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The following column was written by research scientist Lew Incze of the Bigelow Laboratory for Ocean Sciences. He describes studies of lobster life stages being done by himself, research scientist Rick Wahle, also of the Bigelow Laboratory for Ocean Sciences, and Professor Bob Steneck, University of Maine School of Marine Sciences.
Incze submitted this column to Commercial Fisheries News following the publication of a press release based on the same monitoring work. That earlier statement pointed to the decline in newly settled lobsters in the Boothbay, ME monitoring area and the troubling decline in juvenile lobsters from eastern Muscongus Bay and throughout Penobscot Bay and Hancock County as signals of a pending widespread decline in landings. Editor
Making predictions in the marine environment is difficult. It's important for everyone to understand what we know and what its limitations are.
Since 1989, several studies led by myself, Rick Wahle, and Bob Steneck have sought to understand the natural forces influencing the abundance and distribution of lobsters along the coast of Maine. My interests focus on oceanographic processes and the small, swimming planktonic stages (called larvae and postlarvae); Rick has concentrated on the settlers (young-of-year); and Bob has studied the pre-recruit benthic (bottom-living) stages.
Because of the nature of scientific funding, we have usually been funded separately or in pairs to work on various pieces of the puzzle, often not in the same place. In addition to our shorter-term projects and experiments, we have managed to maintain over the past 12 years several time-series sites where we have monitored the abundance of various life stages of lobsters.
We convinced our funders early on that these data sets would one day provide new and useful insights into the life of lobsters and, by extension, into the dynamics of the adult population that supports the fishery.
Time-series results
Let me concentrate just on the time-series results, that is, data from areas where we have yearly observations over a number of years and can observe trends.
In coastal waters off the power plant in Seabrook, NH, I have 12 years of plankton sampling data for lobster postlarvae (weekly samples from June-September beginning in 1989, thanks to the power plant operators and Normandeau Associates, who have made the data available to me) .
I have similar data for the Boothbay/Pemaquid region for seven years, and in just the past two years I have extensive samples from Penobscot Bay.
Rick has 12 years of young-of-year (settler) data from Boothbay/ Pemaquid (beginning 1989). Bob has many years of settler and pre-recruit surveys, including the past four years (1997-2000) at a regular suite of sites along much of the Maine coast.
Note that there is some spatial overlap between these data sets, but also a lot of geographic spread in the samples.
Through a series of analyses and experiments that I won't detail here, we can demonstrate that the general abundance of the various stages follow logically from the planktonic postlarvae to settlers, and from settlers to pre-recruit size.
The relationships in our data are good, but not perfect. Moreover, we have not yet established the quantitative linkage between the early stage abundance and the fishery. We think we're close, but we're not there yet.
This caveat is important, as I will show below.
Life stages decline
The postlarvae from Seabrook, the settlers from the Boothbay region, and the pre-recruits from the Boothbay/Pemaquid region to Mount Desert Island all show declines in recent years.
For postlarvae and settlers, this began in 1995; for pre-recruits in the broad region centered on Penobscot Bay, this shows up in the past one to two years (pre-recruits are older, so the time delay in the signal is expected). The plankton and settler data from Penobscot Bay the past two years (1999-2000) are low just like the values found farther to the west. This is lower than I would expect for this area, but we have no prior Pen Bay data for comparison.
Anyone who looks at these data (and they've been presented at numerous public meetings) has the same information and limitations that we have: one can't deny the downward slope, but no one knows exactly how this will scale out to the fishery.
This is because our scientific data aren't so extensive that we "know" the over-all abundance of any of these stages: we have several key sites where we have been studying processes and we are sure of the trends in our measurements.
The rest is a bit of an experiment in which we will be learning just like everyone else, but we think our warning is only fair and responsible. (Just think of the alternative, in which we would say nothing until we see whether or not a downturn materializes!)
Fishery consequence
I would not attempt to predict the percent decline at this time; we simply do not have the observational history to do this.
The number that recently found its way into some of the news articles (40%) originated in a telephone/radio interview in which Bob Steneck referred to the approximate change in abundance of pre-recruits in his Penobscot Bay data.
But there are too many factors that can influence the exact number in the samples, so this cannot be regarded as a hard and fast prediction of the future. We should be paying more attention to the relative changes rather than the absolute values until we gain more experience with this.
Neither is this a time for complacency, however. Our data, the only advanced information we have, suggest a sizable decline. Whether this returns us to more historically average conditions or some other level of harvest, we have yet to discover.
Some serious discussion is warranted, though, because change in abundance will require adjustment on the part of the fishery.
Planktonic stages at risk
Our data indicate that the changes we are seeing presently are being set during planktonic life. All indications point to ample egg production, so how can this be?
The fact is, most larvae do not survive to adult stage, which is why lobsters and most marine organisms produce thousands of eggs when ultimately (on average) you only need two adult (reproductive) survivors per female to keep the population going at a steady rate.
The planktonic stages of lobsters require 30 or more days to develop at Maine temperatures, so modest changes in the rate of survival, compounded every day, can result in large changes in the number of postlarvae available to settle.
Where they end up also is important, so there are a number of natural forces that could contribute to changes in larval supply and initial settlement to the bottom nursery areas.
Most natural processes are beyond our control and so our studying them may appear a bit esoteric, but it would be undeniably useful to know whether future changes in the fishery are due to nature or manmade causes.
For more information of the lobster settlement work, contact Lew Incze at the Bigelow Laboratory for Ocean Sciences in West Boothbay Harbor, ME; call (207) 633-9500 or fax (207) 633-9641.
