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How depth reception can affect the distributions of marine organisms.

Fraser P.J

Institute of Biological and Environmental Sciences (IBES), Zoology Department, College of Life Sciences and Medicine, University of Aberdeen, Tillydrone Avenue, Aberdeen, AB24 2TZ, UK.

Depth reception is known to be a property of angular acceleration receptors in the vestibular systems of crabs and sharks, and clearly is found in a variety of other marine animals. Resting activity is known to be modulated by small changes in hydrostatic pressure which is a natural proxy for depth. Such modulation follows at up to tidal periods greater than 12 hours, with two directional classes of units known in crabs. The hydrostatic pressure sensing system hence is one of the most tonic, non adapting sensory systems known.  Depth reception is now thought to underlie a variety of significant processes involved in the orientation and locomotion of marine animals ranging from the synchronizing of tidal rhythms to the spectacular compensatory swimming maintaining station in vertical currents which has been shown to account for the horizontal distributions of plankton in inshore bays.

Interactions of sperm whales (Physeter macrocephalus) and bottom-set longlines for toothfish in the High Seas of the Southwest Atlantic.

Goetz S, Laporta M, Portela J & Pierce G J

Instituto Español de Oceanografía (IEO), Cabo Estay – Canido, Apartado 1552, 36200 Vigo, Spain

Sperm whale (Physeter macrocephalus) depredation, i.e. damage or removal of toothfish hooked on bottom-set longlines, can cause considerable economic loss for Spanish fishing vessels operating in SW Atlantic waters. The fishery is also known to have high by-catch rates of seabirds. The main goal of the study was to assess the extent of sperm whale depredation and seabird by-catch in a largely unexplored fishing area and to test the potential of different longline designs, including so-called “umbrellas”, for minimizing depredation. Moreover, we investigated how sperm whale sightings, depredation and catch rates are related with each other and to environmental and fishery related variables using General Additive Modelling (GAM). Data were collected during 297 hauls on a

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