Sixgill Shark Workshop at the Seattle Aquarium

[John Rawlings]

This year's Cow Shark (6-Gill) workshop will be held at the Seattle Aquarium this coming Saturday (April 28th) between 9:00 AM and 4:00 PM. Scientists specializing in these amazing sharks will be speaking on a variety of topics. Anyone fascinated by these sharks would be well advised to attend - I'm already registered and looking forward to it!

Here's a link to the web page giving the proposed agenda and registration information:

http://www.seattleaquarium.org/page.aspx?pid=1199

Maybe I'll see some of you there! If so, slap me up side the head and say hey!

John

[John Rawlings]

You all missed a great informational opportunity today! I thought that I'd at least see a few NWDCers there, but I'm still really glad that I attended.

One of the juicy tidbits was this - remember that big pregnant female Six Gill shark that washed up on a beach down in the South Sound a few years ago? DNA analysis of the 71 pups in her uterus showed that up to 9 males contributed their genes as fathers of her brood, with 4 of those males fathering 80% of the pups. Therefore, some of the pups would have been siblings and the rest half-siblings.

When we were all having all of those six gill sighting s a few years back at Cove 2 and elsewhere in the Sound, most of us thought that we were seeing mature animals. We weren't. We were seeing immature sharks that had not yet reached adulthood and did not yet have the ability to mate. The length of maturity for males is 3 to 3.5 meters while that of females is 4+ meters. NONE of the dozens and dozens of sharks seen at the baiting station beneath the Seattle Aquarium were adults, and I would submit that probably NONE of the ones we saw at Cove 2 were, either, no matter what our eyes told us at the time.

Now, interestingly enough, when the DNA analyses came back on the sampled sharks from beneath the Aquarium, it was found that in most cases each group that came in also consisted of siblings and half-siblings. Sharks in this group that were tagged with tracking devices have now left the Sound - only one of these tracked sharks can be shown to have remained near Vashon Island, all of the others have left.

Now, this cannot be seen as conclusive, but the implication is that pregnant females come in to the Sound to pup, then leave. Pups born of each female then appear to stay together, hanging out in sibling groups within the Sound. Once they reach a certain age, they in turn also leave the Sound for unknown reasons.

It appears that this may be cyclical. Hopefully, this means that within a few years or so we will once again be treated to a BUNCH of Six Gill shark sightings here in Puget Sound. Only time will tell!

- John

[Tom Nic]

Hugely interesting! Really wish I could have been there...

Thanks for the tidbits and nuggets!

[Joshua Smith]

That's really cool! I suspect they are correct regarding the cyclical nature of the sightings. And- oh, yeah:

I can attest to having seen a mature female 6 gill. Calvin shot video of it:

http://www.calvintang.com/blog/2007/01/ ... lki-cove-2

It's hard to get a good sense of her size from the video- also note that the embedded video in the link is crappy flash- scroll to the bottom for a link to the original.

This shark was at least 12 feet (3M, or close enough) long. Calvin, Howard, and I all saw her. We're all close to 6' tall, and she was longer that 2 of us- we had a good, long look at her, because she settled down into the mud near the I beams, and just sat there- it was very strange. Anyway, as Calvin noted, she was not tagged, meaning that she wasn't a regular at the aquarium feeding station.

[spatman]

Damn, I wish I could have gone to that presentation. Sounds really informative.

I have yet to see a sixgill, and it is certainly high up on my list. Hopefully, you are right and the cycle will come back around soon. Did they mention how long it takes the females to reach sexual maturity?

[John Rawlings]

Did they mention how long it takes the females to reach sexual maturity?

They have no idea whatsoever. With certain species, like Great Whites, they can literally count the rings within a vertebrae just like the method used to age trees, but with Cow Sharks that doesn't work well at all due to the shape of their vertebrae.

[seainggreen]

John, thanks for the great sharing of information... It is always great to learn.

I hope I manage to see one more 6 gill somehow, some way, prior to the grand adventure commencing.

Laurynn

[John Rawlings]

John, thanks for the great sharing of information... It is always great to learn.

I hope I manage to see one more 6 gill somehow, some way, prior to the grand adventure commencing.

Laurynn

The really interesting thing about these sharks is that they are apparently world-wide. However, in warmer waters like where you are moving they are far, far deeper!

[diverden]

I appreciate the tidbits of info. I have roughly 400 dives in the Sound in the last 4 years and have never even heard of a sighting. Someday my day will come!