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DEVELOPMENT AND CORRELATION OF PHYSICAL PROCESS INDICES WITH INTER-ANNUAL RECRUITMENT VARIABILITY IN LAKE MICHIGAN
2 Lyles School of Civil Engineering, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN,47907-2051
3 Department of Forestry and Natural Resources, Purdue University, 715 W. State Street, West Lafayette, IN 47907-2061
4 Great Lakes Science Center, United States Geological Survey, 1451 Green Road, Ann Arbor, MI, 48105-2807
This project examined the relationship between interannual fish recruitment variability, synchrony, and potential physical drivers of recruitment. First, multiple fish species in Lake Michigan were examined for spatial synchrony in recruitment, and linkages between this synchrony and interannual climate variation. Fish species examined included bloater (Coregonus hoyi), rainbow smelt (Osmerus mordax), yellow perch (Perca flavescens), and alewife (Alosa pseudoharengus). Residuals from stock–recruitment relationships revealed yellow perch recruitment to be correlated with recruitment of both rainbow smelt (r = 0.37) and alewife (r =0.36). Across all four species, recruitment synchrony was manifested as higher than expected recruitment in 5 years between 1978 and 1987 and then lower than expected recruitment in 5 years between 1996 and 2004. Generalized additive models revealed warmer spring and summer water temperatures and lower wind speeds corresponded to higher than expected recruitment for the nearshore spawning species, and overall variance explained ranged from 14% (yellow perch) to 61% (alewife). For all species but rainbow smelt, higher recruitment also occurred in extremely high or low years of the North Atlantic Oscillation index. Additional work investigated inter-annual (1966–2008) variation in yellow perch (Perca flavescens) recruitment using 16 combined datasets describing populations located in four of the five Laurentian Great Lakes (Erie, Huron, Michigan, and Ontario) and Lake St. Clair. Relative year-class strength (RYCS) was indexed using catch-curve residuals for each year-class across 2–4 years and compared relative year-class strength among sampling locations. Results indicate that perch recruitment is positively synchronized across the region. In addition, the spatial scale of this synchrony appears to be broader – approximately 150km - than previous estimates for both yellow perch and freshwater fish in general. Year-class strength was compared to regional indices of annual climatic conditions (spring-summer air temperature, winter air temperature, and spring precipitation) using data from 14 weather stations across the Great Lakes region. Regional recruitment synchrony was found to be positively related to spring-summer air temperature, suggesting that at least one abiotic factor is responsible for the observed synchrony. Work examining inter-annual variation in recruitment among lake whitefish (Coregonus clupeaformis) populations in lakes Huron, Michigan and Superior was carried out, using fishery-dependent and -independent data from 1971 to 2014. RYCS was calculated from catch-curve residuals for each year-class across multiple sampling years to quantify annual recruitment success. Pairwise comparison of RYCS among datasets revealed no significant associations either within or between lakes, suggesting that recruitment of lake whitefish – unlike yellow perch - is spatially asynchronous. There was no consistent correlation between pairwise agreement and the distance between datasets, and models to estimate the spatial scale of recruitment synchrony did not fit well to these data. These results suggest that inter-annual recruitment variation of lake whitefish is asynchronous across broad spatial scales in the Great Lakes. Because these findings differ from research on some other Coregonus species, they are suggestive that local biotic or density-dependent factors may contribute strongly to lake whitefish recruitment rather than inter-annual variability in broad-scale abiotic factors. Ongoing work seeks to quantify interannual variations in physical processes that may be linked to recruitment synchrony, in particular variations in air/water temperatures and over-lake winds.