Study 466 Trawl Update - 2003

1. Study 466 Trawl Update - 2003 Study Objective: To assess responses of the Saginaw Bay fish community to changing environmental and biological conditions. Of specific interest is the monitoring of fish community responses to management actions and the effects of nonnative species and the gauging of walleye recruitment and population growth. Spottail shiner was the most abundant species in the 2002 fall trawls, with 32,931 captured for a mean cpue of 967 fish per 10 minute tow. Mt. Clemens Fisheries Research Station Prepared for the Saginaw Bay Coordination Meeting - Feb. 26, 2003

2. Locations of 2002 fall trawls on Saginaw Bay - DJ466 • Magenta 2002 • Yellow 2001 • Green 2000 • 2002 tows in yellow - total of 37 trawl tows at 11 Inner Bay grids • Total tow time of 249 minutes • Two outer bay stations (45 and 65 foot depths)

3. Mean secchi depth for SB fall trawl surveys(Inner Bay Only) No statistically significant trend in secchi depths.

4. Mean Secchi Depths by Grids • Magenta=2002 • Yellow=2001 • Green=2000 • Data presented in meters

5. Thirty-two Year Data Time Series of Fall Trawl CPUE for 4 soft-rayed forage species

6. AB B C A A AB AC BC A Comparison of Decade Mean CPUE for primary species captured in fall trawls on Saginaw Bay

7. B A AB A A A B A AB A B A AB Comparison of Decade Mean CPUE for primary species captured in fall trawls on Saginaw Bay

8. Catch rates for the common soft-rayed forage species in Saginaw Bay fall trawl surveys 6 out of the 7 highest totals for soft-rayed forage abundance have occurred since ZM’s colonized the Bay

9. Round goby catch rates declined slightly in 2002 – only 1 johnny darter caught in 35 trawl tows

10. Length frequency distribution for round goby from SB 2002 trawls

11. Round goby mean CPUE by grid for fall trawls • Blue=1999, Green=2000, Yellow=2001, Magenta=2002 • Increasing trend at all grids sampled • Highest cpue near Sag R.

12. Diet of Freshwater Drum from Saginaw Bay(expressed as frequency of occurrence) • Samples collected in trawls, Sept. 2002 • 88 fish examined • Total of 50 non-empty stomachs

13. Diet of Channel Catfish from Saginaw Bay(expressed as frequency of occurrence) • Samples collected in trawls, Sept. 2002 • 19 fish examined • Total of 10 non-empty stomachs

14. Diet of YAO Walleye from Saginaw Bay(expressed as frequency of occurrence) • Samples collected in trawls, Sept. 2002 • 33 fish examined • Total of 25 non-empty stomachs

15. Catch rates for the common spiny-rayed forage species in Saginaw Bay fall trawl surveys

16. SB Forage index and total biomass based on fall trawls Forage index species include: Alewife, Emerald shiner, Gizzard Shad, Smelt, Spottail shiner, Round goby, Trout-perch, White bass, White perch, Age 0 Yellow Perch

17. Age 0 walleye mean CPUE by Grid - 2002 • A total of 84 Age 0 walleye captured in fall 2002 trawls • Yellow indicates Zero grids

18. Age 0 Walleye CPUE for SB Fall Trawls and Walleye Fingerlings Stocked in SB 2002 trawl CPUE of 2.54 per 10 minute tow expands out to an estimated bay population of 838,888 Age 0 walleye

19. Mean CPUE for Age 0 and Yearling+ Yellow Perch in Fall Trawls

20. SB Yellow Perch Year Classes Ranked by YOY Mean CPUE • Ranked year classes based on mean Age 0 YP CPUE for fall trawls • Categorized as strong, moderate, or weak, based on natural breaks in the dataset • 1 strong, 3 moderate, and 6 weak cohorts in last 10 years • 2002 is a “weak” yearclass

21. YOY YP mean CPUE by grid • Green=2000 (8.6) • Yellow=2001 (121.6) • Magenta=2002 (30.7) • Highest 2002 YOY densities at Grid 115

22. Mean length at age for SB YP

23. Lower abundance, faster growth, higher proportion of harvestable fish

24. Commercial fishery catch rates and annual trawl YAO YP cpue for SB

25. Comm. fishery catch rates and total annual comm. YP catch for SB

26. Mt. Clemens Plans for SB 2003 Sampling • Trawl survey in September • Sample Inner Bay and Outer Bay sites • Collect carp pathology samples if available • Sample commercial fishery yellow perch for length, wt, age