Marine Vertebrates and Low Frequency Sound: Technical Report for LFA EIS

Over the past 50 years, economic and technological developments have dramatically increased the human contribution to ambient noise in the ocean. The dominant frequencies of most human-made noise in the ocean is in the low-frequency range (defined as sound energy below 1000Hz), and low-frequency sound (LFS) may travel great distances in the ocean due to the unique propagation characteristics of the deep ocean (Munk et al. 1989). For example, in the Northern Hemisphere oceans low-frequency ambient noise levels have increased by as much as 10 dB during the period from 1950 to 1975 (Urick 1986; review by NRC 1994). Shipping is the overwhelmingly dominant source of low-frequency manmade noise in the ocean, but other sources of manmade LFS including sounds from oil and gas industrial development and production activities (seismic exploration, construction work, drilling, production platforms), and scientific research (e.g., acoustic tomography and thermography, underwater communication). The SURTASS LFA system is an additional source of human-produced LFS in the ocean, contributing sound energy in the 100-500 Hz band. When considering a document that addresses the potential effects of a low-frequency sound source on the marine environment, it is important to focus upon those species that are the most likely to be affected. Important criteria are: 1) the physics of sound as it relates to biological organisms; 2) the nature of the exposure (i.e. duration, frequency, and intensity); and 3) the geographic region in which the sound source will be operated (which, when considered with the distribution of the organisms will determine which species will be exposed). The goal in this section of the LFA/EIS is to examine the status, distribution, abundance, reproduction, foraging behavior, vocal behavior, and known impacts of human activity of those species may be impacted by LFA operations. To focus our efforts, we have examined species that may be physically affected and are found in the region where the LFA source will be operated. The large-scale geographic location of species in relation to the sound source can be determined from the distribution of each species. However, the physical ability for the organism to be impacted depends upon the nature of the sound source (i.e. explosive, impulsive, or non-impulsive); and the acoustic properties of the medium (i.e. seawater) and the organism. Non-impulsive sound is comprised of the movement of particles in a medium. Motion is imparted by a vibrating object (diaphragm of a speaker, vocal chords, etc.). Due to the proximity of the particles in the medium, this motion is transmitted from particle to particle in waves away from the sound source. Because the particle motion is along the same axis as the propagating wave, the waves are longitudinal. Particles move away from then back towards the vibrating source, creating areas of compression (high pressure) and areas of rarefaction (low pressure). As the motion is transferred from one particle to the next, the sound propagates away from the sound source. Wavelength is the distance from one pressure peak to the next. Frequency is the number of waves passing per unit time (Hz). Sound velocity (not to be confused with particle velocity) is the impedance is loosely equivalent to the resistance of a medium to the passage of sound waves (technically it is the ratio of acoustic pressure to particle velocity). A high impedance means that acoustic particle velocity is small for a given pressure (low impedance the opposite). When a sound strikes a boundary between media of different impedances, both reflection and refraction, and a transfer of energy can occur. The intensity of the reflection is a function of the intensity of the sound wave and the impedances of the two media. Two key factors in determining the potential for damage due to a sound source are the intensity of the sound wave and the impedance difference between the two media (impedance mis-match). The bodies of the vast majority of organisms in the ocean (particularly phytoplankton and zooplankton) have similar sound impedence values to that of seawater. As a result, the potential for sound damage is low; organisms are effectively transparent to the sound – it passes through them without transferring damage-causing energy. Due to the considerations above, we have undertaken a detailed analysis of species which met the following criteria: 1) Is the species capable of being physically affected by LFS? Are acoustic impedence mis-matches large enough to enable LFS to have a physical affect or allow the species to sense LFS? 2) Does the proposed SURTASS LFA geographical sphere of acoustic influence overlap the distribution of the species? Species that did not meet the above criteria were excluded from consideration. For example, phytoplankton and zooplankton species lack acoustic impedance mis-matches at low frequencies to expect them to be physically affected SURTASS LFA. Vertebrates are the organisms that fit these criteria and we have accordingly focused our analysis of the affected environment on these vertebrate groups in the world’s oceans: fishes, reptiles, seabirds, pinnipeds, cetaceans, pinnipeds, mustelids, sirenians (Table 1)

Prepared by: Naval Facilities Engineering Command Northwest Prepared for:

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Patterns of habitat use by harbor porpoise (Phocoena phocoena) in central San Francisco Bay

This research takes an innovative approach to modeling distribution of a marine predator explicitly in the temporal domain. Harbor porpoise (Phocoena phocoena) are a small cetacean seen in San Francisco Bay year round. Porpoise presence at the entrance of the Bay varies from zero sightings to over 100 in an hour. The solitary social and foraging behavior of this non-migratory species makes it an especially useful indicator of habitat patchiness along the west coast and of tide-dependent ecological processes in central Bay. Bathymetry data of the Golden Gate channel show steep shelf breaks and complex outcroppings that effect water flow and create spatially stable areas where tidal fronts occur. Oceanographic features associated with tidal fronts are recognized by marine predators as areas in which prey biomass accumulates. Sighting frequencies were hypothesized to vary according to changes in the same spatially consistent, but temporally variable, tidal factors that correlate to lower trophic level congregating mechanisms. Circular statistics were used to describe sightings data over a 24 hour tidal period. Sightings were fit to circular models based on tidal segments that correlated to tidal state: ebb or flood, and changes in current velocity. One year of data show a greater number of porpoises are present during a flood tide, but there are more sightings during an ebb tide. Porpoise sighting frequency showed multimodal distribution and best fit a model with a specific mean direction at the 95% confidence interval with [F=0.34, p = 0.001]. Most sightings occurred within three hours after maximum inflow current velocity on the north side of the channel. The time at which the most sightings occurred over a 24 hour tidal period correlated to the time at which the most defined shear zones occur in central Bay with a circular correlation coefficient of -0.15 (p=0.0006). A three tiered, nested ANOVA found significant variation in porpoise foraging behavior correlated to tidal phase or tidal front presence. Foraging behavior varied significantly according to tidal state with [F=9.96, p = 9.38 x 1 O'08]. The data show that it is the patch in tidal progression, rather than geographic space, which is significant to variations in porpoise sightings and foraging behavior in the Golden Gate. The results produce a temporal habitat model for a federally protected, upper trophic level predator in the Bay. Models like this are an efficient way to inform management in a highly anthropogenic influenced area

Spatiotemporal variation in harbor porpoise distribution and foraging across a landscape of fear

Funding information: Marine Alliance for Science and Technology for Scotland; Marine Scotland Science; University of AberdeenPeer reviewedPublisher PD

The Influence of Topographic and Dynamic Cyclic Variables on the Distribution of Small Cetaceans in a Shallow Coastal System

The influence of topographic and temporal variables on cetacean distribution at a fine-scale is still poorly understood. To study the spatial and temporal distribution of harbour porpoise Phocoena phocoena and the poorly known Risso’s dolphin Grampus griseus we carried out land-based observations from Bardsey Island (Wales, UK) in summer (2001–2007). Using Kernel analysis and Generalized Additive Models it was shown that porpoises and Risso’s appeared to be linked to topographic and dynamic cyclic variables with both species using different core areas (dolphins to the West and porpoises to the East off Bardsey). Depth, slope and aspect and a low variation in current speed (for Risso’s) were important in explaining the patchy distributions for both species. The prime temporal conditions in these shallow coastal systems were related to the tidal cycle (Low Water Slack and the flood phase), lunar cycle (a few days following the neap tidal phase), diel cycle (afternoons) and seasonal cycle (peaking in August) but differed between species on a temporary but predictable basis. The measure of tidal stratification was shown to be important. Coastal waters generally show a stronger stratification particularly during neap tides upon which the phytoplankton biomass at the surface rises reaching its maximum about 2–3 days after neap tide. It appeared that porpoises occurred in those areas where stratification is maximised and Risso’s preferred more mixed waters. This fine-scale study provided a temporal insight into spatial distribution of two species that single studies conducted over broader scales (tens or hundreds of kilometers) do not achieve. Understanding which topographic and cyclic variables drive the patchy distribution of porpoises and Risso’s in a Headland/Island system may form the initial basis for identifying potentially critical habitats for these species

Harbour porpoise movement strategy affects cumulative number of animals acoustically exposed to underwater explosions

Anthropogenic sound in the marine environment can have negative consequences for marine fauna. Since most sound sources are intermittent or continuous, estimating how many individuals are exposed over time remains challenging, as this depends on the animals' mobility. Here we explored how animal movement influences how many, and how often, animals are impacted by sound. In a dedicated study, we estimated how different movement strategies affect the number of individual harbour porpoises Phocoena phocoena receiving temporary or permanent hearing loss due to underwater detonations of recovered explosives (mostly WWII aerial bombs). Geo-statistical distribution models were fitted to data from 4 marine mammal aerial surveys and used to simulate the distribution and movement of porpoises. Based on derived dose-response thresholds for temporary (TTS) or permanent threshold shifts (PTS), we estimated the number of animals affected in a single year. When individuals were free-roaming, an estimated 1200 and 24 000 unique individuals would suffer PTS and TTS, respectively. This equates to respectively 0.50 and 10% of the estimated North Sea population. In contrast, when porpoises remained in a local area, fewer animals would receive PTS and TTS (1100 [0.47%] and 15 000 [6.5%], respectively), but more individuals would be subjected to repeated exposures. Because most anthropogenic sound-producing activities operate continuously or intermittently, snapshot distribution estimates alone tend to underestimate the number of individuals exposed, particularly for mobile species. Hence, an understanding of animal movement is needed to estimate the impact of underwater sound or other human disturbance. © The authors 2016

Abundance trends and environmental habitat usage patterns of bottlenose dolphins (Tursiops truncatus) in lower Barataria and Caminada Bays, Louisiana

The paucity of research into the environmental requirements, stock membership, abundance and residency patterns of bottlenose dolphins (Tursiops truncatus) in coastal Louisiana creates difficulty in understanding how local ecosystems and threats (such as fishery interactions, habitat degradation and pollution) affect populations. This study combined fine-scale environmental measurements and photo-identification techniques to describe patterns of habitat usage and abundance of bottlenose dolphins in lower Barataria Basin from June 1999 to May 2002. In addition I investigated the validity and limitations of using mark-recapture models to estimate abundance from cetacean photo-identification data. Bottlenose dolphins were present year-round in a wide range of water temperatures (10.9 – 33.9 ºC), dissolved oxygen levels (3.7 – 16.6 mg/L), salinities (11.7 – 31.5 psu), turbidity levels (1.4 – 34.0 NTU), distances from shore (3 – 800 m), and water depths (0.4 - 12.5 m). However, feeding activity was concentrated in a narrower range of conditions, 20 – 24 ºC water temperature, 6 – 9 mg/L of dissolved oxygen, turbidity values between 20 – 28 NTU, 200 – 500 m from shore, and depths of 4 – 6 m. Spatial mapping showed differences in the seasonal distribution of individuals and a tendency for feeding activity and larger group sizes to be concentrated in passes. Using distinctive natural markings present on dorsal fins, I identified 133 individual dolphins. Closed-population models were improved by inclusion of temporal and individual heterogeneity as sources of sighting variability and produced estimates of between 138 and 238 (95% CL range = 128 – 297) bottlenose dolphins for the study area. Analysis of Jolly-Seber model assumptions demonstrated the importance of ensuring cetacean surveys accurately represent temporal, geographic and demographic properties of a study population. In addition such factors as non-preferential image acquisition, group size, gender, behavior, stability and distinctiveness of natural markings, weather conditions and boat traffic must be considered. Evidence of a relatively closed Barataria Basin population agrees with current assumptions that bay bottlenose dolphin stocks are distinct from those found in deeper, offshore waters. Furthermore, the characterization of environmental usage patterns for this bay population strengthens adequate description and management of this relatively discrete Gulf of Mexico bottlenose dolphin stock

Habitat modelling of the harbour porpoise (Phocoena phocoena) in southwest UK: effects of depth, slope and tidal state

The harbour porpoise, Phocoena phocoena, is a widespread cetacean species in the Northeast Atlantic, with a year-round distribution around the UK. The south-west experiences the highest bycatch rates in the UK and is the main threat to P. phocoena populations. Yet here there is limited information on their abundance, distribution, and habitat preferences. This study aims to understand harbour porpoise species-habitat relationship in the UK south-west, which may be used to inform conservation management and sustain valuable populations. From boat-based visual surveys conducted over summers 2017-2019 from Plymouth to St Marys in the Scilly Isles, habitat modelling using generalised additive models (GAMs) were used to analyse harbour porpoise occurrence in relation to variables including seabed depth, slope, and tidal state. A total of 197 harbour porpoises were spotted over 111 hours and 35 minutes survey time. The best model explained 15.7% of the deviance with variables sea state, month, depth, slope, and time of day as significant predictors. A low sea state, in the month of August, and at 35-60m depth all resulted in increased sighting rate, as well as regions of higher slope and at 10-12am. These results suggest seasonal movement patterns, reliance on static bathymetric features, and diurnal changes in surfacing behaviour. This study has successfully identified important predictors of P. phocoena distribution within a previously understudied area, to aid towards the species conservation particularly in terms of management and reduction of bycatch