Tagging Program Aims to Improve Knowledge of Living Marine Ecology in the Northwestern Hawaiian Islands

August 5, 2008
Researchers inserting a PIT tag into a spiny lobster
Researchers inserting a PIT tag into a spiny lobster

As they have for several years, scientists of the Pacific Islands Fisheries Science Center (PIFSC) are conducting an annual survey of lobster populations in the Northwestern Hawaiian Islands (NWHI) using a chartered commercial fishing vessel. The study will advance the understanding of living marine ecology and population dynamics in the NWHI.

Information on NWHI lobster populations has been gathered regularly since the mid-1970s, when exploratory surveys were launched to establish a Hawaii-based commercial trap fishery for spiny lobster (Panulirus marginatus) and slipper lobster (Scyllarides squammosus). Although the commercial fishery ended in 2000, the lobster studies have continued as part of the Center's multi-faceted research program in the NWHI ecosystem. Building on the long time series of information gathered over the years, annual surveys of lobster population dynamics help reveal changes in the NWHI ecosystem.

Since 2002, research has been focused on improving knowledge of biological parameters, such as lobster growth rates, movement and migration, and natural mortality that are vital components of population models PIFSC scientists use to predict population changes. The research involves a large-scale tag-and-recapture program recommended by a panel of independent experts who reviewed the lobster models and advised PIFSC on ways to improve them. Scientists first 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. In subsequent research operations, the scientists recapture tagged lobsters and study them carefully before returning them again to the seabed. Biological data collected from recaptured lobsters provide a wealth of information to improve the population models.

Researchers inserting a PIT tag into a slipper lobster
Researchers inserting a PIT tag into a slipper lobster

The tagging research has been carried out by scientists in the Fishery Biology and Stock Assessment Division of PIFSC using commercial fishing vessels chartered by NOAA. The captains and crew of the chartered boats are highly experienced in NWHI lobster trapping and enable scientists to efficiently collect and tag lobsters. Lobster tagging and recapture have been conducted at Necker Island, Gardner Pinnacles, Maro Reef, and Laysan Island. Tagging at different banks over several years allows for identification of spatial and temporal variability in the biological parameters of interest. During the first seven years of the research program involving PIFSC and chartered commercial fishing vessels, more than 51,400 spiny lobsters and 30,000 slipper lobsters were tagged and released. So far, over 6,800 tagged lobsters have been recaptured.

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. PIT tags provide several benefits: they are retained for a longer period of time than ribbon tags, the information they collect can be "read" more easily, and, unlike ribbon tags, they can be used with slipper lobsters. During the last few years, the tagging project has also used new technology enabling data collected during the cruise to be automatically, electronically entered into the research database.

Working on a chartered commercial fishing vessel, a scientist prepares to return live, tagged lobsters 
    back to their seafloor habitat in the NWHI
Working on a chartered commercial fishing vessel, a scientist prepares to return live, tagged lobsters back to their seafloor habitat in the NWHI

For this year's survey, PIFSC has chartered the Katy Mary, a Hawaii-based commercial fishing vessel. The vessel will carry 2 tagging specialists under the direction of Chief Scientist Joseph O'Malley, a NOAA-University of Hawaii Joint Institute of Marine and Atmospheric Research researcher and University of Hawaii, Hawaii Institute of Marine Biology graduate student working with the PIFSC. The research team departed Honolulu on August 5 for spiny and slipper lobster tagging at Necker Island, Gardner Pinnacles, Maro Reef and Laysan Island and will return in mid-September. At each survey 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 the Katy Mary will collect 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 of the University of Hawaii and used to expand knowledge of genetic variation and structure in these species both within the NWHI and across the entire span of the Hawaiian Archipelago.