During warm climatic phases of the Pleistocene, the north polar ice cap mostly or even completely melted. The Arctic Ocean became an ice free corridor when interglacial summers were warmer and longer than those of the 21st century. Many species of marine mammals used this ice free corridor as a migratory route between the Atlantic and Pacific Oceans. A study of gray whale genetics suggests the gray whale enjoyed a gene flow between Atlantic and Pacific populations until the Last Glacial Maximum when the polar ice cap expanded and blocked the Arctic Ocean corridor. It remained blocked from about ~30,000 BP-~10,000 BP. Then, the corridor began opening intermittently and there was some mixing of populations early during the Holocene.
Human hunters extirpated the Atlantic population of gray whales by 1620. It’s amazing how fast this was accomplished. Whalers eliminated this population about a century after bringing their hunting technology to the American side of the ocean. Humans almost overhunted the Pacific population into oblivion, but laws outlawing the practice saved the species, and populations are on the rebound. Present day global warming is causing the Arctic Ocean corridor to open intermittently again. Gray whales are using this corridor again and have recently been spotted in the Atlantic Ocean. Gray whales may recolonize the Atlantic Ocean because of global warming.
Human divers discovered fossil evidence of gray whales off the coast of Georgia. A gray whale jaw and jaw fragments from another individual were found on JY Reef located to the east of St. Catherine’s Island. Today, this site is in deep water, but at the time these whales died, it was a shallow shell bed located near the shore. One of the specimens dates to 41,000 BP, and the other was found embedded in oyster shells dated to 48,000 BP. The vertebrae of an unidentified species of whale was also found here.
Some scientists hypothesize gray whales used the warm waters off the Georgia coast for breeding and calving, much like the small surviving population of right whales (Eubalaena glacialis) does today. Killer whales probably hunted the whale calves as seen in the below video. Gray whales migrate to cooler waters to feed. During cooler phases of the Pleistocene this migratory route may have been shorter.
Video of a mother gray whale protecting her calf from a >2 hour killer whale attack. Scenes like this likely occurred off the coast of Georgia until ~1620 AD.
Scientists are searching the continental shelf off the coast of Georgia for subfossil evidence of the gray whale barnacle, Cryptolepes rhachianecti. This would be additional evidence for the former presence of gray whales here.
Gray whale barnacles. Gray whales help spread the species and provide protection from predators such as starfish, sea worms, and fish.
Gray whales survived the climatic fluctuations of the Pleistocene, but in the Atlantic they couldn’t withstand 100 years of human hunting.
See also https://markgelbart.wordpress.com/2013/03/25/pleistocene-fossils-found-on-the-georgia-bight/ and https://markgelbart.wordpress.com/2014/09/12/the-paleoenvironment-of-the-georgia-bight-when-it-was-above-sea-level-80000-bp-7000-bp/
Alter, S. Elizabeth; et. al.
“Climate Impacts on Transocean Dispersal and Evolution of Gray Whales from the Pleistocene to 2100”
Molecular Ecology April 2015
Noakes, Scott; Nicholas Pyenson, and Greg McFall
“Late Pleistocene Gray Whales (Eschrichtius robustus) offshore Georgia, USA, and the Antiquity of Gray Whale Migration in the North Atlantic Ocean”
Palaeogeography, Palaeoclimatology, Palaeoecology 2013