No. 28–More on Soft Shell Crabs, plus Collecting Creatures
As part of last month’s column I briefly addressed the concerns some have regarding commercial harvesting of female blue crabs for the soft shell market. With April being the height of the soft shell season, a few more comments are in order to further allay those concerns.
Although blue crab mating activity is now at it’s height, it is not limited to the short commercial harvest season. The reason is that not all females reach reproductive maturity and seek mates at the same time. Two factors play a role in this. One, gravid (with eggs) females which mate in the spring don’t all spawn at once in the fall. This means their post larval offspring enter the estuary to begin growing to maturity over a two to three month period. And two, the rate of growth and related molting episodes (determined by feeding success) may vary greatly among individuals. Hence, females are still maturing and mating for months after the soft shell harvest has ended. Hunger alone attracts these individuals to crab traps and even then they will be released if gravid.
I know of no scientific documentation, one way or the other, but anecdotal observation seems to support the idea that females which experience the immature to mature stage molt out of season, so to speak, face better odds of finding a male and mating than their in-season sisters. The number of females being trapped with a single male as bait would tend to support this hypothesis.
The ultimate question is one of sustainability. Under current practices and environmental conditions, is the blue crab spawning rate high enough to assure a sustainable population? The answer, by all accounts, is yes.
The annual collection of new creatures for the Estuarium begins with the warming waters of March and April. I’m often asked how and where I catch the animals we have on display. One prime area for collecting is below the Lady’s Island side of the Woods bridge on low tide. Trips there, however, are limited because of the half mile tote distance from the nearest parking.
The site holds seven tidal pools, four of which can usually be counted on to give up at least one or two species which have been consistently found in each. The two most productive pools will hold small brown shrimp, baby flounder, and young sea trout and red drum along with inch or so long croakers and spot. Also taken but used primarily for feeding purposes are grass shrimp and mud minnows. A cast net us used for collecting in these pools.
Casting in the largest pool on site often produces mullet used to feed both creatures and curator. From it flows a small, shallow, oyster shell rubble bottom creek that is home to blennies and gobies sequestered amid the shell. They are prized from hiding using a net with a metal leading edge that is shoveled beneath the shell. Pistol shrimp are likewise captured in this manner. The relatively clean shell from this creek is gathered for use as substrate in tanks.
Using a cast net, one of the other pools is a source for sub tidal oyster clusters also used in tanks and in yet another are found sea whip coral and ghost anemones which are taken by hand.
While at this location, I also cast from the river’s edge for sea robins and rock sea bass and search the shore for exposed tulip snails. Tulip snails lay flower like egg case clusters that are beautiful in a tank and interesting to observe as the snails develop within their translucent chambers.
The floating docks at Beaufort’s downtown marina attract juvenile burr puffers, spadefish, and trigger fish. They are attracted by small crustaceans that live amid the fouling organisms attached to the dock’s floats. They are easily plucked from the water with a standard six inch aquarium dip net attached to a pole.
Other areas of collection are the beach at Lands End for whelks, Hunting Island for beach creatures, and The Sands in Port Royal for stone crabs, hermit crabs, mud crabs, clams, and mussels.
Some of the Estuarium’s creatures come from third parties. One of our terrapins was rescued from the jaws of a feline collector by it’s owner and another was left on our doorstep. A few species difficult to collect in the estuary are also found off shore and are provided by local shrimpers from time to time. They include spider crabs, batfish, and mantis shrimp. Though not found in estuaries, we currently have a scorpion fish given us by a shrimper on display. It’s here just because it’s neat.