Scientists are able to predict catch rates of bigeye tuna by analysing phytoplankton size Photo: NOAAScientists are able to predict catch rates of bigeye tuna by analysing phytoplankton size Photo: NOAA

Scientists in the Pacific Islands region have published new research that can help predict catch rates in the Hawaiʻi longline fishery.

Drs Phoebe Woodworth-Jefcoats and Johanna Wren found that information about microscopic algae called phytoplankton can be used to forecast catch rates for bigeye tuna, using the size of phytoplankton to forecast catch rates for up to four years. This information could help advance ecosystem-based fisheries management in the Pacific Islands region.

The scientists believe that the size of phytoplankton is an indicator of the quality of food for larval and juvenile bigeye tuna. While bigeye tuna don’t actually eat phytoplankton, they do eat tiny animals called zooplankton which eat phytoplankton. When there is larger phytoplankton, there is likely larger zooplankton and therefore higher quality food for young bigeye tuna.

Scientists can estimate the phytoplankton size from satellite measurements of sea surface chlorophyll and temperature. The majority of bigeye tuna caught by the Hawaiʻi longline fleet are around four years old so using measurements from 1998 to 2017 the scientists were able to forecast catch rates for 2002 – 2021.

This information can also be used to improve stock assessments of bigeye tuna and other species caught by the fishery, particularly useful for bigeye tuna which has been overfished in recent years.

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