Question

A marine biologist randomly selected and placed radio tracking devices on 50 dolphins swimming in the Gulf of Mexico in 2020. He released the dolphins back into the population. A year later he caught 200 dolphins and found that 20 of them had tracking devices on them. What is the best estimate of the population of dolphins swimming in the Gulf of Mexico?

Answer 1

The best estimate of the population of dolphins swimming in the Gulf of Mexico is around 400 individuals, based on the mark and recapture method. This method involves randomly selecting and marking a sample of dolphins and then releasing them back into the population. By counting the number of marked dolphins in a subsequent sample, an estimation of the total population can be made. However, there are limitations and potential bias to this method, and other techniques can also be used to estimate population size and health.

Step-by-step explanation:

The best estimate of the population of dolphins swimming in the Gulf of Mexico can be determined using the mark and recapture method. In this case, the marine biologist randomly selected and marked 50 dolphins with radio tracking devices in 2020 and released them back into the population. A year later, the biologist caught 200 dolphins and found that 20 of them had tracking devices. By using the mark and recapture equation, we can estimate that the population of dolphins in the Gulf of Mexico is around 400 individuals.

This method assumes that the larger the population, the lower the percentage of marked organisms that will be recaptured since they will have mixed with more unmarked individuals. However, there are limitations to this method, such as potential bias or errors caused by sampling methods. Other techniques, like electronic tracking or data from commercial fishing and trapping operations, can also be used to estimate population size and health.

By combining the mark and recapture method with additional techniques, marine biologists can gain a better understanding of dolphin populations and their distribution patterns in the Gulf of Mexico.

Answer 2

Step-by-step explanation:

"The capture-recapture of individually distinctive signature whistles has not been attempted before," says the paper's senior author Dr Tess Gridley, Co-Director of Sea Search and the Namibian Dolphin Project and a postdoctoral fellow in the Department of Botany and Zoology at SU. "The dolphins use these sounds throughout life and each has its own unique whistle. Therefore, by recording signature whistles over time and in different places we can calculate where animals are moving to and how many animals there are in a population."

Working with Dr Simon Elwen of Stellenbosch University, the Namibian Dolphin Project has been researching Namibia's resident bottlenose dolphins for the past 12 years, and built up a catalogue of more than 55 signature whistles dating back to 2009.

This particular study was led by Emma Longden, who began the project during her BSc (Hons) Marine Biology degree at the University of Plymouth. As an undergraduate, Emma completed an internship with the Namibia Dolphin Project for a month in 2016, and returned again in 2018 to complete work on the mark-recapture project.

She analysed more than 4000 hours of acoustic data from four hydrophones positioned along the coast south and north of Walvis Bay, Namibia, during the first six months of 2016.

All in all, they identified 204 acoustic encounters, 50 of which contained signature whistle types. From these encounters, 53 signature whistle types were identified; 40 were in an existing catalogue developed in 2014 for the Walvis Bay bottlenose dolphin population, and 13 were newly identified. Of the 53 signature whistle types identified, 43% were captured only once, whereas the majority (57%) were recaptured twice or more.

"One of the great things about bioacoustics is that you can leave a hydrophone in the water for weeks at a time and collect so much data without interfering with the lives of the animals you are studying," says Emma, whose work on the project was also supervised by Dr Clare Embling, Associate Professor of Marine Ecology at the University of Plymouth.

Dr Embling added: "This work is incredibly important as it allows us to track and count the number of dolphins in small vulnerable populations. It builds on our previous research looking at the impacts of noise on marine organisms and monitoring vulnerable marine mammal populations. It also showcases the fantastic level of research that our marine biology students are able to achieve, and the opportunities available to them through our partnerships with conservation organisations such as the Namibia Dolphin Project and the Ocean Giants Trust."

Future research includes the work undertaken by PhD student Sasha Dines from Stellenbosch University to further refine the technique to better understand the population of endangered humpback dolphins in South Africa. Another PhD student, Jack Fearey from the University of Cape Town, is continuing to conduct research along the Namibian Coast.