Plump Cutthroat Trout and Thin Rainbow Trout in a Lentic Ecosystem

Plump Cutthroat Trout and Thin Rainbow Trout in a Lentic Ecosystem

Joshua Courtney, Jessica Abbott, Kerri Schmidt, Michael Courtney
(Submitted on 17 Oct 2012)

Background: Much has been written about introduced rainbow trout (Oncorhynchus mykiss) interbreeding and outcompeting cutthroat trout (Oncorhynchus clarkii). However, the specific mechanisms by which rainbow trout and their hybrids outcompete cutthroat trout have not been thoroughly explored, and the published data is limited to lotic ecosystems. Materials and Methods: Samples of rainbow trout and cutthroat trout were obtained from a lentic ecosystem by angling. The total length and weight of each fish was measured and the relative weight of each fish was computed (Anderson R.O., Neumann R.M. 1996. Length, Weight, and Associated Structural Indices, Pp. 447-481. In: Murphy B.E. and Willis D.W. (eds.) Fisheries Techniques, second edition. American Fisheries Society.), along with the mean and uncertainty in the mean for each species. Data from an independent source (K.D. Carlander, 1969. Handbook of Freshwater Fishery Biology, Volume One, Iowa University Press, Ames.) was also used to generate mean weight-length curves, as well as 25th and 75th percentile curves for each species to allow further comparison. Results: The mean relative weight of the rainbow trout was 72.5 (+/- 2.1); whereas, the mean relative weight of the cutthroat trout was 101.0 (+/- 4.9). The rainbow trout were thin; 80% weighed below the 25th percentile. The cutthroat trout were plump; 86% weighed above the 75th percentile, and 29% were above the heaviest recorded specimens at a given length in the Carlander (1969) data set. Conclusion: This data casts doubt on the hypothesis that rainbow trout are strong food competitors with cutthroat trout in lentic ecosystems. On the contrary, in the lake under study, the cutthroat trout seem to be outcompeting rainbow trout for the available food.

2 thoughts on “Plump Cutthroat Trout and Thin Rainbow Trout in a Lentic Ecosystem

  1. Joe, you compare it well. Thank you for the clarification about the difference between the Cutthroat Trout and Thin Rainbow Trout. I am not familiar with Cutthroat trout before but I am really acquainted with the Rainbow Trout. In fact it is one of my very favorite fish. I love catching Rainbow Fish. The first time I saw Rainbow fish was when I am fishing in the Pawleys Island fishing charter. At first I thought I saw a real rainbow. I am really proud I read your post it adds to my knowledge.

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