TC-99-07 Lobster Assessment

TC-99-07 Lobster Assessment
June 6-July 4, 1999

     June 10, 1999    On June 8, we arrived at Necker Island reef and set 160 lobster traps that evening. As the traps lay on the bottom over night, we ran an ADCP transect to collect data on the ocean currents around the reef. On June 9 we hauled the traps and reset them in another location. Over night, we ran another ADCP transect.
     As the traps come aboard, the scientists open them up and record what animals are inside. Along with the lobsters, there are crabs, fish, eels, hermit crabs, and various other animals which were attracted by the bait and thus trapped when the trap is hauled up. Most of the animals are released, but some are being retained for use in a Hawaiian Monk Seal nutrition study.
     The lobsters are categorized as to species, sex, size, egg bearing and if they carry tags or not. We are tagging a percentage of the lobsters caught on this trip, but the main emphasis is recording what we catch for population estimates.
     There are three differences to look for (that work for both spiny (upper right) and slipper (below left) lobsters) when determining the sex of a lobster. The easiest to see is the size of the swimmerets (pleopods) under the tail. In males, the pleopods are shorter and narrower. The females' pleopods are noticeably longer and broader and have little hairs. It's these hairy pleopods that the females attach their eggs, enabling them to carry their eggs under their tails.
     The second characteristic can be identified by looking at the tip of the lobster's last leg. In males, the tip comes to a sharp point, while in females the tip is a small claw (called a cheliped) and is used for grasping the eggs as they are laid and sticking them under her tail.
     The third identifying feature is located on the base of the legs where they join the body. On males, there is a tiny pore at the base of the last pair of legs. It is from this pore that sperm is ejected. Females have their pore located at the base of the third pair of legs and it is from this that the eggs are laid. In slipper lobsters, the pores are small and require close examination. In spiny lobsters the females' pore is small while the males' is large and often in the shape of a snail's shell.
     Female spiny lobsters often carry a gray or black sperm plate between the last pair of legs. They use this to store sperm acquired from males during her foraging expeditions. When she is ready to lay eggs, she simply does so while scratching the sperm plate to release the sperm. This fertilizes the egg before she attaches it to the pleopods under her tail. In this fashion she doesn't need to find a male when she is ready to lay eggs.

Yesterdays cruise write-ups for TC-99-07