Page 865 - The Toxicology of Fishes

Reproductive Impairment of Great Lakes Lake Trout by Dioxin-Like Chemicals 845

Field Observations of Exposures and Effects in Great Lakes Salmonines
Correlations of Contaminants with Reproductive
Success in Great Lakes Salmonines
Correlation analysis of chemical contaminant concentrations with observed effects in Great Lakes
salmonines has been another method used to investigate the potential of a causal relationship among
these variables. Although correlations are not absolute proof of causality, correlations can be a strong
piece of evidence for causality in ecoepidemiology (Fox, 1991). Conversely, a lack of a correlation
between a potential causal agent and the effect does not rule out a causal relationship but may simply
imply greater complexity of any potential relationship. Correlation of organochlorine chemical concen-
trations with reproductive performance of salmonines in the Great Lakes has met with mixed success
(Ankley et al., 1991; Fitzsimons, 1995; Mac et al., 1993; Zint et al., 1995). The experimental design for
most of these studies consisted of collecting salmonine gametes from one or more of the Great Lakes,
artificial spawning, rearing the eggs and fry in the laboratory, and observing stage-specific effects,
including mortality. The observed effects were then correlated with chemicals measured in the adults,
eggs, or rearing water. Correlations of PCB or HAH concentrations in the flesh of adults or eggs of
Great Lake salmonines and embryo lethality have been significant in certain cases, while the correlations
with fry mortality have been confounded and not significant in most cases.
The first work of this type on lake trout was conducted by Burdick et al. (1964) on fish collected from
several lakes in upstate New York. Although not from the Great Lakes, their correlation of elevated
contaminant concentrations (DDT) with reduced survival of fry proved to be important information on
chemical effects in lake trout and as a model for future studies. They found no survival in lake trout fry
that contained DDT over 2.95 µg/g wet weight (ww) (Burdick et al., 1964). Laboratory studies at the
time with brook trout (Macek, 1968) confirmed the sensitivity of salmonines to DDT. Later studies found
that adult lake trout fed diets with 6 µg DDT per g feed produced 100% mortality in their offspring
(Burdick et al., 1972). Baltic salmon (Salmo salar) collected from the Baltic Sea indicated that PCBs
could also have effects on egg survival and fry mortality (Jensen et al., 1970). These studies set the stage
for the salmon- and trout-rearing studies with Great Lakes salmonines in which egg and fry survival
was correlated to concentrations of organochlorine chemicals. One of the first rearing studies of lake
trout eggs from the Great Lakes (Mac et al., 1985) found survival of eggs to hatching was greatest when
the adults came from Lake Superior (96%) and lowest when the eggs were derived from females collected
in Lake Michigan (70%). Poor survival was significantly correlated with the source of eggs, not the
source of sperm and not the source of water in which the eggs were reared (Mac et al., 1985). Poor
survival was observed in Chinook salmon swim-up fry derived from eggs that contained greater con-
centrations of dioxin-like chemicals (Ankley et al., 1991). They also found a correlation between hatching
success and PCB content of eggs; however, survival of fry was not correlated to contaminant concen-
trations (Ankley et al., 1991). Later, Mac et al. (1993) found a significant negative correlation between
total concentrations of PCBs and embryo survival to hatch in lake trout collected from Lake Michigan
between 1977 and 1988. Fry mortality in those studies could not be attributed to disease or nutrition
and was characterized by erratic swimming behaviors and loss of equilibrium prior to death (Mac et al.,
1993). Other workers studying Chinook salmon found weak negative correlations between total concen-
trations of PCBs and survival (Edsall et al., 1993; Giesy et al., 1986) or no correlations at all (Fitzsimons,
1995; Smith et al., 1994; Williams and Giesy, 1992).
Simple correlations of chemical contaminants such as PCBs, TEQs, DDT, or mercury have not
demonstrated completely consistent relationships with female-specific reproductive success. The reasons
for inconsistencies are not evident; however, this fact likely speaks to the complexity of the stressors
impinging on salmonine populations in the Great Lakes. Simple correlations of any type are highly
unlikely to address all of the factors important for survival of salmonine offspring; yet, in a number of
studies conducted over a number of years under a variety of conditions, elevated chemical contaminants
have resulted in reduced survival in field-collected salmonines.