Surveys Monitor Populations of Lobster in the Northwestern Hawaiian Islands Marine Ecosystem

June 1, 2009
The NOAA expedition will study spiny lobster and slipper lobster in the Northwestern Hawaiian Islands marine ecosystem.
The NOAA expedition will study spiny lobster and slipper lobster in the Northwestern Hawaiian Islands marine ecosystem.

Researchers from the NOAA Pacific Islands Fisheries Science Center are working in waters of the Northwestern Hawaiian Islands (NWHI) to survey local populations of lobsters, an important component of the NWHI marine ecosystem. As it has almost every year since 1986, the Center will assess the abundance of lobsters, determine the relative numbers of adult and juvenile lobsters, and collect biological data.

NWHI populations of spiny lobster (Panulirus marginatus) and slipper lobster (Scyllarides squammosus) were heavily exploited by a Hawaii-based trap fishery from the mid-1970's until 2000, when the fishery was ended by NOAA. Initially designed to supplement fishery data in support of annual lobster stock assessments, the lobster scientific surveys now continue to provide key information for understanding the NWHI ecosystem. In particular, they provide data for monitoring changes in the lobster populations and associated benthic fauna in the absence of the fishery. The lobster survey data represent one of the longest time-series of biological information available in the NWHI. The 30-day lobster survey is being conducted by the NOAA Ship Oscar Elton Sette under the scientific leadership of PIFSC biologist Robert Moffitt. As usual, the expedition will focus on lobsters at Necker Island and Maro Reef.

The survey will employ a site-specific, depth-stratified research monitoring protocol using standardized lobster trapping gear and techniques. At each selected survey location, baited traps arranged in strings will be set out on the seafloor at depths of 60-300 feet to catch lobsters. The traps will be left on the seafloor overnight, then raised to the surface, brought aboard the ship and emptied. The entire catch, including lobsters, crabs, fish, and all other organisms will be identified to species and the number of each species in the catch will be recorded. Biological information on each lobster caught will be collected, including size, gender, and reproductive status (maturity), and the data will be recorded in a scientific log for later analysis.

Before they are returned to the seafloor, lobsters are scanned to check for presence of a PIT tag.
Before they are returned to the seafloor, lobsters are scanned to check for presence of a PIT tag.

After data are collected, lobsters will be returned alive to the seafloor using a special cage designed to protect them from potential predators during their descent to the bottom. But first they will be checked with a scanner to see if they are carrying a Passive Integrated Transponder (PIT) tag — a tiny microchip. Many lobsters have had such a tag inserted by scientists during previous expeditions to the NWHI. Each PIT tag emits a unique radio-frequency code detected by the scanner. If a PIT tag is found, its unique identification number will be recorded along with the biological data collected for that lobster. Most of the PIT tags were implanted on special lobster tagging charter cruises over the last few years; a smaller number have been applied during previous Sette cruises. The PIT tags allow scientists to monitor changes in the location, size, and other attributes of individual lobsters over time. The data are used to improve understanding of lobster growth, movements, and mortality.

In addition to studying lobsters, researchers will use handline gear on the Sette to catch specimens of deepslope bottomfish species, such as opakapaka and hapu'u'pu'u for use in biological studies. From each specimen, the scientists will collect biological samples including otoliths (ear bones) for determining the fish's age and gonads for analysis of the fish's reproductive status and maturity. The biological data are essential for improving stock assessments of Hawaiian archipelago bottomfish. Algae found attached to the lobster traps will also be collected and given to scientists at the University of Hawaii for taxonomic and bio-geographical studies. All data collected on the Sette expedition will contribute to a comprehensive understanding of the Northwestern Hawaiian Islands marine ecosystem.