WLF 448: Fish & Wildlife Population Ecology 2004

REMOVAL METHODS

A.  Change-in-Ratio

• Can be inexpensive (i.e., use hunters or fishers to "collect" all the data)

• Animals can be categorized into 2 groups (e.g., males and females, adults and juveniles, or 2 species) and removals are selective (i.e., more of one group is removed from the population than the other group)

• Need an estimate of the proportion in each group before and after removal

• Population must be closed during the removal season

    Example: 2 groups x and y

B.  Catch-Effort Methods

• The population is closed

• Probability of each individual being caught is constant throughout the experiment

• All individulas have the same probability of being caught in sample i.

Idea:

    Catch/Effort = Catchability * Population Size

** If population is closed then Population Size at time t = Initial Population Size - Cumulative # removed

We can estimate N₀ and 1/K by regressing y_i and x_i

Example:  Blue Crabs (From Fischler 1965)