Injured dolphins

Dolphins and humans share marine space and resources. Their interactions were in focus of the Blue World Institute’s research program since it’s very beginning. Bottlenose dolphins follow bottom trawlers, steal fish from bottom nets and long lines, approach purse-seiners that catch blue fish and feed near the cages of the aquaculture sites. All these interaction pose a potential threat for dolphins and sometimes cause damage to fishing gear. Depending on the predominant fishing technique in a certain area, these interactions can even be fatal. Having the most extensive photo-ID database on bottlenose dolphin in the Adriatic Sea, we can individually recognize many dolphins. This helps us understand the state of their population (abundance, natality and mortality rates etc.). Besides that, we can determine if certain individuals display different habitat use and behavioral patterns in presence of fishing activities. Monitoring mortality caused by interactions with fisheries or recovery success rates after being injured further enhances our understanding of the ecology of this species. The extension of our research effort from the Cres-Lošinj archipelago to northern and central Dalmatia in recent years showed that human-dophin interactions vary in type and intensity among areas. This enables us to describe and compare the influence that fisheries have on local bottlenose dolphin communities. After 30 years of systematic research, we know many dolphins very well and can follow their fates. Hence, we bring here an overview of several cases of injured dolphins whose fates we were following or still follow.

Lamjana

Dolphin with a severe injury at the root of its fluke

In May 2010 we got notified of an injured dolphin that was loitering around the cages of the aquaculture site near Mala Lamjana bay on the island of Ugljan. Our research team headed out and found the dolphin with a severe injury at the root of its fluke. The injury was caused by a rope which was part of some fishing gear, probably a bottom net. The dolphin got entangled and tried to get itself out. The strong pulling caused the rope to cut the skin and underlying tissues. The dolphin eventually got free but a big part of the rope remained entangled around the fluke and disabled the it from normal swimming and diving.

The dolphin appeared to be well fed, but it’s behavior was unusual. It swam slowly staying at the surface significantly longer than usual. During our stay with this dolphin, another three bottlenose dolphins were seen passing by, but there was no interaction. Our research team tried to approach the dolphin with boat and swimming and snorkeling, with intention to remove the rope from it’s fluke, but the animal did not allow this. Although severely injured, the dolphin still managed to perform dives. After many unsuccessful trials, our researchers had to head home as the night approached. You can read more about this case here.

The same dolphin was seen again 8 days later. This time it was at the aquaculture site near the island of Dugi otok. This time our researchers tried to help the dolphin together with the volunteers of the Croatian Mountain Rescue Service, divers from the diving center Ugljan and the crew of the aquaculture site. Upon approaching the dolphin, we noticed that a new injury has occurred – there was a burn lesion on the back of the dolphin’s body, between the blowhole and the dorsal fin. Since this dolphin was staying at the surface for very long periods, the injury was probably caused by the strong sun (dolphin’s skin is very sensitive to dry conditions and sun).
Despite more people and vessels involved, this rescue attempt also finished unsuccessfully for the same reason – dolphin was simply avoiding all our approaches by diving. As the night fell we had to leave the site and this dolphin was not seen again since. You can find more about this rescue attempt here.

Košara

Dolphin with a visible deep cut on the body

In September 2013 our research team in north Dalmatia encountered a severely injured dolphin at the aquaculture site near the island of Košara. This dolphin had a visible deep cut on the body, just behind the blowhole. Strange humps were visible on the edges of the cut. Upon closer approach, a thin plastic line was seen going through the cut and circumventing the whole body. The line also caused incision at the root of pectoral fins. Below the body the plastic line extended into a piece of rope which the dolphin was dragging. It was obvious that this dolphin got entangled into a net and that his struggle to free itself caused deep cuts. The plastic line that remained in the body did not allow the wound to heal, which probably caused the hypergranulation (the humps on the edge of the cut).

Similar to the Lamjana case, this dolphin also seemed to be well fed, but was swimming very slowly and stayed at the surface for very long periods. Despite this, it did not allow our boat to approach in a rescue attempt. After checking our photo-ID database, we found that this same dolphin was seen in 2010 and that it was one of the three dolphins seen passing by as we were attempting to rescue the Lamjana dolphin (see above)! Then it was spotted again in 2012 by tourists who saw it at the aquaculture site near the island of Dugi otok and managed to make good photographs which enabled us to identify it. Already then the hypergranulation was visible, meaning that this dolphin has been injured for some time already.

Although injured, this dolphin obviously managed to survive by staying at the fish farms where it could catch prey with less effort. In fact, after 2013 our research team kept regularly seeing him each summer, always at the fish farms and always alone. With time, the wound appears to have got worse, probably because each movement of the body causes the plastic line to cut deeper into the tissue. However, with time one thing changed – in 2016 this dolphin was seen twice in a group with others, in one instance even leaping out of the water! Despite being severely injured, socializing with conspecifics and more active behavior could be a sign that the wound is not getting worse anymore or that even a recovery might happen. We certainly hope to see dolphin Košara on the recovery path. You can read more about Košara here.

Krešo

A dolphin called Krešo is our old acquaintant. He was registered for the first time in our photo-ID database in 2005 and has been regularly seen ever since. In 2014 Krešo appeared in Croatian media when a successful rescue attempt was reported. Krešo was found by two fishermen, having been entangled in some type of fishing gear. On one end there was a buoy and the other end of the rope was fixed to the bottom, which also disallowed Krešo to flee. This is why the fishermen could approach the dolphin and cut the ropes.

Being “anchored” to the bottom is actually what saved Krešo, unlike the previous two cases, where dolphins were injured but could still dive and swim. Shortly after, Krešo was seen again in company of another dolphin near Zadar. His visual appearance and behavior were normal, showing no sign of recent entanglement.

A case of intentional injuring

These three cases represent complexity of human-dolphin interactions, but they are unfortunately not the only recorded instances of injured dolphins. In 2015 we recorded a case of entanglement of a bottlenose dolphin calf, which later resulted in death. We even have cases of intentional injuring and killing recorded! In 2014 Bojan, one of the well-known resident dolphins in the Cres-Lošinj archipelago was seen with a harpoon sticking out of his back. This dolphin also was able to swim and dive, not allowing approach. With some luck Bojan managed to get free of the harpoon by himself and is still today regularly seen, completely recovered. There was another case of intentional injuringin 2010, which unfortunately did not have a positive outcome.

Bottlenose dolphins are intelligent opportunists – they adapt easily to peculiarities of the area they inhabit and learn quickly to utilize all advantages. Interactions with fisheries can be advantageous in a way that they present more abundant prey that requires less effort to catch. However, each of these interactions also bears some threats. A good example is feeding strategy where dolphins catch prey near the cages of the fish farms. As the fish in the cages is fed, part of the food passes through the cage net into the surrounding sea. This attracts wild fish, which in turn attracts dolphins. Dolphins tend to utilize this feeding strategy more in areas where the wild fish stock is depleted. But this also means that they have to maneuver around dense chaos of lines, ropes, nets and moorings of the fish farm cages, which increases risk of entanglement. There is also a potential that dolphins damage the nets of the fish farms which could put them in conflict with fish farm operators.

Interaction with bottom trawlers

In the areas where bottom trawling is the predominant fishing tool, the dolphins also interact mostly with bottom trawlers. Depending on the area or operating depth of the bottom trawlers, the dolphins prey on injured or stunned fish around the trawl net, try to pull the fish out of the trawl net or try to catch the fish in front of the trawl net mouth, risking being caught in the trawl net themselves. The predominant kind of dolphin-fisheries interaction can also vary seasonally, depending on which fishing tools is mostly used in a certain season.

The illegal fishing with explosives presents a special threat. It affects not only dolphins, but also the fish. In the Adriatic, this fishing “tool”is ever less used, but unfortunately not yet completely absent. The shock wave caused by explosion spreads through the water and can cause barotrauma of various intensities and even death. The barotrauma are injuries caused by a sudden change in pressure and affect mostly organisms that have gas-filled cavities in their bodies (lungs, inner ear, gastrointestinal tract, etc.), such as dolphins, but also humans.

Solitary dolphin injured in collisions with a vessel

Collisions with vessels are a special case of interactions between dolphins and human activities. Dolphins are generally agile swimmers and can easily avoid collision with a vessel, however solitary dolphins are a special case. The phenomena of solitary dolphins is known, but the reason why some individuals live a solitary life, despite being a highly gregarious species, is not understood. The solitary dolphins usually inhabit crowded harbors where they get used to presence of vessels to such extent that they don’t perceive them as potential threat anymore. There are recorded cases where solitary dolphins were injured in collisions with vessels, particularly by propellers. In recent years there is a solitary dolphin in the Adriatic, called Bobi, who is regularly seen in crowded bays. Our research team has been keeping record of his appearances near populated beaches and changes in his behavior
towards ever stronger habituation to human presence. In 2016 Bobi began to show sign of reckless behavior in presence of boats which poses a great threat to him. This is why we suggest not to initiate contact with dolphins or approach them even if they behave “friendly”.