Carapace sizes

[Steve]

I noticed something interesting about some recent photos of large crabs posted here. Some crabs have different shaped spines than others. Some have very long/straight spines while others have short/curved spines. This would seem to indicate an unfair advantage in determining a crab's size since the spines are what's measured.

Here are two photos of 9+ inch crabs that I spliced together to make one crab which clearly illustrates my point (no pun intended!). It's impossible to determine which is actually larger because there's no real scale in which to size each crab in relation to the other. What would be interesting is to actually cut each physical carapace in half exactly at the center and then splice the actual shells together... I'm sure that would give a clear indication as to which crab has the larger body cavity.

[Steve]

Here are the same two photos with spines superimposed. The anterolateral teeth (the tiny "saw blade" -like spines above the lateral spines) are line up almost perfectly, yet the lateral spines are much different. 

[tattoo]

Interesting.  could it be they were caught at different locations,

[Steve]

Interesting.  could it be they were caught at different locations,

Could be... or could be different species.

The Atlantic blue crab that we all enjoy so much is known as Callinectes sapidus. Another swimming crab that inhabits the same waters and looks nearly identical is known as the lesser blue crab or Callinectes similus. They look almost identical, but they're two different species... I doubt the lay person (including myself) could tell them apart. Then there's Callinectes ornatus, yet another species that could be found in our waters.

http://www.sms.si.edu/IRLSpec/Callinectes_similis.htm
http://www.sms.si.edu/IRLspec/Callinectes_ornatus.htm
http://www.sms.si.edu/IRLspec/Callin_sapidu.htm

[captaincrab55]

Interesting.  could it be they were caught at different locations,

Tat,   I think your on to something....     The crabs I got from Mr Ray @ Christmas from NC were wider/bigger bodied and easy to pick...

[jack1747]

My guess is the length is a result of environment and breeding. I remember the scientist at COMB saying that one worry they had about hatchery crabs was the lateral spines were shorter. They worried that it would make hatchery crabs easier prey then wild crabs.

[Steve]

Whoops, I forgot about Callinectes danae too!

Well, as you can see, many different species of blue crab inhabit our waters... it's just that Callinectes sapidus (the Atlantic blue crab or "Maryland" blue crab) is the most prevalent. This might explain why some people claim that crabs served in Florida or Louisiana taste different than Maryland crabs... or that sometimes one crab has more flavor than another from the same pile... all of these different species inhabit the same waters. As a matter of fact, I read that Callinectes ornatus is impacted by the blue crab fishery because it shares the same waters

Because Callinectes ornatus occupies the same habitats as the commercial species, C. sapidus, it is impacted by the crab fishery along western Atlantic coast (Hsueh et al. 1992).

Looks like a new project for me and bluecrab.info... a new page on the main site which looks at the different species of Callinectes that inhabit our waters and how to tell them apart.

Here's a really good read on the subject:

http://www.dnr.sc.gov/marine/sertc/Blue%20Crab%20SOM.pdf

Steve

[genecrabman]

Looks like the crab on the right is a Sook.. They tend to be longer pointed.. Also crabs that shed in colder more brackish water tend to have longer points, because it takes them longer to harden up after they shed, they have the Maximum growth during every shed cycle, thats why  many of the Larger Crabs are caught up in the rivers..

[Steve]

My guess is the length is a result of environment and breeding. I remember the scientist at COMB saying that one worry they had about hatchery crabs was the lateral spines were shorter. They worried that it would make hatchery crabs easier prey then wild crabs.

Very interesting!

But wouldn't you think that the smaller spines of hatchery-raised crabs would go grow back to normal size after successive molts in the wild? Hmmmm...

[oldsunbear]

That is intersting Steve, and I have noticed that as well. I have caught some huge 8"+ crabs with sort of short points and some in the same size range with long points that did not seem quite as "huge". (by the way the long ones seem to by much more likely to impale the unwary)
At first I wondered if it was a sex thing, but it didn't seem to be by my observation. So I just chalked it up to one of the mysteries of nature.
I have seen guys that are the exact same height & same weight, both in relatively good shape standing next to one another and yet one looks huge in comparison to the other. One has a thin frame with more muscle mass, and the other has a bigger frame and is leaner. The mystery of our designer.
Now as to the different species of crab you mentioned it is interesting to note their different tolerances to salinity with ornatus being least tolerant to fresher water.

[oldsunbear]

And I think I have encountered  "C. exasperatus" on more than one occasion, especially handlining!

[genecrabman]

And I think I have encountered  "C. exasperatus" on more than one occasion, especially handlining!

I knew I should have taken that Latin Class in High school.........

[JIMMYCRAB]

Here's two from the Bush. The one on top is 9 1/4 inches caught 2 years ago. The one on the bottom is from last year. The Same crab my son is holding in the Mumbo post. It's not hard to see he was a much bigger crab A half inch shorter but but by far one of the biggest bodied crabs I've ever caught. He was thick through the middle and had one HUGE claw but relatively short points. ------JC

[Mr. Breeze]

Looks like the crab on the right is a Sook.. They tend to be longer pointed.. Also crabs that shed in colder more brackish water tend to have longer points, because it takes them longer to harden up after they shed, they have the Maximum growth during every shed cycle, thats why  many of the Larger Crabs are caught up in the rivers..

I agree that the one on the right is a sook, and sooks definately have longer points.

[bayou boy]

Could be... or could be different species.

The Atlantic blue crab that we all enjoy so much is known as Callinectes sapidus. Another swimming crab that inhabits the same waters and looks nearly identical is known as the lesser blue crab or Callinectes similus. They look almost identical, but they're two different species... I doubt the lay person (including myself) could tell them apart. Then there's Callinectes ornatus, yet another species that could be found in our waters.

http://www.sms.si.edu/IRLSpec/Callinectes_similis.htm
http://www.sms.si.edu/IRLspec/Callinectes_ornatus.htm
http://www.sms.si.edu/IRLspec/Callin_sapidu.htm

Steve we catch several differant kinds of crabs here.the most common of course is the blue crab,then what we call scissor bill's or gulf crabs,the biggest that we see is maybe 5 1/2,they resemble blue crabs but there are distink differences.next one i catch I'll post pics.then theres a little crab we catch a little farther out thats calico colored.biggest I've seen maybe 5'ish,and we catch lots of little crabs that resemble blue crabs but there are only 1'' to maybe 2''s and the sponges look like its rapped in cellophane.now we catch lots of differant other crabs these are the ones that have the same shape as blue crabs.and i have caught a couple brown crabs over the last couple years.sorry i don't have the scientific name for them.

[Dreampixels]

I agree that the one on the right is a sook, and sooks definately have longer points.

I concur Doctor................I too believe the mature female crab normal has longer straight spines then males.

[Steve]

Here's two from the Bush. The one on top is 9 1/4 inches caught 2 years ago. The one on the bottom is from last year. The Same crab my son is holding in the Mumbo post. It's not hard to see he was a much bigger crab A half inch shorter but but by far one of the biggest bodied crabs I've ever caught. He was thick through the middle and had one HUGE claw but relatively short points. ------JC

Nice photo! Both of these shells from males?

[crabbing4fun]

I agree that the one on the right is a sook, and sooks definately have longer points.

I AGREE WITH MR BREEZE AS ALL THE FEMALE CRABS I CAUGHT DOWN THE WYE LAST YEAR ALL HAD LONGER POINTS THAN THE MALES.

[JIMMYCRAB]

Nice photo! Both of these shells from males?

Yea. Both males from the Bush River.

[jack1747]

"Results indicate that unconditioned hatchery crabs had lower survivorship than wild crabs in the field and differed in carapace color and lateral spine length. Both traits were plastic. Carapace color was changeable within 1-2 days, without a molt, upon the exposure of crabs to new substrates. However, colors within the range produced in this study did not significantly affect survivorship in a field or a laboratory experiment. Change in spine length required exposure to predators for 1-4 weeks. Exposure to fish predators resulted in increased spine length, though exposure to adult blue crabs had no significant effect. Crabs with lengthened spines had significantly higher survivorship in both laboratory and field experiments,"

University of Maryland Biotechnology Institute, Center of Marine Biotechnology, 701 E. Pratt St., Baltimore, MD 21202, ETATS-UNIS
ZOHAR Yonathan

[jack1747]

http://www.searanching.org/program/documents/Youngetal.pdf

"Lateral spines were significantly shorter in hatchery than wild juveniles (Fig. 1), raising concerns about vulnerability to fish predators."

[Steve]

Looks like the crab on the right is a Sook.. They tend to be longer pointed.

I've caught plenty of males with the long spike-like spines, so I'm not convinced that it's a male/female thing.

[Steve]

My guess is the length is a result of environment and breeding. I remember the scientist at COMB saying that one worry they had about hatchery crabs was the lateral spines were shorter. They worried that it would make hatchery crabs easier prey then wild crabs.

I don't think the hatchery crab issue pertains here since we're talking about mature market-sized crabs that have been in the wild for a year or more.

The article that you cited clearly states that "Lateral spines were significantly shorter in hatchery than wild juveniles (Fig. 1), raising concerns about vulnerability to fish predators. However, within ~10 days after release, spine length of hatchery crabs increased to that of wild crabs (Davis et al. 2005)." [emphasis mine]

BTW, Great article Jack! Thanks for sharing!

[Dreampixels]

Heres some good reading and info.......

http://ftp://ftp.fao.org/docrep/fao/009/y4160e/y4160e23.pdf

[Potty Mouth]

This is a VERY interesting topic...

So, Jack's post/article seems to say that the longer spines are the result of the crab's response to a predatory environment and that a crab can effect changing the length of the spike even when it's shell is hard.  That is neat and a surprise to me.  I wonder how the crab effects making the spines more pointy.  Also, I would have guessed that a crab is in just as predatory an environment when it is alone with a bunch of other crabs as it is in the wild.  I mean, if you slough around a bunch of hungry hard crabs then you are toast and a bunch of hard crabs often destroy each other no matter where they are if there's pressure on th amount of food available.

Gene's post says that cooler water means a slower metabolism while molting and therefor a longer time that it takes for a crab to harden after molt.  That seems to make horse-sense to me as well.

If both "points" are true, I guess spike legnth is as much a function of when and where a molt takes place as the crabs environment in terms of predators. 

My friend that crabs the bays by/at the ocean says all the crab are more short-spined than river-crabs but I'm not sure that these crab have fewer predators or that the water is warmer on average at the ocean at the times when the crabs are molting. I know the water temp is more consistent near the ocean and the crabs can molt more often than they do elsewhere.  Perhaps more molts per year averages down the spike length for crabs remaining near to the ocean.

For the Ches. Bay, when crabs are molting and not buried in the bottom, do you think the water temp is cooler in the southern areas nearer the ocean or up near the freshwater fed brackish rivers?  I am just wondering if the cooler water always finds you the longer spined crab.  If the more "football-shaped" ocean crabs eventually migrate north up the bay to become a big, long-spined, river crab, would that mean that it's spines have gotten longer because the crabs are under more predatory pressure or that the crab is preparing for the confrontations?  Gene's post could then dovetail into that because, if the crab is eating well, following food up the bay, it is going to molt somewhere and molting in a river would yield a longer spine yet again due to cooler rain fed river water... or?  Keep up the good work gents.. excellent topic!  I'd like to hear more thoughts on it...