抄録
On the Dôsigawa, tributary to the river Sagami, dainm and waterway were constructed in 1953 (Fig. 1), and the change of discharge occured (Fig. 2, Table 5). The type of river bed chartged (Figs. 3, 4; Table 6, 7) also, and the change involved that of fishing efforts of Ayu, Plecoglossus altivelis T. et S., fisheries in rapids per day (Table 8). Table 3 shows clearly that fishing methods are highly restricted to the types of river beds. Table 4 explains that most of fishing efforts are observed in rapids especially in the case of fishermen belonging too cooperative. Data under unfavorable condition (Table 2) were eliminated, and EbSj, the density of fishing effort were measured in various subregions owing to procedure described bellow:
EbSj=m−k=1n−i=1 EbikSj/m−k=1n−i=1lbikSj
where symbol EbikSj denotes efforts of fishing on some fishing ground (i) which has any types of river beds (b), at any creelcensus day (K), in any subregion (S), in any year (j). Symbol lbikSj denotes length expressed in units of 100m. under the same terminology as mentioned above.
Following above procedure, the results shown in Table 8 were rearranged into as Table 9. Without considering the coefficient of variation shown in Table 11 and corrective coefficient (Table 1), it may be probably -true that under these prediction EbSj may attain 0.5-0.4 and the yearly change of total efforts was brought force from that of total length of rapids.
