NOAA scientists and commercial fishing vessels work to improve knowledge of lobster populations in the Northwestern Hawaiian Islands

June 15, 2007
Researchers inserting a PIT tag into a spiny lobster

Scientists of the Pacific Islands Fisheries Science Center (PIFSC) are now at sea collecting information that will improve the ability of the National Marine Fisheries Service (NMFS) to determine the status of spiny lobster (Panulirus marginatus) and slipper lobster (Scyllarides squammosus) populations in the Northwestern Hawaiian Islands (NWHI). And as they have for several years, the researchers have enlisted the help of experienced commercial lobster fishermen.

In 2000, NMFS noted increasing uncertainty in the mathematical models used to assess lobster population status and took the precautionary step of suspending the 25 year old Hawaii-based NWHI lobster fishery while initiating research to improve the models. The temporary fishery closure became permanent in 2006 when President Bush established the Papahānaumokuākea Marine National Monument in the NWHI. Despite the end of the fishery, NMFS is continuing the research needed to reduce uncertainty in lobster population models, monitor lobster stock dynamics, and gain a better understanding of the lobster's role in the NWHI ecosystem. Population survey statistics for NWHI lobster represent one of the longest biological time-series in the region, providing potentially key information on the status of the NWHI ecosystem.

The lobster research is aimed at providing more accurate estimates of lobster biological parameters, such as growth rates, movement and migration patterns, and natural mortality— all vital components of the population models. The research involves a large-scale lobster tagging program in the NWHI. Scientists catch lobsters using regular lobster fishing gear (traps), place identifying tags on them, and return the lobsters alive to their habitat on the sea floor. When scientists recapture tagged lobsters in subsequent research surveys they are able to use the data to get better estimates of the biological parameters and improve the models of population dynamics.

Researchers inserting a PIT tag into a slipper lobster.

Tagging is being carried out by scientists in the Fishery Biology and Stock Assessment Division with the cooperation of fishing vessels formerly engaged in the lobster fishery. The cooperative surveys started in 2002, when two Hawaii-based commercial fishing vessels were chartered by PIFSC to carry out tagging operations at selected locations in the NWHI. Initially, the primary focus was on tagging spiny lobsters at Necker Island. In 2003, the program's scope was expanded to include slipper lobsters at Maro Reef, and in 2004 and 2005 both species were tagged at both locations. In 2006, both lobster species were tagged at all four banks. The tags used are "passive integrated transponder" (PIT) tags. Data collected during the tag release and recovery operations are automatically, electronically entered into a database.

The chartering of commercial lobster vessels enables scientists to efficiently capture and tag lobsters, as the vessel captains and crew are highly experienced with lobster trapping in the NWHI. High efficiency in catching lobsters is essential, because it is the recapture of tagged lobsters that provides the vital biological information for improved population models. During the first three years of the cooperative research program, more than 41,000 spiny lobsters and 16,000 slipper lobsters were tagged and released. So far, almost 4500 tagged lobsters have been recaptured.

After tagging lobsters, researchers lower them to the seafloor in a special cage that protects them from predation during their descent.

This summer, the PIFSC has chartered two Hawaii-based commercial fishing vessels, the Katy Mary and Marie M. Each vessel will carry 2 tagging specialists under the direction of Chief Scientist Joseph O'Malley, am employee of the NOAA-University of Hawaii Joint Institute for Marine and Atmospheric Research working with PIFSC. O'Malley is also a graduate student at the Hawaii Institute of Marine Biology, University of Hawaii. The chartered vessels departed Honolulu on June 15 for Necker Island, Gardner Pinnacles, Maro Reef and Laysan Island and will return in mid-August. At each visited location, the vessels' crew will set out baited traps to catch lobsters. After the traps are allowed to "soak" on the bottom overnight, they will be brought to the surface and all lobsters removed, tagged and released alive.

The scientists on board also will determine and record the size, gender, and reproductive status (maturity) of each lobster. Before lobsters are tagged, they will be scanned to see if they are already carrying a PIT tag (each PIT tag emits a unique radio-frequency code detected by the scanner). If so, the tag's unique identification number will be detected and recorded. If no PIT tag is detected on the lobster, one will be applied. When lobsters are released, they will be placed in a special cage designed to protect them from potential predators during their descent to the seafloor and the release location will be recorded.

In addition to tagging lobsters, researchers on both fishing vessels will be collecting samples of tissue from crabs, sharks, fish and eels caught incidentally in the lobster traps. Later, DNA will be extracted from the samples by scientists at the Hawaii Institute of Marine Biology and used to learn more about the genetic structure of lobsters, crabs and fish within the NWHI and throughout the Hawaiian Archipelago.