Scientific Method

A hot Pacific Sailfish jumps near boat. It's easy to see why so many tourists visit Costa Rica each year in search of some of the best sailfish action on the planet! 

Sailfish ((Istiophorus platypterus) are found in the temperate waters of the Indian and Pacific Oceans. For the hundreds of anglers visiting Costa Rica each year they provide many days of exciting sport fishing.Sailfish are distinguished from their typically larger cousins the marlin by the large dorsal fin, commonly called the “sail.” Sailfish off of Costa Rica are frequently seen cruising along the surface with their sail extended above the water. There is speculation that they use their sail to make them appear larger than they actually are when herding baitfish into a tightly packed bait ball.

With a voracious appetite sailfish grow quickly by feeding on bait fish such as lanternfish and invertebrates such as squid. As anglers can attest a mature sailfish swims fast and fights hard. When fully grown a pacific sailfish off Costa Rica reaches a length of about 9 feet and weighs about 120 lbs.

Sailfish are well known in the sportfishing community for their acrobatic ability and speed once hooked. Through their central nervous system control of chromatophores in their skin they are able to express an array of colors. When just casually swimming along they are typically blue on their dorsal (top) side with beautiful chrome sides and a white underbelly. Their body colors are often highlighted by iridescent blue vertical stripes. However after a hard fight they tend to display a muddy brown color indicating a buildup of lactic acid in their system.

The Billfish Research Project chose the pacific sailfish to study because of its brilliant colors, athletic ability and its enjoyment by so many anglers.

As you can see from this Google image Quepos is half way down the pacific coast of Costa Rica. It is from the port of Quepos that the TBRP team embarks on its research expeditions. We typically venture 30 to 50 miles offshore in search of sailfish. Note the undersea terrain. This region is full of drop offs and seamounts! 

As the water flows across these seamounts upwellings are created bringing nutrient rich water up from the deep. At night the greatest migration on Earth occurs as plankton and other critters come up from below the thermocline. Sailfish are there to greet them and prey on the squid and lanternfish that are in turn preying on the plankton. It's an amazing site to be immersed in this on a night dive!

The Pop-Up satellite tag, commonly referred to as a PSAT is a sophisticated combination of archival and Argos satellite technology. PSAT tags are designed to track the large-scale movements and behavior of fish and marine mammals that do not spend enough time at the surface to allow for the use of real-time Argos reporting satellite tags. These types of tags are perfect for our research as onboard sensors collect and store data on geo-location, depth and water temperature while attached to the fish.

When the team deploys a PSAT into a sailfish a strict protocol is followed to insure that the fish is not harmed and to maximize the opportunity of gathering the necessary scientific data. Once a fish is hooked the team springs into action. The first mate is in charge of catching the fish while the second mate clears the other lines. Once the fish is to the boat the second mate then takes control of the fish and ensures that the fish is calm and unharmed.

At this point Dr. Dean and Marco, the first mate, prepare to place the tag on the sailfish. Rubber gloves are donned and the tag dart that holds the tag in the sailfish is cleaned with alcohol. When Dr. Dean gives the go-ahead Marco carefully identifies the tag dart insertion point and embeds the dart into the space between the 9^th and 12^th pterygiophore.

Often a second anchoring dart is inserted for additional insurance that the tag will remain attached to the sailfish for the duration of the tag deployment. Medical grade super glue is used to seal the two insertion points. This whole procedure takes an average of just under 4 minutes during which Captain Jose is moving the boat forward slowly to keep water flowing over the sailfish’s gills.

Once the tag has been firmly anchored into the sailfish the sailfish is held by the bill as the boat continues to move forward thus relaxing the fish by providing a constant supply of oxygenated water. Only when Dr. Dean says it’s ok to release the fish does Marco turn the fish away from the boat and back into the wild blue ocean to record its adventures for our study. 

On a pre-programmed date the tag releases from its host, surfaces, and uploads the archived data to Argos satellites. Our team downloads this data and runs it through some computer algorithms in order to turn it into a format that allows us to interpret the information. The procedure results in migration track images such as the one above as well as depth and temperature profiles.

Tag Suppliers: Wildlife Computers and Lotek Wireless