ASBTIA congratulates industry scientist on receiving South Australian Seafood Environmental award

Kirsten Rough, researcher with Australian Southern Bluefin Tuna Industry Association (ASBTIA), has been awarded the SA Environmental Award for her commitment to evidence-based assessment of the risks and consequences of petroleum exploration and development in the Great Australian Bight (GAB).

The work Kirsten undertakes as part of her role with ASBTIA addresses a high priority for not only Southern Bluefin Tuna (SBT) industry, but also the wider seafood sector and has produced outcomes that have contributed to protecting the aquatic environment.

The Great Australian Bight is critical to the global population of SBT. All tuna are known to migrate thousands of kilometres to the area every year for at least the first five years of their life. Older individuals are also known to frequent the area to forage along the slope and throughout the Southern Ocean basin as well as transit the region on their way to the breeding grounds in the Indian Ocean.

An oil spill in the GAB is possibly the single most significant threat to the species. Other threats such as the unregulated fishing that occurred through the 1960’s and 1970’s were addressed by the introduction of catch limits in the 1980’s and further restrictions since then. These international quotas are applied on a global scale to all of the countries that fish for this type of Bluefin Tuna.

An oil spill and the chemicals used to disperse any discharge would inevitably have significant effects on the Southern Bluefin Tuna and consequently the many countries that share the resource. Port Lincoln and the South Australian economy stand to be particularly impacted as the local ranching operations and the large infrastructure and employment base that have developed rely on the wild stocks of Bluefin in the Bight. An oil spill in the Bight would undermine the international effort to rebuild the SBT population. Damage caused by oil exposure and seismic surveys is not confined to Bluefin tuna, research has shown impacts to a range of key species that are important in the wider ecosystem of the Great Australian Bight.

Kirsten says “It was a surprise, and a great feeling to have such wide recognition, and appreciation. But really I wouldn’t be doing my job if I wasn’t checking the finer details of every application that had the potential to impact on SBT through its migration and residency period in the Bight”

Kirsten’s nomination was supported by a broad range of GAB user groups including the other fishing sectors, as well as tourism and conservation groups.


Exposure of SBT to oil

The first and most obvious way that tuna would be exposed to oil would be through direct contact. SBT are migratory fish, usually as they pass through the Great Australian Bight they will surface. However, it is unlikely that SBT would surface if an oil slick was on the surface and thus unlikely they would undergo direct contact.


SBT are more likely to be exposed to the toxic effects of oil via direct ingestion. SBT feed on sardines that pass through the GAB. Sardines are likely to come into direct contact with oil; thus, tuna can ingest oil that is on the sardines.


Natural dispersion (breaking down oil into small oil droplets soluble in water) can result in the presence of oil droplets within the water column. Rough waters, like that in the GAB, exaggerate natural dispersion, increasing the concentration of oil droplets. Migrating SBT can ingest the oil droplets that are present in the water. The use of chemical dispersants will increase the likelihood of tuna being exposed to oil in this way.


It is important to remember that everything in the marine ecosystem (and any ecosystem) is connected. Anything that’s affected at the bottom of the food chain can affect the levels above. For example, zooplankton is sensitive to oil exposure and in response experience developmental abnormalities as well as lower rates of feeding and reproduction. Sardines feed on plankton and tuna feed on sardines. There are two main problems here. Firstly, a reduced population of zooplankton (due to oil caused lethality) results in reduced sardine numbers and consequently reduced biomass of SBT. The second problem is the effect of biomagnification. Biomagnification is the increase of oil concentration over two or more food-chain levels. For example, one organism (e.g. sardines) can ingest and retain oil, and then an organism on a higher feeding level (e.g. SBT) may eat the first organism. If biomagnification were occurring, the organism at the higher level (SBT) would receive an increased exposure to the oil by eating contaminated food. Biomagnification is a problem for human consumption.


Use of chemical dispersants

Application of dispersants – is the cure worse than the ailment?


In case of an oil spill at sea, Equinor has to decide on the most effective response to minimise damage. The dominant strategy remains the removal and containment of spilled oil by mechanical technology. Such containment may be difficult in the Great Australian Bight, considering its rough waters. The other option that Equinor have outlined is the use of chemical dispersants.


Dispersants enhance the natural break-up of floating oil into small drops. In this way, coating of coastal areas and oiling of sea birds and mammals can be reduced. To the human eye, chemical dispersants make oil spills disappear.


However, the treatment could be worse than the ailment. Dispersants essentially break up the oil and reallocate it from the surface to the water column. The effect of an oil spill on surface dwelling marine organisms (e.g. birds and sea-lions) is reduced as a consequence. However, the increased concentration of oil in the water increases the toxic effects on organisms in the water column and on the bottom of the sea floor.


It is important to note that toxic effects caused to organisms in the water column and on the bottom of the sea floor, are likely to work their way back up to the surface dwelling organisms anyway. For example, a bird may no longer be at risk of being coated in oil; however, the fish it feeds on are dying off or contaminated with oil. Thus, that bird may die from starvation or due to the toxic effects of oil.


Additionally, usually less than 100% of the treated oil will disperse. This means that the effect from undispersed oil will still occur.


Understandably, there are conflicting views concerning the potential risks and benefits for human health and the environment generated by the use of dispersants during oil spills. Currently, there is not enough data to make an informed decision on the most environmentally friendly response. Importantly, each case varies so what worked in one scenario may not necessarily work in the Great Australian Bight.


What does appear to be clear is that even cleaning up oil spills has toxic effects. In the words of South Australian senator Tim Storer – the risks of drilling in the Bight simply don’t justify the rewards.