Effects of speed on vessel–whale collisions. Among researchers interested in ship-strikes, there is wide agreement that speeds above 13 knots for large vessels are dangerous to whale survival. This is shown dramatically in charts from a recent paper by Vanderlaan and Taggart (2006). The following chart shows that the probability of a vessel-whale collision being fatal increases by a factor of about 8 when the vessel speed increases from 7 to 18 knots. That is a very large factor. It does not apply to small vessels like whale-watch boats, fishing boats, etc. – but it does apply to vessels like cruise ships which can cruise at about 25 knots.
Why have there been no ship-strikes observed from large vessels in Hawaiian waters??
In a paper by Lammers and Pack published in 2003, it was pointed out that, up until that date, there was no evidence of collisions between large vessels and whales in Hawaiian waters. Many of these large vessels are inter-island cruise ships which have a cruising speed of about 25 knots. The HSF people jumped on this observation stating, in effect, that since inter-island cruise ships cruise at 25 knots and do not hit whales, there is no reason to think that the Superferry will hit whales either.
They even stated that if cruise ships were made to slow down below 25 knots, the Superferry would be willing to slow down also. This was obviously a phony offer because, if the Superferry were really to travel at a slow speed - say about 12 knots - it would take about 9 hours to travel between islands. HSF would go out of business in a hurry.
Anyhow, I wondered if inter-island cruise ships really traveled at their 25 knot cruising speeds because ships traveling at slower speeds usually get improved fuel mileage. From looking at the route map and schedule between the islands for a typical cruise ship (the “Pride of Aloha”), it was easy to show that the overall average speed for this ship was about 13.3 knots.
I discussed this in detail on this web site on the page called “Superferry vs. Cruise ship”. I also pointed out that inter-island cruise ships do not always travel at speeds safe for whales and that collisions might occur that were unreported. Dead whales could sink to the bottom, drift out to sea or be eaten by sharks.
What I did not discuss on the “Superferry vs. Cruise Ship” page was the possibility that there could be vessel-whale collisions from large ships from distant ports which might be traveling at speeds greater than the speeds of inter-island cruise ships. These would include collisions from cruise ships, tankers, and freighters.
Collisions between large vessels and Humpbacks have been reported in other parts of the world. For example, See Laist, et. al. Marine Mammal Science 17(1):35-75 (January 2001) – So why have they not been reported in Hawaii?? I can suggest a number of possibilities.
1. Cover-ups by vessel operators. It is not good publicity to report that your ship has hit a whale.
2. No eye-witnesses. Collisions are often discovered when dead whales are seen riding bow bulbs. This happens mostly with slender whales – like Fin and Bryde’s whales. They sometimes wrap around the ships bow and ride on the bow bulb for long distances and are often observed - but Humpbacks are “stubby” whales and quickly fall off the bow bulb.
3. Dead Humpbacks may sink to the bottom, drift out to sea or may be eaten by sharks but dead Humpbacks may also float.
-
4.As far as I know no necropsies of dead Humpbacks have been done in Hawaii. But there are a number of floating and stranded dead Humpbacks that could have been necropsied. In fact, in a cursory Google search , I found evidence of 5 dead floating or stranded humpbacks and 1 dead sperm whale since 2004 as shown below. Links are provided to 3 of the cases.
-----------------------------------------------------------------------------------------------------------------------------------------------
Hawaii dead whale summary: 2004-2006
from cursory Google search
1. Feb. 22, 2004: Dead Humpback stranded. See
http://tursiops.org/modules.php?name=News&file=article&sid=239
2. June 24, 2004: Injured sperm whale filmed being eaten by tiger sharks. (caught on video by Jimmy Hall who was recently killed in the Arctic). On CNN Sept. 3, 2007. I think this was the same whale despite the 3 year time difference. See
www.underwatertimes.com/stories/whale_attack.htm
3. Feb. 9, 2005: Dead Humpback on shore – Kalaeloa, Oahu. See:
www.thehawaiichannel.com/news/4182887/detail.html
4. Nov. 13, 2006: Humpback near Kona (injured – caught on video being eaten by sharks). See below
5. Feb. 6. 2006: Humpback found dead near Molokai. See below
6. Feb. 22, 2006. Humpback found dead near Kaho’aloe. See below
The last 3 items are listed by the “Pacific Islands Region Marine Mammal Response Network”. It is listed on Google but I could not find a URL
----------------------------------------------------------------------------------------------------------------------------------------
The above 6 whales could have all been killed by the bows of large fast moving vessels. The injuries causing death were probably all internal and are called “blunt trauma” injuries. They can only be detected by necropsies. So why have necropsies not been done in Hawaii?? In other parts of the world necropsies to determine the cause of whale deaths are common. But they cost money. Also, reporting and/or publicizing the cause of whale deaths may not be good for the tourist industry.
Debunking HSF’s claims
1. HSF’s claim that 25 knots is a speed safe for whales.
From the above It should be clear that HSF’s claim that 25 knots would be a safe speed for avoiding ship-strikes would be valid only in an ocean totally devoid of marine mammals. Again, the graph at the top of this page shows that above 13 knots, the probability of death by collision increases rapidly
Of course HSF claims in it’s Whale Avoidance Policy (the WAP) that it has various methods to avoid hitting whales.. None of these could possibly work if a whale surfaces in front of the vessel.
2. HSF’s claim that the Superferry will be easier on whales than cruise ships because the superferry has no propellers which can kill whales - but the 6 floating and stranded whales in the above table that could have been killed by large vessels do not show propeller injuries. Why not??
It may have to do with Humpback whale behavior. This varies over a wide range which is partly what makes them such fascinating animals. Sometimes they totally avoid boats – or they may come right up to boats out of curiosity. On occasions when they are involved in courtship or mating behavior, they will totally ignore the presence of boats. A very common behavior is that they totally break off social activity and dive when a vessel approaches. Dr. Marsha Green has written how Humpbacks abruptly stop activities like flipper –flopping, lob-tailing, etc. when a boat approaches. They then dive and swim away under water. See “Short-Term Impact of Vessel Traffic on the Hawaiian Humpback Whale (M Green and R G. Green, Albright College, Paper presented at annual meeting of the Animal Behavior Society, June 1990, SUNY, Buffalo, NY”
So my guess is that when a large vessel (like a cruise ship) approaches, Humpbacks often feel the water movement as the vessel pushes water out of the way. The water may push them sideways or downwards. If the former, there may be no collision - or it will just be a glancing blow.. If the latter, they may dive as the boat moves over them since diving to avoid approaching boats is a common behavior.. Even if the vessel is a large cruise ship, the whales will have to dive only 25 - 30 ft. to avoid being sucked into the propellers. Of course, if the vessel approaches head-on at high speed, the whales may not have time to dive. They will be struck by the bow and killed.
I have seen three pictures of other types of whales with scars from large propellers – but never Humpbacks. On the other hand, there are many pictures of Humpbacks with scars from the propellers of small boats. Propeller strikes may cause bleeding but the whales usually survive.
3. HSF’s claim about the “Swept Area”
In the WAP, HSF claims that the large “swept area” of cruise ships relative to the Superferry makes it far more likely that cruise ships will hit whales than the Superferry. This is a naive and incorrect claim. I debunked it in my first Superferry video but never got around to putting it on this web site. Anyhow, the term “swept area” refers to what a whale would see if a vessel is headed straight toward it. This is crudely shown in the figure below taken from the WAP.
The part of the diagram in green represents the “swept area” of the Superferry with its two pontoons. The part of the diagram in yellow represents the swept area of a “Container or Cruise ship”. The idea is that, since the area in yellow is much larger than the area in green, a whale is much more likely to be struck by an oncoming large vessel than by the Superferry.
But it won’t really happen that way. Since a conventional vessel pushes water out of the way as it moves forward, it will also tend to push a whale out of the way. As shown in the figure below, the whale may not be hit by the ship at all – or if it is hit by the ship, it will be a glancing blow. This would be equivalent to being hit by a much slower vessel and the injury is not too likely to be serious. This figure was taken from my first Superferry video but this is the first time it has appeared on this web site.
It is a pretty technical slide- but it shows that the whale will be pushed aside along with the water pushed aside by the vessel. Alternate paths are shown because there is no way of knowing exactly how far it will be pushed aside. It might even hit the side of the vessel but, if it does, it will be a glancing blow. Only if the impact is head-on, is the whale likely to be killed. If the whale is on the surface, it would be struck by the bow and then ride along on the bow bulb. But since humpbacks are “stubby” whales, they will soon slip off the bow bulb and struck whales are not likely to be observed.
From the above figure it should be clear that a comparison of “swept areas” is meaningless and misleading. What is significant is the fact that the superferry has two pontoons which can strike whales. This is equivalent to having two bows – compared to only one for a conventional vessel. This single factor doubles the collision probability. Also the Superferry will push relatively little water out of the way. Therefore it will not push a whale out of the way either. Along with its higher speed – about 37 knots in open water compared with an average speed of about 14 knots for an inter-island cruise ship, it should be clear that the Superferry will be a far greater threat to whales and other marine mammals than any inter-island cruise ship.
Finally, it should be emphasized that - as discussed above - in the past 3 years, 6 dead whales (5 Humpbacks and 1 Sperm whale) were observed in Hawaiian waters. Many - or perhaps all - of them could have been killed by cruise ships, freighters or other fast moving vessels - and many more whales may have been killed but not observed. But whatever types of vessels struck the whales, they all traveled much slower than will the Superferry - because no other vessel in Hawaiian waters has traveled - or is likely to travel - at a speed approaching the speed of the Superferry.