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The Casco Bay Bulletin

"Improving and protecting the health of Casco Bay"

Winter 2000

Searching for Lobster Nursery Grounds

Who doesn't love a mystery? Our volunteers may soon be doing some sleuthing to help solve a long-standing enigma: Where do baby lobsters live?

Only within the last decade have scientists reported finding the smallest bottom-dwelling lobsters in sheltered habitats such as cobble bottom, eelgrass beds, and mud burrows. No one ever expected to find these inch-long crustaceans in the rough and tumble environment of rocky tidepools where pounding waves and drying sun deter all but the hardiest marine organisms.

Diane Cowan assembles PVC pipes to construct a transect grid.

Diane uses calipers to measure a baby lobster.

Dr. Diane Cowan, the founder of The Lobster Conservancy, was the first scientist to document that newly-settled baby lobsters also live under loose rocks just above the low tide mark along the rocky shore. A long-term study of one cove on Orr's Island that she began eight years ago has now grown into a comprehensive program of 43 volunteers monitoring lobster nursery grounds at 25 intertidal sites in Maine and New Hampshire.

Lobster Conservancy volunteers record the size, sex, molt stage, and incidence of injury to any resident lobsters they find and describe the bottom type and any other animals and plants in the study area. Diane believes FOCB's skilled Citizen Stewards could be a great help in discovering and monitoring critical lobster nursery habitats in other parts of Casco Bay.

Diane Cowan has had a lifelong passion for the little critters ever since she researched lobsters for a science report in the seventh grade. She discovered that lobsters monitor their environment primarily through their senses of smell and taste, making them extremely sensitive—and vulnerable—to pollutants like oil spills. In her junior high paper she predicted the demise of many lobsters as a result of a catastrophic spill. Her interest in lobsters and their chemical sensibility eventually earned her a doctorate in the Boston University Marine Program at Woods Hole.

After completing her graduate studies, she returned to Maine searching for a suitable place to continue her crustacean research. She visited Lowell's Cove at the end of Orr's Island in Harpswell, and with the help of some neighborhood kids, discovered dozens of tiny lobsters hiding under the rocks.

The Perfect Home
Diane is hoping FOCB can help her locate other potential lobster nurseries in Casco Bay with the same attributes as Lowell's Cove:

A good-sized inlet with a shallow-sloping shoreline and rock ledges may help to protect tiny tidal inhabitants from wave action.
Yet facing the open ocean
A south-trending cove that faces open water would collect lobster larvae washing in from offshore. Diane says currents and southwest winds have a big impact in determining where little lobsters will settle down.
Protrudes into the Bay
Peninsulas and rocky outcroppings are often the first places that baby lobsters reach and then they tend to stay there. Diane found that seemingly suitable sites further up the bays did not harbor baby lobsters. Strewn with loose rocks Little lobsters hide under loose rocks by day and roam about at night.
Absence of extreme conditions
Diane says baby lobsters seem to prefer open coves where the water rarely freezes and the salinity doesn't drop precipitously as a result of spring runoff or heavy rains.

Diane is now in her eighth year of data collecting at Lowell's Cove. Although now a Marine Policy Fellow at Woods Hole Oceanographic Institution in Massachusetts, Diane returns to her study site several days each month to continue her sampling. She hunts for lobsters under rocks along a 20-meter line spread over the rocks. Like her volunteers, she counts and measures baby lobsters. In eight years of monitoring, Diane has only missed one month's data, December, 1994, when storm after storm kept the cove submerged all month.

Lobster Infancy

A lobster starts life as an egg no larger than the head of a pin glued to its mother's abdomen. What hatches ten months later looks more like an insect than a lobster. Feathery hairs on its legs keep the larval lobster suspended in the water for the first month or so after hatching, drifting aimlessly as zooplankton. Sometimes it bumps into something smaller that it can devour. If it encounters any sea creature bigger than itself (which is most of them) it will be eaten. Of the 10,000 eggs an average-size lobster may carry, only about 10 offspring will survive beyond their first four weeks of life.

After a larval lobster has molted four times, it loses its feathery appendages and its two front claws become heavy enough to drag it to the bottom of the ocean. At the diameter of a penny, this newly bottom-dwelling lobster is a miniature version of its adult self. It may bob up and down in the water column for a while until it settles down for good. As Diane Cowan has discovered, its first home may be a rocky tidepool.

Understanding the habitat requirements and abundance of baby lobster like these may eventually enable us to predict the size of future harvests.

Diane tags any baby lobsters longer than about 1.5 inches. Using a modified hypodermic needle, she inserts a coded wire tag the size of a pepper flake between the pinchers of one of the baby lobster's walking legs. Scientists in England demonstrated that this type of tag persists in lobsters into adulthood, whereas most other kinds of tags are lost after one or two molts.

Each month she checks for lobsters she had tagged previously. A lobster outfitted with one of her magnetic tags elicits a loud beep from a portable metal detector that Diane brings into the field with her. She then removes the leg, extracts the tag, and scrutinizes it under a microscope in order to decipher the bar code imprinted on it. After tagg1ng more than 9,000 lobsters since 1994 (an impressive sample size for any species!), Diane has decided to stop tagging and concentrate on documenting returns to Lowell's Cove.

Implications for the Future
Once Friends of Casco Bay secures funding to cover training, equipment, and program oversight, we will join forces with The Lobster Conservancy to expand the lobster nursery monitoring effort. As Diane learned in the seventh grade, lobsters are affected by the chemistry of the sea water. In polluted water, lobsters may not be able to function properly to find food, shelter, or mates. The fate of infant lobsters depends on documenting and safeguarding water quality, one reason our water quality monitoring efforts and the work of The Lobster Conservancy complement each other so well.

Besides, who can resist the appeal of a tiny lobster the length of your thumb? By helping to identify and protect their first hiding places, we can help ensure that Maine's most popular crustaceans grow to take their place in the ecosystem, in their breeding population, and in Maine's coastal economy.

©2003 The Lobster Conservancy.
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