d) Age Structure 



For most Ilount Haggin streams, over 75 percent of the estimated 

 population was accounted for by age I and II fish. This is probably 

 reflective of a normal population structure and corresponds with the 

 findings of McFadden (1960) in studies of large brook trout population 

 in Lawrence Creek, Wisconsin. Due to the difficulty of capturing very 

 small fish, the only available estimate of age fish was from Sixmile 

 Creek where age and age I fish accounted for 84 percent of the brook 

 trout population. This data reinforces the importance of Sixmile Creek 

 as a rearing stream for young trout. Relatively high percentages of 

 the populations of California, Seymour and, to a lesser extent. Deep 

 Creek were concentrated at Age III and older fish. In Seymour and Deep 

 Creeks, populations of Age I and II fish were also relatively high but, 

 in California Creek, only 13 percent of the population was estimated 

 at age I. Again, the apparent low numbers of young fish may be due to 

 unfavorable conditions in water quality or habitat. 



The cutthroat trout population of Willow Creek was heavily shifted 

 toward older fish. This may be a result of competitive factors from 

 the large brook trout population. It is also possible that the study 

 section was located in an area of marginal cutthroat habitat and that 

 larger and more balanced populations exist in other portions of the 

 stream. Likely areas for expanded cutthroat populations would probably 

 be upstream of the study section nearer the headwaters of Willow Creek. 



Brook trout length at age provided a rough index of growth and a 

 basis for comparing Mount Haggin streams. Mean lengths of the different 

 age classes of Mount Haggin brook trout indicated that growth is fairly 

 slow. Comparable data from Prickley Pear Creek, Montana, shows that 

 age II brook trout averaged almost two inches longer than those in Mount 

 Haggin streams (Bishop, 1951) while age II brook trout in Blacktail Creek, 

 Montana, averaged about three inches longer than those from Mount Haggin 

 (Wipperman, 1966). The slov/er growth rates of the Mount Haggin brook 

 trout may be due to harsh climatic conditions associated with higher ele- 

 vations and the severe winters that typify the upper Big Hole basin or may 

 be due to large concentrations of trout in waters of relatively low 

 productivity or a combination of these factors. 



Brook trout growth was generally fairly similar among the Mount 

 Haggin streams. Growth appeared to most rapid in streams that exhibited 

 a high degree of chemical enrichment e.g. Slaughterhouse and Sevenmile 

 Creeks. Growth was slowest in streams that supported extremely high 

 brook trout populations e.g. Sullivan and Willow Creeks. This effect 

 became more pronounced as the fish increased in age. 



e) Recreational Fishing 



The Mount Haggin streams offer an excellent fishery for "pan sized" 

 brook trout and limited opportunities to catch rainbow trout, cutthroat 



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