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Soniferous behavior of the striped cusk-eel, Ophidion marginatum, and other coastal marine fishes based on preliminary laboratory and field observations.
Rodney A. Rountree*1 and Jeanette Bowers-Altman2.
(1)Department of Natural Resource Conservation, UMASS-Amherst, 48 Oregon Rd., Mashpee, MA 02649, USA
(2)NJ Division of Fish and Wildlife, Endangered and Nongame Species Program, Southern Region Office, 220 Blue Anchor Road, Sicklerville, NJ 08081, USA.
Poster presentation at the Fish Bioacoustics Conference, Chicago, IL, May 2001.
We conducted a preliminary study of the reproductive behavior and soniferous activity of the striped cusk-eel, Ophidion marginatum. Three female (225-263 mm TL) and six male (160-193 mm TL) cusk-eels were held in a flow-through tank under ambient conditions from 22 July - 22 September 1989. Cusk-eels remained burrowed during the day and emerged at sunset at the onset of courtship and spawning behavior. All spawning was completed within 2-h after sunset. Eggs were encased in a clear gelatinous mass that gradually expanded until breaking up after about 24 hours. Eggs hatched in 36 hours. The male cusk-eels produced croaking sounds before and during courtship and spawning. Calling was often initiated while cusk-eels were still partially or entirely burrowed. Sounds consisted of 1-27 pulses between 500 and 1800 Hz. These sounds have previously been described as "chatter" from field recordings and were mistakenly attributed to the weakfish, Cynoscion regalis. Field recordings of cusk-eel choruses were made during August and September 2000. Calling began just before sunset and subsided within 2-h after sunset in agreement with our laboratory observations.
The striped cusk-eel, Ophidion marginatum, is an abundant coastal marine species occurring from Long Island, NY to northeastern Florida. However, it rarely occurs as far north as Cape Cod, MA. Relatively little is known about the ecology of this species because of its cryptic nocturnal habitat. It remains burrowed within the sediment during the day, emerging primarily during the evening hours. The striped cusk-eel has been known to be soniferous for many years, because of the presence of well described sonic muscles associated with the swim bladder and cranium. However, sound recordings were not available until we observed spawning in the laboratory during this study, which Mann et al. published in 1996. Although most Ophidids have sonic organs, to our knowledge no other species has been recorded to date (or at least not identified - see poster of Fish Sound Archive). The striped cusk-eel is sexually dimorphic, both in external appearance where mature males have a prominent hump on the nape associated with a dorsal sonic muscle (Fig. 1 ). Females lack the hump and dorsal sonic muscle, but do possess a smaller ventral sonic muscle. In addition, males tend to be somewhat smaller than females. Sound production is prevalent in the males, but is uncertain in females. Our observations suggest that females do produce sounds, but are inconclusive. We observed captive cusk-eels in preliminary spawning studies during 1985, 1989, 1990 and 1991. The largest of these studies was conducted from July 22 - September 21 1989. We also recorded sounds attributed to striped cusk-eels in the Great Bay estuary of southern NJ during August and September 2000.
During the 1989 study, 6 male and 3 female individuals were captured in Great Bay at night by trawl. They were placed in a 1.2 m x 1.2 m by 0.9 m observation tank with approximately 15-20 cm of sand substrate (Fig. 2 ). The tank water was maintained under ambient temperature and salinity via a flow-through sea water system. The fish were fed live grass shrimp, Palaemonetes vulgaris, each night. Observations of spawning behavior were made each night beginning just prior to sunset and ending about three hours after sunset. A red light placed above the tank and small flashlights were used to illuminate the fish for observations. The red light appeared to have no influence on the fish behavior, while the flashlights occasionally startled the fish if moved abruptly. Cusk-eels normally remained burrowed under the substrate during the day and did not emerge until sunset or later. Emergence was usually a gradual process, taking up to many minutes time (Fig. 3 ). Calling was typically initiated at sunset while the fish were still burrowed and continued throughout emergence and spawning until about 2 hours after sunset. Courtship and spawning occurred soon after sunset. Courtship was most often initiated by the male, but was also initiated by the female. Often courtship was initiated while one sex was still partially burrowed. Typically a male would approach a burrowed female and nudge her with his mouth and barbel-like pelvic fins until she emerged from the sand (sometimes the female nudged a burrowed male out of the sand). Once spawning was initiated, the male would grasp the female by the nape (between the eyes and dorsal fin origin) with its head placed at right angles to the female's body, and his body bent sharply backward to allow the male to swim alongside the female (Figure 4 ), also view the real movie "cusk1spawn.rm"). The male would often "mouth" the female vigorously during this stage, while the female would swim rapidly around the tank as if to dislodge the male. Occasionally two rival males would attempt to mate with a single female. They would vigorously push and shove each other in an attempt to dislodge their rival and retain their own hold on the female. After a moment of vigorous twisting and rapid swimming, the pair would rise to the surface where the male often twisted around to accomplish a brief ventral mount. The male would then rapidly flip away while the female often remained at the surface gulping air. This sequence can be viewed in the accompanying movie clip. Note that the gelatinous egg mass can be seen protruding from the female's vent after the male flips away. The egg mass is positively buoyant and superficially resembles a ctenophore in the water (Fig. 5 , and video clip cusk1egg.rm). Its size appears to be a function of the size of the female. The egg mass dissipates within 24 hours. Larvae hatched within 48 hours and survived until about 64 hours before apparently dying of starvation. The largest female began spawning almost nightly (>40 times) beginning on 30 July through 13 September. The second largest female began spawning 3 August and also spawned almost nightly through 13 September (21 times), while the smallest female began spawning 12 August and stopped after 6 September (12 times).
Sounds produced by cusk-eels during spawning in the laboratory were recorded in air with a tape recorder (Fig. 6 ). A sequence recorded simultaneously with spawning by the largest female and male individuals is shown in Figure 6 (see also sound clip cuskeel12aug_1922h.wav). Calling and spawning ceased after 13 September in the laboratory. Field recordings made with an underwater hydrophone during August and September 2000 and attributed to striped cusk-eels (Fig. 7 see also sound clip cuskeel5aug00.wav) exhibited a similar daily and seasonal pattern. Calls were rare after mid-September and occurred from sunset until approximately 3 hours after sunset. Other data suggests that striped cusk-eels may be abundant as far north as Narragansett Bay, Rhode Island (Perkins, in press), and perhaps Cape Cod, MA (pers. observ.). If verified, that would extend the species range and demonstrate the usefulness of passive acoustics in monitoring some fish populations.
Figure 1. Male and female striped cusk-eels (taken from Courtenay, W.R. 1971. Sexual dimorphism of the sound producing mechanism of the striped cusk-eel, Rissola marginata (Pisces: Ophidiidae). Copeia 1971:259-268).
Figure 2. Flow-through seawater tank used during the study.
Figure 3A. Male striped cusk-eel beginning to come out of its burrow. Calling usually begins at this time, or even while still completely under the sand.
Figure 3B. Male striped cusk-eel emerging from its burrow. Emergence is a slow process that can take 10 to 20 minutes.
Figure 3C. Striped cusk-eel fully emerged and swimming slowly along the bottom.
Figure 4. Male (top) and female engaged in spawning.
Figure 5. Single egg mass after release.
Figure 6. Frequency spectra and waveform of striped cusk-eel sounds during laboratory spawning (click here to hear this sound clip).
Figure 7. Frequency spectra and waveform of cusk-eel sounds recorded from the field in Great Bay, NJ during August 2000 (click here to hear this sound clip).
This page was last modified on July 20, 2001
Copyright © 1999 by Rodney Rountree. All rights reserved
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