Catch-Effort Methods

Definition of initial variables:

N = population size

n_i = catch at sample i

f_i = effort expended on sample i

Then, n_i / f_i = K * N_i

where, K is a constant related to catchability

---

We must assume a closed population. If it is closed and we define:

x_i = cumulative catch prior to sample i

x_i = sum (n_j) , where j = sample 1 through sample i - 1

Then population size at the time of the sample will be:

N_i = N₀ - x_i

Therefore:

n_i / f_i = K (N₀ - x_i)

---

Now if we call:

n_i / f_i = y_i

Then we can rearrange our formula as the equation for a line:

y_i = K N - K x_i

So we can estimate K as the slope of a regression equation, and:

^{^}N = mean (x) + [mean (y) / ^{^}K]

Return to Lecture Notes IV. Estimation of Population Parameters - I.

Updated 29 July 1996