Ultra-high foraging rates of harbor porpoises make them vulnerable to anthropogenic disturbance

This study was partly funded by the German Federal Agency for Nature Conservation (BfN) under the contract Z1.2-5330/2010/14 and the BfN-Cluster 7 “Effects of underwater noise on marine vertebrates.” D.M.W. and P.T.M. were also supported by the Danish National Research Foundation (FNU) and the Carlsberg Foundation, and M.J. was also supported by the Marine Alliance for Science and Technology Scotland (MASTS) and by a Marie Curie-Sklodowska award.The question of how individuals acquire and allocate resources to maximize fitness is central in evolutionary ecology. Basic information on prey selection, search effort, and capture rates are critical for understanding a predator’s role in its ecosystem and for predicting its response to natural and anthropogenic disturbance. Yet, for most marine species, foraging interactions cannot be observed directly. The high costs of thermoregulation in water require that small marine mammals have elevated energy intakes compared to similar-sized terrestrial mammals [1]. The combination of high food requirements and their position at the apex of most marine food webs may make small marine mammals particularly vulnerable to changes within the ecosystem [2–4], but the lack of detailed information about their foraging behavior often precludes an informed conservation effort. Here, we use high-resolution movement and prey echo recording tags on five wild harbor porpoises to examine foraging interactions in one of the most metabolically challenged cetacean species. We report that porpoises forage nearly continuously day and night, attempting to capture up to 550 small (3–10 cm) fish prey per hour with a remarkable prey capture success rate of >90%. Porpoises therefore target fish that are smaller than those of commercial interest, but must forage almost continually to meet their metabolic demands with such small prey, leaving little margin for compensation. Thus, for these “aquatic shrews,” even a moderate level of anthropogenic disturbance in the busy shallow waters they share with humans may have severe fitness consequences at individual and population levels.PostprintPeer reviewe

Long-term sound and movement recording tags to study natural behavior and reaction to ship noise of seals

This study was funded by the German Federal Agency of Nature Conservation under the project “Effects of underwater noise on marine vertebrates” (Cluster 7, Z1.2‐53302/2010/14) and “Under Water Noise Effects – UWE” (Project numbers FKZ 3515822000). MJ was supported for development of the tags by a Marie Sklodowska‐Curie career integration grant and by the Marine Alliance for Science and Technology Scotland. PTM and DMW were partly supported by a large frame grant from the Danish National Research Council. DMW was also supported by an Office of Naval Research grant to Jeremy Goldbogen at Stanford University.1.  The impact of anthropogenic noise on marine fauna is of increasing conservation concern with vessel noise being one of the major contributors. Animals that rely on shallow coastal habitats may be especially vulnerable to this form of pollution. 2.  Very limited information is available on how much noise from ship traffic individual animals experience, and how they may react to it due to a lack of suitable methods. To address this, we developed long-duration audio and 3D-movement tags (DTAGs) and deployed them on three harbor seals and two gray seals in the North Sea during 2015-2016. 3. These tags recorded sound, accelerometry, magnetometry, and pressure continuously for up to 21 days. GPS positions were also sampled for one seal continuously throughout the recording period. A separate tag, combining a camera and an accelerometer logger, was deployed on two harbor seals to visualize specific behaviors that helped interpret accelerometer signals in the DTAG data. 4.  Combining data from depth, accelerometer, and audio sensors, we found that animals spent 6.6%-42.3% of the time hauled out (either on land or partly submerged), and 5.3%-12.4% of their at-sea time resting at the sea bottom, while the remaining time was used for traveling, resting at surface, and foraging. Animals were exposed to audible vessel noise 2.2%-20.5% of their time when in water, and we demonstrate that interruption of functional behaviors (e.g., resting) in some cases coincides with high-level vessel noise. Two-thirds of the ship noise events were traceable by the AIS vessel tracking system, while one-third comprised vessels without AIS. 5.  This preliminary study demonstrates how concomitant long-term continuous broadband on-animal sound and movement recordings may be an important tool in future quantification of disturbance effects of anthropogenic activities at sea and assessment of long-term population impacts on pinnipeds.Publisher PDFPeer reviewe

High rates of vessel noise disrupt foraging in wild harbour porpoises (Phocoena phocoena) - scripts and example dataset

This upload contains Matlab scripts used to compute third-octave levels from audio recorded with DTAG-3 tags on free-ranging harbour porpoises. It also contains examples of results, outputs of such scripts (hp12_272a_noisedata.mat and hp12_293a_noisedata.mat), for two of the seven animals in the study, as well as sensor data for all the animals (e.g. hp12_272a_prh625.nc). The metadata for all the uploaded data are stored in netCDF files (.nc) and the overview plots show noise, vessel presence and foraging data for all study animals. Finally, the upload contains scripts that use the results to perform a series of permutation tests to compare foraging buzz count and total buzz duration in minutes with high- and low-level noise

Acoustic gaze adjustments during active target selection in echolocating porpoises

Visually dominant animals use gaze adjustments to organize perceptual inputs for cognitive processing. Thereby they manage the massive sensory load from complex and noisy scenes. Echolocation, as an active sensory system, may provide more opportunities to control such information flow by adjusting the properties of the sound source. However, most studies of toothed whale echolocation have involved stationed animals in static auditory scenes for which dynamic information control is unnecessary. To mimic conditions in the wild, we designed an experiment with captive, free-swimming harbor porpoises tasked with discriminating between two hydrophone-equipped targets and closing in on the selected target; this allowed us to gain insight into how porpoises adjust their acoustic gaze in a multi-target dynamic scene. By means of synchronized cameras, an acoustic tag and on-target hydrophone recordings we demonstrate that porpoises employ both beam direction control and range-dependent changes in output levels and pulse intervals to accommodate their changing spatial relationship with objects of immediate interest. We further show that, when switching attention to another target, porpoises can set their depth of gaze accurately for the new target location. In combination, these observations imply that porpoises exert precise vocal-motor control that is tied to spatial perception akin to visual accommodation. Finally, we demonstrate that at short target ranges porpoises narrow their depth of gaze dramatically by adjusting their output so as to focus on a single target. This suggests that echolocating porpoises switch from a deliberative mode of sensorimotor operation to a reactive mode when they are close to a target.</p

High rates of vessel noise disrupt foraging in wild harbour porpoises (<i>Phocoena phocoena</i>)

Shipping is the dominant marine anthropogenic noise source in the world’s oceans, yet we know little about vessel encounter rates, exposure levels and behavioural reactions for cetaceans in the wild, many of which rely on sound for foraging, communication and social interactions. Here, we used animal-borne acoustic tags to measure vessel noise exposure and foraging efforts in seven harbour porpoises in highly trafficked coastal waters. Tagged porpoises encountered vessel noise 17-89% of the time and occasional high-noise levels coincided with vigorous fluking, bottom diving, interrupted foraging and even cessation of echolocation, leading to significantly fewer prey capture attempts at received levels greater than 96 dB re 1 µPa (16 kHz third-octave). If such exposures occur frequently, porpoises, which have high metabolic requirements, may be unable to compensate energetically with negative long-term fitness consequences. That shipping noise disrupts foraging in the high-frequency-hearing porpoise raises concerns that other toothed whale species may also be affected.</p

gs15_139b_TOLs

TOL levels for the entire recording period for grey seal gs15_139b. Data is structured per day in 30 sec average

hs16_265c_track

Track file for harbour seal hs16_265

gs15_139b_Accel_Depth_5Hz

Movement data for grey seal gs15_139b for the entire recording period

Resting_video_acceleration_data

Acceleration data associated with resting dive from example in manuscript and supplementary materia