Abd El Aziz Mousa Nour
Alexandria University
Egypt
Title: Some factors affecting condition factor of lake whitefish Coregonus clupeaformis in lakes Michigan and Huron, USA
Biography
Biography: Abd El Aziz Mousa Nour
Abstract
Lake Whitefish (Coregonus clupeaformis; LWF) constitutes one of the most commercially harvested fisheries in the Laurentian Great Lakes. As a benthivore, LWF plays an important role in the Great Lakes food webs due to its remarkable ability to transfer energy from lower to higher trophic levels. This study was aimed to investigate the effect of seasonal fluctuated infection parameters of LWF collected from four sites in northern lakes Huron (Cheboygan and De Tour Village) and Michigan (Big Bay de Noc and Naubinway) from fall 2003 through summer 2006. A total of 1284 spawning LWF specimens were examined in order to evaluate whether prevalence, abundance and intensity of infection affected the LWF condition factor (K) after accounting for the effect of lake, sampling site, year and season on LWF growth and condition by calculating the residuals from the Generalized estimating equations (GEEs) and then using simple linear regression to relate the residuals to K. The results revealed a positive relationship between K and GEE residuals for parasitic infection abundance (Slope=26.46, SE=9.42) and intensity (Slope=47.17, SE=24.04) suggesting that individuals with greater than average parasitic infection abundance and intensity had larger condition factors than individuals with lower than average abundance and intensity. The test for whether the model coefficient was different from zero was statistically significant for parasitic infection abundance (t=2.81, P=0.005) but was statistically insignificant, although only marginally so, for parasitic infection intensity (t=1.96, P=0.051). It is important to note, however, that the total amount of variability explained in the parasitic infection GEE residuals by K was low (R2<0.02) for both models.