Risso’s and Pacific white-sided dolphin habitat modeling from passive acoustic monitoring

Abstract

Habitat characterization allows prediction of dolphin distributions in response to oceanographic processes and can be used to understand and predict effects of anthropogenic disturbances. Many habitat models focus on contemporary dolphin occurrence and environmental predictor data, but time-lagged oceanographic data may increase a model's predictive power due to ecological successional processes. Using hourly occurrence of Risso's dolphin Grampus griseus clicks and 2 types of Pacific white-sided dolphin Lagenorhynchus obliquidens clicks in autonomous passive acoustic recordings, we investigate the importance of time-lagged predictor variables with generalized additive models. These models relate dolphin acoustic activity from recordings at 6 sites in the Southern California Bight between August 2005 and December 2007 to oceanographic variables including sea surface temperature (SST), SST coefficient of variation (CV), sea surface chlorophyll concentration (chl), chl CV, upwelling indices, and solar and lunar temporal indices. The most consistently selected variables among the trial models evaluated during cross-validation were SST (100% of models) and SST CV (80%) for Risso's dolphin clicks; solar indices (100%) and SST and SST CV (60% each) for Pacific white-sided type A (PWS A) clicks; and SST CV (100%), solar indices (100%) and SST (80%) for Pacific white-sided type B (PWS B) clicks. Best predictive models for Risso's dolphins and PWS A clicks included time-lagged variables, suggesting the importance of ecological succession between abiotic variables and dolphin occurrence, while best models of PWS B clicks were for current conditions, suggesting association with prey-aggregating features such as fronts and eddies. KEY WORDS: Risso's dolphin · Grampus griseus · Pacific white-sided dolphin · Lagenorhynchus obliquidens · Habitat model · Generalized additive model · Passive acoustic monitoring · Southern California BightResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 423: 247-260, 2011 and cost constraints. The inability to sample during night and rough weather conditions may affect the accuracy or precision of resulting models. Additionally, visual survey data are limited to times when cetaceans are conspicuous at the surface. Models based on these data may not represent 'prime' habitat (i.e. habitat that is important to feeding or breeding, and hence the animals' overall fitness) if the animals are more easily observed when resting or transiting to such key areas (Hamazaki 2002). Alternate sampling methods, such as passive acoustic monitoring, may provide a better representation of cetacean presence and activity in prime habitats and thereby improve model accuracy and precision.The accuracy and precision of habitat models is also dependent on the environmental data upon which they are built. Habitat models developed for predictive purposes should include environmental variables that are easily accessible and available across regions and times of int...

Seasonal distribution and abundance of cetaceans off Southern California estimated from CalCOFI cruise data from 2004 to 2008

“…Along the coast of California, the 2 forms of Pacifi c white-sided dolphins are primarily found in waters over the continental shelf and slope (Forney, 1994). The northern form is thought to enter coastal Southern California waters during the winter months and to congregate with the southern form (Walker et al, 1986;Lux et al, 1997;Soldevilla et al, 2011). Because we were unable to differentiate between the 2 forms, it is possible that the increase in observed abundance during the winter-spring season was a result of capturing both forms that use the study area rather than capturing only the southern form.…”

“…Photographs were reviewed onboard, compared with identifi cation guides (Reeves et al, 2002), and occasionally shared with experienced colleagues for species confi rmation. Additionally, there are 2 forms of Pacifi c white-sided dolphins (Lagenorhynchus obliquidens) along the coast of California (Walker et al, 1986;Lux et al, 1997;Soldevilla et al, 2011); because these forms are indistinguishable from a distance, density and abundance for this species likely includes both forms.…”

Odontocete occurrence in relation to changes in oceanography at a remote equatorial Pacific seamount

“…Predictive modeling for Risso's dolphin acoustic detections in the Southern California Bight showed a positive relationship with SST and negative relationship with SST covariance together with a 4‐week time lag (Soldevilla et al . ). Soldevilla et al .…”

Delphinid behavioral responses to incidental mid-frequency active sonar

“…This may indicate that seasonal and inter-annual oceanographic variability impacts behavior and habitat use more than the presence of sonar (e.g., Croll et al, 2001). Both common dolphins and Pacific white-sided dolphins have been shown to vary their use of the southern California Bight on a seasonal basis (Dohl et al, 1986;Walker et al, 1986;Soldevilla et al, 2011). In addition, the year-to-year sighting rates of different species vary with sea surface temperature, chlorophyll, and other oceanographic parameters (e.g., Gaskin, 1968;Van Waerebeek et al, 1998).…”