NOAA scientists collaborate with industry to improve knowledge of lobster populations in Northwestern Hawaiian Islands

July 16, 2005
Researchers inserting PIT tags into spiny lobster
Researchers inserting PIT tags into spiny lobster

Scientists of the Pacific Islands Fisheries Science Center (PIFSC) are once again at sea, in cooperation with the Hawaii fishing industry, to collect information that will improve the ability of NMFS to determine the status of lobster resources in the Northwestern Hawaiian Islands (NWHI).

In 2000, after 25 years of operations, the Hawaii-based commercial fishery for spiny lobster (Panulirus marginatus) and slipper lobster (Scyllarides squammosus) in the NWHI was closed because of increasing uncertainty about the status of the lobster stocks and the mathematical population models used by PIFSC to assess the stocks and their abundance. This uncertainty was important because the NWHI lobster fishery had been one of Hawaii's largest commercial fisheries and because information on the lobster populations represented one of the longest time-series in the region, providing potentially key information on the status of the NWHI ecosystem.

A panel of independent experts reviewed the models and recommended that collaborative research programs between PIFSC and the industry be developed to provide more accurate estimates of biological parameters, such as lobster growth rates, movement and migration, and natural mortality that are vital components of the population models. The panel recommended that a large-scale lobster tagging program be conducted in the NWHI. To do this, 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. The recapture of tagged lobsters in subsequent research operations provides a wealth of information on the key biological parameters the experts identified as missing from the existing lobster population model.

Researchers inserting PIT tags into spiny lobster
Researchers inserting PIT tags into spiny lobster

Scientists in the Fishery Biology and Stock Assessment Division of PIFSC developed and implemented a large-scale lobster tagging program in the NWHI with the cooperation of the fishing industry. Each summer starting in 2002, two Hawaii-based commercial fishing vessels have been 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 both species were tagged at both locations.

In 2002, plastic "ribbon" tags were used to uniquely identify each lobster studied. Since then, lobsters have been identified with the more sophisticated and versatile "passive integrated transponder" (PIT) tags. One of the benefits of the PIT tags is that they are retained for a longer period of time than ribbon tags, they can be "read" more easily in terms of their basic information, and unlike ribbon tags, can be used with slipper lobsters.

Researchers measure a slipper lobster caught in NWHI prior to tagging and releasing it.
Researchers measure a slipper lobster caught in NWHI prior to tagging and releasing it.

The commercial fishing vessels chartered by NOAA enable scientists to efficiently capture and tag lobsters, and they are highly experienced operating in the NWHI. Because the commercial fishery is currently closed, the chartered vessels are essential as a means to recapture lobsters previously tagged. After all, 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 35,000 spiny lobsters and almost 10,000 slipper lobsters were tagged and released. So far, several thousand tagged lobsters have been recaptured.

This summer, the PIFSC has chartered two Hawaii-based commercial fishing vessels, the Katy Mary and Marie M. Each vessel will carry 3 tagging specialists under the direction of Chief Scientist Joseph O'Malley, a NOAA-University of Hawaii Joint Institute of Marine and Atmospheric Research marine biologist working with the PIFSC. The researchers departed Honolulu on July 16 for spiny and slipper lobster tagging at Maro Reef and Necker Island and return in mid-August. At each 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 the lobsters removed, tagged and released alive. The scientists 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 sharks caught incidentally in the lobster traps. Later, DNA will be extracted from the samples by scientists at the Hawaii Institute of Marine Biology of the University of Hawaii and used for genetic studies of NWHI shark populations. The Katy Mary scientists will also video tape the release of lobsters and, using video cameras mounted on lobster traps, record features of the seafloor. The latter information will be used for habitat studies by scientists in the PIFSC's Coral Reef Ecosystems Division.