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    Growing concerns about the preservation of exploited marine species has lead to the inclusion
of "essential habitat" considerations in recent Federal legislation included in the Sustainable
Fisheries Act. This has caused some confusion about what essential habitat is and how it can be
effectively managed. Essential habitats need to be, defined for each managed species to be useful.
Without such definitions, anywhere an organism is found or could be found might qualify as an
essential habitat. We believe that it might be useful to prioritize the importance of specific habitats
so management actions for their protection can be applied "surgically". Specifically we note that
specific phases during the life history of lobsters require specific habitats and such linkages have a
disproportionately great impact on lobster populations. In our view such habitats should be given
priority for protection and considered as "essentia1 habitats".

    Below we will define our terms, articulate the logic of our conclusion and suggest a means of
proceeding while science continues to fill gaps in our understanding about the biology of this
species..

    "Habitat" is where an organism lives. "Essential habitats" are places that have a
disproportionately great impact on an organisms abundance during some critical phase in their life
cycle. A "critical phase" for an organism is the period in its life when it is most susceptible to
mortality or, for other reasons (e.g., spawning), has a disproportionately great influence on
population size. For many marine organisms this period occurs at the time of settlement as they
make the transition from their planktonic (floating) larval life to bottom-dwelling life (Doherty and
Fowler 1994). The duration of this critical phase, however, can vary and may not exist for some
species (i.e., there may be no developmental change in vulnerability as some organisms mature,
especially very small organisms).

    Some organisms require a specific habitat at a critical phase in their life. Such habitats are
generally called "essential". The linkage between a species and a specific habitat may functionally
control the carrying capacity of the environment for that species. For lobsters, there is considerable
research suggesting habitats supporting broodstock lobsters and those that serve as nursery
grounds are most essential. We hasten to add that this does not mean that habitats where juvenile
lobsters grow are unimportant, only that we know of no studies that show population declines (that
is lobsters die) when juvenile habitats are lost.

    Broodstock habitats include spawning areas and habitats lobsters use while their eggs develop
externally on their abdomen. Rough handling during this phase can cause spontaneous abortion.
Broodstock lobsters are most abundant in deep water and off shore locations especially in the
winter but their exact habitats are unknown. In some locations, gravid females are known to migrate
to shallow water during the summer (Campbell 1986) but the generality ofthis phenomena is not
yet known.

    Lobsters select specific nursery grounds for settlement and studies have shown that their
survivorship is greater in nursery grounds having specific architectural characteristics (Hudon and
Lamarche, 1989; Wahle and Steneck 1991, 1992, Wahle 1992). All known nursery grounds (i.e.,
microhabitats where post-settlement survival is high) for lobsters contain small shelter providing
spaces. In areas around Cape Cod, vegetation root mats have been shown to harbor newly settled
lobsters. In many regions throughout coastal New England, cobble-stones contain the greatest
densities of newly settled lobsters (Wahle and Steneck 1991, Cobb and Wahle 1994, Incze et al.
1997, Palma et al 1998). Newly settled lobsters remain near their settlement site for the first several
years, rarely venturing out of the nursery habitat. They probably sustain themselves during this
phase by feeding on plankton drifting by and through their micro-shelters (Lavalli and Barshaw
1989) as well as benthic organisms found in the immediate vicinity of their shelters. Recent studies
have shown that lobster settlement is largely limited to water shallower than 20 in (Wilson and
Steneck in prep). Moreover, cobbles and boulders comprise only about one-eighth of the shore of
the Gulf of Maine, and an even smaller fraction in deeper waters or along shores to the south
(Kelley 1987, Wilson and Steneck in prep.). These shallow, densely populated lobster nurseries
should be priority essential habitats for protection.

    While broodstock and nursery habitats are priority "essential habitats" for lobsters, there are
other potentially important phases for which we know too little. Because lobsters need habitat for
spawning and nursery grounds to be safe from predators, we suggest those refugia are the most
important "essential habitats".

    We offer our thoughts to indicate how we weigh the importance of specific habitats at specific
life history phases of lobsters. We do this fully realizing these issues are not black and white.
Perhaps by prioritizing habitats as we have, we may give the clearest guidance currently possible for
management action. Our collective opinion reflects the current state of the science but it is not, and
should not be the final word.. If we follow a framework for protecting regionally sign)ficant
habitats (Steneck 1995, Langton et al 1996), we must be prepared to test the assumptions we have
put forward and to periodically reconsider them as prescribed in the practice of adaptive
management

Literature Cited:

Campbell, A. 1986. Migratory movements of ovigerous lobsters, Homarus americanus, tagged off
Grand Manan, eastern Canada. Can. J. Fish. Aquat, Sci. 43: 2197 - 2205.

Cobb, S., Wahle, R. 1994. Early life history and recruitment processes of clawed lobsters.
Crustaceana 67: 1 - 25.

Doherty, P., and Fowler, T. 1994. An empirical test of recruitment limitation in a coral reef fish.
1994. Science. 263: 935 - 939.

Hudon, C., Lamarche, G. 1989. Niche segregation between American lobster, Homarus
americanus and rock crab Cancer irroratus. Mar. Ecol. Prog. Ser. 52: 155 - 168.

Incze, L. S., Wahle, R. A. and Cobb, J. S. 1997. Quantitative relationships between postlarval
production and benthic recruitment in lobsters, Homarus americanus. Mar. Freshwater Res. 48:
729 - 743.

Kelley, J. 1987. Sedimentary environments along Maine's estuarine coastline. In: FitzGerald, D. M.,

Rosen, P. S. (eds) A treatise on glaciated coasts. Academic Press, New York, p. 151 176.

Langton, R., R. Steneck, V. Gotceitas, F. Juanes, P. Lawton. 1996 The interface between fisheries
Research and habitat management. North American Journal of Fisheries Management. 16: 1 - 7.

Langton, R., R. Steneck, V. Gotceitas, F. Juanes, P. Lawton. 1996. The interface between fisheries
research and habitat management. North American Journal of Fisheries Management. 16: 1 - 7.

Lavalli, K. L., Barshaw, D. E. 1989. Post-larval American lobsters (Homarus americanus) living in
burrows may be suspension feeding. Mar. Behav. Physiol. 15: 255 - 264.

Palma, A. T., Wahle, R. A. and Steneck, R. S. 1998. Different early post-settlement strategies
between American lobsters (Homarus americanus) and rock crabs (Cancer irroratus) in the
Gulf of Maine. Mar. Ecol. Prog. Set. 162.215 - 225.

Steneck, R. S. 1995 A framework for protecting regionally sign)ficant habitats: environmental
science considerations. Pages 147 - 152 in Proceedings Nationa1 Research Council Symposium:
Improving the Interaction between Environmental Management and Coastal Ocean Sciences.
National Academy Press. Washington, D. C.

Steneck, R. S., Langton, R. W., Juanes, F., Gotceitas, V. and Lawton, P. 1997 The interface between
fisheries research and habitat management: Response to comment. North American Journal of
Fisheries Management. 17: 596-598.

Wahle, R. A. 1992. Substratum constraints on body size and the behavioral scope of shelter use in
the American lobster. J. Exp. Mar. Biol. Ecol. 159: 59 - 75.

Wah1e, R. A. and R. S. Steneck. 1991 Recruitment habitats and nursery grounds of the American
lobster (Homarus americanus Milne Edwards): A demographic bottleneck? Marine Ecology
Progress Series. 69: 231 243.

Wahle, R. A. and R. S. Steneck. 1992. Habitat restrictions in early benthic life: experiments on
habitat selection and in situ predation with the American lobster. Journal of Experimenta1 Marine
Biology and Ecology. 157: 91 - 114.