Scientists onboard the NOAA Ship Oscar Elton Sette study billfish spawning off the Kona coast of the Island of Hawaii

September 15, 2006
img/oes0610_2.jpg
Scientists in the Sette's laboratory use microscopes to search for eggs and larvae of billfishes caught in surface net tows during a research cruise.

On September 13, the NOAA Ship Oscar Elton Sette began a 10-day research cruise to study billfishes in waters off the Kona coast of the Island of Hawaii. The Kona coast is renowned among rod-and-reel sportfishers as a hotspot for billfishes, a group of species including swordfish, marlins, spearfishes, and sailfishes. Six species of billfishes can be found in Kona waters although only blue marlin, striped marlin, and shortbill spearfish are typically caught by sportfishers. Of the other three species, swordfish are caught seasonally in offshore Hawaiian waters by commercial fishers while sailfish and black marlin are rare catches.

Chief Scientist Robert Humphreys of the NOAA Pacific Islands Fisheries Science Center will lead a team of scientists interested in learning more about the little known spawning activity of billfishes. They will collect eggs and larvae of billfishes at the surface of the ocean by towing a fine-meshed sampling net through the water. The eggs and larvae are offspring of adult billfishes residing and spawning in waters off the Kona coast. By studying the eggs and larvae, the scientists will be able to learn more about which species of billfish are spawning, when and where their eggs and larvae occur, and whether spawning is associated with certain environmental conditions, such as particular levels of water temperature and salinity near the sea surface. Humphreys and his crew expect to collect egg and larvae of blue marlin, as the summer months are when this species is more prevalent in Kona waters and sportfishing activity for this prized fish peaks.

img/oes0610_1.jpg
A 3-inch long larval swordfish caught in a sampling net near the ocean's surface, where billfish larvae reside.

The current cruise extends research that has been underway for several years by Humphreys and his colleagues. Early in the research program, the scientists had to learn how to determine which billfish species were appearing in their larval collections. Furthermore, only swordfish eggs had been previously described, so no one knew what the eggs of the other billfish species would look like. The scientists solved the species identification problems using a DNA method developed by colleagues from the Scripps Institute of Oceanography and the Southwest Fisheries Science Center (both in La Jolla, California). The method, which identifies eggs and larvae based on differences in their DNA, is normally conducted only in a land-based laboratory but was especially adapted to be used at sea onboard the Sette. A small sample of tissue from an egg or larva is analyzed, enabling the specimen to be identified to species in about 3 hours. A great advantage of the DNA identification method is that it is rapid enough to enable scientists to return to an area where adult billfish were caught by rod and reel earlier in the day and tow their nets there to see if eggs or larvae are present. The data collected in these studies help scientists understand the spawning patterns of each billfish species and what environmental conditions promote or retard spawning activity. The knowledge gained may be used to identify other locations in the Pacific where particular species of billfish are likely to spawn.

In addition to extending scientific knowledge of billfish biology, the Sette expedition provides an opportunity to promote marine science education. Joining the scientific field party on this cruise will be Jenny Holen, a teacher at West Hawaii Explorations Academy. Jenny will participate in all the scientific operations and bring back to her classroom both new knowledge and plankton specimens collected from the surface waters off Kona for study by her students. Jenny has been designated as a "teacher-at-sea" for this cruise as part of a NOAA program that places classroom teachers on NOAA research cruises and assists them in developing lesson plans to use on their return to the classroom. Jenny's participation is especially relevant for her students as their school is a designated charter school that emphasizes a marine science curriculum and is ideally located at Keahole Point on the northern Kona coastline.