Have you ever wondered where lobsters go when they leave their homes? Lobsters like all animals have to go find food, avoid scary predators, and make it home safely each day. What makes this particularly difficult to study is the fact that lobsters are nocturnal (active at night). That means while we're asleep in our beds, these lobsters are just waking up to go exploring. So how do marine biologists study the behavior of lobsters at night?
One way is to use acoustic tags. The small transmitter attached to the back of the lobster above sends out a signal a regular intervals (every 90 seconds). With the proper receivers set in the water, it is possible to track the movements of a tagged lobster without even being there. Here's how it works...
First, you need a set of acoustic tag receivers. Think of these as small radio receivers that operate on batteries and are water-tight. Here we have 10 radio receivers mounted in stands and ready to be placed underwater. Once in the water the receivers can keep track of many different lobsters at the same time.
Our experiment relies on the expertise of our friend and senior research biologist Dr. Rodney Bertelsen of the Florida Fish and Wildlife Research Institute. Dr. Rod is an expert at tracking marine animals using acoustic tags. He usually tracks the big adult lobsters out along the coral reef, but for this experiment, he is helping us to track our juvenile lobsters in Florida Bay.
The first step is careful placement of the receivers in a pattern on the ocean floor. On our study site this is shallow water, only about 2 meters deep and the receivers are placed about 20 meters apart. Dr. Mike drives the boat very carefully checking his GPS to find the exact spot for Dr. Rod to release the receiver.
Next, it is time to catch some juvenile lobsters to participate in our experiment. Here Dr. Mike dives down with a hand net to collect a juvenile lobster. The water is a little murky today because the wind has mixed up the sediment making it hard to see very far. A total of three lobsters are collected and returned to the boat.
Dr. Rod carefully attaches the acoustic tag to the shell of the lobster using Super Glue. This sounds painful (and should not be tried at home) but it is harmless to the lobster because their shell is hard. The glue will keep the tag attached for a week or two until the lobster has its next molt. Then as the lobster crawls out of its old skin it will leave the tag behind. Dr. Rod also places a bright yellow tag on the base of the antennae. Can you see the yellow tag in the picture? This helps the divers to recognize a tagged lobster once released.
Now the time has come to release the tagged lobster. Dr. Mike carefully swims the animal back to the same shelter where it was collected. It is not known if lobsters keep the same shelter night after night, but we hope to find out from this experiment. By the end of the day we release three tagged lobsters known by their tag colors as RY, LY, and YY.
Here is lobster RY in his home shelter, an concrete block. This is where he was released on Day 0. We note this on a map printed on waterproof paper. We carry this map on a clipboard underwater each day when we search for our tagged lobsters.
Meanwhile, our acoustic receivers are listening for the 'ping' of each acoustic tag. When a 'ping' is heard it is recorded along with the time of day. Later when we recover the receivers and download the data to a computer, we will know which receivers heard from each lobster. As the lobsters move around, they will only be received by the closest receivers. That way we can estimate their location at all hours of the day and night.
Today is Day 5 and we checked on the location of the lobsters on Days 2 and 4. Lobster RY was found in a hole about 2 meters from it's original release point on both Days 2 & 4. Lobster YY was found 1 meter from it's release point on Day 2 and then 8 meters away on Day 4. Lobster LY was not found on either Day 2 or Day 4, but that doesn't mean its left the site. We'll have to wait until we check the data from the receivers to know if and when it left the area. Check back soon to see what happened to our tagged lobsters.
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