Commercial Fisheries News - March 2001

Runoff threatens nursery areas

The Lobster Conservancy ’s monitoring program quantifies numbers of lobsters by monitoring 26 critical nursery grounds along the Gulf of Maine shoreline from Manomet,MA to Isle au Haut,ME.

I began this work at one location nine years ago because no one else had elucidated quantitatively what comprises these vital lobster habitats or how they are used by juvenile lobsters.

By tagging individual lobsters and sampling monthly on a year-round basis,I discovered that some juvenile lobsters are settling and spending the first four years of their lives in the most vulnerable habitat available — the lower intertidal zone,which is the part of the sea floor that is exposed twice a day at the time of low tide.

These areas are attractive to lobsters because they serve as natural refuges from predators and are locations where food is available in great abundance. Although the lower intertidal zone is not the only habitat used by juvenile lobsters, it is the most vulnerable due to its proximity to human activities.

Until recently,scientists did not know that the lobsters were using this habitat. Now that we know they are,it is our responsibility to protect critical lobster nursery habitats. We should be particularly concerned about contaminants found in stormwater runoff because larval, postlarval, juvenile, and adult lobsters — including females with eggs — are all found in shallow waters adjacent to the coastline. A brief summary of the lobster life cycle can help explain the effects of these contaminants since a lobster ’s sensitivity to toxins varies according to its life history stage.

Lobster embryos are carried externally in eggs attached to the underside of the female’s abdomen.Female lobsters brood their eggs for an estimated 9-12 months before they hatch as first stage larvae. Lobsters spend three planktonic larval stages and a postlarval stage inhabiting lower intertidal zone surface waters. These surface-dwelling lobsters are directly exposed to surface sheen from runoff.

During the postlarval stage,lobsters settle to the sea floor where they continue to molt and grow throughout their lives. As bottom dwellers,these lobsters are also exposed to runoff in the form of both emulsified solutions and surface sheens that contaminate and suffocate the sediments and biota when they are deposited at low tide.

Contamination of our coastal waters bode poorly for the lobster fishery. Postlarval and juvenile lobsters are present year-round at locations where contaminants associated with stormwater runoff will reach them unless the contaminants are contained and treated before being allowed to enter our coastal waters.

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