Ecology Seminar: "Blue and fin whale habitat use off Southern California based on acoustic data"

10/07/2015 - 12:15pm to 1:15pm

Dr. Ana Sirovic, Scripps Institution of Oceanography

Southern California Bight is a highly productive area attracting a large variety of cetaceans. Blue (Balaenoptera musculus) and fin whales (B. physalus) found in this area produce a variety of calls and are therefore good subjects for acoustic studies. Passive acoustic data collected at 16 locations in the SCB from 2006–2012 were used to enhance our knowledge of blue and fin whale presence and habitat use in this region. Over 3 million blue whale calls were detected in these recordings. Blue whale B calls were generally detected between June and January, with a peak in September. Across the years, there was some variability in detection numbers, with a slight peak in 2008, and minima in 2006 and 2007. Fin whale acoustic index, indicative of the 20 Hz calls, was high between September and December, with a peak in November and a secondary, smaller peak in March. Across the years of this study, there was an overall increase in the fin whale acoustic index. Generally, sites around the northern Channel Islands had the highest blue whale call abundances, but their calls were also common at other coastal sites. Fin whale acoustic index was higher farther offshore and to the south during peak calling periods, with highest levels in the basin just to the west of San Clemente Island. The effect of environmental, remotely sensed variables such as sea surface temperature, sea surface height, chlorophyll a concentration, and primary productivity, as well as temporal variables, such as month, season, and year on the distribution of these two whale species was modeled using a generalized additive modeling (GAM) framework. GAMs were used to explain functional relationships, evaluate relative contribution of each significant variable, and investigate predictive abilities of models of calling whales. Seasonal component was an important feature of all models. Additionally, areas of high calling blue and fin whale abundances both had a positive relationship with the sea surface temperature. In areas of lower abundance, chlorophyll a concentration and primary productivity were important variables for blue whale models and sea surface height and primary productivity were significant covariates in fin whale models. Predictive models were generally better for predicting general trends than absolute values, but there was a large degree of variation in year-to-year predictability across different sites.

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