Question

15. Young rainbow trout were sampled along a river to study the population and determine if recreational fishing or other factors might be affecting the size of the population.

A. In the first year of the study, researchers estimated the size of the population. They performed the first stage of their analysis after breeding season had ended. The first week, 92 trout were captured and marked. In a second round of capture one week later, 108 trout were captured; of these, 12 were marked. Estimate the size of the population based on these data. Round your anwer to the nearest whole number.

15B. In the second year of the study, researchers estimated the per capita population growth rate at -0.15. Based on this value, what is the size of the population in the second year of the study? Round your answer to the nearest whole number.

15C. Identify two factors that could have caused the population to change in this way, and briefly explain how each factor could result in this change in 1-2 sentences (each).

Answer 1

15A) If a proportion of the population was marked in some way, returned to the original population and then after complete mixing, a second sample was taken the proprtion of marked individuals in the second sample would be the same as marked initially in the total population, i.e.

here, R=12, M=92, T=108

therefore,

N= 828.

HENCE, the size of population is 828 trouts.

15B) the per capita population growth rate= -0.15

therefore, the growth of population = growth rate* size of population, i.e

-0.15*828=-124

now, the new size of population= 828+(-124)=704.

15C) The two factors causimg this population change are;

a)Overexploitation of the river :- This may be due to the increased recreational fishing, as the rainbow trout is an ideal fish for stocking.

b)Decline in the prey availability;- The reduction in the amount of prey could lead to increase in competition of survival. This in turn causes a decline of the population.