In anticipation of the upcoming gulf corvina, Cynoscion othonopterus, fishery season in the Upper Gulf of California, researchers with the Gulf of California Marine Program from Scripps Institution of Oceanography visited El Golfo de Santa Clara to meet with fishermen and test their active acoustic instruments. On 7 February, 2014, Timothy Rowell, Brad Erisman, Catalina López Sagástegui, Marcia Moreno Baez, and Tammy Wilson met with boat captain Angel Montes, Yazmin Flores, and Josué Montañez to plan the logistics of collecting passive and active acoustic data during periods of heavy fishing and dense corvina spawning aggregations in the waters surrounding Isla Montague. The meeting was an immense success and paves the way for successive trips to El Golfo de Santa Clara.
Tammy Wilson, Yazmin Flores, Angel Montes, and Timothy Rowell (left to right) pose for a team photo during data collection.
On the following day, Timothy, Brad, and Tammy joined Angel and Yazmin aboard Angel’s panga to visit the region of the Upper Gulf of California where the corvina aggregations are believed to be most dense during the months of March through May. In addition to becoming familiar with the panga and region, the researchers installed their active acoustic system and conducted a trial sampling session. An ES60 120KHz Split Beam Echosounder (a scientific fish finder) was lowered into the water with a custom fitting arm specifically designed for Angel’s panga. To everyone amazement, the design fit like a glove and no problems were encountered.
Meanwhile, Tammy and Brad lowered a CTD into the waters to determine the depth profile of temperature and salinity, which later can be used to determine the speed of sound in the water. After all the echosounder instrumentation was fitted and connected to a computer, Timothy directed Angel to start the survey. The team conducted transects across the delta channels near Isla Montague, while actively viewing the Echograms of target signals detected by the echosounder. For the first time, everyone on board was able to see the dynamic bathymetry of the channels with depths ranging from 0 meters to 20 meters. More interestingly, the echograms revealed that beneath the murky waters there were a lot of fish, although they were most likely not corvina as they were not aggregating in these waters at that moment in time. However, the good news was everything worked extremely well; fish were detected, bottom depths were determined, and instrumentation performed beyond expectations. Oh, and Angel is the perfect captain for the work. What a great trip! This trip proved that all the cards are now in place for great, rewarding, and revealing sampling season in the Upper Gulf of California.
An echogram of the recorded active acoustic data, highlighting the abundance of small fish in the survey region. Dark red denotes the surface and bottom depths, while colored pixels indicate the presence of fish.
In the upcoming months, researchers will revisit the region to use active acoustic technologies to determine fish densities and biomass of corvina spawning stocks within the aggregation. Additionally, passive acoustic recorders will document the sounds produced by these courting croakers (Sciaenidae). It is believed that male corvina call to females as part of a courtship behavior that is highly timed to periods of spawning. In previous years, the sounds of aggregating corvina have been recorded (they are very very loud); however, maximum sound levels have yet to be determined. During this upcoming season, researchers will monitor temporal changes in corvina vocalizations and calculate maximum sound levels, which may correspond to the loudest fish aggregation ever to be discovered! Sound levels will be compared to active acoustic density estimates to see how sound levels relate to fish numbers. The results will be groundbreakings, so be sure to stay tuned in for more to come.