Highlights From TC-01-06 Larval Swordfish Cruise (5/31/01-6/6/01)
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The NOAA ship Townsend Cromwell has completed a 7-day cruise to survey billfish
larvae off the leeward (Kona) coast of the Island of Hawaii. The primary focus of the cruise was to collect larval
specimens of 
billfish (which includes swordfish, sailfish,
the spearfishes, and marlins), particularly swordfish larvae, 
for
population genetics and age and growth studies. We were successful in collecting 43 swordfish larvae and 18 spearfish
and/or marlin larvae. Most of these specimens were collected with a 6-foot wide Issacs-Kidd trawl that was towed at the surface alongside the ship. Since billfish
larvae are known to frequent surface waters during the day, our ship tows were conducted with this in mind. When present,
tows were conducted through surface slicks. These smooth band-like features on the sea surface have provided some of our
best catches of billfish larvae in the past. 
The tows lasted 1-hour and then were
retrieved onboard the ship. The fine mesh along the back end of the net is then
washed down so that any fishes clinging to the sides drop down into 
the white cod-end . The cod-end is then removed, a new cod-end is attached and the
net is then ready to be set out again. The contents of the cod-end are brought indoors to our wet lab, the sample poured
out into a tray, and examined for billfish larvae. Billfish larvae are typically rare catches while other animals, such
as the Portuguese-man-of-war jellyfish, are morefrequently caught.
During this cruise, surface tows and surface dip-netting for billfishlarvae were
also conducted from one of the 
Townsend Cromwell's small boats. 
Surface tows were conducted simultaneously on both sides of the small boat using twin 1-meter wide neuston nets which are designed to sample the upper surface of the
water. Two swordfish young, one of them approximately 10 inches in length, were dip-netted when the small boat passed
through a surface slick containing small floating debris. The use of both these small boat collection methods may be
applicable to similar efforts currently being conducted by Chilean scientists
sampling for swordfish larvae adjacent to Easter Island in the South Pacific.
Unfortunately, identifying billfish larvae
(excluding swordfish) to species is difficult, especially if the head has been damaged during collection. In the
laboratory, the use of forensic mitochondrial DNA based techniques can identify
these easily confused larvae to species. This technique, however, has to our knowledge, never been conducted shipboard
while at sea. The eyeballs of unidentified billfish larvae were used to extract the DNA, and among those in which the
quantity and quality of DNA was sufficient, identifications could be made about a day later. Further at-sea test trials
of this procedure will probably be needed, but based on initial results, this technique can be successfully used at sea
to give near-real time species identifications of billfish larvae.
Other research conducted of the Kona Coast during
this cruise
included hydro-acoustic surveys at night for small pelagic organisms that are food items
in the diet of dolphins [insert picture #10] and field tests of computer programs that could yield daily summaries of the direction and speed of water currents by depth in the area
traversed during that day.
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