Goblin Sharks are Giants

Goblin Sharks (Mitsukurina owstoni) may be among the largest of cartilaginous fishes. While generally credited with a maximum total length of 3.8 meters (12’6″), one specimen appears to have exceeded that by far.

In July 2000, an enormous shark was accidentally captured in the northern Gulf of Mexico after being entangled in a line attached to a crab trap (Parsons et al. 2002). Only the jaws of the shark were kept by the fishers (Parsons et al. 2002) and it is unknown why they weren’t examined by the authors. Considering the fishers took the time to dissect the shark (Parsons et al. 2002) I’m puzzled that no measurements were provided. The above photo, while clearly demonstrating Goblin Shark morphology and giving the impression of great size, unfortunately lacks any landmarks which can establish scale. Fortunately, a second photograph focusing on the head was taken and it proved surprisingly informative about the Gulf shark’s size.

The rope proved to be the key. With a known diameter of 2.06 cm (0.8″) Parsons et al. were able to measure a snout to eye distance of 62.9 cm (2’1″). Scaling up from the previously largest known specimen yielded a total length of 5.4 m (17’9″) for the Gulf shark (Parsons et al. 2002). The authors suspected the figure may have been an underestimate as snouts become proportionally shorter with increased total length and so used an exponential regression to calculate a total length of 6.17 m (20’3″). I strongly suspect the latter figure is closest to reality. I calculated the above photograph shows about 3.5 meters (11’6″) of shark despite most of the tail being out of frame. The aforementioned 3.84 m specimen appears to have a proportionally much longer snout, lending credence to the notion that 5.4 m is an underestimate. Of course it would be nice if those jaws showed up – or better yet, a similarly-sized specimen – but the case for gargantuan Goblin Sharks seems compelling.

Is the Gulf shark some one-off freak? I suspect not. The Gulf shark was the first specimen ever recorded from the Atlantic coast of North America (Parsons et al. 2002) and is still apparently the only known (Castro 2011). Adult Goblin sharks have only been “occasionally reported” presumably due to their deep water habitat (Castro 2011) and this list suggests they are very occasional indeed. With such a small sample size, a lack of Gulf shark-sized individuals could just be a statistical quirk. Perhaps there is bias towards the capture of smaller individuals as a ~6 m individual (perhaps approaching a tonne in weight) could be prohibitively large for most vessels to catch, let alone haul on board and preserve. Here’s to hoping that a monstrous specimen scares the hell out of an ROV crew someday!

Goblin Sharks may be giants, but they are far from alone in the lightless depths and far from being the largest. More soon.

References:

Castro, J. (2011) The Sharks of North America. Oxford University Press.

Parsons, G. R., et al. (2002) First record of the goblin shark Mitsukurina owstoni, Jordan (Family Mitsukurinidae) in the Gulf of Mexico. Southeastern Naturalist 1(2), 189-192.

2 thoughts on “Goblin Sharks are Giants

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s