6
Population estimate using Mark-Recapture Technique.
Estimating Population Size
Objective: You will be expected to estimate the size of a sample population using the mark-recapture technique. Be able to apply the technique to new population problems and compare the mark and recapture technique to other methods of population estimating.
1. You are in charge of a team given the responsibility to determine the number of invasive blue-stripe snapper in Kaneohe Bay. Discuss with your partner how would you accomplish this task and describe in detail below.
Background
In a survey conducted by Hawaii’s Fish and Game Division, scientists found that herbivorous fish, which at the time were considered “a useless end in the food chain”, dominated Hawaiian coastal waters. To increase recreational and commercial food fishing opportunities in Hawaii and to fill a perceived vacant ecological niche, they imported the blue-stripe snapper (Lutjanus kasmira). These fish originated from the Marquesas Islands and were released into Hawaiian waters in 1958, and again from Moorea in the Society Islands in 1961. However, local fishermen did not favor this fish, which in turn fetched a low market price. Thus, its population grew rapidly. This species is an aggressive, voracious carnivore. It will eat crustaceans, cephalopods, and other fish species. It out-competes less aggressive, native fish for food and its population needs to be monitored.
Kaneohe Bay
Kaneohe Bay stretches from the Mokapu Peninsula, where the U.S. Marine Corps is based, all the way to Mokolii Island, also known as Chinaman’s Hat This vast stretch of water contains five small islands, including the HIMB’s Coconut Island. In the middle of the bay are a few sandbanks, just a couple of feet deep, as well as numerous patch reefs. The bay is about 13 km long by 4 km wide, with an average depth of about 8 m.
· What is Kaneohe Bay’s volume in m3? (Volume is calculated by length x width x depth; don’t forget to convert to meters; 1 km = 1000m)
· How many gallons is this? (1 cubic meter = 264.1 gallons)
Technique 1: Sampling
A technique called sampling is sometimes used to estimate population size. In this procedure, the organisms in a few small areas are counted and projected to the entire area. For instance, if a biologist counts 10 squirrels living in a 200 square foot area, she could predict that there are 100 squirrels living in a 2000 square foot area.
2. A biologist collected 1 gallon of pond water and counted 50 paramecium. Based on the sampling technique, how many paramecium could be found in the pond if the pond were 1,000 gallons?
3. What are some problems with this technique? What could affect its accuracy?
Technique 2 - Mark and Recapture
DATA
Trial Number / Number Captured / Number Recaptured with mark1
2
3
4
5
6
7
8
9
10
Total:
In this procedure, biologists use traps to capture the animals alive and mark them in some way. The animals are returned unharmed to their environment. Over a long time period, the animals from the population are continued to be trapped and data is taken on how many are captured with tags. A mathematical formula is then used to estimate population size.
Procedure:
· You will receive a bag that represents your population (beans, pennies, chips, beads)
· Capture 10 “animals” by removing them randomly from the bag.
· Place a mark on them using tape or string
· Return the 10 marked “animals” to the container
· With your eyes closed, grab a handful of the population. This is the recapture step. Record the number of “animals” recaptured in total and the number that have a mark on them on the data table
· Return the “animals” to the bag and repeat. Do 10 recaptures.
· When the ten recaptures are completed, enter the totals on the data table
4. Calculations = Find your Population Estimate
Estimated Size ______
5. Use the code-name on your bag to check with the instructor about how many “animals” are really in your population.
Analysis
6. Compare the actual size to the estimated size. Did you overestimate or underestimate?
7. Continue the experiment by filling out the data table.
Recalculate your estimate using the formula. (Show below)
a. Is the second estimate closer than the first one? ______
b. To get the most accurate results, you would generally do [ more / less ] trials . (circle)
11
12
13
14
15
16
17
18
19
20
Total: / (add original data + new data) / (add original data + new data)
8. Pearl and Hermes Atoll is one of the furthest islands out in the Northwest Hawaiian Island chain. It is primarily underwater with numerous islets, which are rising and subsiding above or below sea level. The total land area is only 85 acres, and the reef area of over 200,000 acres is the second largest among atolls in Papahanaumokuakea. The fringing reef encloses a lagoon that measures more than forty miles in circumference, and opens to the West with an amazing variety and abundance of reef habitats. Pearl and Hermes has a diverse assemblage of coral, which make for an exclusive habitat for fish and invertebrates. This area is also a breeding and feeding area for monk seals, and a nesting site for green sea turtles and sea birds. Sharks are also part of the natural marine ecosystem and are an apex predator. Without apex predators, the fish that they feed on would become overpopulated and throw the whole system out of balance. Herbivores might eat too much algae, and coral eaters might eat too much reef. A healthy system is one in which all components are balanced: predators, herbivores, decomposers, and producers. What is so intriguing about the apex predator populations in the NWHI is that this is a healthy, natural ecosystem. However, tiger and Galapagos sharks, in particular, prey on the endangered monk seal. Monk seal populations are currently estimated at 1,200 throughout all the islands. They are declining by four percent every year, with the exception on the main islands, where they are thriving. In a 2007 count, scientists estimated that there were 154 monk seals at Pearl & Hermes.
CALCULATE:
Given the following data, what would be the estimated size of a tiger shark population in Pearl & Hermes Atoll?
To ascertain the population size scientists mark and recapture sharks. This involves capturing sharks on a line baited with tuna. The sharks are then equipped with a small ultrasonic pinger, and then released. The transmitters can reveal directional movement and depth.
A biologist originally marked 10 sharks in coastal waters adjacent to Pearl & Hermes atoll. Over a month long period, biologists caught 25 sharks. Of those 25, 6 were found to have tags. Based on this information, what is the estimated population size of the sharks in Pearl & Hermes? SHOW WORK.
ANSWER THE FOLLOWING:
In order to protect the monk seal populations, scientists have begun a shark culling operation. Do you think this will help to reduce predation on the monk seal? Please elaborate. What other factors affect monk seal populations? Review articles on my website for further information. (type and turn in next lab)
Instructor Notes: Use toys to create your bags. The equations and lab works best if bags contain 30-100 objects.