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Many animals undertaking long-distance migrations use Earth's magnetic field as a 'map' to assess their position for orientation. This phenomenon been particularly well-studied in salmonids using 'magnetic displacement' experiments, in which animals are presented with magnetic field conditions that are characteristic of other geographic locations. However, whether use of magnetic map cues differs among populations of salmon has not been investigated. Here we show that nonanadromous and anadromous populations of Atlantic salmon (Salmo salar) raised under the same conditions within their native range differ in their response to magnetic displacements in the North Atlantic. The directions adopted by anadromous salmon juveniles to each of the magnetic displacements would support their migration from the eastern US to western Greenland, had the fish actually been at those locations. In contrast, nonanadromous salmon did not appear to respond to the magnetic displacements. The findings are consistent with the hypothesis that the innate magnetic map of anadromous salmon is adapted to guide their marine migration. De nombreux animaux qui effectuent des migrations sur de longues distances utilisent le champ magnetique de la Terre comme une << carte >> pour evaluer leur emplacement a des fins d'orientation. Ce phenomene est particulierement bien etudie chez les salmonides dans le cadre d'experiences de << deplacement magnetique >>, dans lesquelles des animaux sont exposes a des conditions de champ magnetique caracteristiques d'autres emplacements geographiques. La possibilite d'utilisations differentes de l'information tiree de cette carte magnetique d'une population de saumons a l'autre n'a toutefois pas ete etudiee. Nous demontrons que des populations non anadrome et anadrome de saumons atlantiques (Salmo salar) elevees dans les memes conditions dans leur aire de repartition indigene reagissent differemment a des deplacements magnetiques dans l'ocean Atlantique Nord. Les directions adoptees par les jeunes saumons anadromes pour chacun des deplacements magnetiques appuieraient leur migration de l'est des Etats-Unis a l'ouest du Groenland, si les poissons avaient bel et bien ete dans ces endroits. En comparaison, les saumons non anadromes ne semblent pas reagir aux deplacements magnetiques. Ces constatations concordent avec l'hypothese selon laquelle la carte magnetique innee des saumons anadromes est une adaptation servant a guider leur migration en mer. [Traduit par la Redaction], Introduction The movements of organisms play a critical role in the life histories of all species, and understanding the mechanisms that shape individual movements is essential to understanding most ecological [...]

The phenomenon of homing by salmonid fishes to natal sites for breeding is well established, but the chemicals in rivers that they learn as juveniles and identify as adults are not fully determined. Dissolved free amino acid (DFAA) profiles have been hypothesized to allow salmonids to distinguish their natal river from others nearby. To evaluate this hypothesis, we sampled DFAAs in spring and autumn (when juveniles learn and adults return, respectively) from 3 rivers in New England, USA, that support the landlocked Atlantic Salmon, Salmo salar Linnaeus, 1758. We used 3 approaches to determine the level of consistency between seasons and difference between rivers that would be needed for DFAA to support imprinting and subsequent homing for reproduction: hierarchical cluster analysis, statistical difference tests, and equivalence tests. DFAAs were not detected in the water column of the study rivers, but sediment porewater samples yielded DFAAs at measurable concentrations. Hierarchical cluster analysis, difference testing, and equivalence testing all indicated that some combinations of sediment porewater DFAA concentrations differed among rivers and were similar between spring and autumn within a river. Specifically, equivalence tests revealed subsets of sediment porewater DFAAs that were seasonally equivalent within each river, and none of the seasonally equivalent DFAAs were common among all 3 rivers (i.e., each river had a unique DFAA profile). However, exceptions detected in the cluster analysis and equivalence testing raise questions regarding the extent to which DFAAs might be sufficient for salmon imprinting and homing. Thus, DFAAs may fulfill some of the hypothesized prerequisites as salmon imprinting and homing odor cues, but our lack of understanding of salmon discriminatory abilities and limited DFAA data preclude definitive conclusions about the sufficiency of DFAAs alone as homing cues. [ABSTRACT FROM AUTHOR]

Current data suggest that lobster (Homarus americanus) populations are less homogenous than once believed. In an effort to better discriminate morphologically among lobsters from different sites, we developed a photographic method using ImageJ and compared it with commonly used 'hand' measurements. We standardized the measuring process using a strap-down board for both dorsal and ventral photographs with a camera mounted at a fixed position above the lobster. Discriminant analysis showed that both hand and photographic methods were useful in discriminating lobsters--both males and females--from three different sites. Additionally, the photographic method improved reproducibility and resolution, it reduced measurement time at the dock, and it created a permanent record for later verification, additional statistical analyses, and observer training. Les donnees actuellement disponibles portent a croire que les populations de homards (Homarus americanus) sont moins homogenes que l'on ne le pensait. Afin d'en arriver a une meilleure discrimination morphologique de homards provenant de lieux differents, nous avons mis au point une methode photographique appelee ImageJ et l'avons comparee a des approaches <> de mesure couramment employees. Nous avons normalise le processus de mesure en utilisant une planche munie d'attaches pour la prise de photographies dorsales et ventrales a l'aide d'un appareil-photo installe a hauteur fixe au-dessus du homard. L'analyse discriminante a demontre l'utilite des methodes tant manuelle que photographique pour la discrimination de homards tant males que femelles provenant de trois sites differents. La methode photographique a en outre ameliore la reproductibilite et la resolution, reduit le temps de mesure au quai et produit un registre permanent pouvant etre utilise pour des verifications ulterieures, d'autres analyses statistiques et la formation d'observateurs. [Traduit par la Redaction], Introduction The phenotype of an organism can provide insight into its habitat and behavior. Morphometrics, the analysis of shape, applies multivariate methods to lengths, widths, and angles. Morphometric analyses using [...]

ABSTRACT Epizootic shell disease in the American lobster, Homarus americanus, is seriously affecting inshore populations in southern New England. The disease can change the biochemical profile of lobsters and could [...]

Salmonid olfactory imprinting during the parr‐to‐smolt transformation (PST) is essential for successful homing to natal spawning sites years later by mature fish. However, in many species, juveniles may move away from spawning sites before the PST, yet home to the natal site as adults, indicating that there may be multiple imprinting windows. To test the hypothesis that olfactory learning can occur prior to the PST, we exposed Atlantic salmon (Salmo salar) to the imprinting odorant L‐arginine at the alevin stage. Odour exposures were conducted in both brook and well water to test whether environmental characteristics of the rearing water affected endocrine and imprinting responses. Changes in thyroid hormone concentration differed over the course of development between water sources (p <.001). In brook water, fish experienced a plateau in thyroxine concentrations coinciding with the L‐arginine exposure, but a continued decline was observed in those kept in well water. In subsequent experiments, migratory stage adults from the brook water‐reared group exposed to L‐arginine spent significantly more time than control fish (p <.04) in the L‐arginine odour arm of a two‐choice maze, whereas the well water‐reared group's responses did not differ from those of the control group. Our findings provide physiological and behavioural evidence supporting the hypothesis that imprinting in Atlantic salmon can occur before the PST. These results indicate that the water source during development may affect the ability to imprint and may have implications for hatchery programmes that often incubate salmonids in well water during the alevin life stage. [ABSTRACT FROM AUTHOR]

American lobsters, Homarus americanus, were paired in two consecutive fight situations to investigate how they maintain their stable dominance relationships. Results indicated that lobsters can remember familiar opponents within 24 hours of their first and second bouts. Subordinates were found to immediately retreat from familiar dominants. These findings suggest that lobsters are capable of individual recognition.