Date of Award

2025

Document Type

Thesis

Degree Name

Bachelors

Department

Natural Sciences

First Advisor

Rycyk, Athena

Area of Concentration

Marine Biology

Abstract

The GLADIS pod of orcas inhabits the Strait of Gibraltar where the waters of the northern Atlantic ocean and the Mediterranean sea intersect. This pod has initiated hundreds of attacks towards vessels in the Strait since May of 2020. Attacks consist of circling boats, ramming hulls, dismantling rudders, and other destructive activities. This review will examine four major hypotheses in an attempt to evaluate the cause behind these attacks. Play is assessed through five key criteria: the behavior does not result in food acquisition or physical reward, differs from functional activities like hunting or grooming, is repeated but not perfected, and occurs when the animal appears relaxed. Social learning is analyzed using a five-stage model: observation, attention, retention, reproduction, and motivation. Defensive behavior is examined through three phases: exploration of a potential threat, positional escape, and disordered withdrawal. Aggression is evaluated as offensive aggression, frustration-induced aggression, or displaced aggression. This review assesses all hypotheses and concludes that play is the most plausible explanation for the observed behaviors. Most if not all attacks satisfy all five criteria for animal play to the fullest extent possible based on available evidence; this hypothesis best summarizes the persistent, organized, and commonly non-detrimental nature of the attacks.

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