Question

Researchers from the Freshwater Institute are studying fish communities in Lake Winnipeg, which has an area of 2375 000 ha. They caught and tagged 172 rainbow smelt in the top 30 % of the lake. Five days later, they recaptured 162 fish in the same area and found that 18 were tagged. (12.1) ku fil

(a) Estimate the population size.
(b) Rainbow smelt are a newly introduced species and are not native to Lake Winnipeg. They occupy the same areas of the lake as a native yellow perch species, and they tend to be more aggressive. Suggest two limiting factors for yellow perch that are illustrated by this situation. Decide whether each limiting factor is density-dependent or density-independent.

Answer 1

(a) To estimate the population size, we can set up a proportion using the number of tagged fish in the recaptured sample.

162 fish were recaptured, and 18 of them were tagged.

So, if we assume that the proportion of tagged fish in the recaptured sample represents the proportion of tagged fish in the entire population, we can set up the following proportion:

18 tagged fish / 162 recaptured fish = x tagged fish / total population size

Solving for x, the estimated population size would be:

x = (18 tagged fish / 162 recaptured fish) * total population size

We know that the recaptured sample represents the top 30% of the lake, so we need to adjust the estimated population size accordingly.

(b) Two limiting factors for yellow perch that are illustrated by this situation could be competition for resources and predation by the more aggressive rainbow smelt.

1. Competition for resources: Both yellow perch and rainbow smelt occupy the same areas of the lake and may compete for food and habitat. This limiting factor is density-dependent, as the intensity of competition increases as the population density of both species increases.

2. Predation by rainbow smelt: The more aggressive rainbow smelt may prey on yellow perch, limiting their population size. This limiting factor is also density-dependent, as the predation pressure increases with higher population densities of rainbow smelt.

It's important to note that these are just suggested limiting factors and their classification as density-dependent or density-independent may vary depending on specific ecological dynamics and interactions in Lake Winnipeg.