World Tuna day: Skipjack Tuna

May 2nd is World Tuna day an to honor this day we thought we would post about the Skipjack Tuna. This species is one of the predominant species caught in the waters surrounding the Marshall Islands.


Skip Jack

The Skipjack got its common name in the early 1700’s. “Skip” refers to the fish’s habit of jumping out of the water and “Jack” is a generic name. The fish’s scientific name is Katsuwonus pelmais and it is one of 15 tuna species found around the world and is in the Mackerel family. The Skipjack prefers to swim in the upper mixed layers of the of the ocean water and is highly migratory and can be found all over the world within tropical waters with waters of at least 59 F (15 C). These fish are commonly 16-23 inches long and weigh about 5.5 # (the record is 45#). Their life cycles are typically 3-4 years but can live up to 7-10 years. They mature relatively fast and are able to reproduce at 1 1/2 years. This young age of reproduction is a characteristic which promotes a rapid turn over of Skipjack populations. They swim in groups up to 50,000 fish and sometimes mix with small yellowfin tuna. The Skipjack feed on fish, crustaceans, cephalopods, and mollusks. It is an important prey species for large pelagic fishes and sharks.

Range

Skipjack are the smallest in size of the tunas subject to the large-scale commercial fishing operations but make up 46% of all tuna caught world wide. In 2014, 2.9 million tons of Skipjack were caught. In the western and central Pacific the biomass of Skipjack is very large and estimated to exceed that of the other 3 main tuna species combined. Although the biomass of Skipjack is about 50% of its original biomass, it is believed it is a species that is hard to overfish because of its highly active reproductive behavior.

Most skipjack are caught using large purse-seine nets. Price per ton in the last several years have ranged between $,1,000 ton and $2,300. Although there are no Marshallese commercial fishing boats, many other countries pay to fish in Marshallese waters and though the Parties to the Nauru Agreement (PNA) provide important revenue to the RMI government. In 2017 commercial fishing revenue contributed $25 million to the RMI national government (>12% of government revenue). Over 90% of Skipjack caught is canned. In America, Skipjack makes up more than 70 percent of canned tuna market (often called chunk light) found in stores.

Normally Dolphins do not like to swim with small skipjack which makes it a more dolphin safe species. When purse-seine nets are set around Fish-Aggregation-Devices (or FADs, which are really just floating structures that act like fish magnets) they result in a tenfold increase in by-catch. Examples of by-catch include: other fish, sharks, rays, sea turtles and, occasionally, whales or dolphins.

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