Stress is
wildly used as an indicator of negative welfare. There are two main types of
stress: acute and chronic stress. Acute stress is often a short-term event
which can have negative or positive physiological effects, whereas chronic
stress has long-term, negative effects1. Animals can either visibly
display their stress, such as behavioural changes, or physiological parameters
can indicate their levels of stress, such as changes in cortisol. Where it is
not possible to gain physiological readings of animals, particularly wild
animals, behavioural observations are the main source used. Therefore the
behavioural indicators for recognising stress in dolphins are described as
follows:
Respiration rate and chuffing
An increase in breathing rate is commonly used as an indicator of stress in farm animals, and as dolphins are mammals, a higher respiration rate could also mean that the dolphin is experiencing stress. However, Serres and Delfour (2019)2 concluded that a change in breathing frequency does not indicate whether the stress is negative or positive, such as excitement, and that other physiological parameters should be measured. Although, as physiological parameters are not always accessible, noticing a change in a dolphins breathing rate is a good place to start. Furthermore, dolphins may exhale sharply and loudly known as “chuffing”, which is used to infer that the dolphin is bothered by something3.
The dolphin’s whistle rate has been studied as a potential indicator of stress. During captive dolphin swim programs, an increased in whistle rate was found which Akiyama and Ohta (2007)4 suggested was due to stress. In a capture and release study, Esch et al (2009) also found that the whistle rate and number of loops were greater during brief capture-release events when compared to undisturbed conditions.
Stereotypies
For most captive wild animals, the appearance of abnormal, repetitive behaviours cause a welfare concern. This has also been observed in captive dolphins, in the form of vomiting, head bobbing, circular swimming and biting on gates and bars5. However it is not fully understood how a stereotypical behaviour reflects an animals’ internal state. The behaviour may have arisen out of feeling a state of chronic stress, however the behaviour may also be a coping mechanism, and therefore performing the behaviour can lower the animals’ stress, as has been found in rhesus macaques6.
Dive duration
An increase in the length of time that a dolphin dives for has been used to indicate stress in dolphins. Dolphins in areas of high vessel traffic were found to dive for longer7, likely as an avoidance tactic. Therefore the longer a dolphin is under the water, the more stress it is likely experiencing. A study on a solitary common dolphin in Scotland found that the dolphin dove for longer as the vessel passed by, compared to when there were no passing vessels in the area (Hurdle unpublished). Ocean noise can also be a stressor to dolphins, causing longer dives.
Increased swimming speed
Often seen in the wild, an abrupt change in a dolphin’s swimming speed and direction caused by vessels can be an indicator of stress. If the dolphin feels disturbed it will flee the area, whereas a dolphin that feels undisturbed will remain. Therefore it is essential that vessel users are mindful of how their boat behaviour affects dolphins.
Body slaps and aerial behaviours
Dolphins may slap the water, with either their head or tail as a sign of aggression. Dolphins have been observed tail slapping when drones are flown too close to the group8, therefore it is assumed the behaviour is delivered as a warning. This has also occurred when vessels are too close in proximity. An increased occurrence in breaches have also been observed, which may also indicate stress.
Slide-outs and strandings
Within captivity, dolphins may be seen “sliding out” onto dry land areas outside of shows and training sessions. This behaviour is often interpreted as play by the trainers, however it could be seen as a sign of stress that the dolphin is trying to get out of the water. In a video of a facility in Japan, a false killer whale slid over the tank glass and onto the concrete ground during a show9. This was obviously not a planned behaviour, and the trainers had to quickly act to get the animal back into the water. These captive instances could be the equivalent of wild cetaceans stranding on beaches. Cetaceans may strand for a variety of reasons, however the stress of intense ocean noise caused by naval activity has been known to cause fatal strandings of cetaceans10.
References
1. Esch HC, Sayigh LS, Blum JE and Wells RS 2009 Whistles as potential indicators of stress in bottlenose dolphins (Tursiops truncatus). Journal of Mammalogy 900(3): 638-650
2. Serres A and Delfour F 2019 Social behaviors modulate bottlenose dolphins’ (Tursiops truncatus) breathing rate. Animal Behaviour and Cognition 6(2): 127-140
3. https://www.bornfree.org.uk/storage/media/content/files/Publications/EU%20DOLPHINARIA%20REPORT.pdf
4. Akiyama J and Ohta M 2007 Increased number of whistles of bottlenose dolphins, Tursiops truncatus, arising from interaction with people. Journal of Veterinary Medical Science 69: 165-170
5. https://cetaceaninspiration.wordpress.com/2011/12/22/stereotypical-behavior-in-captive-whales-and-dolphins/#:~:text=Like%20many%20animals%20in%20captivity,%2C%20or%20abnormal%2C%20stereotypical%20behavior.&text=Some%20examples%20of%20stereotypy%20include,and%20bars%2C%20and%20tongue%20playing.
6. Pomerantz O, Paukner A and Terkel J 2012 Some stereotypic behaviors in rhesus macaques (Macaca mulatta) are correlated with both perseveration and the ability to cope with acute stressors. Behaviour Brain Research 230(1): 274-280
7. Ng SL and Leung S 2003 Behavioural response of Indo-Pacific humpback dolphin (Sousa chinensis) to vessel traffic. Marine Environmental Research 56: 555-567
8. Fettermann T, Fiori L, Bader M, Doshi A, Breen D, Stockin K and Bollard B 2019 Behaviour reactions of bottlenose dolphins (Tursiops truncatus) to multirotor Unmanned Aerial Vehicles (UAVs). Scientific Reports 9: 8558
9. https://www.youtube.com/watch?v=wxzTyQillMQ
10. Parsons ECM 2017 Impacts of navy sonar on whales and dolphins: now beyond a smoking gun? Frontiers in Marine Science 13
An increase in breathing rate is commonly used as an indicator of stress in farm animals, and as dolphins are mammals, a higher respiration rate could also mean that the dolphin is experiencing stress. However, Serres and Delfour (2019)2 concluded that a change in breathing frequency does not indicate whether the stress is negative or positive, such as excitement, and that other physiological parameters should be measured. Although, as physiological parameters are not always accessible, noticing a change in a dolphins breathing rate is a good place to start. Furthermore, dolphins may exhale sharply and loudly known as “chuffing”, which is used to infer that the dolphin is bothered by something3.
The dolphin’s whistle rate has been studied as a potential indicator of stress. During captive dolphin swim programs, an increased in whistle rate was found which Akiyama and Ohta (2007)4 suggested was due to stress. In a capture and release study, Esch et al (2009) also found that the whistle rate and number of loops were greater during brief capture-release events when compared to undisturbed conditions.
For most captive wild animals, the appearance of abnormal, repetitive behaviours cause a welfare concern. This has also been observed in captive dolphins, in the form of vomiting, head bobbing, circular swimming and biting on gates and bars5. However it is not fully understood how a stereotypical behaviour reflects an animals’ internal state. The behaviour may have arisen out of feeling a state of chronic stress, however the behaviour may also be a coping mechanism, and therefore performing the behaviour can lower the animals’ stress, as has been found in rhesus macaques6.
An increase in the length of time that a dolphin dives for has been used to indicate stress in dolphins. Dolphins in areas of high vessel traffic were found to dive for longer7, likely as an avoidance tactic. Therefore the longer a dolphin is under the water, the more stress it is likely experiencing. A study on a solitary common dolphin in Scotland found that the dolphin dove for longer as the vessel passed by, compared to when there were no passing vessels in the area (Hurdle unpublished). Ocean noise can also be a stressor to dolphins, causing longer dives.
Often seen in the wild, an abrupt change in a dolphin’s swimming speed and direction caused by vessels can be an indicator of stress. If the dolphin feels disturbed it will flee the area, whereas a dolphin that feels undisturbed will remain. Therefore it is essential that vessel users are mindful of how their boat behaviour affects dolphins.
Dolphins may slap the water, with either their head or tail as a sign of aggression. Dolphins have been observed tail slapping when drones are flown too close to the group8, therefore it is assumed the behaviour is delivered as a warning. This has also occurred when vessels are too close in proximity. An increased occurrence in breaches have also been observed, which may also indicate stress.
Within captivity, dolphins may be seen “sliding out” onto dry land areas outside of shows and training sessions. This behaviour is often interpreted as play by the trainers, however it could be seen as a sign of stress that the dolphin is trying to get out of the water. In a video of a facility in Japan, a false killer whale slid over the tank glass and onto the concrete ground during a show9. This was obviously not a planned behaviour, and the trainers had to quickly act to get the animal back into the water. These captive instances could be the equivalent of wild cetaceans stranding on beaches. Cetaceans may strand for a variety of reasons, however the stress of intense ocean noise caused by naval activity has been known to cause fatal strandings of cetaceans10.
1. Esch HC, Sayigh LS, Blum JE and Wells RS 2009 Whistles as potential indicators of stress in bottlenose dolphins (Tursiops truncatus). Journal of Mammalogy 900(3): 638-650
2. Serres A and Delfour F 2019 Social behaviors modulate bottlenose dolphins’ (Tursiops truncatus) breathing rate. Animal Behaviour and Cognition 6(2): 127-140
3. https://www.bornfree.org.uk/storage/media/content/files/Publications/EU%20DOLPHINARIA%20REPORT.pdf
4. Akiyama J and Ohta M 2007 Increased number of whistles of bottlenose dolphins, Tursiops truncatus, arising from interaction with people. Journal of Veterinary Medical Science 69: 165-170
5. https://cetaceaninspiration.wordpress.com/2011/12/22/stereotypical-behavior-in-captive-whales-and-dolphins/#:~:text=Like%20many%20animals%20in%20captivity,%2C%20or%20abnormal%2C%20stereotypical%20behavior.&text=Some%20examples%20of%20stereotypy%20include,and%20bars%2C%20and%20tongue%20playing.
6. Pomerantz O, Paukner A and Terkel J 2012 Some stereotypic behaviors in rhesus macaques (Macaca mulatta) are correlated with both perseveration and the ability to cope with acute stressors. Behaviour Brain Research 230(1): 274-280
7. Ng SL and Leung S 2003 Behavioural response of Indo-Pacific humpback dolphin (Sousa chinensis) to vessel traffic. Marine Environmental Research 56: 555-567
8. Fettermann T, Fiori L, Bader M, Doshi A, Breen D, Stockin K and Bollard B 2019 Behaviour reactions of bottlenose dolphins (Tursiops truncatus) to multirotor Unmanned Aerial Vehicles (UAVs). Scientific Reports 9: 8558
9. https://www.youtube.com/watch?v=wxzTyQillMQ
10. Parsons ECM 2017 Impacts of navy sonar on whales and dolphins: now beyond a smoking gun? Frontiers in Marine Science 13
