Conservation & Sustainable Management

How not to hit a whale:  Move the shipping lane

Coming in at around 170 tonnes The blue whale (Balaenoptera musculus) is the heaviest animal known to have existed on Earth.  This huge critter feeds on some of the smallest, filtering zooplankton through its baleen plates that hang from its upper jaw.  The blue whale as a group (there are several sub-species) is unfortunately listed as Endangered on the IUCN Red List.  Commercial whaling certainly took its toll on the global population and was, without a doubt, the most threatening of human activities to these large enigmatic creatures.  With commercial whaling now largely ended, the human threat to their persistence has declined greatly.  But there are still incidents between humans and the blues, like entanglement in fishing gear and marine litter, noise pollution that can hamper their communication, and ship strikes.  Certainly the recovery of the blues in the eastern North Pacific isn’t as good as we would expect, but the reasons for this somewhat lacklustre comeback are much harder to pin down.  Many avenues need to be explored – including seemingly infrequent events like ship strikes.

Ladd Irvine of Oregon State University and a team of researchers wanted to take a closer look at blue whale movements off California, an area which also contains a great deal of shipping activity.  When looking at movement of any population, it’s really important to get as much historical data as possible because animals can vary their movements year on year.  The team used 15 years’ worth of data collected from 171 tagged whales.  These satellite monitored radio tags are pretty nifty pieces of kit, collecting the time and location of the whales at the surface and transmitting to satellites.  With this wealth of data, the team set to work figuring out which areas of the Californian coast are particularly important to blue whales.  Sure enough, some rather interesting patterns emerged.

Blue whales are attracted to the west coast of the US during the summer months to feast on the large numbers of krill found in the California Current System.  The krill are super-abundant during this time as a result of upwellings that increase productivity in the region, and by currents and the bathymetry (equivalent to topography – how the sea floor looks) of the area that concentrate the krill into certain areas.  As you might expect, the blue whales concentrated in areas where krill was most abundant.  Early in the summer the whales tended to stay in the more southerly sections, where upwelling intensity (and thus productivity) is fairly moderate.  During October and November the northern section of California experiences much stronger upwellings, and sure enough that’s exactly where the whales tended to hang out.  The whales don’t just head up north around the same time every year though.  Because the tracking data spanned 15 years, the researchers were able to compare movements over multiple years.  The timing of the more intense northerly upwelling varies year on year, and it was quite apparent that the whales tailored their northerly migration in line with this variation.  With variation in krill availability, you might expect that the whales would stay in California waters as long as krill abundance was high enough to give a decent meal.  Interestingly, the whales didn’t really alter when they continued on their migration out of California in line with productivity timings.  There was only one notable time when they did leave significantly later – in 2004.  What’s so special about 2004?  Well not much.  There was a weak  El Niño, but the researchers note that it didn’t really have an impact in the California Current System.  1999 was a super-productive year in the California Current System and no doubt prey was super-abundant.  Did the whales hang out there for longer than usual?  Nope!

So far so good, but the tracking data also revealed some potential issues.  The blues tended to be most concentrated alongside areas where human population is high, and where there are busy ports.  Busy ports means busy shipping lanes, which run straight through the places where the whales can be found.  Now remember that ship strikes are thought to be relatively infrequent, but the question is how do we know if there has been a ship strike?  Well first of all we have to know we have hit a whale.  Sounds daft, but if you’re in a huge freight vessel you might not notice.  You might also hit a whale and injure it (with unknown survival), or you might fatally hit a whale, and just not report it.  We do have evidence that on the whole ship strikes are on the increase, and this paper makes a seemingly simple suggestion to reduce the likelihood of a strike on a blue whale: move the shipping lane during the months when the whales are migrating through.  Of course such a move is an economic, political, and social minefield, but it’s not impossible – and there is a prescient.  Twelve years ago shipping lanes in the Bay of Fundy, Canada were moved just 6 km away from a key North Atlantic right whale feeding ground.  Since then, the right whale population has shown a small increase.  Of course correlation doesn’t imply causation, but it is food for thought.

This paper is published in the open access journal PLoS ONE.  Have a read of it here

Image:  Blue whales aren’t the only whale species to be susceptible to ship strikes.  This image shows an North Atlantic right whale (Eubalaena glacialis) who died after colliding with a vessel and suffering significant propeller cuts.  Credit: NOAA National Marine Sanctuaries/Center for Coastal Studies (Public Domain Licence)

Conservation & Sustainable Management

Noise pollution in the Moray Firth a concern for dolphins

Most of us have been there.  You’re in a pub or a club trying to have a conversation but the music…it’s just too loud to hear what the other person is saying.  You shout louder and louder, the listener has their ear up close to your mouth but alas, the conversation doesn’t flow as it would do if you could both hear each other easily.  Now imagine that sound wasn’t just important for having a conversation, but for seeing.  And imagine that the loud noise preventing you from hearing properly wasn’t just in the pub, but occurred throughout your day-to-day activities.

Noise pollution is a problem for cetaceans because they use echolocation to ‘see’ and hear.  It’s quite a nifty technique because often the ocean is too murky or too dark for your eyes to see very far in, but sound can still travel.  Thanks to evolution, cetaceans have echolocation down to a fine art.  Not only can they figure out that something is there, but they can work out what it is.  But when it’s too noisy, the echolocation process can be disrupted and activities like hunting, navigation, and pod communication can become difficult to impossible.  Noise has even been linked to stress, and increased energy expenditure in our aquatic brethren.  One of the problems with figuring out just how noise pollution is affecting cetaceans is a lack of baseline data – to a large extent we don’t know the status of cetacean populations inhabiting different areas.  When we do get around to taking measurements of noise, we don’t have a good handle on how noisy different areas were in the first place to know if the noise has increased.  This lack of baseline data includes in conservation areas designated as important marine mammal habitat – just like the Moray Firth up in Scotland.

The Moray Firth is home to a well-studied population of bottlenose dolphins (Tursiops truncates), but it also has strategic importance, forming a base for North Sea oil and gas exploration and potentially in the future, a base for an offshore wind farm.  Noise is likely to increase but to figure out by just how much Nathan Merchant of the University of Bath, alongside Enrico Pirotta, Tim Baron, and Paul Thompson of the University of Aberdeen decided to get some baseline data before developments begin.  Once that data is in place, they argue, more accurate correlations between noise and effects of marine mammals can be determined.

During the summer of 2012, Nathan and his team placed two underwater noise monitors – both in deep narrow channels popular with the dolphins for foraging, as well as prime shipping traffic routes.  They then monitored the noise on a cycle of 1 minute every 10 minutes and tied that data up with Automatic Identification System (AIS) ship-tracking data.  For the other 9 minutes recordings still took place, primarily to provide more analysis of noise events of interest.  And of course, this sound recordings also picked up the bottlenose dolphins as well as other marine mammals, but the team also deployed C-Pods – recorders dedicated for marine mammal noise – at the sites.  Conditions like rain and wind can also create noise in the Firth so meteorological data was also collected.

The acoustic data confirmed that the dolphins were using the two site quite heavily, with recordings of their clicks at both sites being made every day.  The two sites differed a fair bit in their baseline noise levels, with one generally much noisy than the other, with shipping traffic appeared to be the main source of noise pollution.  The researchers hypothesise that increase in noise levels at the already noisy site may be less damaging to the dolphins than increases at the quieter site, because the noisy site has already suffered noise-related habitat degradation to which the dolphins have already become accustomed.  Indeed the Moray Firth population size is showing signs of being stable, and is perhaps even increasing which is a positive sign.  However, the dolphin vocalizations overlapped both in frequency and amplitude with the shipping traffic.  This is concerning because it means that there is a higher risk of the dolphin’s vocalization being masked out by increases in shipping traffic.  Just how much shipping noise is too much is still unclear.

The paper is published in the journal Marine Pollution Bulletin and has been made open access.  You can read it here:

There are also a couple videos up on YouTube where  you can listen to “short real-time clips” of the ship noise monitoring in the Moray Firth, accompanied by ship tracking data, underwater recorders, and time-lapse cameras.  Check them out here Ship noise monitoring in the Moray Firth – The Sutors and here Ship noise monitoring in the Moray Firth – Chanonry.

Image: Adult female Bottlenose Dolphin with two young at side, Inner Moray Firth, Scotland May 2005.  Photographer Peter Asprey/Wikipedia and cropped by Clayoquot/Wikipedia  (CC BY-SA 3.0)