New conference paper: An experiment to test the effects of sound on the time budget of fish

We just published a new conference paper ‘Exploring effects of sound on the time budget of fishes: An experimental approach with captive cod‘ and it’s open access (PDF)! The paper is part of the PCAD4Cod project and is authored by Daniël A. Wille, Hans Slabbekoorn and myself.

There’s an increasing interest into the effects of anthropogenic sound on marine animals including fish. A variety of studies is being conducted to gain insight into these effects. Ultimately, we want to gain insight into the effects of sound on individuals’ fitness and population levels. Modeling studies show that changes in energy expenditure and intake have most potential to lead to population levels effect. So, it’s important to study the effect of sound on individuals’ time and/or energy budget.

Ideally, this is studied in the field, but it’s very challenging to track free-ranging fish in their natural environment at high resolution. For that reason, we conducted a pilot study in a basin. We videoed 3 pairs of Atlantic cod for 7 hours per day, for 6 consecutive days. We exposed them to the playback of seismic survey sound for 3 consecutive days and a silent control for another 3 consecutive days. Each morning, we introduced live crabs in the experimental basin and the cod exhibited natural foraging behaviour by scanning and lifting patches of oysters in search for the crabs.

From the daily 7 hours of video footage, we extracted 20 second clips every five minutes (see example clips below). We scored the most dominant behaviour of both fish (foraging, swimming or stationary). In this way, we got insight in the activity budgets of individual cod with and without sound exposure. This can be translated to energy budgets by determining the energy expenditure and intake in all behavioural states.

The experimental basin.

New paper: Effects of acoustic features of sound exposures on fish’s behavioural responses

We just published a new paper ‘The role of ambient sound levels, signal-to-noise ratio, and stimulus pulse rate on behavioural disturbance of seabass in a net pen‘ and it’s open access (HTML/PDF)! The paper is a collaboration between Leiden University and Wageningen Marine Research and is authored by Errol (Y. Y.) Neo, Erwin (H. V.) Winter, Hans Slabbekoorn and myself.

We are interested in the effects of man-made sound on marine life, including fish. Sound exposures can have a range of effects on fish; it may mask communication or other biological relevant sounds, elicit physiological and behavioural responses, and may even induce physical damage (close to a loud sound source). The sound levels are often used to predict the potential harm of sound exposure, however the acoustic characteristics of the environment (ambient noise) and sound exposure itself (the potentially disturbing stimulus) may also influence the behavioural responsiveness of animals.

Underwater, ambient noise mainly originates from water surface roughness from weather conditions and boat noise. When ambient noise levels are higher, a potentially disturbing stimulus may stand out less strongly (lower signal-to-noise ratio) and thereby elicit a milder behavioural response. Also, the potentially disturbing anthropogenic sounds themselves vary in acoustic characteristics which may affect fish differently, for example the rate at which poles (e.g. of wind turbines) are being driven in the seabed or the rate at which airguns of seismic surveys are being fired.

We tested the effect of such acoustic characteristics by exposing 16 groups of four European seabass to multiple impulsive sound treatments that varied in elevated background level, pulse rate, and pulse level. We implanted the fish with acoustic tags to be able to track the positions of the individual fish. We showed that the seabass increased their swimming depth after the start of the sound exposure, however the variation in the response could not be explained by any of the tested acoustic characteristics. Nevertheless, based on our review of the literature, we think it is worthwhile to continue on this line of research by testing wider ranges of signal and background levels.

Running a sound exposure trial. In the middle, you see the equipment we used to log the acoustic tag recordings and the amplifier of the underwater speaker (photo 2014).
We measured sound levels accross the net pen. On the background, you see the Oosterscheldekering (Eastern Scheldt storm surge barrier).

Citation: Hubert, J., Neo, Y. Y., Winter, H. V., & Slabbekoorn, H. (2020). The role of ambient sound levels, signal-to-noise ratio, and stimulus pulse rate on behavioural disturbance of seabass in a net pen. Behavioural Processes, 170, 103992. DOI. [Open Access: HTML/PDF]

P.s. During the field season in which we collected data for the current paper, the Dutch TV programme ‘Vroege Vogels’ visited our field site to make an item on the effects of sound on fish in general, and about another study we did on an acoustic deterrent device for fish. For this, we also used the floating pen and a highly simular experimental design, so it may be interesting to watch the tv item (from 14:35 min on):

European seabass (our study species).
Assembling the study island and loading it with 150 kg anchoring blocks (photo 2014).
Anchoring the platform at the right location. We used a combination of chains and stretchable bungee ropes to keep the island in place throughout tides (photo 2014).
In the artificial cove ‘Jacobahaven’, our fieldsite (photo 2014).