Cephalopodcast

Eggcase from a skate. © J. Robertshaw

The Great Eggcase Hunt

With the coming of spring in the northern hemisphere also comes a time to hunt for eggs. But it’s not just about birds anymore. The folks over at the Shark Trust also want people to head to the beach to look out for the fecundity of fish.

Colloquially known as mermaid’s purses, eggcases are the protective capsules laid by skates and some rays**. Inside is a tiny baby skate and a big yolk sac. Typically the capsules have odd keels and horns to help them remain tangled in seaweed and camouflaged on the bottom. The young develop for several months before hatching out as miniature adults. But after hatching, the horny cases begin to breakdown and may come loose, washing up on the shore. Storms might also dislodge living ones from the bottom. If you find a lot of eggcases in an area, it may indicate that a skate nursery is located nearby. This kind of information is valuable to conservationist who are trying to protect these species.

Why does the Shark Trust want you to record eggcases? In recent decades several species of skate and ray around the…coast have dramatically declined in numbers…The identification of these critical areas will enable the Shark Trust to propose conservation measures, in order to reverse the decline of these charismatic animals.

So now’s your chance to contribute to skate and ray conservation and have a lot of fun at the same time.

They have a lot of resources for citizen scientists and for educators who want to organize a local eggcase hunt. And if you don’t live near the coast, you can still take some time this spring to create your own giant eggcases (PDF link) out of balloons and papier-mâché. Or better yet, make some chocolate ones that you can send to me!

• Great Eggcase Hunt
• A Fieldguide to Eggcases (PDF)
• **What’s the difference between a skate and a ray?

Rabbitfish Helping to Save the Reef

Continuing with my aquatic version of things vernal, there is news that rabbitfish might be helping to save the Great Barrier Reef. Many herbivorous reef fish species like parrotfish and tangs regularly graze on the fast-growing algae of the reefs. But apparently they only like to eat it when it’s young and not too weedy. This is where the rabbitfish comes in.

“Then, to our even greater surprise a fish we had never seen in this area before was observed grazing on the weed. The rabbitfish (Siganus canaliculatus), came out of nowhere and began to clear-fell the weed placed on the reef crest.”

The rabbitfish were caught on underwater videocams, in schools of up to 15 fish, grazing the crest, slopes and outer flats of the reef, and chomping away at more than ten times the rate of other weed-eaters.

• Red Orbit: Rabbitfish Helping to Save the Great Barrier Reef
• Science Daily: Rabbit Fish To The Rescue Of The Reef

sƎʇɐʞs ɹƎɥ :ɐ*

Today is Steve Irwin Day. It has been over a year since the charismatic, animal-loving Aussie passed away in a freak stingray encounter. There are a number of ways you can remember, appreciate and celebrate Steve’s influence and ethic. The most obvious one is to wear some khaki pants. Or just get outside and enjoy nature.

Steve Irwin Day on November 15 will be a day for remembering the one and only Crocodile Hunter, Steve Irwin. The day will represent the many things Steve was passionate about; family, wildlife and FUN. You can get involved in a number of ways including visiting Australia Zoo for an action packed day, having a Backyard Campout or donning your khakis for Khaki Day.

All proceeds raised from these activities will go to Australia Zoo Wildlife Warriors Worldwide.

I have not gone out to the beach as much as I had hoped when I first started What the Shell. But not too far from the horse conch, we found this little fellow.

Stone Crab (Menippe sp.)

The one pictured below is probably a juvenile M. mercenaria, the Florida Stone Crab. That’s based on the range; I haven’t found anything definitive yet.

2 September 2007
New Pass, Sarasota, Florida, U.S.A.
Found crawling on a dead quahog shell.

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Brachyura
Superfamily: Xanthoidea
Family: Menippidae
Stone Crab (Menippe sp.)

Gortoning Myself

I am probably Gortoning myself with this one, but stone crab season begins today in Florida.

Only legal-sized claws (2 ¾ inches) are harvested in the stone crab fishery; crabs are returned to the water alive to generate new claws. Approximately 13 percent of commercially harvested claws are regenerated. The fishing season is open October 15 through May 15 each year, but the harvest of egg-bearing female crabs is prohibited at all times.

Most of the sources on stone crabs note that this is a “sustainable fishery,” owing to the notion that the crabs will regrow their claws. The rate of regrowth varies, taking anywhere from one to three molts before the new claw approaches the same size as the one removed. The molting rate depends on the initial size, sex and environmental conditions of the animal, among other things.

Duress of the Dungeness*

You can file this under duh, but Mark recently noted some new research that indicates crabs with claws removed have increased stress levels which could affect survival rate. As picked up by ScienceDaily:

Professor Bob Elwood, from the School of Biological Sciences studied crabs’ reaction to declawing. Crabs felt increased stress and had a lower survival rate after the removal of one claw.

Professor Elwood said: “We found a strong stress response within ten minutes of taking off one claw and this stress remained after 24 hours. The stress response was greater if the crab was declawed rather than being induced to cast off a claw. So, the stress is not due specifically to claw loss but to the manner of the claw loss.

I don’t imagine most folks will pay much mind to this news. But personally, I’ve cut back tremendously on the amount of meat I consume, mostly for ethical and environmental reasons. And this research doesn’t incline me make an exception for crustaceans, no matter how deliciously sustainable they may be.

Sources

• Blogfish: Removing claws is harmful to crabs
• ScienceDaily: Declawing Crabs May Lead To Their Death, which is a rehash of the original press release from Queen’s University, Belfast.
• NOAA FishWatch fact sheet: Gulf and Florida Stone Crabs (Menippe adina and Menippe mercenaria)
• The 2006 Stock Assessment Update for the Stone Crab, Menippe spp., Fishery in Florida
• A Proposed Evolutionary History of Stone Crabs
• Observations of the Stone Crab Commercial Fishery. From the 2006 season, with a couple of nice vignettes by Florida Wildlife Commission field crew members.
• Creative Loafing, Sarasota: ‘Tis the Season, Sandy claws are coming to town. Brian works in an jab at vegetarians in both the print and podcast versions.

*Forgive me the poetic license, I know they are different species. This also concludes my Blog Action Day report.