Are There Differences in Growth and Condition between Mobile and Resident Cutthroat Trout?

—There is evidence that actively moving salmonids are of lower condition than the general population, and they are sometimes regarded as inferior to resident fish. However, little information exists on the permanence of this attribute. We used mark–recapture and two-way traps to determine whether there are differences in the condition and growth of mobile and resident Bonneville cutthroat trout Oncorhynchus clarki utah in Beaver Creek, Idaho. Actively moving fish were significantly larger than the general population, and the largest of these mobile fish were in significantly lower condition for a given size. However, mobile fish that were marked and recaptured a year later had regained condition equivalent to that of the general population upon their recapture, and the largest mobile fish had significantly greater condition than fish of equal length in the general population. In contrast, there was no relationship between growth rate and the total distance moved during the 1-year period. These results suggest that the lower condition of actively moving fish does not have permanent effects on future condition or growth in stream-resident cutthroat trout. Much attention has recently focused on the rediscovery of mobility in stream-dwelling trout (Gowan et al. 1994; Rodriguez 2002). Whereas much work has reported on the timing and magnitude of movement, the attributes of mobile and resident fish have received little attention. Recent work has suggested that mobile salmonids have lower condition than the general population (Naslund et al. 1993; Gowan and Fausch 1996). Because many stream-dwelling trout establish territories for feeding (Chapman 1966; Jenkins 1969; Grant et al. 1989), mobility in nonmigratory populations may be a response to an energetic deficit or difficulty in procuring profitable areas for feed* Corresponding author: [email protected] Received January 28, 2003; accepted December 1, 2003 ing (Heggenes 1988; Nakano 1995) and should result in reduced growth and condition. Alternatively, mobile individuals could move for reasons not related to competitive ability but to exploit seasonally or spatially patchy food resources and thus experience greater growth and condition. Our objective was to determine whether the degree of mobility in individuals is associated with differences in growth or condition relative to the general population and whether any differences are transient or long term. Given the findings mentioned above, we predicted that actively moving fish would have lower condition than resident fish and that this would result in lower overall growth of mobile fish recaptured a year later. To test these predictions, we compared the condition of the general population of Bonneville cutthroat trout Oncorhynchus clarki utah with that of mobile fish and analyzed the growth rates and condition of mobile and resident fish recaptured 1 year after marking.