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LOBSTER PREFERENCES

It is only within the last two decades that investigators have focused on lobster habitat preferences when given a choice between two or more similar and tolerable environments. This data combined with intensive biological research on energy requirements strongly suggests that lobster preferences are linked to optimum energy efficiency throughout the lobster's life cycle. This finding is of critical importance when considering lobster habitats because it means that given a choice, a lobster will almost always select a habitat which maximizes survivability, growth, and reproductive capability (see Crossin et al. 1998 and Jury et al. 1994a,b).

There is now a general consensus that the thermal preferences of lobsters represent the temperatures at which their metabolism is most efficient (As cited in Crossin et al. 1998 pg. 371). It has been shown that lobsters are capable of detecting changes in temperatures of less than 2⁰C or about 3.6⁰F. They also showed that lobsters acclimated to summer temperatures (15.5 ⁰C or approx. 60⁰F) "preferred a thermal niche [or range] of 16.5⁰C (61.7⁰F) and avoided water that was warmer than 19⁰C (66⁰F) or colder than 13⁰C (about 55⁰F)" (Crossin et al. 1998).

This temperature preference is not surprising since the "maximum growth of juveniles and adults occurs between 15⁰ and 20⁰C (59⁰-68⁰F) [in this range]Ö locomotion is independent of temperature Ö When standardized for acclimation temperature, lobsters preferred water 1.2 ⁰ (about 2⁰F) above their previous ambient temperature" (Crossin et al. 1998). In addition, most (62.5 %) summer acclimated lobsters left their shelters when water temperature was raised 8⁰C (about 14⁰F) to 23.5⁰C (74.3⁰F). When this experiment was repeated with lobsters acclimated to winter temperatures (4.3⁰C or 39.7⁰F) few left their shelters. In fact, 90% of the winter acclimated lobsters preferred heated shelters which were 5⁰C (about 9⁰F) above ambient temperature. Lobsters in the experiment seemed to avoid areas of the tank they perceived as too warm or too cold. Furthermore, "when a thermal gradient was established [on the bottom of the tank] the range of areas sampled narrowed considerably, and less overall exploration of the tank occurred" (Crossin et al. 1998).

Crossin and others speculated that lobsters which remain in certain habitats (e.g. estuaries) might eventually shift their temperature preference. They cite a laboratory experiment in which some lobsters after 12 days had very high thermal preferences between 26⁰ and 29⁰C (79⁰-84⁰F).

Among lobster larvae, temperature has little effect on survival within the range of 12⁰-18⁰C (54⁰-64⁰F) (Lawton and Lavalli 1995). This is generally consistent with the temperature range for peak occurrences (Fogarty 1983). Bottom water temperatures at peak larval densities were 8.5⁰-16.0⁰C (47.3 to about 61⁰F) in samples collected in northern New England and 12.8⁰-17⁰C (55⁰ to about 63⁰F) in southern areas.

Lobsters are highly sensitive to changes in salinity (see Jury et al. 1994a,b). Lobsters appear to be able to sense decreased salinity of 2 ppt (from 30 to 28 ppt). When given a choice between moving through high salinity (20-25 ppt) or low salinity (10-15 ppt) passageways, nearly 93 % of the time the lobsters chose the high salinity route. In avoidance experiments at ambient temperature of 12⁰-15⁰C (54⁰-59⁰F), some animals were remarkably hesitant to move out of their shelters even when the salinity temporarily reached toxic levels below 14 ppt (Scarratt and Raine 1967, McLeese 1956). On average though, lobsters began moving when salinityís reached a level of 18.4 ppt and definitely moved away from their shelters when levels approached 12.6 ppt. (Jury et al. 1994b).