20100708鬼頭刀延繩釣及雨傘旗魚標識放流

20100708_Dolphinfish longline & sailfish tagging cruise











攝影：江偉全
錄影：陳信志、Matthew
剪輯：洪曉敏

Ocean Field Operations _ July 8 2010
Tuna and Billfish Tagging Project

The FRI Tuna and Billfish Tagging crew minus James set out early morning
with Captain Hsu Twon Ming. Captain’s vessel is a traditional Taiwanese
style vessel with a flat bottom. The construction and bouyancy is developed
from 20 inch PVC pipes running the length of the craft. It has an inboard
engine with it’s propeller mounted mid-ship, allowing for minimal draft. This is
especially helpful for the longlinning fishing technique employed.

The crew met in Riyar’s office at 1 am, the tags and camera gear where
assembled and then, down to the harbor. Shing-zja, Matthew and Riyar
travelled with the Captain directly east from Shinkang. Live and fresh bait
were prepared for the longline. A large holding tank on board contained
approximately 200 Milkfish. The long line is set using 6 hooks spread over 50
meters with a bouy maintaing the line 1 to 2 meters below the surface.

The line is deployed pre-dawn. Each 4 bouys there is a flag and
approximately 6 flags per section. The line then strecths nearly 3 kms. It takes
a little over one hour to complete and as the sun rises there is evidence of the
fish beginning feeding as the sunlight illuminates the varying layers of prey.
Dolphinfish are commonly caught using longline technique. Fishermen note
that they are usually caught in pairs, if the female is caught then the male will
be found in the vacinity however, it is said, if the male is caught the female will
leave.

We patrolled the line travelling west back toward the coast. The object to
tag any sailfish that was caught on the line as soon after being caught as
posssibly. This will assist post release survival and recovery time. Generally
the line is left up to four or five hours, ‘soak time’, then retreived from the
closest end point, reeling the long line back into the boat using a hydraulic
winch. The Captain’s boat was designed as to operate solely. He had steering
and throttle modifications that allowed him to control vessel speed and rudder
from any location on the boat.

Unfortunately the line was set through a deep passage for large container
ships or oil tankers. These ships need hundreds of meters to change course
and even further to stop. After radio communication with the tanker the
Captain has told them they were headed directly to his line, there was little
they could do. We only watched as the large boat severed the line as it
crossed between two markers.

Resuming the patrol, a large sailfish (almost 30 kg) was found attached to the
hook. It still was active presenting itself as a suitable specimen to tag. As the
fish was retreived to the side of the boat the Captain used a shorter harpoon
designed by our lab to tag the sailfish. Approximately 120 cm with beautiful
coloring and majestic sail, the fish was released from the line with the tag
attached just below it dorsal fin.

Our morning had been a success, our tagged sailfish was set free and rest of
the line retreived after using the radio beacon indicating it had drifted much
closer to shore than expected.