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Injuries, Emaciation and Skin Conditions in Cetaceans of the Strait of Gibraltar. An update for the years 2016 till 2020
E.-M. Hanninger, J. Selling, K. Heyer and P. Burkhardt-Holm
The Strait of Gibraltar is an important habitat for seven regularly occurring cetacean species. These waters are heavily used for
fishing operations and face an extraordinarily dense shipping traffic. The immense anthropogenic influence might not only lead to
direct physical trauma but might also impair the immune function of cetaceans. Stress and the occurrence of pollutants may lead to
an increased disease susceptibility. Our work provides an update on the health conditions of cetaceans in the Strait of Gibraltar.
Previous studies covered the time periods from 2001 till 2015 and 2004 till 2007 and reported dermal diseases, malformations and
injuries in several individuals. Photographs are a valuable, non-invasive tool to monitor the health of cetacean populations. External
anomalies can serve as an indicator for anthropogenic impacts. We screened 27,866 pictures taken during whale watching operations
in the years 2016 till 2020 visually for pathological conditions, such as emaciation, injuries, skin alterations and epizoic infestations.
Dermal diseases were detected in 566 cases. The most common skin lesions were light grey skin lesions. Tattoo-like skin lesions
were detected in 16 animals. Rarely observed conditions included expansive annular lesions detected in three pilot whale juveniles.
Skin alterations occurred in all species but seemed to affect bottlenose dolphins the most. We further report on ulcerating wounds.
In three pilot whales, these wounds did not heal for longer periods of time. Epizoic infestations included the observation of
Xenobalanus globicipitis and Pennella balaenoptera. Dermal diseases and parasitic infestations can be an indicator for a stressful,
degrading marine environment. Multiple fin whales were sighted with extraordinarily high numbers of Pennella balaenoptera.
Emaciation was mainly detected in bottlenose dolphins (n=36) and seemed to affect these animals more severely during some years.
This observation may indicate fluctuations in prey availability. Injuries of potential anthropogenic origin were detected in 227
individuals. The severity of the injuries ranged from rather superficial linear marks to severe traumas, which might affect the survival
and fitness. Severe injuries included a gunshot wound, vessel related traumata, signs of previous, severe entanglements and injuries
which may stem from big game fishing lines. In 2007, the Spanish legislation established regulations on how close cetaceans may
be approached by boat. Recreational fishery vessels have been observed to commonly disregard this law. We urge for a stricter
control and enforcement of existing laws and for a collaboration of Moroccan and Spanish authorities to mitigate the observed