The effects of marine traffic on the behaviour of Black Sea harbour porpoises (Phocoena phocoena relicta) within the Istanbul Strait, Turkey

Abstract

Marine traffic is threatening cetaceans on a local and global scale. The Istanbul Strait is one of the busiest waterways, with up to 2,500 vessels present daily. This is the first study to assess the magnitude of short- and long-term behavioural changes of the endangered Black Sea harbour porpoises (Phocoena phocoena relicta) in the presence of marine vessels within the Istanbul Strait. Markov chains were used to investigate the effect of vessel presence on the transition probability between behavioural states (diving, surface-feeding and travelling), and to quantify the effect on the behavioural budget and bout length (duration of time spent in a given state) of porpoises. Further, the changes on swimming directions of porpoises in relation to vessel speed and distance was investigated using generalized linear models. In vessel presence, porpoises were less likely to remain in a given behavioural state and instead more likely to switch to another state. Because of this, the bout length of all three behavioural states decreased significantly in the presence of vessels. The vessel effect was sufficiently large to alter the behavioural budget, with surface-feeding decreasing significantly in the presence of vessels. However, when taking into account the proportion of time that porpoises were exposed to vessels (i.e. 50%), the measured effect size was not large enough to significantly alter the animals’ cumulative (diurnal) behavioural budget. Additionally, vessel speed and distance had a significant effect on the probability of porpoises showing a response in their swimming directions. The southern and middle sections of the Istanbul Strait, which have the heaviest marine traffic pressure, had the lowest porpoise sightings throughout the year. Conversely, northern sections that were exposed to a lesser degree of marine traffic hold the highest porpoise sightings. The effect shown in this study in combination with increasing human impacts within the northern sections should be considered carefully and species-specific conservation actions, including establishment of protected areas, should be put in place to prevent the long-term consequences of marine traffic on the Black Sea harbour porpoise population.

Harbour porpoises respond to recreational boats by speeding up and moving away from the boat path

“…Our findings add valuable insights into how cetaceans respond to vessel disturbance. While porpoises in our study reacted similarly to those observed by Baş et al (2017) and Oakley et al (2017), other studies have documented porpoises to react to vessels over 1 km away (Palka & Hammond, 2001;Wisniewska et al, 2018). This variance underscores the necessity of employing diverse methods to assess the impact of vessels contextually, even within the same species.…”

“…However, this was not what we observed. In a study of Black Sea harbour porpoises in Istanbul Strait, Turkey, porpoises tended to turn more when vessels were nearby (<200 m; Baş et al., 2017 ). A likely reason for this difference could be the fine resolution of our data, which was collected at 1‐second intervals.…”

“…We only analysed data from the last minute of this phase when comparing with data collected during the exposure phase. Porpoises are unlikely to react to boats that are >250 m away (Baş et al., 2017 ; Oakley et al., 2017 ), which was the reason we positioned the boat >300 m from the porpoise. (2) With the drone still filming the porpoise, we started the boat and gradually increased the speed to its maximum (10 or 20 knots) over a period of 30 s. We passed the porpoise without changing direction and continued moving until the boat was >300 m away from the porpoise.…”

Small Cetacean in a Human High-Use Area: Trends in Harbor Porpoise Abundance in the North Sea Over Two Decades

“…As odontocetes, harbor porpoises rely on sound for orientation, predation and intraspecific communication (Clausen et al, 2010;Wisniewska et al, 2016;Sørensen et al, 2018), which is why they are particularly vulnerable to underwater noise and any hearing impairment should be prevented. Beside impulsive noise events, the global underwater soundscape is largely dominated by shipping noise proven to have negative effects on harbor porpoise behavior (Hermannsen et al, 2014;Dyndo et al, 2015;Akkaya Bas et al, 2017;Wisniewska et al, 2018b).…”

The Effects of Ship Noise on Marine Mammals—A Review

“…Similarly, of the porpoise species, only harbor porpoises (Phocoena phocoena) and finless porpoises (Indo-Pacific, Neophocaena phocaenoides; Yangtze, N. asiaeorientalis asiaeorientalis) have been studied with regards to the impact of watercraft. Harbor porpoises moved away from vessels (Palka and Hammond, 2001), showed higher levels of porpoising in the presence of boats (Dyndo et al, 2015), changed behavioral states (Akkaya Bas et al, 2017), reduced foraging behavior (Wisniewska et al, 2018), and experienced decreased communication ranges (Hermannsen et al, 2014). Acoustic tags (DTAGs) placed on harbor porpoises in Danish waters showed that animals encountered vessel noise 17-89% of the time, and exhibited vigorous fluking, bottom diving, interrupted foraging, and cessation of echolocation during some high vessel noise events (received level > 96 dB re 1 µPa at 16 kHz 1/3 octave band; Wisniewska et al, 2018).…”