Sharks are often perceived as solitary predators. However, these powerful ocean inhabitants also engage in aggressive interactions with each other. This behavior, ranging from subtle warnings to physical confrontations, reveals dynamic social structures and survival instincts.
Signs of Shark-on-Shark Encounters
Evidence of aggressive encounters between sharks is frequently observed. Researchers document physical signs like bite marks, scars, and missing fin pieces, indicating past interactions. For instance, a young white shark off Rhode Island displayed tooth marks on its head, suggesting an encounter with a larger shark.
Researchers also observe chase sequences and aggressive displays. Sharks use characteristic swimming patterns, known as agonistic displays, to communicate agitation and intent to fight, often to avoid physical combat. These displays can involve a shark shaking its head, swimming erratically with a hunched back, or pointing its pectoral fins downwards. Such behaviors serve as warnings, signaling dominance or rivalry without immediate physical contact.
Why Sharks Attack Each Other
Inter-shark aggression is driven by motivations tied to survival. Competition for resources, such as food and territory, is a primary factor. When multiple sharks converge on a limited food source, like a carcass, competition can intensify, sometimes leading to a “feeding frenzy” where sharks may inadvertently bite one another. Overcrowding can also heighten aggressive behaviors.
Dominance displays are another common reason, as sharks establish hierarchies. Male sharks may exhibit increased aggression during the breeding season, engaging in biting, ramming, and chasing to secure mating opportunities. Mating rituals often involve males biting females to gain a grip for internal fertilization; females sometimes evolve thicker skin to withstand these bites. Sharks may also attack due to perceived threats or as a defensive response.
Aggression Within the Same Species
Aggression within the same shark species occurs for various reasons, including territorial defense and establishing social hierarchies. While not all sharks are territorial, some species, like reef sharks, maintain patrol areas. Sharks communicate to establish social positions before resorting to physical violence, though conflicts can arise over preferred feeding grounds or resting spots.
Cannibalism is another aspect of intra-species aggression, occurring even before birth. Intrauterine cannibalism involves developing embryos consuming other embryos or unfertilized eggs within the womb. For instance, sand tiger sharks exhibit adelphophagy, where the strongest embryo devours its weaker siblings, resulting in one or two large, robust pups per uterus. Other species, like the blue shark, practice oophagy, where embryos feed on unfertilized eggs. This ensures surviving offspring are larger and better prepared for life.
When Different Shark Species Clash
Aggression between different shark species involves predation or competition for shared resources. Larger shark species may prey on smaller ones. For example, larger white sharks attack and consume smaller sharks if food is scarce, including makos. While mako sharks primarily feed on fish and cephalopods, great white sharks have a diet that includes larger marine mammals, but they are opportunistic predators.
Competitive interactions also occur when different shark species inhabit the same hunting grounds or pursue similar prey. These clashes show how certain species dominate others based on size, speed, or hunting strategies. For instance, tiger sharks are opportunistic apex predators with a broad diet that includes other sharks. Dominance among tiger sharks is usually established by size rather than violent fights when they share space.