Narwhals can be photo-identified

Photo-identification is a simple tool: you have a camera and an animal, and you take a photo of the natural markings and peculiar features that may help identify an individual.

It is a widespread technique used by cetacean researchers worldwide. Dorsal fins, flukes and body pigmentation are often used to tell one dolphin or whale from another. For some species, however, it gets more difficult and the narwhal (Monodon monoceros) is an example.

Until recently, photo-identifying these gentle creatures was considered too difficult, mainly because they do not have a dorsal fin, and body pigmentation changes over time.

But some researchers did not give up and found out that narwhals can be identified. Researchers noticed that narwhals have nicks and notches on the dorsal ridge, located at the posterior half of the back, and this part of the body is always visible during breathing. Although the dorsal ridge isn't an ‘obvious’ dorsal fin, natural marks are found on more than 90% of the individuals, and they differ in location, numbers, shape and size.

Now researchers hope to better understand the narwhal’s ecology, and investigate their population abundance as well as social organisation and migrations through the analysis of photo-identification data.

Silvia Bonizzoni

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Photo: dorsal ridge’s narwhal, by Marie Auger-Méthé.

Auger-Méthé M., Marcoux M., Whitehead H. 2009. Nicks and notches of the dorsal ridge: promising mark types for the photo-identification of narwhals. Marine Mammal Science. DOI: 10.1111/j.1748-7692.2009.00369.x
Abstract - The narwhal is a hunted species for which we have many knowledge gaps. Photoidentification, which uses photographs of naturalmarkings to identify individuals, is widely used in cetacean studies and can address a broad range of biological questions. However, it has not been developed for narwhals. The marks used for other cetaceans are inappropriate for this species either because narwhals lack the body part on which these marks are found or because the marks are known to change with time. We investigated the marks apparent in photographs of narwhals. Nicks and notches on the dorsal ridge are the mark types most promising for photo-identification. They are found on 91%–98% of the individuals, thus allowing the identification of a large part of the population. They can be used to differentiate between individuals, in part because they are variable in their location, numbers, shape, and size. Although our results suggest that nicks and notches are relatively stable over time, rates of change should be formally measured to assess the probability of photographic matches over multiple years. However, we are confident that these marks can be used in studies spanning at least a field season.

Guinness migrations

Speaking about the ‘Guinness World Records’ I thought grey whales (Eschrichtius robustus) and humpback whales (Megaptera novaeangliae) were the animal with the longest migration ever recorded, with approximately 16,000-20,000 jm on their annual journey.

But I had failed to consider the avian world and so, I was completely wrong.

A recent study found out that a little bird weighing less than 125 gr, the Arctic tern (Sterna paradisaea), is the winner in this "competition".

Thanks to tiny devices attached to 11 Arctic terns, researchers were able to track their routes and find out exactly where they went during a full-year of migration. From the breeding to the wintering grounds and back again, travelling between 280 and 670 km per day, they did a pole-to-pole migration totalling 70,900 km!

Never overlook a tiny little bird!

Silvia Bonizzoni

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Photo: Geolocation tracks of 11 Arctic terns, from the Egevan et al. article.

Egevang C., Stenhouse I.J., Phillips R.A., Petersen A., Fox J.W., Silk J.R.D. 2009. Tracking of Arctic terns Sterna paradisaea reveals longest animal migration. PNAS. 4pp.

For more information:
http://news.bbc.co.uk/2/hi/science/nature/8451908.stm

Whales and dolphins in Salento

Today, January 22nd, Giovanni Bearzi gave a 2-hour lecture at the University of Salento (Lecce, Italy), centred around research done by the Tethys Research Institute in the Mediterranean Sea over the past 25 years.

The event, organised by Dr. Paolo Guidetti - one of the foremost experts on marine protected areas - took place in the prestigious University for a selected group of teachers, researchers and students.

Dr. Guidetti kindly introduced the work done by Bearzi and colleagues and presented Tethys as an Italian centre of excellence for cetacean research.

Bearzi’s seminar, titled "Twenty years of cetacean research in the Mediterranean: what for?", started with an overview of the work done by Tethys in several parts of the Mediterranean, to proceed with presentations on research projects focusing on population abundance estimates, interactions between dolphins and fisheries, and today's conservation challenges.

Bearzi also showed the Disappearing Dolphins documentary and then closed with a presentation on the recent mass stranding of sperm whales in Apulia, reporting on the amazing changes occurred in the public perception of these animals.

Silvia Bonizzoni

Divergence in killer whales

Two different types of killer whales Orcinus orca inhabit UK waters, according to an English-Dutch research team.

A study based on morphological aspects, isotopes and genetic analysis provided evidence for differences between two sympatric killer whale kinds (called ‘type 1’ and ‘type 2’).

‘Type 1’ is characterised by eye patch with parallel orientation, worn-out teeth at adult stage, 12 teeth in the lower jaw, and a catholic diet ranging from fish to seals.

‘Type 2’ has eye patch with angular orientation, 11 teeth in the lower jaw and less worn-out, greater body size with adult males almost two metres larger than the other adults, and a more specialised diet, probably focused on whales and dolphins.

"They seem to have occupied completely different ecological niches and have started to diverge morphologically " commented Andrew Foote, leader of the study. Will this divergence bring the killer whales to divide in different sub-species?

Silvia Bonizzoni

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Photo: Adult Type 1 (top) and Type 2 (down) mandibles, by Andrew Foote

Article:
Foote A.D., Newton J., Piertney S.B., Willerslev E., Gilbert M.T.P. 2009. Ecological, morphological and genetic divergence of sympatric North Atlantic killer whale populations. Molecular Ecology 18(24):5207-5217.

For more information:
http://news.bbc.co.uk/earth/hi/earth_news/newsid_8440000/8440002.stm

Cetacean records in the northern Adriatic Sea

A study encompassing 20 years of cetacean sightings in northern Adriatic waters has just become available.

The study intends to complement existing knowledge and it is based on sightings made during visual survey conducted by Tethys in collaboration with CNR-ISMAR (Institute of Marine Sciences) as well as records collected opportunistically by a variety of observers, including biologists and pleasure boaters.

The only cetacean species observed between 1988 and 2007 was the bottlenose dolphin (Tursiops truncatus).

Encounter rates of bottlenosed dolphins in this part of the Adriatic are also reported, and were thought to be generally low as well as highly variable.

SB

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Bearzi G., Costa M., Politi E., Agazzi S., Pierantonio N., Tonini D., Bastianini M. 2009. Cetacean records and encounter rates in the northern Adriatic Sea during the years 1988-2007. Annales Ser. hist. nat. 19(2):145-150.

Manatees must choose between bad and less bad

Researchers observed that the Amazonian manatee Trichechus inunguis, an elusive and pacific marine herbivore who lives in the Amazonian River, mysteriously performs periodical movements from shallow to deep water areas. The reason was unknown, but a recent study found out that this migration is meant to avoid predator attacks during the low-water season.

These manatees live in quiet lakes formed within Amazonian river flood plains during the high-water season (May-June) then, during the low-water season (October-November), they start to migrate as the water level drops. The main reason could be that it’s too dangerous to remain in shallow water: animals can strand and be attacked by predators such as caimans, jaguars, and also humans.

This migration it’s not safe. During the journey, manatees have to pass through narrow channels where they are exposed to illegal hunters (their meat is appreciated). "Amazonian manatees migrate to a habitat that doesn't offer easy living conditions in order to flee from a habitat that becomes inhospitable" - commented Eduardo Moraes Arraut, first author of the study - "When you have two options that are not good, you choose the one that is less bad”.

Researchers warn that these gentle animals are in a greater danger than previously thought: they are vulnerable to hunters but also to climate change, as the flooding regime of Amazonian rivers is strongly related to large-scale climatic phenomena.

Silvia Bonizzoni

Photo credit: SeaPics.com

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To read the article:
Arraut E.M., Marmontel M., Mantovani J.E., Novo E.M.L.M., Macdonald D.W., Kenward R.E. 2009. The lesser of two evils: seasonal migrations of Amazonian manatees in the Western Amazon. Journal of Zoology: doi:10.1111/j.1469-7998.2009.00655.x

For more information:
http://news.bbc.co.uk/earth/hi/earth_news/newsid_8426000/8426287.stm

Sea Shepherd’s trimaran collision

On January 6th, the high-tech carbon fibre trimaran ‘Ady Gil’, belonging to the anti-whaling group Sea Shepherd, was destroyed after a collision with a Japanese vessel.

The Ady Gil was designed to run on low-emission renewable fuels and was built with peculiar materials to reduce the probability to be detected by the radars of whaling vessels. Its goal was to intercept and physically prevent ships from slaughtering whales, and at least reduce the illegal whaling occurring in the Southern Ocean Whale Sanctuary.

After only one month from its official departure, however, the Ady Gil was crashed by the Japanese security ship Shonan Maru 2, the boat used by whalers to "protect" the Japanese fleet.

All six crew members of the Ady Gil were rescued, but there are no chances to save the trimaran.

Despite this catastrophic damage, the anti-whaling group is not giving up. As the Sea Shepherd’s captain, Paul Watson, said: "If they think that our remaining two ships will retreat from the Southern Ocean Whale Sanctuary in the face of their extremism, they will be mistaken.”

Silvia Bonizzoni

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Photo by: AFP/GETTY

For more information:
http://www.telegraph.co.uk/earth/earthnews/6939571/Anti-whaling-ship-sinks-after-collision-with-Japanese-vessel.html
http://www.seashepherd.org/news-and-media/news-100105-4.html

Ancient toothed whale shows Charles Darwin was right

Mammalodon colliveri was a 3 m long animal who lived 25 million years ago. New research by Eric Fitzgerald, a paleobiologist from the Victoria Museum in Melbourne (Australia), revealed that this ancestor of a baleen whale still had teeth and it had not yet evolved the baleen plates.

According to Fitzgerald, it was a bottom-feeding mud-sucker that may have used its tongue and short snout to suck small prey from sand and mud on the seafloor.

Charles Darwin's, in his book ‘On the Origin of Species’, speculated that some of the earliest baleen whales may have been suction feeders and that their mud grubbing served as a precursor to the filter feeding of the modern mysticetes. This was back in 1859. And as usual, Darwin was perfectly right.

Silvia Bonizzoni

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Painting by Brian Choo (Museum Victoria, Melbourne, Australia)

For more information:
http://news.bbc.co.uk/2/hi/science/nature/8430402.stm
http://www.sciencedaily.com/releases/2009/12/091222105055.htm

Fitzgerald E.M.G. 2010. The morphology and systematics of Mammalodon colliveri (Cetacea: Mysticeti), a toothed mysticete from the Oligocene of Australia. Zoological Journal of the Linnean Society. DOI: 10.1111/j.1096-3642.2009.00572.x

ABSTRACT - Mammalodon colliveri is an unusual toothed archaic mysticete (Cetacea) from the Upper Oligocene Jan Juc Formation of south-east Australia. The morphology of the holotype skull and postcrania are described in detail. Superimposed on the generally plesiomorphic archaeocete-like morphology of Mammalodon are subtle mysticete synapomorphies. Derived features of Mammalodon include a short and bluntly rounded rostrum, reduced premaxillae, and anterodorsally directed orbits. Within Mysticeti, this suite of features is unique. The aberrant rostral morphology of Mammalodon suggests specialization for suction feeding. Janjucetus hunderi is placed in an expanded family Mammalodontidae. Phylogenetic analysis corroborates the monophyly of Basilosauridae, Neoceti, Odontoceti, and Mysticeti, and yields a novel hypothesis of toothed mysticete relationships: a basal clade of undescribed toothed mysticetes from South Carolina, a Llanocetidae + Mammalodontidae clade, and monophyletic Aetiocetidae are posited as successive sister taxa to edentulous baleen whales (Chaeomysticeti). Toothed archaic mysticetes clearly employed diverse prey capture strategies, with exaptations for filter feeding evolving sequentially in stem group Mysticeti. A stratigraphically calibrated phylogeny implies that the initial diversification of Mysticeti occurred during the Late Eocene.