"Some people talk to animals. Not many listen though. That's the problem."

-A.A. Milne

Fish 'n Ships:
Understanding the communication space of fishes in anthropogenic influenced environments

Massachusetts Bay is located off the densely populated coastal zone of the northeast coast of the United States and appropriately experiences high anthropogenic activity. Subsequently, its inhabitants are exposed to increased levels of anthropogenic underwater sound, particularly due to large commercial shipping. The current study investigated the alteration of estimated effective communication spaces at three ecological relevant spawning locations for populations of the commercially and ecologically important fishes, the Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus). Both the ambient sound pressure levels and the estimated effective vocalization radii fluctuated dramatically during the 3 month recording periods at each of the three recording sites. Increases in sound pressure level appeared to be largely driven by large vessel activity, and accordingly exhibited a significant positive correlation with the number of Automatic Identification System tracked vessels within a 10 nmi radius of the recording site. The near-constant high levels of low frequency sound, and consequential reduction in the communication space, observed at these recording sites during times of high vocalization activity raises significant concerns that communication between conspecifics may be compromised during critical biological periods, i.e., migration, courtship and spawning. This study takes the first steps in evaluating these animals' communication spaces and alteration of these spaces due to anthropogenic underwater sound.

Sound is an efficient way to communicate in the marine environment, and animal inhabitants and people alike have developed ways to exploit this fact. Many organisms occupying the oceans actively use and produce sound. Marine mammals use sound as a primary method for communicating underwater over large distances. Over shorter spatial scales, fishes do the same. Marine invertebrates produce sound both actively for behavioural display purposes, as well as passively due to feeding or movement. Many marine organisms utilize ambient sound to navigate, choose their settlement or residence location, and to modify their daily behaviour, e.g., breeding, feeding and socializing.

Features of ambient sound are a result of the characteristics of all of the contributing sound sources, including those composed of biological sounds such as animals vocalizing (biotic), physical sounds such as wind and water movement (geophysical or abiotic), and anthropogenic sounds such as shipping or construction.

Visual representation of sounds from vessel and fish together

Example of visual representation of 1-hour vessel passage and haddock vocalizations at haddock winter spawning site.
Spectrogram of 1-hour vessel passage, (b) Full spectrum sound level over 20-1000Hz frequency range, (c) Power spectra of 20 sec length of recording when vessel is at its closest approach to hydrophone with a full spectrum sound level of 113.5dB re 1 ÁPa in the 10-100Hz frequency range (>90th percentile), (d) Power spectra of 20 sec recording when vessel left immediate vicinity of hydrophone with a full spectrum sound level of 101.2dB re 1 ÁPa in the 10-1000Hz frequency range (50th percentile). In plot a, red box indicates time section for plot c and black box indicates time section for plot d. Colour bar units are dB re 1 ÁPa2 Hz-1. FFT: 1024, Hann window, 80% overlap.

Anthropogenic sound in certain ocean regions has increased considerably in recent decades due to various human activities such as resource acquisition, global shipping, construction, sonar, and recreational boating. As ocean sound increases, so does the concern for its effects on populations of acoustic signalers. Effects of anthropogenic sound exposure can be seen in the physiology and behaviour of a range of marine organisms, from invertebrates to marine mammals, with studies on these effects to date largely focusing on high-amplitude sources. However, few studies have addressed the effects of lower-level and chronic sound exposures.

One of the most widespread, yet poorly understood means in which fishes could be affected by chronic, lower-level anthropogenic sound, such as vessel sound, is through the disruption of acoustic communication by masking. In this situation, the receiver experiences an increase in the threshold of detection or discrimination of the signal which could potentially lead to complete or partial loss of received signal, misinterpretation of the signal, and/or subsequently changes in the response. To date, there have been very few documented studies on the potential of anthropogenic sound to mask, disrupt or reduce acoustic communication in fishes, and fewer still on the means of avoiding masking in the presence of extraneous sound.

For these reasons, working in partnership with the Stellwagen Bank National Marine Sanctuary, we investigated the alteration of estimated effective communication spaces at three spawning locations for populations of the commercially and ecologically important fishes, Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus). We found that the ambient sound levels at the three spawning locations varied significantly and ranged from 84.7 139.9 dB in the full spectrum band (10 - 1000 Hz) (hourly averages). Both the "grunt" and "knock" vocalizations emitted by Atlantic cod and haddock occupy the same frequency range as many underwater anthropogenic sound sources (Stanley and Jeffs, 2016), with the peak of acoustic energy in the 50-260Hz frequency band (Finstad and Nordeide, 2004; Hawkins and Amorium, 2000).

The results (Stanley, Van Parijs & Hatch, 2017) illustrate that ambient sound across the Atlantic cod and haddock spawning sites varied significantly, and as a result so too did the estimated effective vocalization radius. These spaces were extremely reduced in the presence of sound produced by large vessels and at times the vocalizations of fin whales. While high intensity sources hold much of research and management attention, more moderate sounds of much longer duration, like those produced by commercial shipping vessels, dominate background noise conditions over much larger areas and thus have the potential to effect greater numbers of marine animals.

figure showing vocalization radius for cod and haddock

Figure 4: Estimated effective vocalization radius (m). a) Atlantic cod grunt, b) Haddock knock. The broken line (----) indicates mean vocalization radius and star (*) indicates 10th and 90th percentiles.
Fish images reproduced with permission from Scandinavian Fishing Yearbook.

Partners: NOAA Stellwagen Bank National Marine Sanctuary, Cornell University

Primary Funders: Massachusetts Environmental Trust, International Fund for Animal Welfare, National Oceanic Partnership Program (NOPP), U.S. NOAA's National Marine Sanctuary Program, US NOAA Fisheries' Northeast Fisheries Science Center and Regional Office
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(File Modified Jan. 11 2018)