Just in from the Ship

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

     June 14, 1999    We have continued our lobster assessment operations on the reef surrounding Necker Island. Every morning at 8:00 AM, we start hauling lobster traps and measuring and recording the sex, species and size of the lobsters caught. This data will be used to estimate the size of Necker's lobster population and how much fishing the population can support. During most of the evenings, we perform 40 mile ADCP transects to gather data on the ocean currents around Necker Island reef. The planktonic lobster larvae are very dependent on these currents.
     Lobsters reproduce by laying eggs (right). The female lays her eggs and attaches them to the pleopods (swimmerets) under her tail. Female pleopods are larger than a male's and have hairs on them which assist in the attachment of eggs to them. In Hawaii, egg laying occurs year around and its peak rate happens over the summer months (June - August). Female lobster caught during this time often have thousands of eggs attached under their tails. When first laid, the eggs are a bright orange/yellow color. As the eggs near hatching they turn a brownish color.
     The larvae (below, left) hatch out at about the size of this "O". In order to grow, lobsters (and all crabs and shrimps) must shed their hard exoskeletons. After the laborious job of wriggling out of its old exoskeleton, the lobster immediately goes into hiding from predators. The lobster's new shell is very soft at this stage and most animals will readily make a meal of it if possible. During this time, the lobster's body absorbs sea water and swells (thus grows) and over the next few hours the lobster's new shell hardens. Once hardened, the lobster remains that size until the next molting.
     Larval lobsters look nothing like the adults as they are planktonic (free drifting) in nature. Slipper lobsters are planktonic for the first 3 months of their lives, while spiny lobsters are planktonic for the first 12 months or so. During the day, the larvae can be found as far down as 80 meters (about 240 feet) and during the night they are usually with in the 0-20 meter (0-60 feet) depths. They maintain this lifestyle for about 15 molts, during which they eat other zooplankton (free floating animals) and phytoplankton (free floating plants). The larvae are themselves food for larger organisms and a large percentage of them are eaten. By the 15th molt (or so), those that survive are about 2-3 inches long, clear, with circular but flat (almost paper thin) bodies.They have small legs and very short, almost minuscule tails.
     About this time, the larvae molt into what is termed the "transition" stage. During this molt, the body actually folds upon itself, giving the animal height and reducing its length and width. The larvae emerges from its former self looking like a small clear adult and it's exoskeleton hardens into a protective shell. During the first stages of its life, the young lobster simply drifted with the currents and used feathery paddle-like appendages to maintain its preferred depth. In the transition stage, the juvenile becomes an active swimmer and begins looking for a bottom of suitable (0-30 meters or 0-90 feet) depth on which to live. Research in Australia suggests lobster juveniles can swim as much as tens of miles in their search for bottom habitat. The same researchers also discovered that juvenile lobsters usually swim directly for a reef or sea mount, possibly sensing water borne chemicals (similar to smell) to determine the direction in which to swim. If the animal is not successful within a certain time, it will sink beyond what it can survive and perish. Thus the importance of ocean currents in bringing juvenile lobsters near a suitable reef near the end of their planktonic stages.
     Upon reaching a suitable bottom, the juveniles begin a life of hiding under coral and rocks during the day, and foraging for food at night. One of the main predators they must be wary of is octopi, which love to eat lobsters. A lobster's main locomotion is by crawling over the bottom. To escape predators they use the powerful muscles in their tails to explosively propel them backwards in quick jerky movements.

Yesterdays cruise write-ups for TC-99-07