A Stinking Mess
Last week a school of fish caused quite a stink in Marina del Rey. Sadly, an entire school of anchovies ended up in a shallow dead-end basin of the marina, and before they managed to swim out to more open waters, the thousands of fish used up the available oxygen and suffocated. These mass mortality events are tragic, but not necessarily a sign of foul play. Much like the mass mortality event that occurred in King Harbor in March 2011, the cause is likely just a perfect storm of conditions that lead to a lack of oxygen in the water so extreme it caused fish to die. In this case it was the recent heat wave, poor circulation in the basin and timing of the large school of fish that resulted in significant oxygen reduction in the basin and ultimately caused mortality of the fish. When oxygen levels drop below 2mg/L, waters are considered hypoxic and fish begin to be stressed.
This is what likely happened late Saturday night on May 17th in Marina del Rey. By Sunday morning Community Program Manager, Michael Quill, and LA Waterkeeper volunteers witnessed thousands of dead fish blanketing the basin. LA Waterkeeper, in collaboration with Marina Harbor, quickly acted to activate volunteers for a cleanup effort and monitor the dissolved oxygen levels with some help from Dr. John Dorsey at Loyola Marymount University. In the first couple days after the mortality event we observed dissolved oxygen levels below those capable of supporting marina life. In fact, the farthest back corners of the basin the water were anoxic (no oxygen). After an extensive cleanup of the decaying fish thanks to some awesome LA Waterkeeper volunteers and the temporary installation of some water circulation pumps, the basin is now showing signs of recovery from the episode. Dissolved oxygen levels were up above 2mg/L a week later and most noticeably the smell has subsided.
LA Waterkeeper hopes to continue to work with LMU to monitor and collect data on dissolved oxygen levels throughout the marina and hopes to better understand the health of the marina and predict when low oxygen conditions are a risk to fish and marine life.
Big thank you to Dr. John Dorsey, LA Waterkeeper volunteers and Marina Harbor.
-Lara Meeker, Watershed Program Manager