Page 844 - The Toxicology of Fishes

824 The Toxicology of Fishes

ago. Natural reproduction of lake trout was observed in northern Lake Huron in the early 1990s (Hansen
et al., 1995; Holey et al., 1995; Johnson and VanAmberg, 1995), and Lake Superior has always maintained
a natural, self-sustaining stock of lake trout (Bronte, 1993; Holey et al., 1995). Lake Ontario has only
had evidence of a small amount of natural reproduction over the past two decades (Marsden and Krueger,
1991; Marsden et al., 1988). Thus, even though adult populations of lake trout exist, natural recruitment
of young of the year lake trout is nonexistent (Lake Michigan), slight (Lake Ontario), or not enough to
maintain self-sustaining populations (Lake Huron) in the lower Great Lakes, which historically had
thriving populations of lake trout.

Chemical Contamination of the Great Lakes and Lake Trout

Concentrations of chlorinated hydrocarbons, as well as some metals, have been monitored in the tissues
of fishes of the Great Lakes since the mid-1970s (Allan et al., 1991; Clark et al., 1984; DeVault, 1985;
Fitchko 1986; Hitchin et al., 1993; Veith, 1975; Willford, 1980). Over this period, literally hundreds of
studies have measured the concentrations of chlorinated hydrocarbons in fishes from the Great Lakes
(Baumann and Whittle, 1988; DeVault et al., 1986; Hickey et al., 2006; Rodgers et al., 1993). Numerous
reports on monitoring programs conducted by state, provincial, and federal laboratories and annual
reports have been published; thus, extensive information is available regarding the status and trends of
concentrations of contaminants in fishes of the Great Lakes (Baumann and Whittle, 1988; Fitchko, 1986;
Hickey et al., 2006). The focus of most monitoring efforts has been on the high-use, persistent, bioac-
cumulative chemicals such as organochlorine pesticides, PCBs, and mercury (Tillitt et al., 1998). Mon-
itoring programs have been designed to determine trends for known pollutants, rather than identify new
types of compounds. More recently monitoring efforts in the Great Lakes have included chemicals other
than the classical organochlorine pesticides and PCBs (Giesy et al., 2006); however, trend data are not
available for many of these more modern chemical contaminants, unless they are persistent enough to
allow screening of archived samples (Zhu and Hites, 2004).
Concentrations of hydrophobic contaminants in fishes are dependent on a number of parameters, such
as species, age, gender, season, food sources, and collection location, in addition to chemical-source-
related factors. In general, the larger, older, fish, including lake trout, have greater concentrations of the
HAHs. Also, fish with greater lipid content and those at the top of the food chain tend to have the greatest
concentrations of HAHs. Thus, fish, such as lake trout and brown trout tend to have the greater
concentrations of HAHs and organochlorine pesticides as compared to other top predators and species
lower on the trophic chain. Walleye, for example, are the top predator in Lake Erie, but generally
concentrations of these contaminants in walleye do not reach the same concentrations as measured in
salmonines due to the smaller lipid content in walleye, their lower trophic status, and the reduced
longevity of walleye compared to lake trout (DeVault et al., 1986; Hickey et al., 2006).
The greatest concentrations of HAHs and organochlorine pesticides in Great Lakes fish tend to be
found in fish from Lakes Ontario and Michigan (Allan et al., 1991; Fitchko, 1986; Bauman and Whittle,
1988). This has been true over the past 40 years and remains true today. Fish from Lake Ontario contain
the greatest concentrations of the insecticides mirex, DDT, and dieldrin, while the concentrations of
toxaphene are greatest in fishes from Lake Superior (Allan et al., 1991; Baumann and Whittle, 1988;
Hickey et al., 2006). Concentrations of persistent chlorinated hydrocarbons have historically been least
in fishes from Lake Superior and Lake Huron (Armstrong and Lutz, 1977a;b; Baumann and Whittle,
1988; Simmons, 1984). The trends of most of these compounds in fish from the Great Lakes have been
declining until recently (DeVault et al., 1996; Hickey et al., 2006). Currently, most of these contaminant
concentrations in Great Lakes fish have reached an apparent steady state or only slightly decreasing
concentrations (Hickey et al., 2006). The greatest rates of declines in fish contaminant concentrations
have occurred in Lake Ontario and Lake Michigan (Baumann and Whittle, 1988; Maack and Sonzogni,
1988). These lakes have experienced the greatest decreases largely due to the fact they had the greatest
contamination from industrial point-sources or agricultural activities; yet, current concentrations of PCBs
and DDT in fish from Lakes Michigan and Ontario remain the greatest in the Great Lakes, due to the