Analysis of body condition indices reveals different ecotypes of the Antillean manatee.

Assessing the body condition of wild animals is necessary to monitor the health of the population and is critical to defining a framework for conservation actions. Body condition indices (BCIs) are a non-invasive and relatively simple means to assess the health of individual animals, useful for addressing a wide variety of ecological, behavioral, and management questions. The Antillean manatee (Trichechus manatus manatus) is an endangered subspecies of the West Indian manatee, facing a wide variety of threats from mostly human-related origins. Our objective was to define specific BCIs for the subspecies that, coupled with additional health, genetic and demographic information, can be valuable to guide management decisions. Biometric measurements of 380 wild Antillean manatees captured in seven different locations within their range of distribution were obtained. From this information, we developed three BCIs (BCI1 = UG/SL, BCI2 = W/SL3, BCI3 = W/(SL*UG2)). Linear models and two-way ANCOVA tests showed significant differences of the BCIs among sexes and locations. Although our three BCIs are suitable for Antillean manatees, BCI1 is more practical as it does not require information about weight, which can be a metric logistically difficult to collect under particular circumstances. BCI1 was significantly different among environments, revealing that the phenotypic plasticity of the subspecies have originated at least two ecotypes-coastal marine and riverine-of Antillean manatees.

Size-dependent social attraction and repulsion explains the decision of Atlantic cod Gadus morhua to enter baited pots.

The present study tested whether the presence of already retained fishes inside baited fish pots acted as a social attraction and affected the entrance probability of Atlantic cod Gadus morhua in a fjord in northern Norway. Video analysis revealed that the probability of an entrance initially increased with the presence of low numbers of fishes inside the pot, but subsequently decreased at a critical number of caught fishes. The critical number was dependent on the size of the G. morhua attempting to enter. This demonstrates that social attraction and repulsion play a role in G. morhua pot fishing and has important implications for the capture efficiency of fisheries executed with pots.

School density affects the strength of collective avoidance responses in wild-caught Atlantic herring Clupea harengus: a simulated predator encounter experiment.

An experimental study in a semi-controlled environment was conducted to examine whether school density in wild-caught Atlantic herring Clupea harengus affects the strength of their collective escape behaviours. Using acoustics, the anti-predator diving responses of C. harengus in two schools that differed in density were quantified by exposing them to a simulated threat. Due to logistical restrictions, the first fish was tested in a low-density school condition (four trials; packing density = 1.5 fish m(-3); c. 6000 fish) followed by fish in a high-density school condition (five trials; packing density = 16 fish m(-3); c. 60 000 fish). The C. harengus in a high-density school exhibited stronger collective diving avoidance responses to the simulated predators than fish in the lower-density school. The findings suggest that the density (and thus the internal organization) of a fish school affects the strength of collective anti-predatory responses, and the extent to which information about predation risk is transferred through the C. harengus school. Therefore, the results challenge the common notion that information transfer within animal groups may not depend on group size and density.

[An interpretation of the codification of emigration and the emergence of a wage-earning class: the examples of Italy and Spain]. / Una interpretacion de la codificacion sobre emigracion y nacimiento del salariado: los casos de Italia y Espana.

PIP: "This article deals with the genesis of the statistical categories and the official standards that regulated emigration in Italy [and] in Spain, from the last decades of [the] last century until the First World War. By underlining or negating the population drain in the traditional sector, the codification of migration encouraged or discouraged the emergence of wage earning. Spain and Italy showed marked differences." (EXCERPT)^ieng