Crayfish Experiments 
No significant mortality was seen at any station, and 
autopsies failed to disclose any obvious difference that could be 
related to treatment between the crayfish that died during the 
experiments and those that survived. 
DISCUSSION 
Oyster Experiments 
Since one of the principal objectives of these studies was to 
identify possible causes of oyster mortality in the Chester River 
since 1974, it is unfortunate for the study that no large-scale 
mortality occurred at any of our stations. Observations by sci¬ 
entists, watermen and representatives of the Department of 
Natural Resources have noted that oysters that die in the "mor¬ 
tality areas" of the Chester River have unusually clean shells 
showing little or no fouling. We did note a dieoff of fouling 
organisms. This dieoff was first noted at the two most upriver 
stations on 12 July and coincided with a fishkill in the river. 
Our personnel noted that the fishkill was a widespread phenomenon 
with dead fish, mostly catfish and carp occurring from near the 
mouth of the river to well above the mouth of Morgan Creek. It 
might be speculated that the two phenomena are related in some 
manner. 
The dieoff of fouling organisms was never detected downstream 
below Station 6 (clamline buoy A off Corsica Neck) and seeming 
full recovery was noted by 18 September. An examination of Table 
3 will show an interesting pattern of deaths. If we ignore the 
unusual high mortality at Station 10 on 14 June, which may be re¬ 
lated to high runoff and silt, 6 of the 13 remaining mortalities 
occurred during the period of the fouling organism dieoff and at 
the stations where commensal organism dieoff was noted. It may 
be that the oyster dieoff did occur during the study, but for 
some reason this was an unusually mild year for it. 
An examination of Table 4 shows that summer growth rates of 
our oysters placed in the Chester River were significantly lower 
than that of the control oysters held in the Patuxent River. 
This reduced growth rate coincides with the period of time when 
the dieoff of fouling organisms occurred. 
Table 5 shows that oysters in the four most upriver stations 
had significantly higher observed conditions scores. These may 
well relate to salinities being too low for spawning. These 
oysters may simply have never lost gonadal material or glycogen. 
One possible hypothesis for the dieoff has been suggested by 
Donald Heinle (personal communication). He suggests that heavy 
loading of the system with organic material will cause the water 
36 
