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The smallest, geologically youngest, and physically most complex of the world’s three major oceans, the Southern Indian Ocean is also the warmest, having a significant impact on global climate due to its interaction with the atmosphere. Its waters are also affected by unique oceanic currents and upwelling patterns. Together, this results in limited marine animal life and offers little scope for plankton and other species to grow. 

While the ocean has less marine life than others due to these low plankton levels, sea turtles, sharks, sea snakes, and dugongs can be found in specific areas and islands, some of which are extremely rare. Many are endangered, or nonexistent in other parts of the world. These unique animals congregate around the seamounts in the region, which are especially abundant between Réunion and Seychelles in the Central Indian Basin and the Vening Meinesz group near Wharton Basin. 

There are an estimated 1,746 seamounts in the region covered by the Southern Indian Ocean Fisheries Agreement (SIOFA) (Yesson et al., 2011), alongside numerous other vulnerable marine areas such as Saya De Malha Bank, a unique, shallow feature which is host to the world’s largest seagrass beds.  

The Southern Indian Ocean is somewhat of a mystery region, and is one of the least researched and understood areas of the global ocean. However, with every new study, interesting animal behaviors and species discoveries are reported. There is still so much to discover about the species inhabiting, and traveling through, this region.

Researchers studying the migration of the southern right whale – or tohorā – recorded the species traveling away from north eastern foraging grounds where they had historically visited. One tagged whale, nicknamed Bill, traveled far into the Indian Ocean, then south, swimming thousands more kilometers into the krill-rich waters of the Southern Ocean. Bill’s migration through the Southern Indian Ocean is the first modern evidence that tohorā are once more visiting Antarctica; a compelling reason to ensure measures are in place to safeguard this vulnerable species.

There is some fishing activity, including bottom trawling, occurring in both the shallow waters of Saya de Malha Bank, over precious seagrass meadows, and in deeper seamount waters. Thailand and the Cook Islands are either currently trawling the area, or have authorized future fishing activities. Currently, no vulnerable marine ecosystems (VME), including seamounts, have been protected from fishing activity, although a few deeper features have been protected from bottom trawling. 

Much of the fishing activity in the region, which is a mixture of bottom and mid-water trawling, focuses on orange roughy and splendid alfonsino. The species congregate around the area’s seamounts, habitats which are hotspots of biodiversity, but vulnerable to damage from bottom trawl gear, which drags heavy gear along the seamounts’ surface. Orange roughy is a long-lived and slow growing species, with many in the Indian Ocean region believed to be around 200 years old. The species don’t start breeding until they are at least 40 years old, making them highly susceptible to overfishing. Likewise, splendid alfonsino is believed to be longer-lived than first expected, with some studies aging the species around 40 years old. 

The DSCC is attending the Southern Indian Ocean Fisheries Agreement meeting in Seoul, Korea, to draw attention to the importance of this region, with priorities including the protection of vulnerable marine ecosystems, and progress toward setting aside areas from all bottom-impact fishing for biodiversity, ecosystem maintenance and climate resilience. You can read the DSCC’s full priorities here