The thresher shark family (Alopiidae) consists of three species: the common thresher, the bigeye thresher, and the pelagic thresher. These sharks are easily identified by their incredibly long, whip-like tail, which can be as long as their body and is used to stun prey. They are highly migratory and are found in tropical and temperate oceans worldwide, including the Atlantic Ocean where Tenerife is located.
While often seen at the surface, these sharks are also known for their deep-water habits. The common thresher (Alopias vulpinus) typically inhabits depths from the surface down to 550 meters (1,800 feet). The bigeye thresher (Alopias superciliosus) is particularly adapted to deep, dark waters, with large eyes that help it hunt. It is known to dive to at least 500 meters (1,600 feet) and has been recorded at depths of up to 1,500 meters in some studies.
Based on the search results, here is information about thresher sharks and their presence in deep water, with specific relevance to the environment off the coast of Tenerife.
Biology and Habitat of Thresher Sharks
The thresher shark family (Alopiidae) consists of three species: the common thresher, the bigeye thresher, and the pelagic thresher. These sharks are easily identified by their incredibly long, whip-like tail, which can be as long as their body and is used to stun prey. They are highly migratory and are found in tropical and temperate oceans worldwide, including the Atlantic Ocean where Tenerife is located.
While often seen at the surface, these sharks are also known for their deep-water habits. The common thresher (Alopias vulpinus) typically inhabits depths from the surface down to 550 meters (1,800 feet). The bigeye thresher (Alopias superciliosus) is particularly adapted to deep, dark waters, with large eyes that help it hunt. It is known to dive to at least 500 meters (1,600 feet) and has been recorded at depths of up to 1,500 meters in some studies.
Thresher sharks exhibit a behavior called vertical migration, moving to deeper, cooler waters during the day to hunt and avoid predators, and ascending to shallower, warmer waters at night. This behavior is possible due to a unique biological adaptation called regional endothermy, which allows them to maintain a body temperature higher than the surrounding water. This helps them stay active in the cold, deep ocean.
Thresher Sharks off the Coast of Tenerife
The deep-water environment around Tenerife, where the continental shelf drops off sharply, provides a suitable habitat for thresher sharks. While there isn’t extensive public information on a dedicated research project on thresher sharks specifically in Tenerife, the presence of organizations like ElasmoCan, which monitors elasmobranchs (sharks and rays) in the Canary Islands, suggests that the region is a known habitat for these species. The dramatic drop-off to depths of 1,000 meters or more creates a habitat that is perfect for the vertical migratory patterns of thresher sharks, allowing them to remain close to shore while still accessing their preferred deep-water environment. The documentary film project highlights the importance of using submersibles to study this elusive species in a location where they are found at such considerable depths.
The Physiology of Regional Endothermy and Hemoglobin-Oxygen Binding
Regional endothermy in high-performance fishes, such as tuna and certain sharks, represents a remarkable physiological adaptation that allows them to maintain specific tissues at temperatures well above ambient water. This capability is a significant evolutionary advantage, enhancing muscle power output, neurological function, and swimming speed in cold-water environments. While the primary mechanism for heat retention is a specialized circulatory system, this system’s efficacy is critically linked to the unique properties of the hemoglobin molecule itself.
The Role of the Rete Mirabile in Thresher Sharks
The core of regional endothermy is the countercurrent heat exchange system, known as the rete mirabile (Latin for “wonderful net”). This intricate network of densely packed arteries and veins is strategically located within the fish’s body, particularly near the red aerobic swimming muscles. As the muscles generate metabolic heat, the warm, deoxygenated venous blood returning from these tissues flows through the rete. It runs in a countercurrent fashion (in the opposite direction) to the cold, oxygenated arterial blood entering from the gills.
Due to the close proximity and opposing flow, heat from the warm venous blood is efficiently transferred to the cold arterial blood. This process, which can be up to 99% efficient in species like the bluefin tuna, conserves metabolic heat within the body core and prevents it from being lost at the gills. The arterial blood, now warmed, can deliver oxygen to the muscles at an elevated temperature, while the venous blood, having cooled down, returns to the gills at a temperature close to the ambient water, minimizing heat loss.
The Effect of Temperature on Hemoglobin-Oxygen Affinity
For most vertebrates, including ectothermic fish, the binding affinity of hemoglobin (Hb) for oxygen decreases as temperature increases. This is a fundamental property of the exothermic nature of O2 binding. This temperature dependence is also influenced by the Bohr effect, where an increase in carbon dioxide (CO2) or a decrease in pH (acidity) lowers hemoglobin’s affinity for O2, facilitating its release in active tissues.
However, in regionally endothermic fishes like tuna and lamnid sharks (e.g., thresher and mako sharks), this relationship is uniquely altered. Their hemoglobin has evolved a reduced temperature sensitivity, and in some cases, even a reverse temperature dependence, meaning Hb-O2 affinity increases with rising temperature.
This adaptation is crucial for several reasons:
- Ensuring Oxygen Delivery: As blood travels from the cold gills to the warm muscles via the rete mirabile, its temperature increases. If the hemoglobin had a normal temperature-dependent affinity, it would prematurely release O2 in the arteries as it warmed up, before reaching the oxygen-demanding muscles. The modified hemoglobin prevents this, ensuring that the O2 remains bound until it reaches the targeted tissues.
- Facilitating Oxygen Offloading: While the hemoglobin is less sensitive to temperature, it still offloads O2 efficiently in the muscles. This is achieved through a powerful Bohr effect, where the high levels of CO2 and lactic acid produced by the intensely active muscles cause a drop in pH, forcing the O2 to dissociate from the hemoglobin and enter the cells.
In essence, these animals have evolved a dual system: a physiological heat exchanger (rete mirabile) that raises muscle temperature, and a biochemical adaptation in their hemoglobin that allows it to function optimally across the resulting internal temperature gradients, ensuring a continuous and robust supply of oxygen to power their high-performance metabolism. This synergistic relationship highlights a remarkable example of convergent evolution in a challenging marine environment.
