K.C.S.E Biology Q & A - MODEL 1996PP1QN15

K.C.S.E Biology Q & A - MODEL 1996PP1QN15

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

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

ANSWERS

• (b) There was even distribution of  crabs;
• No movement  in and out  of regions; no migration;
• There was random distribution of errors after the first capture.
• (c) Capture/ recapture; capture release recapture.