Seasonal and sexual differences in the thermal preferences and movements of American lobsters

Thermal preferences of lobsters (Homarus americanus) were determined in the laboratory and compared with seasonal movements and distribution of lobsters in the Great Bay Estuary, New Hampshire. Lobsters preferred 11.0 ± 0.6 °C, or 2.8 ± 0.7 °C warmer than ambient temperature, during the colder months of the year. However, during the warmer months they selected 15.7 ± 0.4 °C, which was 0.2 ± 0.4 °C warmer than the ambient temperature. Overall, the lobsters tested had a final preferred temperature of 15.9 °C, and males selected warmer temperatures than females. Catch per unit effort was highest at sites where temperatures were similar to the temperatures lobsters preferred in the laboratory studies and lowest at sites ≥18 °C or <12 °C. Significantly more males than females were captured in areas with temperatures >16 °C. Lobsters tagged, and subsequently recaptured within 7–35 days, moved relatively little when released into areas where temperatures were similar to their preferred temperatures. Thermal preferences may influence the movement of lobsters in thermally heterogeneous habitats, and climate change is expected to have a major impact on lobster distribution, especially in estuarine and coastal habitats.

The influence of energetic requirements on the preferred temperature of overwintering juvenile Atlantic salmon (Salmo salar)

We used a horizontal temperature gradient to investigate the effect of alternate life history strategies and nutritional state on the preferred temperature of overwintering juvenile Atlantic salmon (Salmo salar L.). Contrary to our prediction, there was no significant difference in final preferred temperature between juvenile Atlantic salmon that will migrate to sea the following spring (early migrants) and those that show reduced growth and delay migration for at least another year (delayed migrants). Both migrant groups preferentially selected relatively low temperatures (<10°C), likely owing to their low appetite and growth rates. Food deprivation resulted in a significant increase, rather than our predicted decrease, in the final preferred temperature of the juvenile Atlantic salmon of approximately 2°C. We suggest that this is due to the need for an increased foraging effort to offset the projected energy deficit later in the winter. The final preferred temperature of delayed migrants increased from winter to spring, as predicted, coincident with increases in natural food availability and endogenous seasonal increases in appetite and growth rates. We conclude that the preferred temperature of overwintering juvenile Atlantic salmon may be influenced by future energetic requirements rather than the current level of energy reserves.

Temperature Preference and Avoidance Responses of the Crayfish, Orconectes obscurus, and Associated Statistical Problems

Acute temperature selection and avoidance responses of the crayfish, Orconectes obscurus, acclimated at field collection temperatures of 1.5–26.0 °C and determined in a spatial thermal gradient, were similar to those noted for fishes. Acclimation temperature was positively correlated with the acute preferred and avoided temperatures; both were several degrees higher than the acclimation temperature. A large proportion of the total variance in these data was unexplained. Most variable responses occurred at low acclimation temperatures. The estimated final preferred temperature ranged from 29.8 to 33.9 °C depending upon the method of calculation. Methods of estimating final preferenda from acute tests are considered arbitrary due to statistical problems and the associated high variability. Statistical problems were also noted in the determination of avoidance temperatures of crayfish due to nonindependence of observations on the same organism. No differences were noted (P < 0.05) between the preferred or avoided temperatures when the direction of field temperatures was rising or falling. A statistical comparison of the new and published data on this species revealed general similarities, particularly over an acclimation temperature range of 18.0–30.0 °C. The analysis minimizes the importance of site-specific studies on this species using the current acute testing methods.Key words: crayfish, temperature preference, avoidance, populational variation, statistics, experimental and statistical problems