Few whales survive a close shave with a ship’s propeller. This is one of the lucky ones. Photo: Alisa Schulman-Janiger, CC BY.
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To save blue whales, move California shipping lanes
29th July 2014
Long after Blue whales have ceased to be hunted, their numbers have failed to record substantial increases, writes Luke Rendell. Are ship strikes to blame? A 15-year scientific study says the answer may be yes - and advises moving California shipping lanes.
Moving the shipping route southwards would reduce the risk of ship strikes for blue whales, particularly during July to October.
When commercial whaling was banned in 1986 it put an end to a harvest that threatened the existence of some of the most majestic animals on Earth.
With several species reduced to tiny fractions of their original populations, once the moratorium was introduced the expectation was that whale populations would recover. But in the decades since, only some have.
There are many possible reasons why this might be, including chemical pollution, climate change, man-made noise, and loss of cultural knowledge among whales that prevent their descendants returning to habitats in their former range.
Are ship strikes to blame?
A further risk, highlighted by a new study of blue whales off the coast of California, is deaths and injury caused by being struck by ships. In most populations, we don't yet know how big a problem it is, but for some it is almost certainly holding back recovery.
Of course, these are only those cases that make it to port - an unknown number of strikes leave their victims at sea, and are sometimes encountered by chance.
In fact the impact on the vessel is so insignificant that the crew is typically unaware that it has happened until it reaches port. But why this apparent increase in numbers?
Is there just more interest, or are there now more whales to hit, are newer ships somehow more dangerous (modern, more efficient technology is often quieter), or are the whales moving into more dangerous busy shipping lanes?
We don't know, which is why studies like one published in the open-access journal PLoS One are so important: 'Spatial and Temporal Occurrence of Blue Whales off the U.S. West Coast, with Implications for Management'.
171 Blue whales tracked for 15 years
Oregon State University researcher Ladd Irvine and his colleagues attached satellite tags to 171 blue whales over a period of 15 years starting in 1993. For a study of whales this is a huge dataset representing a massive investment, largely in terms of researcher time, and provides a really robust insight into the whale's habitat use.
The whales' presence there wasn't year-round, but heavily concentrated between July and October as they followed high concentrations of their food, krill, that accumulate after the spring plankton bloom in these productive waters.
Some individuals returned to the same spots at the same times over many years, suggesting the whales relied on their knowledge and sense of location rather than an ability to track prey, highlighting the important role that habitat knowledge plays in these animals' lives.
Pacific shipping lanes transect blue whale lanes
By plotting the whale distribution maps against those of heavily-used shipping lanes along the California coast, the problem is clear. The shipping lanes run through some of the areas most heavily used by the whales, putting them at high risk of ship strikes.
The shipping lanes are typically placed where they are heavily used and most economical, such as the shortest distance between two points. No shipping companies would change their routes and incur costs without solid evidence of a problem, and this is exactly the kind of evidence this study provides.
It's hard to comprehend in an age when we are mapping the surface of Mars just how ignorant we are about these huge ocean creatures. How do you figure out how many blue whales there are in the deeply inhospitable Southern Ocean?
Sometimes technology can help, such as the satellite tags used for this study. Shipping lanes into Boston on the eastern US seaboard are now equipped with acoustic buoys that report detections of critically endangered right whales in near real-time, hopefully reducing significant numbers of deaths from ship strikes.
Of course, we could find out more - it just takes money. The constraint is economic and political, not a lack of technology or ingenuity.
What did the whales ever do for us?
Scientists are accumulating evidence that might help us appreciate just how much healthy whale populations could be doing for us.
As large, apex predators they structure the ecosystems in which they live, they provide ecosystem services by recycling nutrients throughout the water column, and their huge carcasses fuel entire deep-sea ecosystems for years.
Even their excrement plays a vital role in fertilising nutrient-poor surface waters, seeding the seas with iron, which boosts phytoplankton growth and potentially plays a part in the dynamics of climate change.
It seems that marine habitats with healthy whale populations might actually be more productive than ones without. It's never made more sense to invest in saving the whales.
So, what can be done to reduce blue whale strikes?
A separate study by Redfern at al published in Conservation Biology in 2013 ('Assessing the Risk of Ships Striking Large Whales in Marine Spatial Planning') assessed ship-strike risk for three whale species, including humpback, fin and blue whales, and it warns:
"Reducing ship-strike risk for blue whales may be necessary because our estimate of the potential number of strikes suggests that they are likely to exceed allowable levels of anthropogenic impacts established under US laws."
However it is unclear as to how that could be achieved since "Blue whales are distributed more evenly across our study area than humpback and fin whales; thus, risk could not be ameliorated by concentrating shipping traffic in any of the routes we considered."
But the PLos One study contests that finding - and makes its case for moving California shipping lanes to protect whales: "This contrasts with the core areas identified from the telemetry data in our study", state the authors.
"While we show that blue whales used the entire southern California waters, the high-use area at the western part of the Santa Barbara Channel suggests that moving the shipping route southwards would reduce the risk of ship strikes for blue whales, particularly during July to October."
Luke Rendell is MASTS Lecturer in Biology at the University of St Andrews. He receives funding from the Marine Alliance for Science and Technology Scotland (masts.ac.uk), and the Leverhulme Trust.
Editorial note: the entire final section containing direct quotes from the PLoS One and Conservation Biology papers was added by The Ecologist.
The PLoS One paper: 'Spatial and Temporal Occurrence of Blue Whales off the U.S. West Coast, with Implications for Management' is open access.
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