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<br />14 <br /> <br />Table 1. <br /> <br />Distribution of northern pike captured in the Yampa River, 1987- <br />1990. RK=river kilometers <br /> <br /> Number of pike sampled <br />Sample Reach RK 1987-88 1989 1990 <br />Hayden-Craig 188 - 274 31 100 83 <br />Juniper Springs 145 - 188 3 36 16 <br />Maybe11-Sunbeam 93 - 143 35 23 24 <br />Lily Park 72 - 90 32 13 20 <br />Total 101 172 143 <br /> <br />length from 87 to 1016mm total length and averaged 625 mm (Figure 2). These <br />fish ranged in weight from 170 to 8100 gm, and averaged 1930 gm. The length <br />frequency distribution in Figure 2 illustrates the shift in mean length of <br />pike since 1988. No influx of pike in the 420-540 mm size range was observed <br />in 1990 compared to 1989; the peak also has remained at 580-620 mm. The <br />abundance of pike 700-800 mm observed in 1986-88 was reduced in 1989, and <br />further reduced in 1990. Only a slightly increased abundance of 800-900 mm <br />fish is evident in 1990. The relatively abundant influx of smaller pike in <br />1989 had no discernable impact upon the length frequency distribution in 1990. <br />Each year class or group of year classes that make upon the modal peak appear <br />to rapidly diminish as larger size groups in subsequent years. <br /> <br />Comparison of length frequency distribution by the four study reaches <br />indicates pike are relatively more abundant in the upstream Hayden-Craig reach <br />(based on sample size alone), and that fewer small pike were observed in each <br />downstream reach (Figure 3). The abundance of modal size pike also appears to <br />decline with downstream distribution. Larger size pike (>700 mm) are most <br />abundant in the Hayden-Craig reach and they persist in the Maybe11 and Lily <br />Park reaches. Very few larger pike occur in the Juniper Springs reach. The <br />change in mean size of pike with downstream distribution is shown in Figure 4. <br />With the exception of the Juniper Springs reach, the trends were quite <br />consistent. Average length of pike in the Hayden-Craig reach did not change <br />appreciably over time. The average lengths of pike increased consistently at <br />the Maybe11 and Lily Park reaches relative to the Hayden-Craig reach. In the <br />Juniper reach, however, the size of pike captured were quite variable between <br />years. <br /> <br />The estimated length-weight relationships for pike over 1988-1990 also <br />reflect the shifts in length frequency distributions (Figure 5). Length- <br />weight relationships for the three time periods in Figure 5 are as follows: <br /> <br />1986-1988: <br />1989: <br />1990: <br /> <br />log W <br />log W <br />log W <br /> <br />2.981 log L - 5.097, R2 <br />3.437 log L - 6.387, R2 <br />3.264 log L - 5.920, R2 <br /> <br />0.979, n = 107 <br />0.935, n = 162 <br />0.951, n = 130 <br />