Boat Noise And Fish Communication
Countless marine organisms use ambient sound to navigate, choose habitats, and modify their daily behaviors such as breeding, feeding, and socializing. Ambient underwater sound is an incredibly important feature of marine habitats, and it’s widely suspected that elevated levels of anthropogenic underwater sound, particularly due to commercial shipping, could affect how well the animals can communicate among themselves. In this study, researchers monitored Atlantic cod and haddock in the Stellwagen Bank National Marine Sanctuary off the densely populated New England coast. There, they investigated changes in estimated effective communication spaces at three spawning locations for these two ecologically important fish species.
To set the context, the researchers note that 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. One of the most widespread but poorly understood ways fishes may be affected by chronic, lower-level artificial sounds (for example, vessel sound) is through the disruption of acoustic communication by auditory masking (e.g., when one sound is obscured by the presence of another sound). Masking occurs when sound-receiving fishes experience an increase in the overall sounds they receive, which can potentially lead to complete or partial loss of intended signals from other fishes, misinterpretation of such signals, and/or involuntary changes in the response.
The study found that ambient sound across Atlantic cod and haddock spawning sites varied significantly, and as a result, so did their estimated effective vocalization radius (that is, the distance at which the fishes can communicate properly). These spaces were extremely reduced in the presence of sound produced by large vessels and, at times, by fin whale vocalization. Although cod populations are overfished in many areas — the population in the Gulf of Maine is at a historic low of about 80% less than it was a decade ago — the haddock population in the studied area is currently considered to be stable, meaning that many individuals are continuously affected by anthropogenic noise. On a side note, the researchers note that fishing quotas have recently increased dramatically for the latter species because of their population growth and to compensate for stricter control enforced over other fish populations like cod.
Among fishes, it’s common for females to visit groups of males, initiate a spawning event with an individual, and return to their previous locations. For successful courtship, effective attraction cues are essential. On the other hand, it’s also hypothesized that the chorus of large groups of male Atlantic cod may serve as long-range signals to attract females to the area. Naturally, if any of these signals are undetected or misinterpreted, it could lead to the mistiming or unsuccessful location of spawning groups, presenting a critical threat to the survival of these populations.
Meanwhile, haddock vocalization during spawning seasons may also be used to mediate the migration or attraction to spawning locations in transient populations, and at distances of more than 10 meters. What’s more, researchers have often observed male haddock repeating long knocking sounds for hours at a time, even in solitude with no other fishes close by. This indicates that males exhibit clear sexual readiness to females in their occupied territories. Mounting evidence suggests that acoustic communication can indeed affect the survival and reproductive success of fishes, and direct evidence shows this is true for Atlantic cod populations.
The findings of this study highlight the ever-increasing need to better understand the role anthropogenic sound plays in the disruption of acoustic communication within marine environments. The authors recommend future research into which species can compete with anthropogenic noise through adaptation or adjustment of their acoustic signals, and how other multisensory cues supplement each other when fishes experience behavioral and physiological effects of prolonged exposure to low-frequency sound. Such studies could pave the way for creating anthropogenic noise-free sanctuaries for marine fauna, and could even bring improvements to marine environments that may be adversely affected by whale watching and other wildlife tourism activities. Further research in these areas will also offer animal advocates more information about the effects of human activities on wild roaming fishes.