The interactive effects of human activities, stress and aggression on disruptive behaviour in orcas (Orcinus orca)

Jelluma, Leonie (2024) The interactive effects of human activities, stress and aggression on disruptive behaviour in orcas (Orcinus orca). Bachelor's Thesis, Biology.

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Abstract

In 2020, the Iberian orca (Orcinus orca) subpopulation started ramming boats, called ‘disruptive behaviour’, and since then this behaviour has started to spread among the subpopulation. This behaviour consists of their bodies colliding with the rudder of almost exclusively sailboats. A combination of different factors could have led to the rise of this behaviour, however, the decline of their main prey, the Atlantic bluefin tuna, could be seen as a trigger. Therefore, the downward spiral starts with human activities, mainly fisheries, as well as, tourism. Stress is caused by the vessels, and low prey abundance results in nutritional stress, which in turn causes an increase in the glucocorticoid hormones. These hormones in turn affect the behaviour of orcas, like aggression. Whereas stress is most prone in adult males, delivering and pregnant females, who have the highest levels of cortisol and corticosterone. Aggression is most expressed in males, but more research needs to be done on pregnant females. Additionally, the presence of vessels leads to a sensory overload leading to hyperaggression in some rare cases. Within captivity, only 1% of orca behaviour consists of ramming, but in case of the Iberian subpopulation, almost half of their interactions with vessels result in disruptive behaviour. This leads to a lot of damage to the boats but also negatively impacts the orcas who are already critically endangered. To eliminate this behaviour heatmaps created by orca sightings

Item Type:	Thesis (Bachelor's Thesis)
Supervisor name:	Birker-Wegter, M.L.M.
Degree programme:	Biology
Thesis type:	Bachelor's Thesis
Language:	English
Date Deposited:	23 Jul 2024 13:48
Last Modified:	23 Jul 2024 13:48
URI:	https://fse.studenttheses.ub.rug.nl/id/eprint/33308

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