Thriving Oceans

Spyhop - For more of the funniest videos, click here

It’s not rocket science!  When the vocalizations of an animal experience a world-wide decline one of the most obvious answers is a population decline…or is it?  Well, the answers definitely don’t fall within the territory of rocketry but are more suited for marine biology.  And researchers are beginning to wonder if the decline in the pitch of Blue whale songs is actually a signal of good things to come.  According to the Scripps Institute of Oceanography:

The sound level of songs blue whales sing across the vast expanses of the ocean to attract potential mates has been steadily creeping downward for the past few decades, and a scientist at Scripps Institution of Oceanography at UC San Diego and his colleagues believe the trend may be good news for the population of the endangered marine mammal.

Mark McDonald of WhaleAcoustics in Bellvue, Colo., along with John Hildebrand of Scripps Oceanography and Sarah Mesnick of NOAA Fisheries Southwest Fisheries Science Center studied blue whale song data from around the world and discovered a downward curve in the pitch, or frequency, of the songs. The decline was tracked in blue whales across the globe, from off the Southern California coast to the Indian and Southern Oceans.

“The basic style of singing is the same, the tones are there, but the animal is shifting the frequency down over time. The more recent it is, the lower the frequency the animal is singing in, and we have found that in every song we have data for,” said Hildebrand, a professor of oceanography in the Marine Physical Laboratory at Scripps.

The study’s results are published in the most recent issue of the journal Endangered Species Research.

The researchers examined a list of possible causes for the frequency drop-from climate change to a rise in human-produced ocean noise-and believe it may be explained by the increase of blue whale numbers following bans on commercial whaling activities.

While the function of blue whale songs is not known and scientists have much more to learn, they do know that all singers have been determined to be males and that the high-intensity, or loud, and low-frequency songs propagate long distances across the ocean. Blue whales are widely dispersed during the breeding season and it is likely that songs function to advertise which species is singing and the location of the singing whale.

In the heyday of commercial whaling, as blue whale numbers plummeted, it may have been advantageous for males to sing higher frequency songs, the researchers believe, in order to maximize their transmission distance and their ability to locate potential mates (females) or competitors (other males).

“It may be that when (blue whale) densities go up, it’s not so far to get to the closest female, whereas back when they were depleted it may have been that the closest female was a long way away,” said Hildebrand.

In the 1960s, when blue whale numbers were substantially reduced and recordings of the animals were first made, there may have been a tradeoff in which the male suitors chose to sing higher frequencies that were louder and heard over greater distances, Hildebrand said. In more recent years, as population sizes have increased, it may now be more advantageous for males to sing songs that are lower in frequency rather than louder.

“When they make these songs they need to use most of the air in their lungs,” said Hildebrand. “It’s like an opera singer that sees how long he can hold a note. The (male) songs are made to impress the females and/or other males, so I think that’s how the boy blue whales are impressing the girls, or are showing off to other boys: by making a loud and long song.”

The scientists say the same downward pitch phenomenon may be true in other whales such as fin and humpbacks, but the blue whale song, with a comparatively easier song to analyze, is a good springboard to study other species. Hildebrand says such knowledge about whale songs could be important in monitoring whale populations and recovery efforts.

During the study the researchers analyzed thousands of blue whale songs divided into at least 10 worldwide regions. These include the Northeast, Southwest and Northwest Pacific Ocean; the North Atlantic; the Southern Ocean near Antarctica; and the North and Southeast Indian Ocean. Blue whale songs have been recorded for the last 45 years through scientific and military applications by seafloor seismometers tracking regional earthquakes and dedicated whale acoustic recording packages.

The heavy rains currently beating down on the East San Francisco Bay Area has reminded me about the incredible amount of debris that will be entering our waterways and oceans.  We are all aware of the Great Pacific Garbage Patch, but there is an enormous amount of other debris that is left to surf the waves.  Take for instance fishing nets.  Unattended and discarded fishing nets pose danger to the entire ocean system, even whales.  Check out the following pictures from The Marine Mammal Center and the results of their necropsy of a dead sperm whale recovered in March 2008.

“On March 16, The Marine Mammal Center’s Director of Veterinary Science, Dr. Frances Gulland, assisted in the necropsy of a 51-foot-long sperm whale that  had washed up on a beach near Tomales Point in Point Reyes, CA. When the necropsy team reached the animal’s internal organs, they discovered nearly 450 pounds of fishing net, mesh, braided rope, plastic bags, and even a plastic comb in the whale’s stomach.“

The Marine Mammal Center, August 2008

Photo: Chris Whittier

Photo: Chris Whittier

Coming off the heels of Hope for small sea turtle populations, there is yet another stint of positive ocean conservation news; this time for our cetacean friends.  A new publication in Conservation Biology has actually documented voluntary cooperation by shipping vessels to avoid whale strikes. 

Fin, humpback, right and gray whales have the unfortunate distinction of being the most frequently reported victims of collisions based on historical records.  But whale strikes are not limited to only those species as deaths have been noted for sei, blue and minke whales as well.  However, one particular cetacean stands out above the whale strike crowd with victimhood reaching 2 orders of magnitude above the others.  Perhaps its affinity for urbanized coastal waters around the globe, the endangered North Atlantic right whale is in need of a little shipping compassion. Especially when a 2008 report found that  53% of North Atlantic right whale deaths were attributed to vessel strikes.

To curb the problem, conservation policies have been discussed and even implemented, including the establishment of an ‘area to be avoided.’  In 2007, “The International Maritime Organization adopted the Roseway Basin Area to be avoided on the Scotian Shelf as a voluntary conservation initiative to reduce the risk of lethal vessel strikes to right whales.”  This voluntary area to be avoided went into effect on May 1, 2008 and was designed to be seasonally effective from June 1 to December 31st of each year.  With shipping companies traditionally against the execution  of speed reduction regulations and alteration of shipping lanes (i.e. time is money), the notion of a voluntary avoidance area was definitely a concept that needed confirmation of compliance.

To my surprise, the researchers found:

” Estimates of vessel-operator voluntary compliance ranged from 57% to 87% and stabilized at 71% within the first 5 months of implementation. Our estimates showed an 82% reduction in the risk of lethal vessel strikes to right whales due to vessel-operator compliance. We conclude that the high level of compliance achieved with this voluntary conservation initiative occurred because the area to be avoided was adopted by the International Maritime Organization.”

But the caveat with ocean-going vessels avoiding a conventional shipping lane was that they needed to find a new travel route.  And although the newly adopted course was quite favorable to the right whale, it has the potential to increase fin whale ship strikes by approximately 7%.  The argument, however, is that the fin whale population is 250 times more than that of the endangered North Atlantic right whale, right whales are more abundant than fin whales in the ‘area to be avoided’ , and the ship-strike risk to humpback whales and to sei whales will be reduced by 11% and 74% respectively.

So what does a reduction in ship strikes ultimately mean to the endangered North Atlantic right whale, well it may very well be the difference between recovery and extinction.

“Preventing as few as two female deaths per year would increase the population growth rate to replacement levels that would initiate recovery.  Such prevention is particularly relevant given that contemporary probability estimates of deaths from vessel strikes could be as high as 10 individuals in any given year.”

 

Reference: Vanderlaan, A.S.M., Taggart, C.T.(2009) Efficacy of a Voluntary Area to Be Avoided to Reduce Risk of Lethal Vessel Strikes to Endangered Whales. Conservation Biology