Both natural (e.g., snapping shrimp) and anthropogenic(e.g., shipping noise) sound sources can increase the level of background or ambient noise in the environment. Masking occurs when noise interferes with a marine animal's ability to hear a sound of interest. The significance of the masking effect is influenced by the amount of time that the noise is present and its level. Just as it can be difficult to hear someone talking at a loud party, elevated noise levels may mask important sounds for marine animals. This is of particular concern to marine fishes when the noise is at frequencies similar to those of biologically important signals, such as mating calls (for more information on frequency ranges of underwater sounds, please see What are common underwater sounds?). Low frequency anthropogenic noise below 1 kHz overlaps with the hearing range and sounds produced by most fish species and may cause masking.
Many fish species produce sounds (for more information see How do fish produce sounds?). For example, fishes may vocalize during spawning aggregations and courtship interactions. Problems with detection and recognition due to the presence of anthropogenic noise could therefore have impacts on reproductive success . Masking could lead to a reduction in detection distance, the distance at which a biologically significant signal is detected, or signals may be detected, but important information in the signals may get lost. In the presence of ferryboat noise, hearing of the Lusitanian toadfish, a coastal, bottom-dwelling fish, was masked at multiple frequencies . Ship noise also appeared to interfere with the fish being able to acoustically detect other members of their species. Nesting males produce characteristic boatwhistle calls to attract females for mating. The ability of females to detect nesting males may therefore be restricted in the presence of shipping noise.
The life history of most coral reef fishes includes a pelagic larval stage that undergoes metamorphosis to the juvenile stage. Late stage larvae and transforming juveniles need to seek out suitable reef habitats. There is evidence that underwater reef sounds can be detected by the coral reef fish (and invertebrate) larvae guiding them to coastal areas and allowing them to identify suitable settlement habitats      . If anthropogenic sounds on coral reefs mask natural sounds, and if larval fishes use acoustic cues to find suitable reef habitats, then coral reef fish populations may be negatively impacted. More research is needed on the hearing abilities of early life history stages of fishes and the physical and special characteristics of natural reef sounds to which fish may be attracted.
- How do fish hear?
- How do fish produce sounds?
- Snapping Shrimp
- What are common underwater sounds?
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- Vasconcelos, R.O., Amorim, M.C.P. and Ladich, F. 2007, "Effects of ship noise on the detectability of communication signals in the Lusitanian toadfish." The Journal of Experimental Biology. 210, 2104-2112.
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