It looks to me it could be either a propeller cut an entanglement in some sort of fishing gear.

This looks like a healing scar from a propeller blade from an outboard motor of a boat, or possibly a deep incision from a gill net.  This is most likely not from a shark or killer whale.

Hi Bruno, I agree; the wound healing pattern sure looks a lot like a propeller strike. I have seen a few of these in manatee.

I agree that this is not a killer whale or shark attack.

Hi Bruno, no doubt about it. This individual presents the remains of a propeller strike of at least two years old (the scar is not longer whitish). I have seen these wounds quite frequently in Chilean Patagonia with the increasingly busy fjords due to the salmon farm expansion. I have several photos just like this one but mainly on L. australis. Despite the photo is not very big, you can see at least four contact points all separated by the same distance. Your photo is great since it almost replicates the position the dolphin had a second before the collision happened. The cuts are at the same distance but the two biggest are also at the same depth. They are not in straight lines but slightly curved both in the same manner regardless of the amount of mass involved (active source).

In contrast, in my experience net wounds tend to be located at the closest section to the flukes and frequently they include longitudinal cuts on the flukes themselves. The net slides back since the peduncle gets thinner towards the tail but then can get stuck on the tail producing the cuts at that level. The lesions of this individual are not grouped close to the tail but positioned at same distance from each other regardless of the thickness of the peduncle. Also the cuts from the surface (dorsum) present a forward direction. They are not even vertical but towards the front of the individual. Whatever did these cuts, had "its own energy" in order to achieve that direction and the high speed needed as well to counterfeit the movement of the dolphin. Anybody with experience performing necropsies on cetaceans can confirm how hard is to cut at this level of the body. The tissue is very dense. These lesions are not due to a passive source. Nets tend to produce only a superficial damage unless getting stuck on structures like flippers or the tail due to their dragging effect. Therefore the cuts, when due to nets, tend to cut towards the back of the affected individual.

In conclusion, considering the direction of the wounds, their period, number and slight curved shape, we have no nets here but the "classic" small propeller blade wounds in perhaps the most frequent site where dolphins get these lesions. I am always surprised how some individuals can survive and keep up with these wounds but at the same time we do not know the rate of mortality. Perhaps these cases of survival are only a small percentage. We simply do not know.

It is important to report these collision cases to IWC and IMO since there is a worldwide database collecting information about this threat to both wildlife and vessels. Speed and/or path restrictions can be implemented in areas with high rates of collisions. Governments are required to report these cases to IMO but the details of this procedure depend on each country.

I recommend you to check some of the pics we posted in this paper:

https://www.researchgate.net/publication/228458600_Vessel_collisions_with_small_cetaceans_worldwide_and_with_large_whales_in_the_Southern_Hemisphere_an_initial_assessment?ev=prf_pub

kind regards

Article Vessel collisions with small cetaceans worldwide and with la...

Hi Bruno,

I have to agree that it looks like the humpback dolphin carries propeller scars. I have observed such scars in white-beaked dolphins and minke whales I study here in Iceland. It helped me over the years to consult this article to learn more about anthropogenic marks on whales and dolphins:

Moore, K.M.T. and S.G. Barco. 2013. Handbook for Recognizing, Evaluating, and Documenting Human Interaction in Stranded Cetaceans and Pinnipeds. U. S. Department of Commerce, NOAA Technical Memorandum, NOAA-TM-NMFS-SWFSC-510, 102p.

I like this article too on a similar topic:

Moore, MJ, van der Hoop, J, Barco, SG, Costidis, AM, Gulland, FM, Jepson, PD, Moore, KT, Raverty S, McLellan, WA. (Editors) (2013). Criteria and case definitions for serious injury and death of pinnipeds and cetaceans caused by anthropogenic trauma: underwater entrapment, chronic entanglement, sharp and blunt vessel, and gunshot. Diseases of Aquatic Organisms. 103: 229–264.

I hope this helps!

Chiara

Hi Bruno

we have seen similar but fresh propellor wounds on  T aduncus

shame eh

Thanks everyone for your answers, I have to agree that it looks like a wound produced by an old propeler. These are my first observations in the area however in this waters the marine traffic is increasingly busy due to the transport and extraction of oil and natural gas.

Thanks Gian Paolo, I will inform the ABu Dhabi Goverment to report the IWC and IMO all these collision cases as this is only one example of many individuals with truncated dorsal fins, wounds etc, caused by propellers.

Hola. Definitivamente es por helice de lancha.

Donde fue esto?

Sandra bessudo

Dear Sandra, the picture was taken in the Persian Gulf along the ABu Dhabi coastline.

Hola Sandra, la foto fue tomada en el Golfo Pérsico a lo largo de la costa de Abu Dhabi.

Saludos

Gracias por la información. saludos

I`ve seen quite a few, adn that's definetively a properler caused injury.

Hi all, 

it seems to be a propel cut. 

Regards

Hi Bruno,

I see you have got already a lot of very useful comments to your post, but I thought I would add my comment, too. I do agree with the others, these wounds look like propeller scars. 

I am attaching here Visser 1999, Dwyer et al 2014, Kiszka et al 2008, and Parsons and Jefferson 2000 which all helped me in the past when I investigated these marks on white-beaked dolphins, and which described in Bertulli et al 2015. 

Van Waerebeek et al 2007 it is also a very good article to read.

Hope this helps!

Cheers

Chiara