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Scientists See Early Indications Of Lobster Decline

January 23, 2001
University Of Maine
A team of scientists from the University of Maine and the Bigelow Laboratory for Ocean Sciences has found early indications of a decline in the lobster population in the Gulf of Maine.

ORONO, Maine -- A team of scientists from the University of Maine and the Bigelow Laboratory for Ocean Sciences in West Boothbay Harbor, Maine, has found early indications of a decline in the lobster population in the Gulf of Maine.

"The abundance of juvenile lobsters in key lobster producing regions of mid-coast Maine appears to be declining," say Robert Steneck of the UMaine School of Marine Sciences and Lew Incze and Richard Wahle of Bigelow. "We expect landings in those regions and possibly elsewhere to decline sometime during the next two to four years. Given that lobsters are the single most valuable species in Maine’s fisheries, we think it is important to alert the lobster industry, state managers, policy makers and the general public to our findings."

Preliminary estimates suggest that the decline in Penobscot Bay alone may be on the order of 40%.

For more than a decade, Steneck, Incze and Wahle have been working to develop a means of predicting lobster abundance and landings. Their approach differs from those traditionally used in Maine and New England by independently monitoring three different lobster life stages: 1) larvae in the water, 2) newly settled individuals on the bottom, and 3) older juvenile lobsters.

Their research has measured linkages between each of these three successive stages. Larval lobsters in coastal zones dive to become the new year-class of lobsters on the bottom, and if these lobsters survive, they become juvenile lobsters and eventually future landings of adult lobsters. "It's similar to counting the number of seeds you sow in your garden and finding that they correspond to some reduced number of seedlings and eventually the plants you harvest," says Steneck.

"Predicting lobster abundances or landings is no easier than predicting the economy or the weather. While local lobster landings may generally reflect local lobster abundance, measuring abundance is fraught with uncertainty. We can never be sure that we ‘know’ the abundance of any phase in a lobster's life. However, by going to the same locations and using the same methods over many years, we can detect trends."

Since any single measure of abundance may be flawed, Steneck, Incze and Wahle used a different means of detection to monitor the abundance of each stage. Taking a census of different developmental stages in juvenile lobster populations over time is similar to monitoring the total number of students in elementary schools as an indicator of future high school class sizes. If significant changes occur in the abundance of lobster larvae, those changes should immediately translate to changes in that year-class on the bottom. A couple of years later, changes should be evident in the older juvenile lobsters as well.

Since 1995, the scientists found, newly settled lobsters on the bottom have been declining in the Boothbay monitoring region. Similar trends were detected in larvae in New Hampshire and new settlers in Rhode Island. The larvae and settlement studies suggest widespread declines at least west of Penobscot Bay. No larval monitoring has been done east of there.

Censuses of juvenile lobsters that are two to four years old (two to five years prior to harvest) have been conducted statewide at nearly 40 sites from York to Jonesport. "Most troubling is the consistent decline since 1997 of juvenile lobsters from eastern Muscongus Bay, throughout Penobscot Bay and Hancock County," says Steneck. "This broad swath includes Maine's most-productive lobster-producing regions. While not all of our indicators at all of our study regions are consistent, there is enough consistency for us to announce that signals of a widespread decline in landings are now evident."

The scientists note that many lobstermen will quickly point out that they have seen more egg-bearing lobsters over the past decade than ever before. The scientists agree with those observations. In fact, in the most recent lobster stock assessment, there is evidence that the reproductive potential of lobster stocks is currently high.

The scientists say, however, that the decrease in larval lobsters and year-classes on the bottom must be the result of other factors, possibly changes in the ocean environment itself which could affect survival or delivery of the larval stages to the ocean bottom.

"Just as we cannot explain the dramatic increase in lobster abundances and landings over the past two decades throughout the Northeast, from Delaware to Newfoundland, Canada, we cannot explain the pending decline," says Steneck. "Further, larvae and young-of-the-year lobsters in Rhode Island and Maine are showing similar patterns of change despite being located in two oceanographically and reproductively distinct systems separated by Cape Cod. Thus the environmental factors responsible appear to be very wide-spread."

The scientists suggest that the lobster industry and state agency managers need to develop a response to this trend. "As scientists, we feel it’s important to alert the public and stakeholders. No one has prior experience with the type of data we have. So we can’t be sure how closely the harvest will follow our findings. However, if the patterns we see turn out to be accurate predictors of declining harvest and are primarily controlled by the environment, then some traditional management actions, such as increasing egg production, may do little or nothing to reverse the situation."

"Nevertheless, steps should be taken to preserve existing broodstock. Certainly, a decline in lobster stocks, given the large fishing capacity that exists, could threaten the reproductive potential of the stock and reduce chances of recovery," says Steneck. "If lobster landings are to decline, it might be a good idea to wait before making large new financial commitments. Nature may still have more surprises for us, and this trend could turn around. However, this is an excellent time for industry and managers to discuss the most appropriate actions so that the stocks and the fishermen both survive the fluctuations inherent in nature."

This is the first scientific prediction ever made for the future population size of the American lobster. The same method has been used successfully to predict the abundances of the western Australia rock lobster, says Steneck, with a 90% success rate over the past 20 years.

Story Source:

The above story is based on materials provided by University Of Maine. Note: Materials may be edited for content and length.

Cite This Page:

University Of Maine. "Scientists See Early Indications Of Lobster Decline." ScienceDaily. ScienceDaily, 23 January 2001. <www.sciencedaily.com/releases/2001/01/010122120547.htm>.
University Of Maine. (2001, January 23). Scientists See Early Indications Of Lobster Decline. ScienceDaily. Retrieved September 22, 2014 from www.sciencedaily.com/releases/2001/01/010122120547.htm
University Of Maine. "Scientists See Early Indications Of Lobster Decline." ScienceDaily. www.sciencedaily.com/releases/2001/01/010122120547.htm (accessed September 22, 2014).

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