Imminent Danger: Indonesian Seas Warming, Fish Sizes Shrinking

The sea has long served as one of Indonesia’s largest pillars of food security. Amidst population growth and increasing protein demands, fishery yields remain a primary source of livelihood for millions of coastal families and a vital food supply for the wider population.

The Ministry of Marine Affairs and Fisheries (KKP) reported that Indonesia’s capture fisheries production reached 7.81 million tonnes in 2024, a significant increase from 6.99 million tonnes in 2020. Over the last five years, national catch volumes have grown by more than 820,000 tonnes. The largest production originated from marine waters, contributing 7.33 million tonnes, while inland waters produced approximately 480,000 tonnes.

Skipjack tuna was the largest species produced in 2024, reaching 681,000 tonnes, followed by scad at 549,000 tonnes, skipjack mackerel at 411,000 tonnes, mackerel at 396,000 tonnes, snapper at 385,000 tonnes, and tuna at 345,000 tonnes. Most of these species are critical commodities for both domestic consumption and export.

While these figures suggest the Indonesian fisheries sector remains stable, recent research indicates profound changes occurring beneath the ocean surface. According to research published in the journal Science by a team from Monash University, climate change is not only affecting fish habitats but also influencing the evolutionary processes of fish species globally. As sea temperatures rise, fish tend to grow faster and reach reproductive maturity at a younger age. Consequently, the size of adult fish is becoming smaller than normal.

Using models tested against nearly 3,000 fish species across 43 of the world’s largest fishing regions, researchers estimate that every increase in global temperature will reduce potential fishery yields. In some regions, declines in both income and catch volumes could reach as high as 50%.

International studies are also finding shifts in fish distribution due to ocean warming. According to the Journal of Animal Ecology, the warming Eastern Australian Current is now carrying tropical fish species into regions previously too cold for them to inhabit, allowing larvae that once struggled to survive to settle in temperate waters.

Similar changes pose a significant challenge for Indonesia. As an archipelagic nation situated between the Pacific and Indian Oceans, Indonesia’s waters are highly sensitive to sea temperature fluctuations. A study by the Sepuluh Nopember Institute of Technology (ITS), using Aqua MODIS satellite data from 2007–2016, found Indonesian sea surface temperatures ranging between 27 and 31 degrees Celsius. Western regions, including the waters of Sumatra, the Malacca Strait, the Java Sea, and the Makassar Strait, are relatively warmer than eastern areas like the Banda and Arafura Seas.

A 2024 report by the World Bank, in collaboration with the Ministry of Marine Affairs and Fisheries and the University of British Columbia, predicts that rising sea temperatures will affect several of Indonesia’s key commercial fish species. Lemuru, scad, mackerel, and skipjack are projected to see catch volumes decline by 20–30% between 2030 and 2050.

The risks are substantial. The World Bank notes that the fisheries sector contributes approximately US$26.9 billion to the Indonesian economy annually, provides over seven million jobs, and supplies about half of the nation’s protein needs. These pressures will be felt directly by coastal communities.

Data from the Central Bureau of Statistics (BPS) shows that the number of Indonesian fishers reached 3.21 million in 2023, up from 2.74 million in 2019. Of these, approximately 2.77 million are marine fishers and 430,000 work in inland waters. During the same period, around 2.18 million fish farmers also supported the national food supply.

The increase in the number of fishers is occurring even as the growth space for capture fisheries becomes more limited. While national production remains high, much of the productive waters have been exploited for decades. Climate change adds a new layer of difficulty by affecting the location, growth, reproduction, and migration patterns of fish.

The World Bank estimates that the economic benefits of the fisheries sector in Indonesia’s Exclusive Economic Zone (EEZ) could drop by 15% under a low-emission scenario and by as much as 26% under a high-emission scenario by 2050. These calculations do not yet account for secondary impacts such as rising vessel operational costs, changes in fishing seasons, or the increasing frequency of extreme weather events.

Therefore, the greatest challenge for Indonesia’s fisheries sector in the coming decades may not be the total disappearance of fish, but rather facing a changing ocean. The fish will remain, but they may be smaller, their locations may shift, and the available catch may decrease. For millions of Indonesian fishers, these changes will determine the future economic stability of coastal communities.