Use of whole-stream patterns of age segregation to infer the interannual movements of stream salmonids: A demonstration with arctic grayling in an interior Alaskan stream
Nf. Hughes, Use of whole-stream patterns of age segregation to infer the interannual movements of stream salmonids: A demonstration with arctic grayling in an interior Alaskan stream, T AM FISH S, 127(6), 1998, pp. 1067-1071
I show how patterns of whole-stream age segregation can be used to infer in
terannual movements of stream salmonids. First, estimates of recruitment an
d mortality rates for the population as a whole are calculated using data f
rom fish sampled along the entire length of the river. These rates are used
to simulate the age structure of an idealized population. Next, each age-c
lass is divided among lower, middle, and upstream reaches, according to the
proportions observed in the real population. Finally, the amount of intera
nnual movement is estimated from the pattern of age segregation that would
exist after 1 year if recruitment and mortality were allowed to act on the
simulated population but no fish moved between reaches. Application of this
technique to the "older-fish-upstream" distribution pattern of Arctic gray
ling Thymallus arcticus in an Alaskan river showed that substantial movemen
ts are required to maintain the observed pattern of age segregation. Annual
emigration was estimated at 24%, 11%, and 0% for downstream, midriver, and
upstream reaches respectively, estimated immigration was 2%, 30%, and 51%.