A new study conducted by Oregon State University has found that gray whales in the Pacific Northwest have experienced a significant decrease in body length since around the year 2000. This decline in size could have serious implications for the health and reproductive success of the whales, as well as raise concerns about the state of the food web in which they live. The researchers behind the study suggest that this reduction in size may be an early warning sign of declining population abundance or overall health.
The study focused on the Pacific Coast Feeding Group (PCFG), a subset of about 200 gray whales within the larger Eastern North Pacific (ENP) population. The PCFG whales stay closer to shore along the Oregon coast, feeding in shallow, warmer waters. Recent research has shown that these whales are smaller and in poorer body condition compared to their ENP counterparts, and the current study reveals that their size has been decreasing in recent decades. By using drone images from 2016-2022 to measure the size of individual whales, researchers found that adult gray whale born after 2000 are expected to be over 5 feet shorter than those born prior to that year.
The lead author of the study, Enrico Pirotta, emphasized the importance of size for animals in terms of behavior, physiology, life history, and its effects on the wider community. Smaller whale calves may struggle with independence, impacting survival rates, while adults may have difficulty reproducing effectively with reduced energy reserves. Scarring from boat strikes and entanglement in fishing gear further add to the concerns about the resilience of smaller whales to injuries. The study also looked into how oceanic upwelling and relaxation patterns influence food availability for the gray whales by affecting the growth of plankton and other prey species.
The researchers found that changes in the balance between upwelling and relaxation coincided with declines in whale size, indicating a potential connection between these environmental patterns and the body size of the whales. While the study did not specifically examine the role of climate change in these oceanographic changes, the researchers noted that climate change can impact wind patterns and water temperature, which in turn influence upwelling dynamics. With knowledge that the size of PCFG gray whales is decreasing, researchers are now interested in exploring the downstream effects of this decline and investigating the various factors contributing to it.
As the study enters its ninth field season, the researchers will continue to collect data on the PCFG gray whales to monitor changes in their body condition and examine the environmental drivers behind these changes. The research team hopes that their findings will shed light on the broader implications of declining whale size and help inform conservation efforts to protect these marine mammals.