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Between 1996-1999, nonnative fish consistently used the passageway the most <br />in July (1,083), followed by June (348), and August (425)(Table 2; Appendix; <br />Figure D.1.). Only in 2000 did nonnative fish use the passageway more in June <br />rather than July (Appendix; Figure D.1.). White sucker was the most numerous <br />nonnative fish in the fish trap (695), followed by channel catfish (619), common <br />carp (428), and black bullhead (350)(Table 1). Use of the passageway by channel <br />catfish coincided mostly with that of Colorado pikeminnow. July was the highest <br />use-month by channel catfish (219), followed by August (159), June (150), <br />September (71), and May (20)(Appendix; Table G.4. and Figure G.2.). Up until <br />2000, channel catfish had not been found in the fish trap during May. White <br />sucker usage was highest in July (271) and June (124)(Appendix; Table G.S. and <br />Figure G.2.). Black bullhead used the passageway the most in July and August <br />(Appendix; Table G.6. and Figure G.2.) whereas common carp used the passageway <br />the most in July and June (Appendix; Table G.7. and Figure G.3.). Other fish <br />that were incidental captures in the fish trap were largemouth bass (6), northern <br />pike (2), bluegi11 (1), smalImouth bass (1), grass carp (1), and Iongnose sucker <br />(1)(Table 1). <br />White sucker was most numerous during 1996 (189) and 1997 (253; Appendix; <br />Figure H.2.) but channel catfish were the most numerous in 1998 (157) and 1999 <br />(196; Appendix; Figure H.2.). Black bullhead numbers were highest in 1997 (110) <br />and 1999 (80; Appendix; Figure H.2.). Catches of common carp in the fish trap <br />steadily declined each year from a high of 108 in 1996 (Appendix; Figure H.3.). <br />In 2000, the number of native (1,245) and nonnative (314) fish that used <br />the passageway from June through September was the lowest of all five years <br />monitored (Table 2; Appendix; Figure D.1.). For native fish, the number of fish <br />enumerated i n the fi sh trap duri ng 2000 was 67% 1 ess than that from both 1999 and <br />1998 and 84% less than 1997 and 1996. For nonnative fish, the number of fish <br />enumerated in the fish trap during 2000 was less than all other previous years: <br />1999 (38% less); 1998 (26% less); 1997 (48% less); 1996 (36% less). During <br />October 2000, however, numbers of both native (294) and nonnative (20) fish that <br />were collected in the fish trap were the highest of all" five years (Table 2). <br />There is no obvious reason for this. Water volume and upstream water delivery <br />patterns (Figure 3) during this 2-1/2-month period were similar in 1996, 1998, <br />and 2000. <br />Surge/Pulse Migration <br />Fish use of the passageway was sporadic, if not random, from day to day. <br />On several occasions between seasons and among years, large numbers of fish were <br />27