As we’ve talked about in recent posts, we’re co-organising the INPAS symposium – exploring the latest research on the effects of impulsive noise on and harbour porpoise and seals. We’re delighted to announce the abstracts for the presentations. Check them out below! And REGISTER HERE!

The symposium will be opened by our Chair, Rene Dekeling – Project Leader: Sound in the Marine Environment, Ministry of Infrastructure and Water Management, Netherlands and Jakob Tougaard from Aarhus University, Denmark will provide a general introduction keynote to set the scene for the INPAS symposium. From there, we’ll head straight into the following presentations, with lots of time for discussions to explore where this research field needs to go next and how to effectively plug our gaps in knowledge!

Impact areas – Christ de Jong et al. – TNO Acoustics and Sonar, The Hague, The Netherlands

An essential step in assessing impacts is to determine the area around the source in which the impulsive noise may have a significant impact on porpoises and seals. The likeliness for effects on the behaviour (e.g. avoiding the sound source) or on the hearing (particularly PTS) to occur depends on the dose of sound to which the animals are exposed. Acoustic models for sources, such as marine pile driving, airgun arrays for seismic surveys and explosions, and for sound propagation in the marine environment have been developed to quantify the sound distribution around the source. A short update will be given on the current status of the models and the associated uncertainties. Significant effects are assumed to occur when the sound exposure quantity exceeds a defined threshold value. Recent developments suggest that incorporation of animal hearing sensitivity in that quantity provides a more robust impact assessment, though further research is required.

Avoidance of pile driving by harbour seals; results of an animal-borne telemetry study – Gordon Hastie et al. – Sea Mammal Research Unit, St Andrews, UK.

The Wash (southern North Sea) is an area of extensive wind farm development and hosts >3,500 harbour seals.  To quantify interactions with wind farms, we deployed GPS-tags on 24 seals prior to wind farm development (2003-2005) and on 25 seals during wind farm construction and operation (2012). Using the GPS data, we compared seal distribution between pre-development and during both construction and operation, and during the construction phase between piling and non-piling periods.  Results showed no significant decrease in seal abundance within operational wind farms; in fact, one seal appeared to be attracted to the turbine foundations. Further, there was no large-scale displacement of seals during construction overall. However, during piling periods, seal abundance was significantly reduced up to 25 km from the piling; there was a 19 to 83% (95% CIs) decrease in usage compared to non-piling periods, equating to a mean estimated displacement of 440 seals.

Uncontrolled sound exposure experiments: behavioural reactions of wild grey seals to pile-driving – Geert Aarts et al. – Wageningen Marine Research, Wageningen University & Research

Pile-driving during the construction of offshore windfarms produces high energy, broad spectrum sound that can be detected by marine mammals, causing changes in behaviour that could reduce condition and reproductive potential. Grey seals (Halichoerus grypus) are abundant predators in the North Sea, but their responses to anthropogenic sounds are still largely unknown. To examine if movement and behaviour could be influenced by pile-driving, we tracked grey seals during the construction of the Luchterduinen windfarm in 2014 and Gemini windfarm in 2015. Reactions of the grey seals to the pile driving were diverse, and included: altered surfacing or diving behaviour, and changes in swim direction including swimming away from the source, heading into shore or travelling perpendicular to the incoming sound, or coming to a halt. Also, during a large number of exposures, the seals did not appear to change their diving behaviour or movement. The change in behaviour most often observed in response to pile-driving was a decline in the descent speed, which suggests a transition from foraging (diving straight down to the bottom), to more horizontal movement. The analysis showed that these changes in behaviour were on average larger and occurred more frequent at smaller distances (<30km) from the pile driving events.

Porpoise displacement at different noise levels during construction of an offshore windfarm – Isla Graham et al. – Lighthouse Field Station, University of Aberdeen, UK.

A key area of uncertainty in the assessment of the potential impacts of offshore developments remains the extent of marine mammal displacement to different levels of underwater noise. Recent environmental assessments have used range-dependent acoustic models that predict unweighted single-pulse sound exposure levels, but information on the likely responses of harbour porpoises at different received levels is lacking. In 2017, the foundations of the 84-turbine Beatrice Offshore Windfarm (BOWL) were piled. Harbour porpoise responses were studied using passive acoustic monitoring in two phases during the initial and later stages of pile installation. Changes in porpoise occurrence in response to piling noise, vessel activity and acoustic deterrent devices were estimated using echolocation detectors (CPODs) moored at different distances from the construction vessel. Underwater noise levels were recorded using autonomous noise recorders (SM2Ms and SoundTraps).  A porpoise behavioural dose-response curve was estimated from these data and factors affecting variation in responses at different received levels and distances from construction activity were explored. These results will inform impact assessments and measures to mitigate the impact of underwater noise from marine renewable technologies on marine mammals.

Porpoise disturbance during noise mitigated construction of seven offshore wind farms – Miriam J. Brandt et al. – Bioconsult SH GmbH, Germany

Disturbance effects of offshore windfarm (OWF) construction on harbour porpoises were investigated using acoustic porpoise monitoring data and noise measurements at the first seven large-scale OWFs in the German Bight between 2010 and 2013. Six OWFs were constructed mainly under active noise mitigation systems (NMS), one without.

Based on GAM analyses, declines in porpoise detections were found at noise levels exceeding 143 dB re 1 μPa²s (SEL05) and up to 17 km from piling (14 km for piling events with NMS). Effect size, however, declined with distance and decreasing noise level and was greater at piling events without NMS: Porpoise detections during piling measured at 10-15 km distance from piling declined by 50 % without NMS but only by 17 % with NMS when compared to 25-48 h before piling.

When effect distance during piling was investigated in dependence of the noise levels measured at 750 m distance, there was a clear reduction in disturbance range when noise was reduced down to 165 dB SEL05. Further noise reduction, however, did not further reduce effect ranges on porpoises. Potential reasons for this are discussed.

Porpoise foraging and disturbance based on acoustic tags – Jonas Teilmann et al. – Aarhus University, Denmark

Understanding where and how marine mammals acquire food is essential to management and conservation, in particular for species challenged by high metabolic demands. By using acoustic behavioural tags (DTAG) to study how often echolocating porpoises forage in the Danish Straits. Porpoises forage with on average 80 buzzes per hour for adults and 125 buzzes/hour for juveniles, amounting to a mean of 1920-3000 prey pursuits over a 24-hour period. Based on echoes from the tail beats of the chased fish, we estimated the target fish size to be mostly below 5 cm in length. Assuming the weight of each fish to be around 1 g, and a 90% prey capture success rate, a juvenile porpoise would consume 2.7 kg/24 h, which is roughly 10% of the body weight. Tagged porpoises encountered vessel noise 17–89% of the time and occasional high-noise levels coincided with vigorous fluking, bottom diving, interrupted foraging, leading to significantly fewer prey capture attempts at received levels greater than 96 dB re 1 mPa (16 kHz third-octave).

Harbour porpoise (Phocoena phocoena) energetics and fish catch ability related to offshore pile driving – Ron Kastelein, et al. – SEAMARCO, Netherlands

Results from studies under controlled conditions give information on the potential impact of pile-driving noise on harbour porpoise energetics. Upon exposure of two porpoises to playbacks of pile driving sound (SELss between 134 and 152 dB re 1 µPa2s), their ability to catch fish was negatively affected. In both animals, the number of aborted trials increased, and one was also less successful in catching the prey. The potential impact of decreased foraging was studied measuring the effect of fasting for 24 h on the body condition in 4 seasons. It showed that the average body mass loss (up to 4%) was greatest in autumn and lowest in summer. Some insight into the potential ability to recover from periods of food deprivation could be derived from the study in which four porpoises were fed larger meals than usual. If food is abundantly available after a period of fasting, harbour porpoises can eat a large percentage (~ 95%) of their daily food requirement in one feeding bout. One should take into account that the daily requirement varies with the season, being the highest in winter.

Can short, medium and long-term elements of energetics and physiology help understand the effects of disturbance on harbour and grey seals – David Thompson, SMRU

By necessity modelling exercises such as PCOD or IBMS must make simplifying assumptions about prey acquisition, food processing and short, medium and long term energetics.  Predators on the other-hand are making sophisticated fine-tuned decisions about foraging and diving behaviour in the context of :

  • short term energetic/oxygen consumption constraints; divers face absolute unavoidable constraints in individual dives due to limited oxygen stores. How they deal with these has important implications for foraging efficiency
  • satiation constraints; short term limits (e.g. stomach capacity), medium term limits (e.g. food processing) and long term limits (e.g. lean tissue growth or fat storage capacity) will all influence foraging efficiency.
  • long term energetic goals; e.g. reproductive v growth.

All of these factors will influence how successfully seals exploit their environment and how their responses to anthropogenic disturbance will affect their foraging efficiency and long term status.   In this talk I will use information from grey and harbour seals to try to address some of the implications of this mismatch in level of detail for energetics models and their predictions of disturbance effects.

Forecasting the population consequences of disturbance: insights from simple bioenergetics models – John Harwood – Centre for Research into Environmental and Ecological Modelling, University of St Andrews, UK. 

The PCoD conceptual framework provides a comprehensive structure for developing models to forecast the population consequences of disturbance (defined as a deviation in an animal’s physiology or behaviour from patterns occurring without predator or human influences).   However, there is limited empirical information on the effects of disturbance on an animal’s health (usually measured by its energy reserves), and on the effects of variations in health on individual vital rates (survival, probability of giving birth, and age at first reproduction).  Simple bioenergetic models can provide insights into how disturbance that results in either reduced energy intake or increased energy expenditure may affect an individual’s health.  The importance of these effects depends on when during the individual’s life cycle disturbance occurs and on the species’ life history strategy.  The same models can also provide predictions of the potential effects of changes in health on vital rates.  However, these predictions depend on how an individual choses to use its own energy reserves if these are depleted.

Using individual-based models to assess impacts of disturbances on marine populations – lessons learned from the DEPONS project  Jacob Nabe-Nielsen – Aarhus University, Aarhus, Denmark

Agent-based models are unique in allowing population impacts of anthropogenic disturbances to emerge from their impact on individual animals. In the DEPONS model individual animals get deterred by noise, which reduces their foraging efficiency and potentially also their fitness. It has been parameterized based on movement and distribution data for harbor porpoises to assess population impacts of wind farm construction. These impacts were negligible when simulating the construction of a realistic number of wind farms in the North Sea. They only became visible when increasing simulated noise levels to let animals respond up to 20–50 km from the construction area. In that case the population impacts depended on the piling schedule. This demonstrates how agent-based models can be used for spatial planning to reduce impacts of anthropogenic disturbances based on well understood processes and empirical data.

A harbour seal IBM –  an attainable management tool? – Bernie McConnell et al. – SMRU, UK

A quantification and modelling of harbour seal movement is required to predict the consequence of environmental change on both population distribution and movement connectivity.  One approach to this challenge is a mechanistic individual based model (IBM) of seal movement.  IBMs predict emergent behaviour from physiological capabilities and constraints using a set of biologically realistic behaviour rules within a simulated ecological environment.

A simple prototype harbour seal IBM has been constructed with two currencies: energy and information (following Nabe-Nielsen et al., 2013).  This model is now being developed and expanded.  A major challenge is to find and parameterise the appropriate level of complexity that can be supported by data and yet can also provide realistic, defensible and useful outputs.  The model is scalable such that it will be able to incorporate future information about individual response to anthropogenic disturbance and to the consequence of individual condition on population demographic parameters.

We can’t wait to see you there at the INPAS symposium! Register here!