Blue Whales Vulnerable to Being Hit by Cargo Ships: GPS Tracking to the Rescue
11 Jun 2015The world’s oceans hold far too much possibility of ship and whale collisions. In fact, there is a huge threat to the survival and recovery of certain endangered whale populations from ship strikes.
Certain factors that can affect the occurrence and seriousness of the collisions include the hydrodynamic forces around ships, how fast they go, and the spatial co-occurrence of ships and whales.
Understanding whale behavior when in the presence of ships could be the key to understanding the difference in interaction.
This understanding of interactions between the large whales and ships has become a protection concern globally attributable to the increase in commercial ship traffic and its growth within the industry.
There have been few studies on the behavior of whales when approached by large ships, however, this is most likely how we are to understand the vulnerability of the whales, how reduced speed might reduce collisions, and how effective mitigation would be.
Between the years of 1998 and 2007, there was a report of 21 blue whale deaths along the coast of California and 4 of these deaths happened in 2007 in the fall in the Santa Barbara Channel (SBC).
Since the SBC is recognized as being a high ship-strike risk area for whales, this region was targeted in a study that was published by McKenna MF, Calambokidis J, Oleson EM, Laist DW, Goldbogen JA in Endangered Species Research on April 29, 2015 to learn the behavior of the blue whales when in the path of ships as well as inform the ship’s management in areas of high ship traffic.
High-quality GPS tracking devices were used during this study, which helped define whale positions and defensive behaviors. Three satellite positions were used to calculate these positions.
According to Stanford’s Hopkins Marine Station’s assistant professor, Jeremy Goldbogen,
“It’s not part of their evolutionary history to have cargo ships killing them, so they haven’t developed behavioral responses to this threat,”
Therefore, there has been no behavioral response developed by the whales to this threat, Goldbogen, who is senior author of the study, says.
During this study, there were 20 ship passages and 9 whales used. They were observed at different distances that ranged from 60 to 3600 m. The dive response of the blue whales while in an oncoming ship’s path was documented in 55 percent of ship passages, however, no evidence was found for lateral avoidance.
After using the suction-cup tag deployments, things like duration, descent rate and maximum depth combined with ship hydrodynamic forces were observed to gather behavioral data and determine the maximum speed a ship could use to enable whales time to get out of its path. The analysis showed the whales were relatively slow in their descents and showed no horizontal movements to avoid ships.
This study is just an initial step to figure out whale behavior in the path of heavy ship traffic. There is another round of tests being planned where GPS tracking units will remain on the whales, including humpback whales, for several weeks.
Having more data about whale behavior and how frequent near misses are, Goldbogen has hopes to offer a compelling recommendation to the shipping industry and boaters on how collisions risk can be minimized.
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