Question
To estimate the population size of crabs in a certain lagoon, traps were laid at random. 400 crabs were caught, marked and released back into the lagoon. Four days later, traps were laid again and crabs were caught. Out of the 374 crabs, 80 were found to be marked.
(a) calculate the population size of the crabs in the lagoon using the formula below
N = (n x M) ÷m
Where N = Total population of crabs in the lagoon
n = Total number of crabs in the second catch
M = Number of marked crabs during the first
m= Number of marked crabs in the second catch
(b) State two assumptions that were made during the investigation
(c) What is the name given to this method of estimating the population size
(a) calculate the population size of the crabs in the lagoon using the formula below
N = (n x M) ÷m
Where N = Total population of crabs in the lagoon
n = Total number of crabs in the second catch
M = Number of marked crabs during the first
m= Number of marked crabs in the second catch
(b) State two assumptions that were made during the investigation
(c) What is the name given to this method of estimating the population size
Answer
a) (3374 x 400) ÷ 80 = 1870;
b)
1. released crabs mixed freely and evenly with the remaining population
2. No movement in and out of regions/ no migration
3. Marked crabs have enough time to mix with others
4. No death of study crabs after first catch
5. The mark does not alter the crabs' behavior or frighten other crabs
c) Capture-recapture method/capture-release-recapture method;
b)
1. released crabs mixed freely and evenly with the remaining population
2. No movement in and out of regions/ no migration
3. Marked crabs have enough time to mix with others
4. No death of study crabs after first catch
5. The mark does not alter the crabs' behavior or frighten other crabs
c) Capture-recapture method/capture-release-recapture method;
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