Monday, May 27, 2013

How low can they go?

You didn't think I forgot about answering the questions from our crab chat did you? Nope! The next question to answer is:

Just how deep in the ocean do king crabs and snow crabs live?

To answer this I looked at the crab survey data from 2012. This is only looking at Bering Sea crabs in summer, so it's a little limited, but I figured it was a great place to start. Here's what I learned:

King crabs really stay out of each others' way! Every sampling location that found red king crabs was absent of blue king crabs. Also, on average, blue kings were found deeper in the Bering Sea than red kings; the average blue king crab depth was 87.6 meters (287.5 feet) and the average red king crab depth was 51.7 meters (169.7 feet). This was interesting to me because the bycatch of blue king crabs in red king crab fisheries has closed down red king fisheries in the past (due to low blue king crab abundance), but it would seem that for the summer of 2012 that might not have been a concern.

Heading deeper into the Bering Sea, I found the Chionoecetes crabs! Both Chionoecetes bairdi and Chionoecetes opilio liked an average depth around 91 meters (91.5 m and 91.4 m, respectively), which is close to 300 feet. Unlike the king crabs, these Chionoecetes cousins hung out together quite a bit, which isn't too shocking since they're known to hybridize.


The thing that caught my eye with hybrid Tanner crabs was that their average depth was slightly shallower than the two "pure blooded" crabs (88.1 meters). If I didn't have a real job, I would look into the sex distribution of male and female bairdi and opilio crabs and compare that to the distribution of hybrids to finally answer who's mating with whom. Anyone else want to check it out!?!? Let me know. (Seriously. I'm totally interested.)

average depths (in meters) for the locations where red king crab,
blue king crab, Chionoecetes bairdi, C. opilio, or their hybrids were present

The other thing that caught my eye is that hybrid crab presence was NOT dependent on both "pure" crabs being there (during the survey, that is). Of the 157 sites that had hybrids, 25 sites were missing on of the original species. Plus, there were 70 sites that had both bairdi and opilio crabs but no hybrids. (Fun fact: those sites had a deeper average at 107.4 meters.)

So, that's how low king crabs and snow crabs can go! For perspective, if the Bering Sea's depth was in line with a football field, red kings would make it just past the 50 yard line while blue kings and hybrid Tanners would be in the red zone. But bairdis and opilios would go ALL. THE. WAY!!!

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