QUIMICA

The spatial and temporal distribution of cetaceans is influenced by a series of environmental factors such as physical, chemical, and climatological variables; biotic factors such as competition and predation; and anthropogenic factors such as fishing activities and boat traffic, amongst others (Au et al., 1979; Jefferson et al., 1993; McLeod et al., 2004). Interactions between these differentaspects vary according to the geographical area involved (Jefferson et al., 1993; T.I.O., 1995). Specifically, variations in temperature and salinity of different water masses have a great influence on the distribution of different species (Dohl et al., 1986; Evans, 1987; Baumgartner & Mate, 2005).
In the Eastern Tropical Pacific (ETP), differences in temperature of at least five degreescentigrade and in salinity of two or more units allow the distinction of two dolphin communities (Au et al., 1979). Kenney (1990) determined that inshore and offshore distribution areas of the bottlenose dolphin vary significantly in surface water temperature values, although not in depth values. In the gulf of Mexico, bottlenose dolphins from both the shallow continental shelf and just seaward of theshelf break seemed to prefer regions with high surface temperature variability, suggesting an association with ocean fronts (Baumgartner et al., 2001).
Other studies have found variations related to distance from shore (Blaylock & Austin, 1982) and depth (Blaylock & Austin, 1982; Davis et al., 1995) when comparing two species sharing the same geographical area. Off the northeastern United States, thebottlenose dolphin seems to prefer significantly shallower zones than the spotted dolphin (Kenney, 1990). There is little information about this matter in coastal areas of the ETP.
In general terms, the bottlenose dolphin is mostly distributed in coastal areas, whereas the spotted dolphin prefers deep waters (Jefferson et al., 1993; Sylvestre, 1993). Based on those general tendencies and onprevious results found by Acevedo-Gutiérrez & Buckhart (1998) for the two dolphin species in Golfo Dulce, different spatial distribution patterns were predicted for the two species, with a higher probability of finding the bottlenose dolphin close to shore.
Higher proximity to shore in this species was expected to be associated with shallower areas and with lower salinity and temperature valuesresulting from the stronger influence of cool and fresh river waters. Swell and wind conditions in the distribution areas of the bottlenose dolphin were expected to be lower. No differences were expected in terms of cloud cover and wind speed between the distribution areas of the two species.
The clearly different behavioral patterns observed for the two dolphin species in Golfo Dulce are suggestedto be a strategy to avoid competition (Cubero-Pardo, 1998a, 1998b). Separate distribution areas are expected as part of those strategies. The objective of this study was to determine the physical environmental variables governing the spatial and seasonal distribution patterns of the bottlenose (Tursiops truncatus) and pan-tropical spotted (Stenella attenuata) dolphins in Golfo Dulce.

RESUMEN.Este estudio, efectuado de junio 1996 a julio 1997, fue dirigido a determiner factores ambientales abióticos que regulan la distribución del delfín bufeo (Tursiops truncatus) y el delfín manchado (Stenella attenuata) en el Golfo Dulce. El delfín manchado estuvo asociado a zonas significativamente más profundas (t-test = -9,761; p < 0,001; n = 202) y con mayor salinidad (t-test = -3,538; p = 0,001,n = 202), comparadas con el delfín bufeo. La combinación de variables ambientales en las áreas de distribución de cada especie en el Golfo Dulce fue diferente tanto a nivel espacial (F = 9,724; df = 12; p < 0,001) como estacional (F = 9,735; df = 12; p < 0,001). Entre todas las variables ambientales consideradas, el Análisis Múltiple Discriminante (MDA) reveló la profundidad como el factor con...