ME70 Water Column Sonar Data Collected During RL1706

The sampling resolution was not expected to allow for a comprehensive assessment of all anchovy sub-populations. In particular, those residing in the Southern California Bight and off the Columbia River plume would likely require additional effort given their patchy distribution. The modeled distribution of potential sardine habitat, and information recently gathered from other research projects (e.g., CalCOFI samples) or the fishing industry (e.g., sardine bycatch) were used to determine whether the survey domain also encompassed the northern sub-population of sardine. A brief, cooperative survey of CPS was also conducted in coordination with the F/V Lisa Marie in nearshore areas off Washington and Oregon. Two industry observers from Lisa Marie embarked Lasker before she conducted echosounder, sonar, and purse-seine sampling along nearshore extensions of Lasker&#8217;s transect lines. In the same region, Lasker coordinated with the fishing industry&#8217;s aerial-photographic sampling. Multi-frequency (18, 38, 70, 120, 200, and 333 kHz) General Purpose Transceivers (Simrad EK60 GPTs) and Wideband Transceivers (Simrad EK80 WBTs) were configured with split-beam transducers (Simrad ES18-11, ES38B, ES70-7C, ES120-7C, ES200-7C, and ES333-7C, respectively). The transducers were mounted on the bottom of a retractable keel or &#8220;centerboard&#8221;. The keel was retracted (~ 5-m depth) during calibration, and extended to the intermediate position (~7-m depth) during the survey. Exceptions were made during shallow water operations, when the keel was retracted to ~ 5-m depth; or during times of heavy weather, when the keel was extended to ~9-m depth to provide extra stability and reduce the effect of weather-generated noise. To minimize acoustic interference, transmit pulses from two multibeam sonars (Simrad ME70 and MS70), an omni-directional sonar (Simrad SX90), and acoustic Doppler current profiler (Teledyne RD Instruments Ocean Surveyor Model OS75) were triggered using a synchronization system (Simrad K-Sync). All other instruments that produce sound within the echosounder bandwidths were secured during survey operations. Exceptions were made during stations (e.g., plankton sampling and fish trawling) or in shallow water when the vessel&#8217;s command occasionally operated the bridge&#8217;s 50- and 200-kHz echosounders (Furuno), the Doppler velocity log (Sperry Marine Model SRD-500A), or both. Nighttime trawl sampling was conducted where echoes from CPS schools where observed earlier that day. Trawls were towed at ~ 4 kn for 45 min. The total catch from each trawl was weighed and sorted by species or groups. From the catches with CPS, up to 75 fish were selected randomly for each of the target species. Those were weighed (g) and measured to either their standard length (Ls; mm) for sardine, anchovy, and herring, or fork length (Lf ; mm) for jack mackerel and Pacific mackerel. Regional species composition was estimated from the nearest trawl cluster, i.e., the combined catches of up to three trawls per night, separated by ~ 10 nmi. During the day, fish eggs were collected using CUFES (Checkley et al., 1997), which collects water and plankton at a rate of ~640 l min-1 from an intake on the hull of the ship at ~ 3-m depth. The particles in the sampled water were sieved by a 505 &#956;m mesh. All fish eggs were identified to lowest taxa, counted, and logged. Typically, the duration of each CUFES sample was 30 min, corresponding to a distance of 5 nmi at a speed of 10 kn. Because the duration of the initial stages of the egg phase is short for most fish species, the egg distributions inferred from CUFES indicate the nearby presence of actively spawning fish. CalCOFI Bongo Oblique (CalBOBL, or bongo) nets (71-cm diameter; 505-&#956;m mesh) were used to sample ichthyoplankton and krill at each station. Where there was adequate depth, 300 m of wire was deployed and then retrieved at 20 m min-1, at a nominal wire angle of 45\0x0E. Paired vertical egg tow (Pairovet; formerly CalCOFI vertical egg tow or CalVET, (Smith et al., 1985)) nets (25-cm diameter; 150-&#956;m mesh) were used to sample fish eggs from a depth of 70 m to the sea surface at a rate of 70 m min-1 in areas where their densities exceeded a threshold of &gt; 0.3 eggs min-1. Day and night, conductivity and temperature versus depth to 350 m were measured with calibrated sensors on a CTD rosette or underway probe (UCTD) cast from the vessel. These data were used to estimate the time-averaged sound speed (Demer, 2004), for estimating ranges to the sound scatterers, and frequency-specific sound absorption coefficients, for compensating the echo signal for attenuation during propagation of the sound pulse from the transducer to the scatterer range and back (Simmonds and MacLennan, 2005). These data also provided indication of the depth of the upper-mixed layer, where most epipelagic CPS reside during the day.

Tags: acoustic scattering, acoustic sounders, aquatic ecosystems, aquatic sciences, bathymetry, bathymetry/seafloor topography, benthic, biosphere, doc/noaa/nesdis/ncei, doc/noaa/nesdis/ngdc, earth science, ecosystems, fisheries, in situ/laboratory instruments, marine ecosystems, national centers for environmental information, national geophysical data center, nesdis, noaa, north pacific ocean, ocean acoustics, oceans, pelagic, profilers/sounders, seafloor topography, u.s. department of commerce, vertical location, water column, water column mapping system, wcms
Organization: National Oceanic and Atmospheric Administration, Department of Commerce