Black Marlin

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A few weeks ago a Black Marlin Istiompax indica washed up on Central Beach in Plettenberg Bay measuring 3.8 m. Unfortunately, I was not in town to see it but I was inspired to do some research into the species. Black Marlins are found in tropical and subtropical Indian and Pacific Ocean, preferring to stay above the thermocline in water temperatures between 15 – 30 °C. Although Black Marlin can be found to a depth of 100 m, they are often found close to land masses, islands, and coral reefs. Black Marlins are one of the largest bony fishes, growing up to 700 kg – the all-tackle record for this species is 708 kg! This species has a varied diet, feeding on fish, squid, cuttlefish, octopods, and large crustaceans.

As with most apex predators the only real threats to the Black Marlin are humans and human activities. Black Marlin are caught as bycatch in commercial long-liners, trolling, harpooning, set nets, gill nets, and surface tuna long liners. There are a number of conservation efforts in place, such as angling size limitations, the encouragement of catch-and-release fishing, and the use of circle hooks instead of the standard J-hooks when fishing as this improves the post-release survival of the fish. The Black Marlin is listed as Data Deficient by the IUCN as there is very little data on the catch, by-catch, mortalities, and discards for this species.

As for the Black Marlin that was washed up in Plettenberg Bay, it is suspected that the cold waters may have been the cause for the individual to end up on our shores. Keep an eye out for other species that are also affected by cold water, and sudden drops in water temperature.

Written by: Minke Witteveen

For further reading:

  • Collette, B., Acero, A., Canales Ramirez, C., Carpenter, K.E., Di Natale, A., Fox, W., Miyabe, N., Montano Cruz, R., Nelson, R., Schaefer, K., Serra, R., Sun, C., Uozumi, Y. & Yanez, E. 2011.Istiompax indica. The IUCN Red List of Threatened Species 2011 Accessed: 2016-04-24. URL:
  • Serafy, J.E., Kerstetter, D.W. & Rice, P.H. 2009. Can circle hook use benefit billfishes? Fish and Fisheries 10: 132-142.
  • Stander, Y. 2016. Cold water may be cause for marlin beaching. Accessed: 2016-04-24. URL:

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