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Thermal acclimation for lobsters transferred from 14.5 °C. to 23.0 °C. is complete in 22 days. Substantial acclimation to low salinity and to low oxygen occurs within one week. Lethal levels of these three factors are not altered by differences in size within the range 16–34 cm., by difference in the areas where lobsters were caught, or by starvation for up to 57 days. Moulting lobsters are less resistant to high temperature, low salinity and low oxygen conditions than hard-shelled lobsters.Upper lethal temperature levels and lower lethal salinity and oxygen levels were investigated for hard-shelled lobsters acclimated to each of the 27 combinations of three levels of temperature (5, 15 and 25 °C.), salinity (20, 25 and 30‰), and oxygen (2.9, 4.3 and 6.4 mg./l.). The upper lethal temperature is raised by an increase in thermal acclimation, and is lowered by a decrease in the salinity and oxygen acclimation levels. The lower lethal salinity is raised by an increase in the level of thermal acclimation and a decrease in the level of oxygen acclimation. It is lowered by acclimation to reduced salinity. The effect of salinity acclimation is not always the same, but depends on the temperature acclimation. The lower lethal oxygen is raised by either an increase in the temperature acclimation level of a decrease in the salinity acclimation.The lower lethal temperature is 1.8 °C. for 17° acclimated lobsters, and 5.0° for 27.5° acclimated lobsters.Ultimate and maximum or minimum lethal levels of temperature, salinity and oxygen—the highest and lowest lethal levels that can be attained by acclimation—were interpolated from the results. These measures were used to integrate the lethal levels of the three factors into a single three-dimensional graph which describes the boundary of lethal conditions for lobsters exposed to the three factors operating together (Fig. 7).

The activity (walking rate) of lobsters acclimated to various temperatures increased fronr 2 to 10"C. and from 20 to 25"C. but was constant between 10 and 20'C. Lobsters acclimated to low temperatures were most active above the acclimation temperature, Those acclimated to intermediate and high temperatures were most active at the acclimation temperatures. Experimental ffshing of a relatively constant stock sholved that the catch per 100 standard trap hauls (index of catchability) was linearly related to temperature. Slope of line is, however, dependent on stock density. Catchability is shown to be proportional to activity minus a constant. This relationship permits use of catch per unit efiort and accumulated catch data to estimate lobster populations. 1315

Hemolymph samples drawn from 2035 lobsters captured in five areas off the Canadian Atlantic coast were individually tested for the bacterium Gaffkya homari, using a qualitative, presumptive test, followed by a confirmatory procedure. Ninety-six lobsters, or almost 5% of the total, were confirmed as being infected. The approximate range of G. homari incidence was from 2 to 40% indicating that G. homari is resident in the natural lobster population of this region. Evidence suggested that a high natural incidence can lead to an epizootic among stored, captive lobsters. The possibility that an infection source exists in addition to the G. homari strains resident in the lobster population is discussed.

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