I sure remember the first time I got really "tagged" by a blue crab. I was conducting field work in coastal South Carolina, netting diamondback terrapins for a population study with a group of graduate students. We positioned two jon boats along the edge of a trammel net so everyone could see any turtles caught in the mesh. As I reeled the 50 foot net into the jon boat, I rested a swath of bundled net across my legs so I could collect another section into my hands. Feeling a jolt of searing pain, I looked down to see a blue crab pinching the inner portion of my thigh with one of his claws. I squirmed around on the boat seat and wiggled my body in an awkward attempt to remove the net and (more importantly) the crab from my lap. This seemed to irritate the feisty crustacean, causing him to sink the other claw into my leg. I stood up on the boat bench and shook my legs and hips violently performing an impromptu "crab dance" until the little guy fell off. Although I escaped the ordeal with very little physical damage and provided unplanned entertainment for the students, this event probably left some significant scars on my psyche.
The scientific name of the blue crab (Callinectes sapidus) loosely translates into "beautiful savory swimmer". Adult blue crabs are adorned with a pleasing complement of blue and red hues on a light gray background. They are excellent examples of form following function because every body part is designed for mate acquisition, feeding or protection. The first pair of legs (claws) is important for feeding, fighting and holding a female during mating. These appendages possess great power allowing a crab to crush small mollusks and to rip apart fish and other marine animals into bite-sized pieces. The middle legs are for traditional walking but the last pair of legs are flattened paddles giving the crab great swimming ability.
Crabs are formidable predators feeding on just about any type of marine life small enough to capture and overpower. They often rest beneath the sand or "pluff" mud with just their eye-stalks exposed. Since they have excellent vision, they wait for an unwary victim to venture too close and blast out from under cover and grab it. Blue crabs are cannibals feeding on their own kind especially "softshell" crabs that have recently molted. They may also venture up into the high salt marsh and pluck periwinkles and other snails off the spartina grass for eating.
Blue crabs are extremely important to the economy of the lowcountry. They are harvested in local waters and shipped all over the world as food. Many of our crabs are shipped up the coast and marketed as Maryland blue crabs. During certain periods of the year when the crabs are about to molt they are collected for the seafood industry. Experienced crabbers are very adept at identifying animals that are about to shed their exoskeletons. Crabs in this condition ("peelers") are placed in tanks until they molt and marketed as "softshells".
Blue crabs mate throughout the warmer months of the year with peaks in the Spring and Fall in lower salinity waters. Although males likely mate many times, females mate only after their final molt and must be in a softshell condition. The adult females called ‘sooks" give off chemical signals (pheromones) to announce their reproductive condition. The larger males or "Jimmies" will stay with the female until she molts and mating is accomplished. He will continue to "cradle" her to keep other males away and let her shell harden before releasing her.
Two to nine months later, females will develop a mass of about two million eggs under the apron of the shell. This "sponge" of eggs bulges out on all sides and remains attached to her abdomen until the eggs are ready to hatch. After hatching, the larvae are "wisked" away by the tides to fend for themselves. If they are not eaten by a variety of marine predators, they will molt frequently and go through a series of larval stages reaching maturity a year and a half later. At this point these guys can mate themselves and produce the next generation of tasty crustaceans.
For this nature note...I thought it would be interesting to relate a story that happened to us a few weeks ago.
Paul Gravil and I were sitting in lawn chairs on the Spring Island boat ramp fishing. Paul had agreed to help me with some preliminary field work for a potential bonnethead shark study in Chechessee creek. We are interested in marking individuals to determine if the adult and juvenile sharks caught here exhibit a high degree of site fidelity (in other words do they come back to the same creeks and docks year after year). I realize that this description sounds suspiciously like fishing but hey, somebody has to collect the data.
It was a beautiful quiet evening with a nice cool breeze. The sun was dipping low in the sky giving the marsh banks a pleasant glow and turning the Spartina grass to a wonderful shade of green. Paul and I were sitting on the dock in lawn chairs facing the marsh eating leftover blue crabs that he and Lisa had prepared the night before. Dixie (the Gravil pooch) and Bill Allen's dog "DD" were also in attendance. We noticed a group of dolphins feeding in the mouth of the creek across from the dock. We could also hear the distinctive sounds of the dolphins splashing and breathing. Strand feeding on Spring Island is a pretty common occurrence but it is always a treat to see dolphins sliding up in shallow water and sweeping fish up on to the bank. The dogs got pretty excited about the spectacle and began to whine and pace up and down the dock. Fishing, good food, dogs, dolphins...now this is about as good as it gets!
I took a minute to change the bait on my hook and when I looked up, I noticed that the dolphins had moved much closer, swimming within 20 feet of the dock. One of the animals glanced up at us, did an extreme headfirst dive and disappeared under water. I assumed that the show was over and the dolphins had gone under the dock and up the creek. An instant later, a wall of water erupted up from the waterline and across the dock soaking Paul and narrowly missing me. Paul sprang to his feet just in time to see a dolphin fluke fling another twenty gallons of water across his chest and body. Talk about awesome! The splashing subsided and the dolphins disappeared leaving a wet dock and soaked Paul. For the record, neither me nor the dogs got a drop of water on us. Paul and I proceeded give each other high fives, recounting the adventure and laughing hysterically.
Weeks later, I am still not sure what caused that dolphin or dolphins to splash us. Maybe the dogs were actually the target and they leaped out of the way just in time. I guess there are a lot of possible explanations but I am convinced the dolphins accomplished exactly what they intended to do. I think they were playing with us, splashing water on Paul to see how we would react. Come to think of it, I am pretty sure that I heard the muffled, underwater sounds of dolphin chuckling right after it happened
Check out the video below of dolphins strand feeding off of Hilton Head.
I think most of you guys realize that I have a real fondness for sharks; I am rarely not more than one association away from a conversation about these cartilaginous creatures. Beaufort County is heaven for a shark enthusiast, because we have an incredible diversity of elasmobranch fishes in the waters of Port Royal Sound. The creeks, rivers and sounds around here are home to an amazing diversity of fish, especially sharks and rays. Approximately 20 species of these non-bony fishes patrol our local creeks and rivers. Most of our sharks are relatively small species rarely exceeding 5 feet in length but many of the larger species use our local waters as "pupping" grounds venturing into Broad river and others to have their young . Port Royal Sound is even home to some of the "big boys" including tiger sharks and great hammerheads often exceeding twelve feet in length.The closely related rays are pretty abundant here as well. We have southern stingrays, Atlantic stingrays, butterfly rays, cow nosed rays and even an occasional manta ray (a species that grows to twenty feet across) as well as others.
Tiger shark
I realize this sounds like a bit of a horror story to have so many sharks around but it really is a good thing. High diversity of sharks indicates healthy waters and surrounding marsh. PRS has some characteristics that make it quite different from other aquatic systems including deep water, high salinity and high tidal amplitude. These features allow certain offshore species a place to spawn safely. We have high shark diversity for the very same reasons that we have good cobia spawning ground and great habitat for red drum.
Although shark pups can be a real nuisance as aggressive bait stealers, there is no reason to believe that sharks reduce numbers of game fish in local waters. Sharks are probably beneficial to our fishery. Certain species are indicator species (analogous to a canary in a coal mine) letting us know about water quality and the presence of certain pollutants. If particular shark species are not in an area then there is probably a good reason for it. Besides small shark pups are likely an important food source for certain commercially important species like cobia and others as well as food for bottle nosed dolphins.
