, 1995). For example, substantial decreases in the abundance of the amphipod Diporeia occurred during the 1990s and early 2000s and were attributed to the zebra mussel invasion ( Nalepa et al., 1998 and Nalepa et al., 2006). Diporeia then became a much smaller portion of the diet of alewives (Alosa pseudoharengus; Madenjian et al., 2003 and Madenjian et al., 2006), which had
previously been the dominant forage of Lake Michigan salmon ( Jacobs et al., 2013, Madenjian et al., 1998 and Madenjian et al., 2002). Diporeia contain C59 in vitro the highest PCB concentration of all invertebrates consumed by alewives ( Madenjian et al., 1999); and as their abundance declined, average PCB concentrations in large alewives in Lake Michigan decreased at a rate of − 11% per year during 1995–2001 ( Madenjian et al., 1993, Madenjian et al., 1999 and Madenjian et al., 2004). It is
highly likely therefore that Lake Michigan salmon PCB concentration dynamics are in part a response not only to restrictions on PCBs and ongoing remediation efforts but also to ongoing dramatic changes in the Lake Michigan food web. Others have found that PCB trends may vary by click here location in Lake Michigan (Carlson and Swackhamer, 2006). We did not find significant differences in PCB concentrations or trends among locations perhaps due in part to small numbers of fish collected from some areas. Chang et al. (2012) did not find regional differences in PCBs in lake trout collected from two different locations in Lake Michigan. Other factors that are likely important are gender and age, but again this dataset limited our ability to examine those factors. We found that PCB concentrations G protein-coupled receptor kinase in both salmon species increased with body length and % lipid, and were higher for individuals caught in the fall. The condition of Lake Michigan chinook and coho over the study period has varied reflecting changes in the forage base, stocking and harvest rates,
and introduction of invasive species (Lake Michigan Fisheries Team, 2004). Accounting for % lipid and body length of the individual fish collected over the study period is important for an accurate estimate of PCB trends (de Boer et al., 2010, Gewurtz et al., 2009, Hickey et al., 2006 and Sadraddini et al., 2011). Interestingly temporal declines in PCB concentrations differed between chinook and coho in a way that might be attributable to differences in characteristics of the two species. The point of transition between fast and slower rates of decline was one year later and the rate of decline in the early period was lower for chinook compared to coho. In Lake Michigan, chinook spend more time in the lake, consume about twice as much forage, grow to larger sizes, and have exhibited higher PCB concentrations compared to coho (Becker, 1983, Lamon et al., 2000 and Stewart et al., 1981) which could explain the lag in the transition and early period declines.
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