Spatiotemporal patterns of marine mammal distribution in coastal waters of Galicia, NW Spain

Abstract

The spatial and seasonal distribution of cetaceans and possible links with environmental conditions were studied at the Galician continental shelf. Data were collected between February-August 2001 and June-September 2003 during opportunistic surveys onboard fishing boats. Seven species of cetaceans were identified from 250 sightings of 6,846 individuals. The common dolphin (Delphinus delphis) was by far the most frequently sighted and the most widely distributed species. Spatiotemporal trends in cetacean distribution and abundance, and their relationships with environmental parameters (sea depth, SST and chlorophyll-a) were quantified using generalised additive models (GAMs). Results for all cetaceans were essentially the same as for common dolphins alone. Modelling results indicated that the number of common dolphin sightings per unit effort was higher further south. The number of individual common dolphins seen per sighting of this species (i.e. group size) was however higher in the north and west of the study area, higher later in the year and higher in 2001 than in 2003. In contrast, the number of common dolphin calves seen (per sighting of this species) was higher in the south. Models including environmental variables indicated larger common dolphin group sizes in deeper waters and at higher chlorophyll concentrations (i.e. in more productive areas). There was also a positive relationship between survey effort and group size, which is probably an artefact of the tendency of the survey platforms (fishing boats) to spend most time in areas of high fish abundance. Numbers of common dolphin calves per sighting were found to be higher in shallower waters. The results are consistent with common dolphins foraging mainly in deeper waters of the Galician continental shelf, while more southern inshore waters may represent a nursery area.

Inter-species differences in polychlorinated biphenyls patterns from five sympatric species of odontocetes: Can PCBs be used as tracers of feeding ecology?

“…Results of redundancy analysis (RDA) on the best CB ratios combination (i.e. 49,105,110,138,170,180,183,187,194 and 189) Adapted from Santos et al, 2007Santos et al, , 2013Santos et al, , 2014Spitz et al, 2006Spitz et al, , 2011Pierce et al, 2010;Fernández et al, 2011a;Spyrakos et al, 2011;Méndez-Fernandez et al, 2012. Fig.…”

Can Static Habitat Protection Encompass Critical Areas for Highly Mobile Marine Top Predators? Insights from Coastal East Africa

“…The ensemble predictions obtained for sightings and group size on each grid cell were multiplied to predict abundance of dolphins [ 40 ]. As we did not apply line transect methodologies [ 41 ], we calculated an approximate effective sampling width with the distance and angles data from the 2008–2009 sightings (those data were not recorded for the 2006–2007). The average effective sampling width was 92 m (SD ± 92).…”

Habitat preferences of two deep-diving cetacean species in the northern Ligurian Sea

“…In order to model this gradient, we included longitude as a variable in the habitat model (Certain 2008). Spatial variables, such as longitude and latitude, though not directly related to the biology or ecology of the species, nor to their prey, can be considered proxies for variables that cannot be measured, such as sub-regional differences in species distribution (Ashe et al 2010, Pirotta et al 2011, Spyrakos et al 2011, Bonizzoni et al 2013). The variables used as predictors are summarized in Table 1.…”