A curious little article was published yesterday titled “Whales ‘hit by seaquake” (link). In it the authors state that “…a seaquake, occurred off the Norwegian course on August 30, and scientists believe it may have caused the group of 26 whales to veer off course”
The possible link between strandings and earthquakes is both fascinating and complex. Some believe that quakes in fact explain everything about strandings (link). We take a middle path because there are too many factors that favor the earthquake hypothesis of strandings and just as many factors that contradict it. Let’s examine some factors in detail.
Hypothesis #1: Earthquakes are to blame for strandings
1. Historical strandings and records seem to support earthquake hypothesis because quakes (and strandings) have been happening for eons, way before sonar or airguns.
2. One study documented a fin whale fleeing the earthquake (but see discussion below) (link)
3. Many stranding hotspots, such as New Zealand for example occur in seismically active regions.
4. Earthquakes release a lot of energy, in fact the quake of magnitude a little above M5, is capable of producing low frequency sounds that are very intense 240-239 dB re: 1 µPa at 1 m (Gallo-Reynoso et al., 2011). It is of course a very low frequency but it is definitely within large whales’ hearing range of 16 and 44 Hz (human hearing range 20 Hz-20 kHz for reference). The debate is actually is far from being settled about toothed whales and dolphins thresholds for low frequencies (it is a whole new topic for another post).
Hypothesis #2. Earthquakes are not to blame for strandings
1. Our planet is extremely seismically active and has always been so. In fact just over past 30 days more than 1000 quakes happened worldwide. Almost at any given moment there is a quake happening somewhere. To help you visualize this here is a video for quakes occurring on Earth in just 2 months
2. There is no way whales and dolphins did not evolve some sort of adaptation to deal with quakes. The response of a fin whale in the above study might demonstrate this adaptation. When the quake is detected, marine mammals could be moving away from it. Look at the maps from this study. The observed fin whale was 245 km in relation to the epicenter, he was also close to shore, but he did not do a mad dash towards the shore and strand. Instead he breached (actually very interesting behavior that could be a communication to other whales that something is up) and started moving fast away from the quake but PARALLEL to the shore.
3. Mass and single stranded cetaceans do not float passively with currents after experiencing some sort of “damage” possibly induced by a quake. Instead they swim actively towards the shore often at their normal or even accelerated speed. Here are two examples of documented strandings:
a) In July 2010 a rare Sowerby’s beaked whale stranded in Netherlands (link), it was reloated by members of the public but it restranded and died on July 21, in Kent, UK (link). We helped to unravel this mystery because we were curious if it was the same whale and later the lifeguard that helped to refloat the whale confirmed the marks that were clearly seen on a whale stranded in Kent. So in 3 days this whale covered 185 miles and he did not float with currents, but actively swam towards his final destination.
b) We have been posting this video all the time, this is famous rescue from Brazil. And you can see once again that a pod of dolphins swims actively towards the shore and does not just “float with currents”.
4. In New Zealand which is seismically active area there is a significant population of dusky dolphins and they are almost never mass strand. In fact we were only able to find one documented mass stranding in Australia in 90s.
5. Chile is another seismically active region, and while there have been live strandings there, they were not nearly as abundant in terms of animals involved and number of stranding events compared to other areas, such as UK for example. And Chile has very abundant marine life offshore, its not like they do not have whales and dolphins there.
6. Even California with all its seismic activity has less live strandings compared to the US East Coast.
Hypothesis #3. The Middle Ground
1. We think that quakes should not be completely disregarded nor should they be blamed for all strandings.
2. Whales and dolphins most likely can detect quakes or perhaps even their precursors and move away from the harm.
3. Whales and dolphins can still be affected when the quake erupts just below them, or in proximity or during a deep dive. So there are several important factors to consider:
a) quake magnitude
b) distance in regard to a quake
c) activities during the quake
We think that due to unfortunate circumstances sometimes whales’ and dolphins’ adaptations are not enough and if they are caught off guard, in close proximity to a powerful quake and during a deep dive they can be vulnerable.
4. We have been talking a lot about stranding as behavioral response. This could be another way how a quake AND sonar/airguns can induce mass or single live stranding. We think if a pod or a whale are caught between the shore and the source, and cannot move towards the source due to some circumstances/factors we do not fully understand, coming ashore is the only thing the pod or a whale can do. There are many unknowns in this theory however.
Questions to be answered
1. How far is too far? How close to the source a marine mammal should be to be damaged physically or to evoke behavioral fleeing response? The study of a fin whale and a quake shows that M5 quake at 245 km evokes fleeing response but not stranding. Sound travels fast, and what we need to know at what levels sound ceases to become nuisance and turns into danger or even becomes lethal.
2. Sadly cetaceans now live in the environment where not only quakes happen almost all the time, but also where seismic surveys happen all the time along with Navy sonar, Navy “hazardous operations”, missiles tests, explosives, low flying aircraft tests, you name it. With so many possible culpits, the blame can be shifted and the truth can be obscured. Earthquakes are easy to blame as there is always a quake going on somewhere. Given how things stand now, in the future there will be also always some seismic survey or Navy test nearby. How can we determine the cause of stranding? Only by studying it carefully, taking into consideration all culpits, by getting full necropsy, by doing statistical analysis. This is the only way.
Do we think 4 mass strandings that happened in past 2 weeks were due to quakes?
No. And here is why. There were no quakes close by Cape Verde prior and during stranding. The quake up North while powerful was still 1744 km from a stranding site. Let’s say whales were half way between a quake and a stranding site in Scotland, it would take them 3.6 days to cover this distance at their normal speed of 10 km/h. As for Florida and Cape Cod, no quakes in Cape Cod and very minor quakes in Puerto Rico region and one small quake 187 km E of Georgia (see interactive website here, you can check all quakes small and big ones last 30 days link)
The bottom line:
While quakes can affect marine mammals in one way or the other but they cannot be blamed for all live strandings. Quakes can be important as cetaceans might evolve the reflex or reaction to flee the quake and they might as well try to flee many other sources such as sonar or airguns. Or they may be even more vulnerable to anthropogenic noise as they do not know how to deal with it and did not evolve successful coping strategy.
As you see live strandings are very complicated events and we need to take as many factors into consideration as possible, but we also have evaluate all factors based on plausibility and data available.