Externally visible lesions and diseases

What impact do shipping, fishing, noise and pollution have on the health of marine mammals in the Strait of Gibraltar? With the help of photos we investigated possible reasons, which we also presented to the IWC.


Photo identification plays an important role in the work of firmm by which we can also document conspicuous features which point to injuries or illnesses of the animals. Our marine biologist Jörn Selling evaluated these photos for the period 2001 to 2015: Having spent over 13,000 hours on sea covering almost 100,000 nautical miles, we had more than 35,000 photos to our disposal. On 788 of these pictures 494 animals with 502 conspicuous features could be identified.

Possible reasons for these features were recorded in the work "Epidermal conditions, lesions and malformations in cetaceans of the Strait of Gibraltar", which was presented at the IWC conference in 2016.

We are grateful for the cooperation within the scope of this work:

  • Dr. Helena Herr, University of Hamburg, Centre for Natural History (CeNak)
  • Prof. Dr. Patricia Holm, University of Basel, Department of Environmental Sciences
  • Prof. Prof. Dr. Ursula Siebert, University of Veterinary Medicine Hannover, Institute for Terrestrial and Aquatic Wildlife Research

According to the results of our investigation, many anomalies are directly or indirectly attributable to humans. We therefore believe that there is an urgent need for improved regulation of activities in the Strait of Gibraltar.


Großer Tümmler mit Kalb (beide abgemagert)
Bottlenose dolphin mother with her calf (both emaciated)

33 Bottlenose Dolphins and one Orca were exceptionally lean, with clearly visible ribs. Emaciation is a sign of malnutrition and mostly a result of lack of food, pathogens, diseases or injuries.


We observed two Striped Dolphins and one Orca with a bent down fin. Two Bottlenose Dolphins showed swelling: one in the genital area, another at the base of the dorsal fin. The latter is probably due to an injury, as the spinal column is also affected.


The most frequent abnormalities were injuries: we found these in 245 cases. Some are due to natural causes, others are caused by humans.

Natural causes include injuries from other animals. For example Sperm Whales show traces of the suction cups of squids.

Scars on the skin of a Fin Whale indicate traces of lampreys. These eel-like parasitic fishes suck on fish and whales and feed on their blood. They often glide along the host's body in search of a better position, which explains the long scars.

Often, however, the cause cannot be determined with certainty. Some scars may indicate clashes with other predators or may have been caused by humans.

Shipping and fishing are the greatest threats to whales and dolphins.

Pilotwal mit Schnittverletzung durch Angelleine
Pilot Whale with cut caused by fishing line

Among man-made external injuries, shipping and fishing pose the greatest threats to marine mammals. In the busy Strait of Gibraltar, collisions with ships are not uncommon. This often results in serious injuries to the back or skull, as we have seen with Sperm Whales.

Fishing lines of big game fishermen seem to be responsible for cuts, especially at the base of dorsal fins. Sometimes parts of the fins, sometimes even complete fins are cut off. Further injuries are caused by fishing nets or hooks. Some dead finds indicate by-catch due to net fragments - cut fins as well as stones attached to the fluke indicate intentional mutilation or sinking of the animals by fishermen.

Also the marking of whales and the equipping with transmitters for scientific purposes can cause damage, which is not surprising considering the water pollution in the Strait of Gibraltar.

Effect of an injury on Curro

In some cases we have been able to observe and document the effects of the injuries for years. One example is the fate of a Pilot Whale called Curro, which we know well.

In July 2008, Curro was seriously injured at the back in front of the dorsal fin, either by a ship's propeller or by fishing equipment. In May 2009, the wound had worsened, showing necrotic tissue that could have been infected with pathogens.

Our encounter with Curro in September 2010 gave us hope as the wound seemed to heal. But in July 2011 the fin began to break apart. In August of the same year more and more inflamed tissue rotted away. During the sighting in March 2013 the injury seemed to heal again, although roughened yellowish tissue was visible. However, this was our last encounter with Curro.

Cutaneous anomalies

Großer Tümmler mit Tumoren
Bottlenose Dolphin with tumours

On the skin of some marine mammals we could spot parasitic epizootics, including copepods and barnacles. The latter were the most common and are probably an indication of a weakened immune system: an increasing infestation was observed, among other things, during the first morbillivirus infection in the Mediterranean in 1990. The carcinogenic industrial chemical PCB, to which marine mammals in this area are very heavily exposed, is also associated with a weakening of the immune system.


We found tumours in Bottlenose Dolphins and Orcas, mostly in jaws and adjacent skin areas. This could be caused by viruses or chemicals.

In a young Bottlenose Dolphin an injury could also be responsible for what looked like a tumour, which is indicated by the scratches below the blowhole.

Skin pigmentation

A conspicuous pigmentation is not necessarily associated with a disease, but can simply be part of the individual appearance of an animal.

The pigment patterns in our photos also indicate healing skin diseases or viral diseases. The morbillivirus is known to change the colour of the blubber and sometimes to cause oedema in the subcutis, resulting in dark spots. Light spots in Bottlenose Dolphins, on the other hand, are often associated with herpes viruses. However, the causes cannot be clearly proven only on the basis of photos.

Disorders caused by humans favour pathological skin changes.

Skin diseases caused by viruses, bacteria and fungi are often caused by altered environmental conditions and human-induced disorders. Persistent pollution, for example, has a negative impact on marine mammals. In the blubber of Bottlenose Dolphins in the western Mediterranean and North-East Atlantic, a high concentration of organochlorine compounds was found, which can be found in pesticides for example.


Sportfischer nähern sich den Tieren
Many big game fishermen do not respect the whales

Big game fishing, commercial fishing and shipping seem to be responsible for the majority of marine mammal injuries. In addition, there is lack of food, noise and pollution, which can indirectly lead to visible changes by weakening the immune system.

Big game fishing needs to be better regulated.

Where can we start? The number of boats and fishing activities in the Strait continues to increase, but there are hardly any regulations. Big game fishing has been restricted to a certain period of time, but illegal activities are not uncommon. Moreover, measures to protect marine mammals only apply in Spanish waters. They are binding on all boats, but at best only whale watching boats respect them. Big game fishermen approach the animals ruthlessly, especially because they are caught up in the popular belief that there are large quantities of tuna fish in their vicinity. Controls should urgently be tightened .