Are Ocean Plastics Behind The Gray Whale’s Recent Demise?

In the North Pacific, a shadow grows as a song goes quiet. Another gray whale falls victim to the tide. A tide poisoned by an insidious product of man. In recent years, gray whale strandings have become frequent along the west coast of North America. So frequent, that scientists have declared an unusual mortality event for the species. Sadly, there is nothing unusual here. A toddler at kindergarten would be able to join the dots. The gray whale undertakes the longest annual migration of any mammal, straight through the eye of the Great Pacific Garbage Patch (GPGP). The gray whale navigates many perils from the arctic to the shallow breeding grounds of the Americas – illegal whaling, boat or ship strikes, acoustic stress and low availability of invertebrate prey – however, it is the creature’s feeding behavior that is an Achilles heel. Gray whales are bottom feeders that sift through and swallow ocean floor sediment for the nutritional reward of  miniscule shrimp-like creatures called amphipods. While feeding usually occurs in arctic waters during the summer months, gray whales will opportunistically forage along their 10,000 mile migration in the winter. This is where the problem lies for the gray whale: most plastic from the GPGP eventually finds its way to the seafloor. Gray whales, diving on their sides, swallowing seabed substrate, are directly ingesting plastics and toxic polychlorinated biphenyls (PCBS). Accounts of recent gray whale strandings indicate that the whales appear malnourished and starved. These reports correlate to observations that have been made for other marine animals that have fallen victim to plastic contamination.

However, most hypothesis’ credit thermal changes in the arctic, which have demolished invertebrate prey abundances, as the primary causation of the gray whale’s woes. While declining prey abundances are a worry for gray whale populations, it is naïve to ignore the spread of plastics from the Great Pacific Garbage Patch into gray whale migratory paths and foraging fields. Furthermore, the bioaccumulation of plastics from benthic amphipods to gray whales is a sobering truth. Research published in the Royal Society Open Science journal found that more than 80% of amphipods collected from six of the ocean’s deepest trenches contained plastic fibers within their digestive systems. Alarmingly, 100% of amphipods sampled from sediment at the bottom of the deepest trench, the Mariana Trench, were found to have consumed plastic. 

It is easy to dismiss the recent ‘unusual mortality event’ of the gray whale. Abundances of the animal have fluctuated dramatically over the years but have always rebounded to natural replacement levels – indicating a rather resilient mammal. Pre-commercial whaling, there were 60 0000 gray whales in the North Pacific. By the turn of the 20th century, a mere 4000 individuals were left. During this shameful period, gray whales were known as devil fish. The nickname is thought to have originated from whalers’ interactions with “difficult, protective mother whales” who fought for the lives of their calves. 

Following international outcry and conservation interventions, gray whale populations recovered in the 1980s but continued to endure significant variations in the years that followed. Such variations are likely attributed to traditional anthropogenic threats, already mentioned in this article. However, the recent ‘unusual mortality event’ of the whale may be a function of something more invisible at play. Plastic. 

Indeed, we need to find out more just how much ocean plastics are affecting gray whales. From the available literature, it is not obvious that plastics and PCBs of the GPGP have ever been listed as a threat to the whale. Given the nature of the gray whale’s feeding behavior and the overwhelming evidence of plastics blanketing the Pacific ocean floor, it is strange that there has been no inquiry into how plastics might be harming this magnificent animal. 

Threats to species evolve and change. What may have hampered the gray whale at one point in time may now have dissipated or been endured by the mechanism of resilience and replaced by the emergence of another threat. Take heed, a synthetic ocean is in construction. The gray whale is no devil fish but marine plastics are.