lean Lake Trout Lake Superior, 1986-2000 19861988199019921994199619982000 0 2 4 6 8 10 Marks per 100 Fish Average 1986-99

13. 19861988199019921994199619982000 Year 0 2 4 6 8 10 12 Marks per 100 Lake Trout Canada U. S. Lamprey Marking of Lake Trout Lake Superior, 1986-2000

14. Sea Lamprey Marking East & West U. S. Waters Lake Superior 1986-2000 19861988199019921994199619982000 Year 0 5 10 15 Marks per 100 Lake Trout West East

15. Lake trout yield to sea lampreys and humans in Lake Superior during 1993-2000 Year Biomass (x 1000 kg) 0 100 200 300 400 500 600 700 800 900 1,000 1,100 1,200 199319941995199619971998199920001983-92 (avg.) Humans Sea lampreys

16. From Hansen et al. (1994) Mean length of age 7 lake trout in US waters of Lake Superior, 1970-92

17. Mean length at age 7 for lake trout in Lake Superior, 1993-2000 ONTARIO-EONTARIO -W MINNESOTA WISCONSIN MICHIGAN HATCHERY WILD TOTAL LENGTH (mm) 480 500 520 540 560 580 600 620

18. Siscowet

19. CPUE (Kg/km net) Relative abundance of siscowets in commercial fisheries 19501960197019801990 0 50 100 150 200 250 300 U.S. commercial fisheries

20. Relative abundance of siscowets in Lake Superior (Agency surveys) Siscowet Lean Date

21. MN-1MI-2MI-4MI-5MI-7 Management Unit 0 5 10 15 20 25 Fish /305 m Lean Siscowet 16:1 12:1 2:1 18:1 13:1 Mean = 14:1 Ratio of siscowets to leans by management unit

22. 1357911131517192123252729313335 Age (yr) 0 5 10 15 20 25 30 Number of fish MI-4 MI-7 MI-2 Age compositions of siscowet by management unit in 1996

23. Recent analyses of lake trout dynamics in Michigan waters of Lake Superior Statistical catch-at-age models for wild lake trout in MI-5, MI-6, and MI-7 (MSC, TFC) Stock-Recruitment analyses for lake trout in MI-3 through MI-7 (Jessica Richards) Comparison of historic and modern abundance in Michigan waters (Mike Wilberg)

24. Statistical catch-at-age models GLFC workshops. Models integrate age-specific data from diverse sources. Models used in 1836 Treaty waters to estimate quotas.

25. 0 200 400 600 800 1,000 1,200 1,400 1,600 1975197719791981198319851987198919911993199519971999 Year MI-5 MI-6 MI-7 Wild lake trout abundance (ages 3+) Number of fish x 1,000

26. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 1975197719791981198319851987198919911993199519971999 Year MI-5 MI-6 MI-7 Target maximum Total Mortality Rate Total annual mortality rates for ages 6-11 lake trout

27. Mortality rates for ages 6-11 wild lake trout in MI-5 Instantaneous mortality (year -1 ) Year 0 0.05 0.1 0.15 0.2 1975197719791981198319851987198919911993199519971999 Sea Lamprey Commercial Fishing Recreational Fishing Natural

28. Mortality rates for ages 6-11 wild lake trout in MI-6

29. 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 1975197719791981198319851987198919911993199519971999 Year Sea Lamprey Commercial Fishing Recreational Fishing Natural Mortality rates for ages 6-11 wild lake trout in MI-7 Instantaneous mortality (year -1 )

30. Spawning stock biomass to project safe harvest levels SSBR=the theoretical amount of mature female biomass produced per given recruit through its life. SSBR Target =The total amount of spawning stock biomass produced per recruit that suffers the target maximum mortality The SSBR values will vary over time as the mortality and maturity schedules vary over time.

31. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 MI-5MI-6MI-7 Management Unit Avg. 1998-2000 Target SSBR (kg) Spawning stock biomass

32. From: Doemel (2000) Lake trout stock-recruitment relationships in Michigan (Based on 1970-98 data)

33. Historic and Modern lake trout relative abundance MI-2MI-3MI-4MI-5MI-6MI-7MI-8 CPUE 1984-98 40.58.114.839.720.811.11.3 Historic CPUE (1929-43) 7.27.46.89.08.116.119.6 From: Wilberg (2000)

34. Status of lake trout in Lake Superior 2000 Wild lake trout abundance increasing MN & WI and high levels MI waters Current abundance MI higher than historic values –recruitment peaked recently –indications of density dependence most areas. Growth rates continue to decline and began in 1970s. Siscowet abundance high & may be increasing Sea lampreys kill more lake trout than fisheries.

35. Recommendations Further develop & evaluate statistical population models Quantify movement patterns. Evaluate FCOs and reference points. Monitor and assess siscowet populations. Expand understanding of lake trout forms. Develop bioenergetics models to assess food web stability. Map and quantify lake trout habitat.