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The next Marine Mammal Highlights blog is the Spectacled Porpoise – the strange, very unique porpoise that we know almost nothing about!

Definitely one of the strangest looking marine mammals, the spectacled porpoise (Phocoena dioptrica) is also one of the least well known.

Rare photograph of a spectacled porpoise breaching.
Photo: https://otlibrary.com/spectacled-porpoise/

This strange marine mammal was first identified in 2012 after one washed up on a beach near Buenos Aires, Argentina…and its markings were unique. With a black back and striking white underside and flanks, the Spectacled Porpoise also has facial markings that include black lips and white rings around its eyes. This strange porpoise was given the Latin name Phocoena dioptrica, which refers to these glasses-like markings. They were briefly considered to be their own species, however after more genetic and morphometric studies were conducted it was decided that they should be classed back into the Phocoena genus again.

The male Spectacled Porpoise also has a very large, rounded dorsal fin with a wide base that almost looks disproportionate to its body. Females have a more typical porpoise dorsal fin that is smaller and more triangular. Males also have a slightly larger body-size than females, growing up to 2.25 meters versus the females that only grow to 2 meters. It is one of the larger porpoise species, however has relatively small flippers that are situated far forward on the body adding to its overall unique appearance.

The male Spectacled Porpoise fin is oddly large and rounded for a porpoise.
Photo: Porpoise Conservation Society.

There have been very few sightings of the Spectacled Porpoise in the wild, but those that have been made are typically found off the SE coast of South America, and seem to consistently show up in groups of 1-5 individuals. They are fast, active swimmers but the lack of observations of them in the wild suggests they might actively avoid boats. We don’t have a good idea of what they eat as very few stomach contents have been examined, but from what was found it seems that anchovies and shrimp are staples in their diet.

Unfortunately, the Spectacled Porpoise’s general avoidance of boats and lack of sightings also means we have no idea what their total population is! As far as we know, their range extends throughout the Southern Hemisphere and includes temperate and cold sub-Antarctic waters. Individuals have been sighted off Tasmania, Falkland Islands, South Georgia Islands and southern New Zealand.

Spectacled Porpoise primary threats include pollution and entanglement in fishing nets. Despite the lack of sightings in the wild they are actually the second-most frequently stranded cetacean in Tierra del Fuego (South America). There is a still a large gillnet fishing industry in this area, and this porpoise are likely more susceptible to entanglements either because they are foraging for the same fish that the industry is targeting, or the gillnets extend into their range and they swim into the nets frequently. There is also some evidence of historical hunting of Spectacled Porpoise by the indigenous people of Tierra del Fuego.

So that pretty much sums up what we know about the Spectacled Porpoise…not a lot! But I think we can all agree: it looks pretty cool.

cindy.elliser@pacmam.org

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