Around the world, estuaries provide habitat for economically important fish species. Monitoring estuarine fish communities is a vital step in preserving ecosystem health, as well as the socioeconomic well-being of coastal populations. In the Gulf of Mexico, extractive methods such as gillnet, trawl, and seine net sampling are required to assess the health of fish populations as the high turbidity and shallow depths found here don't support the use of visual surveys or deep-water techniques (e.g. active acoustic sonar). While these techniques yield critical population assessments, they can result in high fish mortality and suffer from relatively low temporal resolution, making it difficult to detect community shifts following acute natural or anthropogenic disturbances that often impact estuaries.
Passive acoustic monitoring (PAM), which captures the many sounds produced by aquatic animals, offers a potential complementary means for monitoring estuarine fish communities. PAM is non-invasive and can be deployed to continuously monitor aspects of fish community health for weeks to months at a time. Estuarine soundscapes are often characterized by a broad range of drums, knocks, and croaks of soniferous (sound-producing) fish which are often tied to courtship and spawning behaviour. By quantifying these sounds, researchers can monitor soniferous fish biodiversity and the spawning activity of selected species through time. However, the capacity of PAM to track changes in fish abundance and biodiversity of entire communities has yet to be tested in low-visibility estuarine systems.
The authors of the latest Editor's Choice article in ICES Journal of Marine Science use simultaneous acoustic and gillnet surveys to assess the utility of PAM for tracking the relative abundance and biodiversity of fish in a turbid estuary in south Texas. The results show clear, positive relationships between gillnet fish catch (a proxy for overall fish abundance) and both sound levels and scored fish-calling activity, especially among species in the ecologically important Sciaenidae family during the spring months. This suggests that PAM can be deployed to monitor fish populations in Gulf of Mexico estuaries during active spawning seasons in a near-continuous, long-term fashion.
Estuarine systems worldwide are expected to experience more frequent and severe disturbances over the coming decades associated with anthropogenic pressures. The authors suggest that researchers could apply the methodology to validate similar acoustic-community relationships in their own estuarine systems. Once established, these relationships can be used for adaptive management where PAM is used to detect sudden community shifts and policy is adjusted to conserve local fisheries.
Read the full paper, Paired passive acoustic and gillnet sampling reveal the utility of bioacoustics for monitoring fish populations in a turbid estuary, in ICES Journal of Marine Science.
Left: Recreational fisher holding a spotted seatrout (Cynoscion nebulosus), an economically important soniferous fish. Right: Acoustic recorder used to capture estuarine sounds.