Scott A. Holt
University of Texas at Austin
Marine Science Institute
Fisheries and Mariculture Laboratory
750 Channel View Drive
Port Aransas, Texas 78373
The overall goal of our research program is to provide new knowledge about
the ecology and biology of coastal fishes, with emphasis on sciaenids,
through field and laboratory investigations. Our field investigations
focus on the egg and larval stages and investigations of spawning activity
are an essential component of analysis of larval supply issues. Passive
acoustics is being employed as a primary tool in locating spawning sites
of soniferous sciaenids.
Our current efforts are directed almost exclusively at red drum (Sciaenops
ocellatus). This species spawns primarily in coastal waters and within
tidal inlets. We are using two techniques to locate spawning sites and
to investigate spawning activities. One employs a fixed hydrophone on
a pier extending into the Aransas Pass tidal inlet. This hydrophone is
connected to a desktop computer that records 20 seconds of audio every
15 minutes, every evening from 1700 hrs to 0100 hrs in the morning during
August, September, and October. Previous research has shown that red drum
spawn during the fall season and only in the evening (Holt et al 1985).
The time window encompasses the daily spawning period. These investigations
are designed to document daily drumming activity at a single spawning
site. Results from the previous two years (2000 and 2001) show that drumming
occurs essentially every night at the site and peaks during a two hour
period beginning about dusk.
The second technique is to use a towed hydrophone array to determine the distribution of red drum spawning sites in nearshore coastal waters. We have found that an array can be towed at about 3.0-4.0 kts and still produce good quality recording of red drum calls. Based on the results of the fixed hydrophone results described above, we can sample only during a 4-5 hour period each evening and thus can cover approximately 20-25 km per day. Initial surveys along a portion of the central Texas coast line have shown that spawning is relatively widespread along the 10 meter contour. Additional surveys will be conducted to outline the total extent of the red drum spawning area.
Our primary focus will be to determine the extent of the red drum spawning
sites along the central and southern Texas coast. In addition to the towed
array, we intend to employ remote, fixed hydrophones to study site fidelity
and daily activity. Huge volumes of data are collected during these investigations
and we will work with other investigators to develop means for automated
processing of both archived and real-time data. Passive acoustic data
also has the potential to reveal substantial insight into the behavior
of fish at spawning sites. Observations of red drum spawning in captivity
at the Fisheries and Mariculture Lab will aid in these interpretations.
We ultimately intend to extend our investigations to other sciaenids in
the area, especially spotted seatrout and Atlantic croaker.
Holt, G.J., S.A. Holt, and C.R. Arnold. 1985. Diel periodicity
of spawning in sciaenids. Marine Ecology Progress Series 27(1-2):1-7.
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