Fish Choruses Research Articles

Continental shelf fish choruses in Australian waters

Almost everywhere the authors have sampled ambient noise on Australia’s continental shelves, in tropical and temperate waters, evening choruses have been recorded. Chorus maximum frequency varies from a few hundred Hz to a few kHz and may result from different species, but the consistency of the timing and similar chorus nature suggests that different source species are following similar behavior. Individual chorus signals are comprised of single pops or clicks of <200‐ms duration, similar to those described from fish. We hypothesize that these chorus sources are nocturnally active fishes that mainly forage in the water column at night. In the Perth Canyon, Western Australia, shelf break choruses centered at 2 kHz have been measured since 1992. Here each evening the chorus begins shortly after dusk, reaches a maximum around 2 hours post dusk, drops to a lower level, rises again predawn, and then disappears during the day. Canyon net sampling through the water column has only recovered fish of the family Myctophidae as potential chorus sources. Long sea‐noise time series records from the Canyon indicate significant seasonal trends in chorus levels and differences between years, possibly indicating that chorus activity reflects secondary productivity.

Sound detection of reef sounds by larvae of coral-reef fishes

Nearly all teleost reef fishes are pelagic during the larval stage, returning at the end of this stage to settle in a reefal habitat. Little is known about their sensory capabilities or how larvae detect and locate a reef. Sound is the most likely cue, particularly since reef shrimp and fish choruses are audible at considerable distances. Playback experiments off Lizard Island, Great Barrier Reef, broadcast nocturnal reef sounds and artificial sounds (pure tones) in the presence of settlement stage larvae of the coral-reef damselfish Chromis atripectoralis, released during the day within 100 m of the underwater speaker 500–1000 m from the nearest reef. Larvae consistently swam to the south in the absence of playback and during playback of artificial sounds. During playback of reef sounds, they showed no overall swimming direction, indicating that they can hear and can distinguish between a sound with potential biological significance and one without. Light traps with and without playback of reef sounds on 33 paired (playback: nonplayback) trap nights resulted in higher catches for 14 of 17 families for which &amp;gt;10 individuals were trapped. This suggests that not only can larvae hear, but they also have some aural localization capability.

Evening fish choruses near coral reef systems in the Great Barrier Reef, Australia

The nighttime ambient sea noise on and around coral reef systems in northern Australia is characterized by choruses produced by nocturnally active fishes. These choruses are produced year round, from dusk to dawn. Choruses are composed of many ‘‘pops’’ of between 5 and 28 ms length, with a decay envelope suggestive of a lightly damped swimbladder and with source levels calculated at 154–157 dB re: l μPa2 at 1 m peak to peak. Sources are found mostly concentrated over 6–20 m water depth. Choruses have a mean spectral peak at 550 Hz (normal range 500–750 Hz) but may influence sea noise from 100 Hz to 3 kHz. The highest chorus levels occur just after dusk or in the early evening, reaching up to 35 dB above background levels. The recorded levels of choruses displayed distinct daily patterns, lunar patterns with higher levels around new moon periods, and seasonal patterns of highest level during the austral summer. Choruses occur over large spatial scales, with active sources heard at up to 15 km from reef systems and chorus influence on ambient sea noise extending considerably further. It is believed that nocturnal planktivorous fishes, such as those from the families Holocentridae and Priacanthidae, are responsible for choruses. [Work supported by the Australian Defence Science and Technology Organization.]

Late night fish choruses in the shallow waters off San Diego

Two major experiments, SWellEx-1 and SWellEx-3, and one engineering sea test recently have been conducted in 200-m-deep water 8 miles west of the mouth of San Diego harbor. SWellEx-1 was conducted in August of 1993, the engineering sea test in May 1994, and SWellEx-3 in July 1994. For both of the summertime SWellEx experiments, an unusual oscillation in the background levels between 275–550 Hz and 575–700 Hz was observed, typically starting around midnight local time and lasting until sunrise. The repeating pattern to the oscillations is that of a 3–5 dB increase in spectral levels, which lasts on the order of 20 s, and then followed by 25 s or so of lower levels. Azimuthal beamforming has indicated that the predominant direction of this ‘‘cycling sound’’ is from near coastal waters. In the data from the May 1994 engineering sea test, no such cycling sound was present. The character of these signals, i.e., their spectral content, their diurnal variation, their seasonal variation, and their directionality, correspond to those described in year-long, single-hydrophone measurements made from a shallow water tower off San Diego in the early 1960s and ascribed to sounds made by fish of the croaker family [G. A. Clapp, NEL Tech Mem 1027 (1966)]. Additional properties of these signals, including a recording of the sounds made by a single individual, will be presented. [Work supported by ONR Code 321.]

Biological sources of noise in coastal waters

Underwater biological sounds are transient events. Durations range from microseconds to tens of seconds, frequencies from ≤10 Hz to ≥100 kHz, and source pressure levels up to ≥220 dB re : 1 μPa at 1 m. While each sound is produced by one individual, many sounds occur in choruses that may involve thousands of simultaneous sources. Some crustaceans produce loud impulsive noise in the 2–20 kHz range. These animals are common enough in many shallow areas to dominate the ambient near 10 kHz. Evening fish choruses seasonally dominate the ambient in many shallow waters in the 100–1000 Hz frequency range. While whales and dolphins are less numerous than the animals listed above, many species produce sounds of sufficient intensity to affect the ambient. For example, during their winter breeding season fin whales produce series of 20-Hz pulses lasting 1 s at source levels of 180 dB re : 1 μPa at 1 m. Dolphin echolocation clicks may reach source pressure levels ≥220 dB with spectral peaks 50–150 kHz. Dolphins are also skilled mimics of manmade sounds, which may lead to unpredicted interference.