York River.- Mean meristic counts for the York River samples were similar between years and locations (table 7). Based on the

Table 6.--Frequencies of meristic counts from juvenile American shad in

samples from the Rappahannock River, Va.

Location

Year

Number of

pectoral fin rays

11 12 13 14 15 16 17 18 19 20

Mean

Standard deviation

Frequency

Long Point

1954

5 27 17 1

15.25

0.6713

Batchelors Bay 1958

1 22 26 1

15.54

0.5789

Number of

dorsal fin rays

14 15 16 17 18 19 20 21 22 23

Frequency

Long Point Batchelors Bay

Claremont Beach samples the differences between years were not significant.

Comparison between Chesapeake Bay tributaries.--Data for all locations and all years for which collections were available were combined in testing for significant differences in meristic counts between two rivers. There was a significant difference in the meristic counts between the York and James fish in all instances; between the Rappahannock and James, the Rappahannock and York, and the James and Susquehanna in three instances; and between the Rappahannock and Susquehanna, and the York and Susquehanna in two instances (table 9). Where applicable, the interaction between years and rivers was not significant. The differences in meristic counts between rivers indicated that discrete populations of shad occurred in the Chesapeake Bay tributaries.