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To estimate the population in a rookery, 4965 fur seal pups were captured and tagged in early August. In late August. 900 fur seal pups were captured. Of these, 218 had been tagged. Based on these figures, estimate the population of fur seal pups in the rookery. [Source: Chapman and Johnson, "Estimation of Fur Seal Pup Populations by Randomized Sampling." Transactions of the American Fisheries Society. 97 (July 1968\(), 264-270 .\)

Short Answer

Expert verified
The estimated population of the rookery is approximately 20,453 fur seal pups.

Step by step solution

01

Understanding Capture-Recapture Method

This problem uses the capture-recapture method to estimate the population size. In this method, a sample of individuals from a population is captured, marked, and then released. After some time, another sample is captured, and the number of marked individuals in this second sample is noted. The ratio of the total number of individuals in the first sample (marked) to the total captures in the second sample should be approximately equal to the ratio of the number of marked individuals recaptured in the second sample to the entire population, assuming that the marked individuals have had enough time to mix back into the population.
02

Set Up the Proportion

Set up a proportion using the capture-recapture data. Let N be the total pup population.
03

Solve for N

The proportion from the capture-recapture data can be written as:\[ \frac{\text{initially tagged}}{\text{total population}} = \frac{\text{tagged in second sample}}{\text{total in second sample}} \]. Substituting in the given numbers gives us:\[ \frac{4965}{N} = \frac{218}{900} \]. Now solve for N by cross-multiplying and dividing.
04

Calculate the Estimated Population

After solving for N, we get the estimation of the fur seal pup population in the rookery.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Population Estimation
Understanding how many individuals are in a certain area is crucial for effective wildlife management and conservation efforts. The capture-recapture method provides a practical approach to estimating animal populations when it is infeasible to count each individual.

In the case of the fur seal pups, population estimation allows researchers to monitor trends, assess the impact of environmental changes, and implement measures to protect the species. The underlying idea is to capture a sample of the population, tag the individuals, and release them. After some time, a second sample is captured, including both tagged and untagged individuals. The ratio of tagged individuals in the second sample serves as a basis for estimating the total population.

For effective population management, this estimation method needs to be both accurate and ethical, ensuring minimal disruption to the wildlife.
Wildlife Management
Wildlife management involves the balancing act of protecting natural habitats while also addressing the needs of human populations. The estimation of animal numbers using techniques like capture-recapture plays a significant role in this domain.

In managing the fur seal pup population, decisions about protective regulations, hunting quotas, and habitat conservation can be informed by accurate population figures. The data gained through the capture-recapture method aids in creating sustainable management strategies that can help in preserving species and ecosystems for future generations.

Wildlife biologists and conservationists strive to use population data to predict potential threats, plan recovery efforts for endangered species, and track the success of conservation programs.
Mathematical Modelling
The capture-recapture method is a great example of mathematical modeling in ecology. Mathematical models utilize mathematical language to describe real-world scenarios, allowing scientists to make predictions and understand complex systems.

For population estimation, the model employs simple ratios and proportions to infer the total population size from a smaller, more manageable set of data. This approach involves assumptions, such as equal probability of capture for all individuals and no influence of tagging on individual behavior.

In our fur seal pup example, the model presumes a closed population with no significant births, deaths, immigrations, or emigrations between the two sampling events. When the model's assumptions hold true, it can provide reliable estimates that are instrumental in further ecological studies and policy-making.
Statistical Sampling
Statistical sampling is core to the science of statistics, dealing with techniques for collecting and analyzing a subset of data to infer conclusions about the larger population. The capture-recapture method is a specialized form of sampling used in ecological studies.

The initial tagging session represents the first sample. From this, we gain insight into a fraction of the total population. The second sample yields the number of previously tagged individuals recaptured. This data is crucial, as it helps in establishing a relationship between the known sample size and the unknown total population.

By applying statistical sampling principles within the context of capture-recapture, researchers can reduce the cost and logistical difficulties of counting every individual. Moreover, this method allows for a degree of statistical confidence in the population estimates, which is essential when the data informs conservation decisions.

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Most popular questions from this chapter

Darroch's method. is a method for estimating the size of a population using multiple (more than two) captures. For example, suppose that there are four captures of sizes \(n_{1}, n_{2}, n_{3},\) and \(n_{4},\) respectively, and let \(M\) be the total number of distinct individuals caught in the four captures (i.e., an individual that is captured in more than one capture is counted only once). Darroch's method gives the estimate for \(N\) as the unique solution of the equation \(\left(1-\frac{M}{N}\right)=\left(1-\frac{n_{1}}{N}\right)\left(1-\frac{n_{2}}{N}\right)\left(1-\frac{n_{3}}{N}\right)\left(1-\frac{n_{4}}{N}\right) .\) (a) Suppose that we are estimating the size of a population of fish in a pond using four separate captures. The sizes of the captures are \(n_{1}=30, n_{2}=15, n_{3}=22\), and \(n_{4}=45 .\) The number of distinct fish caught is \(M=75 .\) Estimate the size of the population using Darroch's formula. (b) Show that with just two captures Darroch's method gives the same answer as the capture-recapture method.

One implicit assumption when using the capture-recapture method to estimate the size of a population is that the capture process is truly random, with all individuals having the same likelihood of being captured. Sometimes that is not true, and some populations have a large number of individuals that are "trap-happy" individuals (more prone to capture than others, more likely to take the bait, less cagey, slower, dumber, etc.). If that were the case, would the capture-recapture method be likely to underestimate or overestimate the size of the population? Explain your answer.

A large jar contains an unknown number of red gumballs and 150 green gumballs. As part of a seventh-grade class project the teacher asks Carlos to estimate the total number of gumballs in the jar using a sample. Carlos draws a sample of 50 gumballs, of which 19 are red and 31 are green. Use Carlos' sample to estimate the number of gumballs in the jar.

Name the sampling method that best describes each situation. Choose your answer from the following (A) simple random sampling, (B) convenience sampling, (C) quota sampling, (D) stratified sampling, (E) census. (a) George wants to know how the rest of the class did on the last quiz. He peeks at the scores of a few students sitting right next to him. Based on what he sees, he concludes that nobody did very well. (b) Eureka High School has 400 freshmen, 300 sophomores, 300 juniors, and 200 seniors. The student newspaper conducts a poll asking students if the football coach should be fired. The student newspaper randomly selects 20 freshmen, 15 sophomores, 15 juniors, and 10 seniors for the poll. (c) For the last football game of the season, the coach chooses the three captains by putting the names of all the players in a hat and drawing three names. (Maybe that's why they are trying to fire him!) (d) For the last football game of the season, the coach chooses the three captains by putting the names of all the seniors in a hat and drawing three names.

Informal surveys. In everyday life we are constantly involved in activities that can be described as informal surveys, often without even realizing it. Here are some examples. (i) Al gets up in the morning and wants to know what kind of day it is going to be, so he peeks out the window. He doesn't see any dark clouds, so he figures it's not going to rain. (ii) Betty takes a sip from a cup of coffee and burns her lips. She concludes that the coffee is too hot and decides to add a tad of cold water to it. (iii) Carla got her first Math 101 exam back with a C grade on it. The students sitting on each side of her also received C grades. She concludes that the entire Math 101 class received a C on the first exam. For each of the preceding examples, (a) describe the population. (b) discuss whether the sample is random or not. (c) discuss the validity of the conclusions drawn. (There is no right or wrong answer to this question, but you should be able to make a reasonable case for your position.)

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