Annie B. Douglas

Habitat-Based Density Models for Three Cetacean Species off Southern California Illustrate Pronounced Seasonal Differences

Managing marine species effectively requires spatially and temporally explicit knowledge of their density and distribution. Habitat-based density models, a type of species distribution model (SDM) that uses habitat covariates to estimate species density and distribution patterns, are increasingly used for marine management and conservation because they provide a tool for assessing potential impacts (e.g., from fishery bycatch, ship strikes, anthropogenic sound) over a variety of spatial and temporal scales. The abundance and distribution of many pelagic species exhibit substantial seasonal variability, highlighting the importance of predicting density specific to the season of interest. This is particularly true in dynamic regions like the California Current, where significant seasonal shifts in cetacean distribution have been documented at coarse scales. Finer scale (10 km) habitat-based density models were previously developed for many cetacean species occurring in this region, but most models were limited to summer/fall. The objectives of our study were two-fold: 1) develop spatially-explicit density estimates for winter/spring to support management applications, and 2) compare model-predicted density and distribution patterns to previously developed summer/fall model results in the context of species ecology. We used a well-established Generalized Additive Modeling framework to develop cetacean SDMs based on 20 California Cooperative Oceanic Fisheries Investigations (CalCOFI) shipboard surveys conducted during winter and spring between 2005 and 2015. Models were fit for short-beaked common dolphin (Delphinus delphis delphis), Dall’s porpoise (Phocoenoides dalli), and humpback whale (Megaptera novaeangliae). Model performance was evaluated based on a variety of established metrics, including the percentage of explained deviance, ratios of observed to predicted density, and visual inspection of predicted and observed distributions. Final models were used to produce spatial grids of average species density and spatially-explicit measures of uncertainty. Results provide the first fine scale (10 km) density predictions for these species during the cool seasons and reveal distribution patterns that are markedly different from summer/fall, thus providing novel insights into species ecology and quantitative data for the seasonal assessment of potential anthropogenic impacts.

Delphinid behavioral responses to incidental mid-frequency active sonar

Opportunistic observations of behavioral responses by delphinids to incidental mid-frequency active (MFA) sonar were recorded in the Southern California Bight from 2004 through 2008 using visual focal follows, static hydrophones, and autonomous recorders. Sound pressure levels were calculated between 2 and 8 kHz. Surface behavioral responses were observed in 26 groups from at least three species of 46 groups out of five species encountered during MFA sonar incidents. Responses included changes in behavioral state or direction of travel, changes in vocalization rates and call intensity, or a lack of vocalizations while MFA sonar occurred. However, 46% of focal groups not exposed to sonar also changed their behavior, and 43% of focal groups exposed to sonar did not change their behavior. Mean peak sound pressure levels when a behavioral response occurred were around 122 dB re: 1 μPa. Acoustic localizations of dolphin groups exhibiting a response gave insight into nighttime movement patterns and provided evidence that impacts of sonar may be mediated by behavioral state. The lack of response in some cases may indicate a tolerance of or habituation to MFA sonar by local populations; however, the responses that occur at lower received levels may point to some sensitization as well.

Southern California behavioral response study—Overview and synthesis of results to date

The Southern California Behavioral Response Study (SOCAL-BRS) is an interdisciplinary, multi-team collaboration that uses high-resolution, multi-sensor tags to document behavioral responses of cetaceans to Navy mid-frequency (2.5-5 kHz) active sonar (MFAS). Individual animals are monitored before, during, and after controlled exposure experiments (CEEs) using either simulated or [the first-ever use of] actual U.S. Navy ship-based MFAS. Over 175 tags have been deployed on individuals of ten cetacean species and over 80 CEEs have been conducted. Results including baseline behavioral data, as well as behavioral responses to sound exposure have been published in more than a dozen scientific publications. Behavioral responses to MFAS and other mid-frequency sounds have been documented in several species with changes in diving and feeding behavior and avoidance of sound sources being the most common responses observed, though some individuals did not respond despite relatively high received sound levels. Responses appear to depend on species, exposure context (e.g., behavioral state, prey distribution, proximity to sound sources), and source type (simulated versus real). These experiments provide controlled, scientific measurements of response, or lack of response, that are directly applicable to improving Navy environmental compliance assessments of behavioral response to MFAS.

Additional file 3: of Sound production and associated behavior of tagged fin whales (Balaenoptera physalus) in the Southern California Bight

Acoustic audit file listing the calls that were manually identified in the acoustic record for tagged whale bp13_258b. The whale name signifies the species name, Balaenoptera physalus (bp), the two digit year of deployment, the three digit Julian day of deployment, and a letter representing the successive number deployment for that day. The file has three columns: time cue of the call in seconds since deployment; duration of the call in seconds; and a label indicating whether the call was produced by the tagged whale (‘1’) or a different whale (‘0’).