Eva-Maria Hanninger, Jörn Selling , Katharina Heyer, Patricia Burkhardt-Holm

Abstract:

The Strait of Gibraltar is an important habitat for seven regularly occurring cetacean species. These waters are heavily used for fishing and therefore experience extraordinary levels of shipping traffic. Photography provides a valuable and non‐invasive tool to monitor the health of cetacean populations, where external injuries may indicate specific anthropogenic impacts, such as vessel strikes or fishery interactions. We manually screened 27,866 photos taken during whale‐watching operations between 2016–20 for human‐induced injuries. Injuries of potential anthropogenic origin were detected in 228 cases. The severity of these injuries ranged from superficial linear marks to severe traumas that may affect survival and fitness. Severe injuries included a gunshot wound, vessel‐related traumata and abrasions, signs of previous severe entanglements and deep lacerations which could stem from recreational fishery activities or propellor cuts and occasionally served as an entry point for dermal infections. In 2007, Spanish legislation introduced regulations on how to approach cetaceans by boat, but recreational fishery vessels have been commonly observed to disregard this law. We therefore urge stricter control and enforcement of existing laws and collaboration between the Spanish and Moroccan authorities to mitigate the human impact on cetaceans in this region.

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Helena Herr, Patricia Burkhardt-Holm, Katharina Heyer, Ursula Siebert, and Jörn Selling

Abstract:

The Strait of Gibraltar is a heavily used marine area, with intense fishing operations and one of the busiest shipping lanes worldwide. Concurrently, the Strait of Gibraltar is home to eight regularly occurring species of cetaceans. Thus, the potential for conflict between man and cetaceans is high. Injuries and external anomalies may serve as indicators for anthropogenic impacts and exposure to human activities. To explore potential impacts to cetacean populations inhabiting the Strait of Gibraltar, we analysed photographs taken opportunistically during whale-watching operations from 2001 to 2015. Externally visible conspicuous features and anomalies were detected in all of the eight regularly occurring cetacean species: long beaked common dolphin (Delphinus delphis), striped dolphin (Stenella coeruleoalba), common bottlenose dolphin (Tursiops truncatus), long-finned pilot whale (Globicephala melas), killer whale (Orcinus orca), sperm whale (Physeter macrocephalus), fin whale (Balaenoptera physalus), and minke whale (Balaenoptera acutorostrata). Altogether, 502 anomalies were documented in 494 cases of affected cetaceans, including injuries, skin anomalies, emaciation, and neoplasia. Highest prevalence was noted for injuries (245 incidences) of which a minimum of 44 (17%) were consistent with anthropogenic injuries. Our results suggest that human activities in the Strait of Gibraltar, especially fishing activities, pose a threat, particularly to small and medium-sized cetaceans. We, therefore, recommend stricter management enforcement of existing guidelines and laws, as well as the implementation of an area-wide management plan.

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