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To Live or Die? ... That Is The Question.

This marvelous Earth we call home provides us with everything we need to live, with just one exception. Our sun provides energy to fuel the food chains on which we depend and to keep Earth from freezing. Only a very small amount of matter comes to Earth, and an even smaller amount leaves Earth permanently. Thinking of Earth in this way allows us to see it as a closed set of ecosystems and biomes that scientists call the biosphere.

With fantastic tolerance for changes in both abiotic and biotic factors, Earth's systems stay amazingly stable over long periods of time. Viewing this apparent stability in Earth's biosphere, one might think that everything, both living and nonliving, could remain forever. Why is it, then, that species go extinct? Today humans have a major impact on living things in areas where we choose to live. We have many choices to make regarding the value of wild lands versus lands that are managed for human use. While it is true that human activity can cause the extinction of species, we are not the only influence that can do so.

Throughout Earth's history species have evolved and then disappeared, leaving evidence of their existence in the fossil record. Curious scientists have studied and theorized about the reasons why species have become extinct.

 
In order to understand large-scale extinction, you need to study the factors that govern the survival of organisms. This activity will provide you with a chance to do just that.
 
The following is information about the Bluefin Tuna, which can live up to 30 years, reach a length of ten feet, weigh 1,500 pounds, and sell for up to 100,000 dollars.
 

Bluefin Tuna Facts

Basic Information:
Giant Bluefin tuna is the largest living specie of tuna, the largest bony fish in the world, and considered by many to be the strongest. Their torpedo-shaped bodies and ability to retract their pectoral fins and eyes enable them to move through the water with reduced friction, reaching up to 25 mph in short spurts. Bluefin can migrate through up to 5,000 miles of open ocean, dive to depths below 3,000 feet and swim the length of the entire sea in search of food and mates— in just 50days!

Where do you find bluefin tuna:
Bluefin tuna have been found in all of the world's oceans. Two decades ago the channels that separate the Adriatic Islands were brimming with giant Bluefin tuna, a specie so plentiful that tourists used to climb ladders by the sea to watch the schools swim by. In the western Atlantic, their range has extended from Labrador to Brazil; in the eastern Atlantic, from the Lofoten Islands off Norway to northwestern Africa. In the eastern Pacific, Bluefin tuna have been known to have migrated as far north as the Gulf of Alaska. Generally they have been found in the waters off Baja California and southern California. In the western Pacific, depending on the time of year, they have been found in concentrations around Japan and the northern Philippines.

A Valuable Commodity:
Just one these animals can net from $5,000 to $60,000 at the dock, although typical prices in the late 1990's range from $3-$12 per pound. Fishermen used to use rod and reel, or hand-thrown harpoon, or purse seine techniques to catch the fish. Much of the Med’s tuna is no longer caught by traditional means. High-tech “tuna ranches” began appearing in the late ‘90s and have proliferated over the past decade. Fish Farms consisting of circular floating cages about 50 m in diameter and 50 m deep, set up 2-3 km from shore. The ranches are most often controlled not by small European operators but by large multinational corporations. In the cages, tuna fatten up on smaller fish, often for months at a time, before they are slaughtered and shipped off to Japan. The Market for nearly 80% of the bluefin catch.

Problem:
Believed by many to be fast becoming a depleted resource, Bluefin tuna have been at the center of a heated debate. The International Council for the Conservation of Atlantic Tuna (ICCAT), the body responsible for glob tuna regulation, has been recommending increasingly stringent fishing limits. According to ICCAT, the Bluefin population has declined by more than 70-80% during the last 20 years. The tuna population in the Mediterranean is nearing extinction, a new World Wildlife Fund report concludes, with catches down 80 percent over the past few years. Because of pollution and intensive fishing there is a complete collapse of the tuna population.

With tuna prices going as high as $45 dollars a pound in Tokyo, European trawlers fish for tuna aggressively and illegally, far exceeding international quotas meant to protect the species. It is difficult for the relatively poor fisherman to compete in tuna fishing because hunting the species now requires long trips and expensive technology. High tech boats use sonar and airplane spotters to find schools in the remaining tuna grounds off Cyprus, Egypt and Libya. Now even small juvenile tuna, captured in open seas, can be brought to the vast underwater cages that line the Croatian coast, where they are fed for months or years until they are ready for market. The huge, three-a-day feedings on the fish farms put pressure on local fish stocks, since the food is often bought from local fishermen, and the waste produced in the aftermath of the meals also leads to pollution.

What is going on here? Let’s find out.

Why is the population declining? Biologist from around the world have been tracking the migration and spawning areas since 1996. Scientists catch and tag the Bluefin tuna with electronic tagging devices, then use computers to follow the tuna from the Atlantic Coast of New England to as far north as Norway and as far south as Brazil.

 

Let’s Tag a Few Fish.

 

Procedure:

  1. Construct a large map of your school or campus and mount it on the wall of your room.
  2. Different hours/periods will be different species of Bluefin tuna in this activity. Each class will have a different color and track that color.
  3. You will need a data log.
  4. The “Bluefin tuna” must track their movements for one full day.
  5. Every student will record sightings of the tagged individuals and write down the length, or duration, and location of the sightings.
  6. When your class next meets, you will compile all the sightings on the map.
  7. Compare the sightings made by your class with the log kept by the tagged individual.
 

Analysis:

  1. How accurate was your tracking effort at defining the places visited by the person being tracked?
  2. How could you improve the accuracy of your tracking?
  3. Students observed the subject in a limited area. Is this an accurate reflection of the area where he or she might move about in a day? A week? A month?
  4. Is the Bluefin tuna in trouble? Why or why not?
  5. How could you create a win/win situation for the tuna and the people that love to eat the tuna?
  6. What are the factors that are contributing to the declining Bluefin tuna population?
 

Extension:

  1. Research the tuna’s migration paths and plot them on a world map.
  2. Write a persuasive paper representing your opinion of the Bluefin tuna problem.
  3. Write a one-page report, double spaced, 12 point font, 1” margins, about the effects of temperature on alligator eggs or the effect of salinity of the Dead Sea on the organisms that live there.
 
Visit Pioneer Libraryand search e-Media for the video "Ecosystems: Organisms and their Environment"
 
Review science lab safety rules here.

Get the plug-ins: Get Adobe Acrobat Reader and Get Quicktime Player. (The QuickTime plug-in is needed to play sounds and movies correctly.)

Want to share photos of you or your friends doing this activity? Send it in an e-mail with the following information:

  1. The title of the activity
  2. The URL (Internet address)
  3. Your name.

Remember that no pictures can be used that show student faces or student names on it. 

Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE Earth Systems Science core.

 


Updated October 24, 2008 by: Glen Westbroek

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