PIFSC Scientists Monitor Lobster Populations in the Northwestern Hawaiian Islands Ecosystem

June 5, 2006
Lobster traps are deployed from the deck of the NOAA Ship Oscar Elton Sette

The NOAA Ship Oscar Elton Sette, based in Honolulu, Hawaii, is in the Northwestern Hawaiian Islands (NWHI) surveying lobster populations at Necker Island and Maro Reef. Each year since 1986, scientists at the NOAA Pacific Islands Fisheries Science Center have traveled to remote banks of the NWHI to study the life history and population dynamics of lobster. Regular surveys of the lobster stocks have provided the data needed to monitor changes in this important component of the NWHI marine ecosystem and establish biological guidelines for lobster harvests.

Commercial trapping of spiny lobster (Panulirus marginatus) and slipper lobster (Scyllarides squammosus) in the Northwestern Hawaiian Islands began in the mid 1970's and reached a peak of activity in 1986 when 1.3 million trap hauls were recorded. Regular research surveys by NOAA began that year, adding to lobster data collected during earlier scientific expeditions to the region. During the annual survey operations, researchers have set out lobster traps at designated locations, primarily at Necker Island and Maro Reef, to collect fishery-independent information on lobster abundance and a variety of biological data needed to better understand lobster growth, mortality, movements, and reproduction.

Spiny and slipper lobster caught in the traps are studied and then returned alive to the seafloor.

This year's survey will be directed by Chief Scientist Robert Moffitt of NOAA Pacific Islands Fisheries Science Center. At each survey location, baited lobster traps will be set on the seafloor at depths of 90-300 feet below the water's surface to collect samples of lobster. The traps will be left on the bottom overnight, then brought to the surface and emptied. In addition to lobster, some other organisms like crabs and fish may be attracted to the bait. The entire catch from each trap --- lobsters, crabs, fish, and all --- will be identified to individual species and the number of each species found in the catch will be recorded. All lobsters in the sample will be carefully examined and measured by PIFSC biologists, and their size, gender, and reproductive status (maturity) documented.

Each lobster brought aboard in the catch will also be scanned with a special instrument to see if it is carrying a tiny microchip called a Passive Integrated Transponder, or "PIT" tag, used to uniquely identify an individual lobster. Each PIT tag emits a different radio-frequency code detected by the scanner. PIT tags have been implanted into several thousand lobsters by scientists on previous Sette surveys or biologists working on cooperative commercial lobster boats chartered by PIFSC for research. Each recovery of a lobster tagged and released on earlier surveys provides important information for improving population models. For example, biologists can analyze tag recovery data to determine how fast lobsters are growing.

If a PIT tagged lobster is found, biologists will record its unique identification number along with its current size and other biological data. All lobsters caught will then be returned alive to the seafloor, conveyed in a special release cage designed to protect them from potential predators during their descent.

As a precautionary measure, Hawaii's commercial fishery for lobster in the NWHI was closed in 2000 because of increasing uncertainty about the status of the lobster stocks and the mathematical population models used to assess changes in lobster abundance. The accumulated data collected in NOAA's annual research surveys were instrumental in pointing out weaknesses in the prevailing models of lobster population dynamics and confirming that additional studies were required to reduce model shortcomings and uncertainties.

The annual lobster population survey data constitute one of the longest collections of information from the NWHI ecosystem. The survey data are especially valued because they help reveal how an important component of the ecosystem has changed over time, affected by both natural and anthropogenic factors. This year's continuation of the lobster survey by the Sette therefore provides key information for monitoring the status of the NWHI ecosystem.

While the primary focus of the Sette survey is to ensure the long-term monitoring of NWHI lobster populations and their fluctuations, the scientific staff also will gather biological specimens and data from other marine life to expand NOAA's knowledge of NWHI ecosystem structure and dynamics. Researchers will collect samples of tissue from other crustaceans and various species of sharks and bony fishes caught incidentally in the lobster traps and from bottomfish hooked during scientific operations on the deep slope habitats around Necker Island and Maro Reef. Later, DNA will be extracted from the biological samples by scientists at the Hawaii Institute of Marine Biology of the University of Hawaii and used for genetic studies of NWHI populations. Algae found attached to the traps will also be collected and given to University of Hawaii scientists for taxonomic and bio-geographical studies. Biological data collected from bottomfish species like onaga, opakapaka, and hapu'upu'u will be used by PIFSC scientists to improve population models for those species.