Cape fur seals are playful and curious animals. Because of this, they are prone to becoming tangled in loops of plastic pollution or discarded fishing line, which they find interesting, or which may smell like food. Over time, these nooses work their way down a seal’s neck, becoming tighter, incising into their skin and flesh, and ultimately resulting in severe infections and death.

In most circumstances, the Marine Wildlife Management Programme team and partners rely on stealth or nets to safely get close enough to seals to disentangle them. Credit: Steve Benjamin/Animal Ocean

Human intervention is the old way to disentangle these seals, but relies on a large degree of stealth or luck for a rescuer to be able to approach and help a seal without being injured or the seal fleeing into the water – a problem that is especially difficult to overcome in complex, built environments like the V&A Waterfront. A tool that sea rescuers have long wanted is safe tranquiliser darts that can be used on hard-to-reach seals – but these carry their own set of risks, and until recently, little information existed to help rescuers.

Custom made hooks are usually used to snag fishing line and other nooses from around seals' necks and cut them free, but these aren't suitable in every situation - for example, nooses that have become tight enough to cut into a seal's flesh deeply. Credit: Steve Benjamin/Animal Ocean

Anaesthetising seals is considered higher risk than darting a land mammal. Because seals are always near to water, there is the risk that a partially sedated seal could escape into the water and potentially drown or injury itself. Seals are also physiologically adapted to life in the water, and it has been unclear how these adaptions might influence the effectiveness of common anaesthetic drugs and their reversal agents.

Using a dart gun to sedate a seal, allows veterinarians to help animals in hard-to-reach places, when the need for intervention is urgent. Credit: Steve Benjamin/Animal Ocean

The Two Oceans Aquarium Education Foundation has, over the past two years, worked closely with veterinarian Brett Gardner of Zoos Victoria, and the Department of Forestry, Fisheries and Environment to trial a protocol for the use of sedative darts and stimulants on high-risk Cape fur seals. The paper Disentanglement of Cape fur seals (Arctocephalus pusillus pusillus) with reversible medetomidine-midazolam-butorphanol published in the Journal of the South African Veterinary Association is a reflection of this collaboration.

Sedating the seal has the added benefit of giving the veterinary team time to examine and treat any wounds a seal might have - something they cannot do easily by other means. Credit: Steve Benjamin/Animal Ocean

How did the study work?

Based on a best-understanding of fur seal sedation, from the review of similar studies on the South American fur seal, New Zealand sea lion and California sea lions, draft protocols for the sedation of Cape fur seals were drawn up. No veterinary guidelines existed for this type of work with seals in South Africa, and this work appears to be the first-ever use of this drug on wild Cape fur seals.

Sedating a seal near to the water carries a risk of drowning - that's why a fast spotter boat is always ready to follow an escaping seal and notify rescue divers and swimmers in a larger boat. Credit: Steve Benjamin/Animal Ocean

The study was done on eight Cape fur seals identified by the seal patrol in the V&A Waterfront and by members of the public in the Hout Bay harbour. When a seal was darted, two boats were kept in the area – a smaller one to follow it and confirm that the dart hit, and a larger boat that would allow a veterinary support team and scuba divers to enter the water to recover the seal should the sedation kick in while it was swimming, free it of entanglement and administer the reversal agent.

Once a sedated seal has been spotted,  the larger boat moves in to collect it. Credit: Steve Benjamin/Animal Ocean

What were the results of the study?

The study found that the sedative took approximately 4 minutes to act on a seal, that the average time from darting to the handling of the seal was 20 minutes, and that it took seals about 27 minutes to fully rouse after being given the reversal agent. The study also revealed that partially sedated seals could be stimulated by noisy neighbours and by the approaching boats, so protocols for the administration of additional sedative were necessary.

Of the eight high-risk seals that were part of this study, six were successfully retrieved and disentangled, and one could not be sufficiently sedated, but was able to fully recover without the need for the reversal agent. A final seal, unfortunately, was able to hide or escape after being administered the sedative and could not be found by the divers deployed to recover it – this, unfortunately, was found dead several days later, but an independent necropsy could not determine the cause of death. Despite this unfortunate death, these initial findings do suggest that the use of MMB has a lower mortality rate than other drug combinations used in previous Cape fur seal studies, and it’s important to keep in mind that these seals would not be able to survive without an attempt to free them of their entanglements.

In short, this study proved that the dosages for sedative and reversal agents were reliable, and has helped to better define a safe protocol for the darting and retrieval of severely injured and entangled Cape fur seals.

Credit: Steve Benjamin/Animal Ocean

What’s next?

Credit: Steve Benjamin/Animal Ocean

The Two Oceans Aquarium and Two Oceans Aquarium Education Foundation continue to work in collaboration with the Department of Forestry, Fisheries and Environment to refine the methods used in this study so that darting becomes a practical tool that can be used safely and effectively when suitable.

As a proof-of-concept, this study was an incredible success, and further studies on a larger number of animals will help us narrow down the dosages or the sedatives and reversal agents for safer future use.

The progress in protocols for the sedation and anaesthesia of otariid seals, like the Cape fur seal, has advanced significantly in the past decade, particularly in safer outcomes of the animals. Darting will remain a last resort option for seals that cannot be reached or helped in other ways, but we are glad to have this new life-saving option.

We look forward to being able to save even more seals!

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