Tag Archives: marine biology

Dottyback reef fish is a “wolf in sheep’s clothing”

A new study by researchers at the University of Cambridge has shown that the dottyback, a small predatory reef fish, can change the colour of its body to imitate a variety of other reef fish species, allowing the dottyback to sneak up undetected and eat their young. Its Latin name, Pseudochromis, means false damselfish – giving clue to its mimicry abilities.

The dottyback also uses its colour-changing abilities to hide from larger predators by colour-matching to the background of its habitat – disappearing into the scenery with its camouflage.

While using mimicry to hunt or hide from other species is commonplace in nature – from cuckoos to cuttlefish – scientists point out that if the same physical deception is encountered too frequently, species on the receiving end become more vigilant and develop tactics to mitigate the mimics.

The dottyback, however, is able to colour-morph depending on the particular colour of the surrounding species it is currently hunting: different types of damselfish being a popular target.

Scientists say that this flexibility of physical mimicry makes it much harder for the dottyback’s prey to develop detection strategies and avoid getting eaten.

Dottybacks are generally solitary and highly territorial predators of around eight centimetres in length, commonly found in Indo-Pacific coral reefs.

While dottybacks can vary their colouration from pink to grey, the researchers focused on two colour ‘morphs’ – yellow and brown – that both occur on the reefs surrounding Lizard Island, off the coast of north-east Australia. This is because the area has populations of both yellow and brown damselfish, and habitat consisting of live coral and dead coral ‘rubble’.

Dottyback and damselfish

The scientists built their own simulated reef outcrops comprising both live coral and rubble, and stocked them with either yellow or brown damselfish. When released into reefs with damselfish of the opposite colour, scientists found the dottybacks (Pseudochromis fuscus) would change from yellow to brown or vice versa over around two weeks.

Anatomical study of dottyback skin cells revealed that while the level of ‘chromatophores’ – pigment-containing cells that reflect light – remain constant, the ratio of yellow pigment cells to black pigment cells shifts to move the dottyback from yellow to brown or back again.

The team conducted lab experiments with adult and juvenile damselfish to test whether this colour change affects dottyback hunting success. They found that once the dottyback matched the colour of the damselfish, they were up to three times more successful at capturing juvenile damselfish.

“This is the first time that an animal has been found to be able to morph between different guises in order to deceive different species, making the dottyback a pretty crafty little fish” says Dr William Feeney, co-author of the study from the University of Cambridge’s Department of Zoology.

Further Reading
University of Cambridge (CC BY-NC-SA 3.0)

Photo credits: Christopher E Mirbach, Justin Marshall.

Ocean bacteria “pumped-up” by dying plankton

Scientists have discovered a surprising new short-circuit to the biological pump. They found that sinking particles of stressed and dying phytoplankton release chemicals that have a steroid-like effect on marine bacteria feeding on the particles. The chemicals juice up the bacteria’s metabolism causing them to more rapidly convert organic carbon in the particles back into CO2 before they can sink to the deep ocean.

The ocean has been sucking up heat-trapping carbon dioxide (CO2) building up in our atmosphere – with help from tiny plankton. Like plants on land, these plankton convert CO2 into organic carbon via photosynthesis. But unlike land plants, plankton can sink into the deep ocean, carrying carbon with them. Along the way they decompose when bacteria convert their remains back into CO2.

It’s called the “biological pump,” and if it operated 100 percent efficiently, nearly every atom of carbon drawn into the ocean would be converted to organic carbon, sink into the deep ocean, and remain sequestered from the atmosphere for millennia. But like hail stones that melt before reaching the ground, some carbon never makes it to the deep ocean, allowing CO2 to leak back into the upper ocean and ultimately exchange with the atmosphere.

In a new study published April 27 in the Proceedings of the National Academy of Sciences, scientists at Woods Hole Oceanographic Institution (WHOI) and their colleague from Rutgers University discovered a surprising new short-circuit to the biological pump. They found that sinking particles of stressed and dying phytoplankton release chemicals that have a jolting, steroid-like effect on marine bacteria feeding on the particles. The chemicals juice up the bacteria’s metabolism causing them to more rapidly convert organic carbon in the particles back into CO2 before they can sink to the deep ocean.

“We think these compounds are acting as signals to the bacterial community to let them know phytoplankton are dying, lots of ‘free’ food on the way, and to ramp up their metabolisms,” said Bethanie Edwards, lead author of the study and a graduate student in the MIT/WHOI Joint Program in Oceanography. “When the bacteria consume phytoplankton faster, more CO2 is given off in the shallow depths, where it can return to the surface of the ocean and the atmosphere more quickly.”

Typically, the detritus of phytoplankton have no special effect on bacteria; they are simply a food source. But the phytoplankton in this study—diatoms—are different. When stressed, some diatoms release bioactive molecules known as polyunsaturated aldehydes (PUAs). The researchers found that these molecules kick the bacteria’s metabolism and CO2 respiration rates into hyperdrive—like skinny weightlifters after a steroid shot. The bacteria start devouring the falling particles like they are at an all-you-can-eat buffet, and significantly reduce the amount of sinking detritus while releasing CO2.

To collect the particles, the team submerged 6-foot-wide, funnel-shaped sediment traps 150 meters down (picture huge traffic cones dunked upside down in the ocean) for 24 hours. Once the traps were brought back to surface, the scientists incubated collected particles with PUAs and analysed changes in bacterial metabolism over a 24-hour period.

The sediment traps were placed at several locations across the North Atlantic, including the Sargasso Sea, the subarctic North Atlantic near Iceland, and the western North Atlantic near Massachusetts. The traps were submerged at depths of 150 meters for 24 hours and then the collected particles were analyzed in the lab. (Photo by Suni Shah, Woods Hole Oceanographic Institution)
The sediment traps were placed at several locations across the North Atlantic, including the Sargasso Sea, the subarctic North Atlantic near Iceland, and the western North Atlantic near Massachusetts. The traps were submerged at depths of 150 meters for 24 hours and then the collected particles were analyzed in the lab. (Photo by Suni Shah, Woods Hole Oceanographic Institution)

“Very rarely do you see organisms respond positively to PUAs. In fact, in higher concentrations, they often have a toxic effect, causing a decrease in phytoplankton growth rates and mutations,” Edwards said. “But our results were very surprising. We saw an increase in CO2 production rates, enzyme activity, and bacterial cell growth.”

The scientists also found much higher concentrations of PUAs within the sinking particles than had been previously been observed in the water column. “This suggests that sinking particles are ‘hotspots’ for PUA production,” Edwards said.

“This study shows that when it comes to long-term biological sequestration of atmospheric carbon dioxide in the ocean, not all species of phytoplankton are created equal,” said Don Rice, program director for the National Science Foundation (NSF)’s Chemical Oceanography Program, which partially funded the research.

Further Reading
Bethanie R. Edwards, Kay D. Bidle, and Benjamin A. S. Van Mooy. Dose-dependent regulation of microbial activity on sinking particles by polyunsaturated aldehydes: Implications for the carbon cycle
PNAS 2015 ; published ahead of print April 27, 2015, doi:10.1073/pnas.1422664112

Photo credit: CSIRO [CC BY 3.0]

How warm-bodied tuna hearts keep pumping in killer cold

Pacific bluefin tuna are unique amongst bony fish as they are warm bodied (endothermic) and are capable of elevating their core body temperature up to 20°C above that of the surrounding water. They can also down below 1000 m into much colder water that would stop a human heart.

Scientists at The University of Manchester, working with colleagues at Stanford University in America, have discovered how these tuna keep their hearts pumping during these extreme temperature changes.

The research helps to answer important questions about how animals react to rapid temperature changes, knowledge that’s becoming more essential as the earth warms.

Dr Holly Shiels at the Manchester University’s Faculty of Life Sciences says: “When tunas dive down to cold depths their body temperature stays warm but their heart temperature can fall by 15°C within minutes. The heart is chilled because it receives blood directly from the gills which mirrors water temperature. This clearly imposes stress upon the heart but it keeps beating, despite the temperature change. In most other animals the heart would stop.”

The mis-match between oxygen demands of the tunas’ warm swimming muscles and the cardiac system that operates at water temperature is a puzzle the team has long been trying to solve.

“Tunas are at a unique place in bony fish evolution” says Professor Barbara Block at Stanford. “Their bodies are almost like ours – endothermic, but their heart is running as all fish at ambient temperatures. How the heart keeps pumping as the fish moves into the colder water is the key to their expanded global range.”

To study the problem the team, including Dr Gina Galli from Manchester’s Medical and Human Sciences Faculty, worked at the Tuna Research and Conservation Center at Stanford University one of the only places on the planet with live tuna for research.

Professor Block’s team used electronic tags to monitor bluefin tuna in the wild: “These fish are born in the waters off Japan and will swim across the ocean in their first year of life to California. Here we tag the tunas and follow their migrations for years. The data reveals the tuna are very broad ranging in their thermal tolerances and the team from Manchester and Stanford University have worked together for nearly two decades to reveal how the heart of this unique fish is specialised for meeting these temperature changes.”

Tracking bluefin tuna in the wild using archival tags, the researchers were able to measure three things: the depth of the fish; its internal body temperature and the ambient water temperature. They then used the wild data to set the experimental conditions in the lab with single tuna heart cells to see how they beat. The results have been published in Proceedings of the Royal Society B.

Dr Shiels explains their findings: “We discovered that changes in the heart beat due to the temperate, coupled with the stimulation of adrenalin by diving adjusts the electrical activity of the heart cells to maintain the constant calcium cycling needed to keep pumping. If we went through this temperature change our calcium cycling would be disrupted, our hearts would stop beating and we would die.”

Professor Block says that the discovery may explain some strange behaviour they’d monitored in the tagged tuna: “We were recording the fish swimming down into colder depths only to resurface quickly into the warmer surface waters, a so-called “bounce” dive. From work at sea and in the lab we now know the fish hearts slow as they cool and as they resurfaced it sped up. Our findings suggest adrenalin, activated by the stress of diving, plays a key role in maintaining the heart’s capacity to supply the body with oxygen.”

Dr Shiels concludes: “This research was about understanding how animals perform under dramatic environmental changes. This gives us a clear insight into how one species maintains its heart function over varying temperatures, something we will need to study further given recorded changes in the earth’s temperature.”

Further Reading
Cardiac function in an endothermic fish: cellular mechanisms for overcoming acute thermal challenges during diving. H. A. Shiels, G. L. J. Galli, B. A. Block Proc. R. Soc. B: 2015 282 20141989; DOI: 10.1098/rspb.2014.1989. Published 24 December 2014

Loggerhead turtles home in on nests magnetically

Mother turtles find their way back to nesting beaches by looking for unique magnetic signatures along the coast, according to a new study published in Current Biology.

Loggerhead turtles, for example, leave the beach where they were born as hatchlings and traverse entire ocean basins before returning to nest, at regular intervals, on the same stretch of coastline as where they started. How the turtles accomplish this natal homing has remained an enduring mystery until now.

Loggerhead Sea Turtle
Loggerhead Sea Turtle. Photo credit: Brian Gratwicke, (CC by 2.0)

Several years ago, Kenneth Lohmann, the co-author of the new study, proposed that animals including sea turtles and salmon might imprint on magnetic fields early in life, but that idea has proven difficult to test in the open ocean. In the new study, Brothers and Lohmann took a different approach by studying changes in the behavior of nesting turtles over time.

“We reasoned that if turtles use the magnetic field to find their natal beaches, then naturally occurring changes in the Earth’s field might influence where turtles nest,” Brothers says.

The researchers analysed a 19-year (1993–2011) database of loggerhead nesting sites on the Atlantic coast of Florida, an area encompassing the largest sea turtle rookery in North America. Their analyses confirmed the predictions of the geomagnetic imprinting hypothesis.

In some times and places, the Earth’s field shifted so that the magnetic signatures of adjacent locations along the beach moved closer together. When that happened, nesting turtles packed themselves in along a shorter stretch of coastline, just as the researchers had predicted. In places where magnetic signatures diverged, sea turtles spread out and laid their eggs in nests that were fewer and farther between.

Turtles are long lived, and females undertake reproductive migrations periodically throughout their adult lives. Thus, the population of turtles that migrate to a given beach to nest each year consists of two subsets: a group of first-time nesters, and another, typically larger group of older “re-migrants” that have nested in the area during previous years.

Loggerhead turtles are thought to reach adulthood when they are between 23 and 29 years old. Much younger than this they return to coastal areas from the open sea and continue to mature there.

Sea turtles likely go to great lengths to find the places where they began life because successful nesting requires a combination of environmental features that are rare: soft sand, the right temperature, few predators, and an easily accessible beach.

“The only way a female turtle can be sure that she is nesting in a place favorable for egg development is to nest on the same beach where she hatched,” Brothers says. “The logic of sea turtles seems to be that ‘if it worked for me, it should work for my offspring.'”

These findings, in combination with recent studies on Pacific salmon, suggest that similar mechanisms might underlie natal homing in diverse long-distance migrants such as fishes, birds and mammals.

Further Reading
Evidence for Geomagnetic Imprinting and Magnetic Navigation in the Natal Homing of Sea Turtles, Brothers, J. Roger et al., Current Biology DOI: http://dx.doi.org/10.1016/j.cub.2014.12.035

Casale P, Mazaris A, Freggi D (2011). Estimation of age at maturity of loggerhead sea turtles Caretta caretta in the Mediterranean using length-frequency data. doi: 10.3354/esr00319

Strange marine animals found around the Canary Islands

Marine conservation group Oceana have found an amazing array of marine life in their expedition around the Canary Islands.

Oceana - Siphonophora
Siphonophora, photo © Oceana

Using ROVs (remotely operated underwater vehicles) down to 1000 m as well as scuba divers to shallow depths, they documented large colonies of deep-sea white coral, crystal aggregations of sponges, dense forests of black corals, oceanic puffers, giant foraminifera, carnivorous sponges and sharks, as well as many other biological communities and species in the south of the El Hierro Island.

Oceanic Puffers
Aggregation of Oceanic puffers (Lagocephalus lagocephalus lagocephalus) with reproductive purposes. El Desierto, El Hierro, Canary Islands, Spain. photo © Oceana

“Although there are some habitats that are specific to certain depths, in all dives and environments we have documented many different species, demonstrating the richness in biodiversity of southern El Hierro”, says Ricardo Aguilar, Research Director at Oceana in Europe. “With information gathered from this expedition, we intend to promote the creation of a marine national park in the southern part of El Hierro island; the first one in Europe.”

Nemichthys sp
Nemichthys sp, photo © Oceana

El Hierro boasts highly diverse and valuable marine habitats and species, which led Oceana to propose the protection of its waters in 2011. Earlier this year El Hierro became the first island in the world to use 100 percent renewable energies, making the island unique from an environmental point of view.

Carnivorous sponge
Carnivorous sponge photo © Oceana

As well as documenting the sea life around El Hierro, the expedition is exploring for the first time seamounts in the Eastern Atlantic. These have hardly ever been filmed before.

Brown-snout spookfish (Dolichopteryx longipes)
Brown-snout spookfish (Dolichopteryx longipes), photo © Oceana

The Canary Islands and their adjacent seamounts hold the most diverse elasmobranchs (sharks and rays) community of the whole European Union, with up to 79 species identified.

Bigeye thresher shark (Alopias superciliosus)
Bigeye thresher shark (Alopias superciliosus) photo © Oceana

Oceana was founded in 2001 and is the largest international organization focused solely on ocean conservation, protecting marine ecosystems and endangered species.

Vampire Squid
Vampire Squid, photo © Oceana
Sea urchin (Phormosoma placenta)
Sea urchin (Phormosoma placenta), photo © Oceana
Tripod Fish (Bathypterois dubius)
Tripod Fish (Bathypterois dubius), photo © Oceana
Sea Cucumber Elasipodida
Sea Cucumber Elasipodida, photo © Oceana

All photos copyright Oceana

Further Reading:
Oceana – Canary Islands Expedition 2014

Shark Fin Sales Halved in China

Prices and sales of shark fin are falling in China by 50-70% according to a report by environmental group WildAid.

Around 7% of all sharks are killed every year. This exceeds the average rebound rate for many shark populations, meaning that if things don’t change they are condemned to extinction. Shark products include meat, skin, teeth and oil, but it is the higher market value of shark fins – primarily in China – that has driven the demand for these beautiful animals and their population declines. However things are changing. A campaign in China to raise awareness of the effects of buying shark products has been very successful.

Demand reduction can be very effective” says Peter Knights, Executive Director of WildAid. “The more people learn about the consequences of eating shark fin soup, the less they want to participate in the trade. Government bans on shark fin at state banquets in China and Hong Kong also helped send the right message.

The new report documents:

  • 82% decline in sales reported by shark fin vendors in Guangzhou, China
  • 85% of Chinese consumers surveyed online said they gave up shark fin soup within the past 3 years. Two thirds cited awareness campaigns with 28% citing the government banquet ban as a reason.
  • 24 airlines, three shipping lines and five hotel groups have officially banned shark fin from their operations

Up to 73 million sharks are killed for their fins. Of the fourteen shark species most prevalent in the shark fin trade, all have experienced regional population declines ranging from 40-99%, and all are classified as Threatened or Near Threatened by the International Union for the Conservation of Nature (IUCN)

In the Guangzhou markets, assumed to be the new centre of China’s shark fin trade, wholesale traders are now complaining of dwindling sales and falling prices. Retailers who were selling medium-sized shark fins for as much as US$642 per kilogram are now able only to charge half as much. One Guangzhou wholesaler commented that “shark fin is a dying business” and another is quoted saying that “Yao Ming’s commercial impact single-handedly smashed my business,” in reference to WildAid’s ongoing multimedia public awareness campaigns.

The sharks most commonly killed for fins are: tiger shark, great hammerhead, scalloped hammerhead, oceanic whitetip, thresher shark, blue shark, shortfin mako shark, bull shark, silky shark, dusky shark and sandbar shark.

Tiger shark

Although the report is good news for sharks, the shark fin trade continues, both legally and illegally. For example in March 2014, WildAid interviews with Belizean fishermen revealed they continue to get US$75 per pound (approximately US$165 per kilogram) for medium to large shark fin and, comparatively, only US$7 per pound (approximately US$15 per kilogram) for the meat. Evidence of locally protected nurse sharks being targeted for their fins was also noted. In April 2014, the Belizean Fisheries Department arrested two fishermen for the attempted illegal export of 73 dried shark fins and other marine products to Guatemala.

So, good news for sharks but still work to be done to save the sharks and their oceans.

Images: Xvic, Terry Goss (CC BY-SA 3.0)

Deep sea octopus broods eggs longer than any known animal – 4 years

Researchers at the Monterey Bay Aquarium Research Institute have observed a deep-sea octopus brooding its eggs for four and a half years – longer than any other known animal. Throughout this time, the mother kept the eggs clean and guarded them from predators.

deep sea octopus
Deep-sea octopus (Graneledone boreopacifica) protecting her eggs. Photo credit: Robison et al (CC-BY)

Octopuses typically have a single reproductive period and then they die. Once a clutch of fertilized eggs has been produced, the mother protects and tends them until they hatch. In most shallow-water species this brooding period lasts between one and three months. Very little is known though about the maternal behaviour of deep-living species. In the cold, dark waters of the deep ocean, metabolic processes are often slower than their counterparts at shallower depths.

Every few months for the last 25 years, a team of Monterey Bay researchers led by Bruce Robison has used a remotely operated vehicle (ROV) to survey deep-sea animals at a research site in the depths of Monterey Canyon that they call “Midwater 1.” In May 2007, during one of these surveys, the researchers discovered a female octopus clinging to a rocky ledge just above the floor of the canyon, about 1,400 meters (4,600 feet) below the ocean surface.

Each time the researchers returned, they found the same octopus clutching the vertical rock face, arms covering her eggs.

deep sea octopus
Here she is again. Photo credit 2007 MBARI.

As the years passed, her translucent eggs grew larger and the researchers could see young octopuses developing inside. Over the same period, the female gradually lost weight and her skin became loose and pale.

The researchers never saw the female leave her eggs or eat anything. She did not even show interest in small crabs and shrimp that crawled or swam by, as long as they did not bother her eggs.

The last time the researchers saw the brooding octopus was in September 2011. When they returned one month later, they found that the female was gone. As the researchers wrote in a recent paper in the Public Library of Science (PLOS ONE), “the rock face she had occupied held the tattered remnants of empty egg capsules.”

Previously, the longest octopus brooding known was 14 months. The longest guarded incubation known for fish eggs is 4–5 months, by the Magellan Plunder Fish Harpagifer bispinis in Antarctic waters. For birds, the longest uninterrupted egg brooding is 2 months, by the Emperor Penguin. Among live-bearing species, elephants gestate for 20 to 21 months, frilled sharks carry their embryos internally for about 42 months, and the internal gestation period of alpine salamanders can reach 48 months before birth.

The prolonged brooding period for the deep sea octopus is a result of two factors, low temperature and the advantage of producing highly-developed hatchlings.

Further Reading:
Robison B, Seibel B, Drazen J (2014) Deep-Sea Octopus (Graneledone boreopacifica) Conducts the Longest-Known Egg-Brooding Period of Any Animal. PLoS ONE 9(7): e103437. doi:10.1371/journal.pone.0103437

42,000 Turtles legally killed each year

Over 42,000 turtles are legally killed each year, 80% of them endangered green turtles (Chelonia mydas), a study suggests.

British scientists investigated which countries allowed turtles to be killed, and how many of each species died, the Diversity and Distributions Journal reported.

Ten countries account for more than 90% of the catch, with Papua New Guinea, Nicaragua and Australia taking almost three-quarters between them. Legal take of turtles is comparable to estimates of by-catch.

Widespread commercial catch of turtles has contributed significantly to their decline.

The first place to protect turtles was Bermuda, as early as 1620. Although 42,000 seems an enormous number now, in the 60s Mexico alone was catching over 380,000 a year. The IUCN Red List of threatened species has listed marine turtles since 1982, giving them protection from the 198 countries now signed up to the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

The IUCN writes that “Perhaps the most detrimental human threats to green turtles are the intentional harvests of eggs and adults from nesting beaches and juveniles and adults from foraging grounds.“. Other threats include bycatch in marine fisheries, habitat degradation at nesting beaches and feeding areas, and disease.

As well as 37,339 green turtles, an estimated 3456 hawksbill turtles, 1051 loggerhead turtles, 263 olive ridley and 62 leatherback turtles are captured.

Further Reading:
Humber, F., Godley, B. J., Broderick, A. C. (2014), So excellent a fishe: a global overview of legal marine turtle fisheries. Diversity and Distributions. doi: 10.1111/ddi.12183

Google adds more Virtual Dives to Underwater Street View

With the help of the Catlin Seaview Survey, Google has added more underwater locations to its “Street View“.

Google put the first marine images up in September 2012, with dives in Australia, the Philippines and Hawaii. Now it covers 16 more countries, including the Galapagos, Monaco, Bermuda and Mexico. It really is a fantastic way to gauge potential dive sites before visiting a country. And it isn’t just for fun. The seaview survey will make ocean change plainly visible for all to see.

For shallow reef surveying – from 0 to 30 m – marine biologists use cameras attached to underwater scooters. Three 360o cameras take pictures from different angles to produce a panoramic seascape. For each image captured, a geo-location and camera direction is also recorded, meaning it’s possible to retake the photograph at a later date from the exact same camera position as the original.

Underwater camera used to make Google Underwater Street View
Mapping the Ocean Floor

Marine creatures like manta rays and turtles apparently find it particularly fascinating. The Catlin Seaview team often catch them checking out their own reflection in the wide-angle camera-lens-housing ports.

An underwater tablet has been developed especially for the project, which can connect to the internet and communicate live with the world from underwater.

For dives deeper than 30 m, the survey team sends down under underwater robots. They use data loggers to track changes in water temperature and light level.

The new locations you can now view on Google include Cozumel’s Santa Rosa Wall and Columbia Deep; Monaco’s Larvotto Marine Reserve and Roche Saint Nicholas (featuring the Oceanographic Museum of Monaco); the Cancun Underwater Museum and whale sharks at Isla Contoy in Mexico



Emily’s Pinnacles, Bermuda

Further Reading
Google Underwater Street View
Catlin Seaview Survey
Catlin Global Reef Record

Whale Watching from Space

But not by astronauts or space tourists. Scientists from the British Antarctic Survey are using satellite images to detect and count southern right whales (Eubalaena australis).

In recent years there have been over 420 deaths of these whales in their nursery grounds at Península Valdés in Argentina. (Out of a population last estimated at 2577 whales.) Most of the dead were calves. This number of deaths suggests that the right whale population, and its ecosystem, may be less healthy and robust than previously thought. The whales at Península Valdés comprise the largest single population and the high mortality rate has raised fresh concern for the future of the species.

Traditionally whale population size has been assessed by counting from boats, planes or shore. This is labour-intensive, costly and can be inefficient. Detection probabilities are high for ship surveys, but where surveys are carried out by small airplanes rates can be down to 40%. The researchers have tested a method of identifying whales automatically from high resolutions satellite images. They chose southern right whales to evaluate their method, as, they say “The southern right whale is an ideal subject for this work for many of the same reasons as it was an ideal whale to hunt, specifically its large size and a tendency, in the breeding season, to bask near the surface in large aggregations around sheltered coastal waters.”

The researchers – Peter T. Fretwell, Iain J. Staniland and Jaume Forcada – analysed the images manually and using image processing software.

Probable whales found by automated
Probable whales found by the automated analysis. Several of the images could be interpreted as whale pairs, or as a mother and calf, others may be displaying behaviour such as tail slapping, rolling or blowing. On several images there is a strong return at one end of the feature which is mostly likely the calluses on the whales head. Reprinted under a CC BY license with permission from British Antarctic Survey and DigitalGlobe.

Manually identified whales were put into three classes; shapes that are whale-like and whale-sized are classed as probable whales, other objects are classed as possible whales, but may include bubble slicks and some groups of seabirds. The third class are objects interpreted as sub-surface feature that are potentially whales. Their automated method found 89% of the objects manually classed as probable whales, with 23.7% false positives.

How do they know a whale-like blob is a whale? They used three criteria used to identify any objects in remotely sensed imagery:

  1. The object is the right size and shape to be a whale
  2. The object is in a place we would expect to find whales
  3. There are no (or few) other types of objects that could be misclassified as whales to cause errors of commission.

Overall the researchers were satisfied with their results and suggested that larger surveys over whole calving areas, which could potentially measure thousands of square kilometres, could be automated with a degree of success using their techniques.

Southern right whales were hunted extensively from the 17th through to the 20th century. The pre-whaling population has been estimated at 55,000–70,000 dropping to a low of just 300 animals by the 1920s.

Further Reading:
Fretwell PT, Staniland IJ, Forcada J (2014) Whales from Space: Counting Southern Right Whales by Satellite. PLoS ONE 9(2): e88655. doi:10.1371/journal.pone.0088655

Photo credit: Southern right whale (Peninsula Valdés, Patagonia, Argentina) by Michaël Catanzariti