Scientists studying the German Bight in the North Sea have discovered that the mysterious “pockmarks” on the ocean floor were not caused by methane gas as previously thought, but rather by porpoises and eels. The shallow pits that emerge and disappear every few months are believed to be formed as porpoises hunt for sand eels buried in the sediment. Satellite imagery and behavioral biology analysis supported this hypothesis, and further research is being conducted to confirm the connection. The findings challenge the assumption that all depressions on the seafloor are caused by one mechanism and highlight the important role of biological life in shaping the seafloor.
https://www.atlasobscura.com/articles/ocean-floor-holes-purposes-eels