PIFSC Scientists Monitor Lobster Populations in the Northwestern Hawaiian Islands Ecosystem

June 13, 2007
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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 improve quantitative models of lobster populations and monitor changes in this important component of the NWHI marine ecosystem.

During the survey operations, researchers will set out lobster traps at designated locations to collect information on lobster abundance and a variety of other biological data needed to better understand lobster growth, mortality, movements, and reproduction. The At each survey location visited, baited lobster traps will be set on the seafloor at depths of 60-300 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 the lobster's 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 PIT tag 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.

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

Data from the annual lobster population survey constitute one of the longest collections of information for monitoring the status of the NWHI ecosystem. The survey data are especially valued because they can help reveal changes in an important component of the ecosystem over time and the effects of both natural and anthropogenic factors on population abundance and structure. NWHI lobsters were trapped by Hawaii-based commercial fishing vessels for 25 years. NMFS suspended the fishery temporarily in 2000 as a precautionary measure when studies showed increasing uncertainty in the lobster population models used to set annual harvest quotas. The fishery was closed permanently in 2006 when President Bush established the Papahānaumokuākea Marine National Monument in the NWHI. This year's survey by the Sette will provide valuable additional information on responses of lobster populations to the fishery closure.

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.