The yellowfin tuna that is commonly used to make sashimi and other dishes like poke bowls may become scarce if overexploitation rates don\u2019t improve, particularly in the Indian Ocean, a press release from international research initiative the Sea Around Us said.<\/p>\n
A new study by an international team of researchers has found that, since the industrial exploitation that began in 1950, the weight of a yellowfin tuna population in the water has decreased by an average of 54 percent throughout the four tuna populations managed by Regional Fisheries Management Organizations (RFMO).<\/p>\n
The biomass of yellowfin tuna in the Indian Ocean has declined by 70 percent in the last 70 years.<\/p>\n
\u201cIf we look at more recent years, we can see that global yellowfin tuna populations continue to struggle. Biomass continues to decline everywhere except for stabilizing trends in the Western Pacific Ocean, prompted by management interventions,\u201d said Kristina Heidrich, the study\u2019s lead author and a Ph.D. candidate with the University of Western Australia (UWA)\u2019s the Sea Around Us \u2013 Indian Ocean, in the press release.<\/p>\n
The study, \u201cMultiple lines of evidence highlight the dire straits of yellowfin tuna in the Indian Ocean,\u201d was published in the journal Ocean & Coastal Management.<\/p>\n
\u201cIn most places, extractions have regularly surpassed the maximum sustainable yield or MSY limit, which is the level that would allow for the highest possible catches to be sustained over time, given that environmental conditions don\u2019t change much,\u201d said Dirk Zeller, one of the study\u2019s co-authors and director of the Sea Around Us \u2013 Indian Ocean, in the press release.<\/p>\n
The researchers used the results of RFMO\u2019s time series and assessment of yellowfin biomass in order to estimate the yearly changes from 1950 to 2020. They also used the CMSY++ stock assessment method, which mostly uses a time series of catches to gauge the level of fish stocks. They then examined 955 yellowfin tuna records from samplings independent of fisheries using Baited Remote Underwater Video Systems (BRUVS), which record ecological and biological data like biomass and species size and abundance in a certain area.<\/p>\n
\u201cThe data collected with BRUVS provided a more holistic and fisheries-independent picture of the pelagic community and the status of the populations, which can complement fisheries-dependent data and analyses,\u201d said Jessica Meeuwig, a study co-author and director of the Marine Futures Lab at UWA, in the press release. \u201cThese fisheries-independent BRUVS data suggest that, since 2014, yellowfin tuna in the Indian Ocean are the least common, least abundant, have the lowest biomass, and are the smallest yellowfin tuna in the existing dataset.\u201d<\/p>\n
The CMSY++ method showed that yellowfin tuna were not currently being subjected to overfishing in the Atlantic and western and eastern Pacific Ocean, despite their exploitation rates slightly exceeding the MSY limit over the past decade.<\/p>\n
Overfishing is ongoing in the Indian Ocean.<\/p>\n
\u201cBeyond yellowfin tuna fisheries contributing more than US$16 billion to the global economy yearly, the species is an apex predator that plays a critical role in the functioning, productivity and overall health of marine ecosystems,\u201d said Daniel Pauly, study co-author and the principal investigator of the University of British Columbia\u2019s the Sea Around Us initiative, in the press release. \u201cThe risk of population collapse is high if current management does not adapt. Stringent management constraints must be implemented to reduce overall fishing capacity, rebuild overfished populations, and reduce the collateral damage these fisheries cause to other species such as sharks.\u201d<\/p>\n
The research team pointed out that management organizations can enhance the transparency, confidence and accuracy of the information they use in decision-making by also employing multiple lines of evidence to cross-validate each other. They also suggested using stricter management measures like implementing effective catch limits, reducing fishing capacity and enforcing the MSY limit.<\/p>\n
\u201cIn the Indian Ocean in particular, a catch reduction of 30 per cent from 2020 levels is urgent to halt and reverse the decline in yellowfin tuna population,\u201d Heidrich said in the press release.<\/p>\n