there were no mass strandings at other times. They did not propose a theory for the strandings. Fernández et al. in a 2013 letter to Nature, reported that there had been no further mass strandings in that area, following a 2004 ban by the Spanish government on military exercises in that region. In May 1996, there was another mass stranding in West Peloponnese, Greece. At the time, it was noted as "atypical" both because mass strandings of beaked whales are rare, and also because the stranded whales were spread over such a long stretch of coast, with each individual whale spatially separated from the next stranding. At the time of the incident, there was no connection made with active sonar; A. Frantzis, the marine biologist investigating the incident, made the connection to sonar because he discovered a notice to mariners concerning the test. His report was published in March 1998. Peter Tyack, of Woods Hole Oceanographic Institute, has been researching noise's effects on marine mammals since the 1970s. He has led much of the recent research on beaked whales (Cuvier's beaked whales in particular). Data tags have shown that Cuvier's dive considerably deeper than previously thought, and are in fact the deepest-diving species of marine mammal yet known. At shallow depths Cuvier's stop vocalizing, either because of fear of predators, or because they don't need vocalization to track each other at shallow depths, where they have light adequate to see each other. Their surfacing behavior is highly unusual, because they exert considerable physical effort to surface by a controlled ascent, rather than passively floating to the surface as sperm whales do. Every deep dive is followed by three or four shallow dives. The elaborate dive patterns are assumed to be necessary to control the diffusion of gases in the bloodstream. No data show a beaked whale making an uncontrolled ascent, or failing to do successive shallow dives. This behavior suggests that the Cuvier's are in a vulnerable state after a deep dive – presumably on the verge of decompression sickness – and require time and perhaps the shallower dives to recover. Summary review De Quirós et al. (2019) published a review of evidence on the mass strandings of beaked whale linked to naval exercises where sonar was used. It concluded that the effects of mid-frequency active sonar are strongest on Cuvier's beaked whales but vary among individuals or populations. The