Tracking the mysterious underwater migration of female lobsters

A marine biology researcher from the University of North Carolina is trying to figure out how far a female lobster will go to lay eggs.

Heather Koopman, senior scientist at the Grand Manan Whale and Seabird Research Station, has enlisted the help of Grand Manan fishermen to tag any female lobsters they catch and to report when they recapture one that's been tagged.

"Some … have gone nine or 10 nautical miles in the space of a little over a week," said Koopman.

"That's kind of a distance for an animal ... that size."

It's hoped the research will shed light on the range of the species and the health of the resource.

"I think our members are actually excited to see what's happening with them," said Bonnie Morse, Grand Manan Fishermen's Association project manager.

More than 200 lobsters had been tagged for the project by Tuesday. Koopman said the project hopes to reach the 1,000 mark in the next few weeks.

Last study was in the 1980s

A similar study was done 35 years ago, led by Department of Fisheries and Oceans biologist Allan Campbell.

The big question then was how lobsters divided their time year-round. 

It was thought females carrying eggs probably moved offshore in winter.

"The deeper you are, the more stable the temperature you're going to have," said Koopman.

Campbell and participating fishermen tagged and tracked about 2,000 lobsters for their study and found most of them stayed in the Bay of Fundy.

Although some went much farther. One travelled 320 kilometres down to the coast of Maine.

Campbell found that, generally, females released in summer would indeed migrate a ways offshore in fall and winter and then return the following spring and summer.

"Likely following temperature trends that they need to have while they're carrying their eggs around," said Koopman.

"Temperature is really important for lobsters."

Have migration patterns changed?

She wants to find out whether those migration patterns have changed since the 1980s, where female lobsters with fertilized eggs go in late winter and spring and just how far they go to find the temperatures they need.

"I'll be very curious to see if our fellow fishers on the Nova Scotia shore, down in the Maine coast happened to catch any of our females."

She's also interested in how often tagged lobsters will be recaptured in the same area.

The tags being used for the project are "not very sophisticated," said Koopman — just a little zip tie with a tracking number and a phone number.

"We just attach them loosely to one of the claws. 

"If anybody else happens to catch her, we just ask them to record the tag number and where they were and call it in."

Fishermen keen to take part

Fishermen have been keen to do their part, said Koopman.

"Every time they report in a tag number they kind of want to know where was that animal released and how far she's gone. … I think some of them are amazed at the fact they can travel a mile a day."

Morse has been following along on social media as fishermen post about their recaptures.

"I think they're really curious to see where the lobsters that are around Grand Manan in the fall — where they go from here and where they do end up."

Morse said it's exciting to see research going on in the Bay of Fundy and in particular on Grand Manan.

Southern fishery has collapsed

Anything that can be learned about the species is important, said Morse.

It may help make future decisions about fishery management.

It's possible that changing ocean temperatures are having an impact, said Koopman.

"We have seen some evidence further to the south of us, in the southern New England fishery, the lobster fishery down there has essentially collapsed and we suspect that's because temperatures are warming up there."

Water temperature in the Bay of Fundy has been measured throughout the year by a variety of means, said Koopman. 
And there has not been a "consistent march" to higher temperatures.

But there has been a lot of variability, she said.

Some years have been really warm. Some years have been colder. And the timing of the peaks and and valleys on the temperature chart has shifted around.

Temperature key to lobster life cycle

That could be playing havoc with lobster reproduction.

Female lobsters have a two-year reproductive cycle. 

For the first year, eggs develop internally.

In March and April of the first year the female needs cool water, said Koopman, in order for the eggs to develop properly before they are extruded.

"If she doesn't get that, then that's a problem for her eggs."

For the second year, the eggs are carried around on the female's underside until larvae hatch in late spring or early summer.

At that point, temperature is also key, she said. It affects the availability of plankton, which the baby lobsters eat.

Female lobsters likely seek cool water

Koopman said scientists suspect female lobsters can and do follow temperature.

"We know they're sensitive to temperature down to about 0.1 degree, so that's quite phenomenal."

Their movements may be influenced by water currents or odour plumes.

"We're not exactly sure how they navigate to where they're going but they definitely do seem to seek out temperatures that are ... critical to them being able to reproduce successfully."

Changing temperatures may already be having an impact that will only show up in the fishery seven years after the fact.

That's how long it takes for a lobster to grow to market size.

International fishery dispute

The study may also serve to alleviate tensions between U.S. and Canadian fishermen.

"I certainly don't think it's going to hurt it," said Morse.

They both fish in a disputed "grey zone" under different rules. 

Maine fishermen can fish year round. The Bay of Fundy regular season goes from the second Tuesday in November until the end of June.

"Certainly [the lobsters] don't recognize where that line is, so maybe this just gives us a little bit more concrete information about how the lobsters are moving through the Bay of Fundy and the Gulf of Maine."