Keewenaw Bay (Lake Superior) Lake Trout

Use catch curve methods to estimate mortality of a population of Lake Superior Lake Trout.
Catch Curve

Derek H. Ogle


Mar 8, 2019


Feb 13, 2023

The population biology of Lake Superior Lake Trout (Salvelinus namaycush) prior to 1950 was examined in detail by Sakagawa and Pycha (1971). In Table 1 of their paper, they presented the number of Lake Trout by age (from scales) collected in 4.5-inch mesh gillnets that were set between the Keweenaw Peninsula and Munising, MI in 1948. The numbers of Lake Trout caught for ages 3 to 14 were 5, 18, 21, 10, 45, 109, 95, 63, 42, 25, 13, and 4. Use these data to answer the questions below.

  1. Is this an example of a cross-sectional or longitudinal catch curve?
  2. Plot log(catch) versus age. Which ages best represent the descending portion of the catch curve? Explain.
  3. Using the unweighted regression method, find the following (with 95% confidence intervals):
    1. Instantaneous total mortality rate.
    2. Annual total mortality rate.
    3. Annual survival rate.
  4. Repeat the previous question using the weighted regression method.
  5. Repeat the previous question using the Chapman-Robson method.
  6. Mathematically show how to convert the instantaneous mortality rate to an annual mortality rate.


Solution Code:

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Sakagawa, G. T., and R. L. Pycha. 1971. Population biology of Lake Trout (Salvelinus namaycush) of Lake Superior before 1950. Journal of the Fisheries Research Board of Canada 28:65–71.