Update for council on the results of the sound from Ultra Music Festival on toadfish kept at the University of Miami Experimental Hatchery:
Toadfish were used because they produce low frequency sounds and are able to hear similarly to other fish species. They have also already been studied extensively at RSMAS. Both of these reasons make them a good model for studying acoustic stress.
Fish stress levels, air sound levels, and underwater sound levels were all recorded before during, and after Ultra.
The toadfish exhibited cortisol (stress hormone) levels that were a 4- to 5-fold increase from their ambient rest levels. This is generally higher than the levels they experience when hearing a simulated predator (specifically, when they hear dolphin pop sounds, their cortisol may increase as much as 4-fold).
Because there is a complex, multi-step reaction that must take place within the body of the toadfish to cause a rise in cortisol, there is always some measure of variability in cortisol levels. Taking this variability into account, the measured 4- to 5-fold increase during the sound from Ultra is considered a statistically significant elevation.
Elevation in cortisol can cause physiological effects such as shutting down digestion, reproduction, and communication in order to maintain short-term survival. Long-term effects of high cortisol levels can be detrimental. However, at this time the researchers cannot conclude whether Ultra will cause any long-term effects on the toadfish.
To paraphrase Dr. Danielle McDonald, one of the researchers on this project and an Associate Professor at the Rosenstiel School, the toadfish could be considered a canary in the coal mine. They are very hardy fish, and a result that finds a significant stress response in such a resilient fish may indicate a similar response in more sensitive fish. At the very least, the researchers cannot conclude that a less-hardy fish would have responded differently.
The air sound levels in the hatchery generally did not exceed 80 decibels, but underwater noise levels in the tanks were on average 7-9 decibels higher (due to the difference in sound traveling in air versus water). They also found that there was a 2-3 decibel increase in sound in the water in Bear Cut, specifically in the low frequency range (meaning bass); however, they cannot draw any conclusions as to how this may have affected wildlife in the area.
Finally, to follow up on a question from the previous Council Meeting about the possibility of illegal mosquito spraying, after consulting with other environmental experts, it was determined that it is unlikely illegal spraying could be proven. Ultra claims to have used Essentria-IC3 as a spray, and BTI dunks in the water to prevent larval recruitment (that is, to prevent larvae survival). Both of these are comparatively good options, environmentally speaking. Essentria is made from a mix of natural ingredients, predominantly plant oils, and BTI dunks involve using a type of bacteria that specifically preys on mosquito larvae. Both are “organic” in that they do not use synthetic compounds. Essentria is not regulated by FIFRA, and BTI Dunks are regulated but seem to be registered for liberal use.