Johnson et a I.: Reproductive success of Clupea pallasi after the Exxon Valdez oil spill 
759 
PWS SE AK 
„ St. Mathews Bay P-0.434 Sitka P-0.005 
1 
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U 1 1 1 f " 1 " 1 "'1 1 1 1 1 1 1 1 1 , — - T ■ | 1 
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Age (years) 
Figure 8 
Mean (±SE) percent spinal abnormalities of larval Pacific herring by female 
parent age, site, and region in Alaska, 1995. Sample sizes are indicated in 
Figure 5. Overall P-value from ANOVA is listed above each graph. Signifi- 
cant differences were Sitka, ages 3 and 4 < age 7 (P=0.024). 
Measurable effects likely declined most rapidly dur- 
ing the first year as the most adversely affected in- 
dividuals died. Although oil-related abnormalities 
were observed in larvae immediately following the 
spill, both developmental and genetic damage pro- 
gressively decreased with time (Brown et al., 1996a) 
and were undetectable in 1990 and 1991 (Hose et 
al., 1996). The extent of spawning-site fidelity in 
herring is poorly understood, but unaffected individu- 
als from other geographic areas have probably joined 
remaining, less affected spawners, diluting possible 
residual effects. The disease epidemic observed in 
PWS in 1993 (Meyers et al., 1994) may have removed 
additional marginal spill survivors. Thus, it is not 
particularly surprising that reproductive impairment 
was not detected in 1995. 
