🦈8.11 Shoals Marine Lab: Study Notes

Here are my lecture notes (I’m putting them here for now to keep them organized).

Throughout this class, I have gained a comprehensive understanding of shark anatomy, behavior, and foraging strategies, which has expanded my knowledge of their unique adaptations and ecological roles. The evolution of sharks and their phylogeny was highlighted by their early diversification around 540 million years ago, particularly their adaptation to various ecological niches. Notably, sharks, rays, and skates are all part of the class Chondrichthyes, distinguished by their cartilaginous skeletons, heterocercal tails, and placoid scales. The class includes the Elasmobranchii (sharks, rays, and skates) and Holocephali (chimaeras), with differences in their anatomical features, such as the number of gill slits, fin structures, and reproductive modes.

One significant aspect I learned was the differentiation between sharks, rays, and skates. For example, skates are oviparous, laying eggs encased in protective shells, whereas rays are ovoviviparous, retaining their eggs internally until hatching. Skates also possess bi-lobed pelvic fins, a characteristic absent in rays, which have single-lobed pelvic fins. Additionally, skates typically have thorns along their midline, unlike rays, and their tails are fleshy and lack spines, distinguishing them from the more slender, spine-equipped tails of rays. These distinctions reveal how these species have adapted to their respective environments, with rays often being more pelagic and skates more benthic.

The anatomy of sharks is notably suited for efficient locomotion and foraging. Sharks possess streamlined, fusiform bodies that reduce drag in the water, enabling swift movement. Their pectoral fins, which are fused to the head in rays and skates, provide lift and stabilization. Shark species differ in their tail and fin structures depending on their ecological roles, with pelagic species such as white sharks having large, tall caudal fins for thrust and stabilization. In contrast, benthic species like nurse sharks have more asymmetrical tail fins that aid in maneuvering close to the ocean floor.

Sharks exhibit a variety of foraging strategies that are highly specialized for different environments. For instance, sharks utilize six senses, including mechanoreception, chemoreception, electroreception, and vision, which aid in locating prey. The lateral line and ampullae of Lorenzini are particularly specialized for detecting water movement and electrical pulses, respectively, allowing sharks to hunt effectively in low-visibility conditions. Sharks also employ various methods of prey capture, including suction, filter, ram, and bite capture, which vary based on the size and shape of the mouth, as well as the species' habitat. For example, pelagic sharks with larger mouths tend to rely on ram or bite capture, while demersal sharks often utilize suction capture due to their smaller mouths.

Additionally, the differences in swimming strategies among shark species reflect their ecological needs. For example, pelagic sharks like the thresher have elongated tails adapted for high-speed swimming, while benthic species like nurse sharks use pectoral fin undulation to move slowly along the ocean floor. The variation in muscle function between red and white muscle fibers also plays a role in swimming and migration. Red muscles, used for long-distance swimming, are aerobic and have a high capacity for endurance, whereas white muscles are anaerobic and are suited for short bursts of speed. This anatomical flexibility enables sharks to adapt to various ecological roles, from continuous swimming in open water to slow, deliberate movements in complex habitats.

In terms of reproduction, sharks exhibit a range of strategies, including oviparity, viviparity, and ovoviviparity. Many sharks practice viviparity, where embryos develop internally and receive nutrients from the mother, while others, such as skates, lay eggs that hatch externally. In some cases, like the sand tiger shark, embryos may engage in oophagy, eating other embryos to ensure survival. The diversity in reproductive strategies reflects the adaptability of sharks to different environmental pressures, such as resource availability and predation risk.

Overall, this class has provided a deep understanding of the unique anatomical and behavioral traits that define sharks, rays, and skates, shedding light on their evolutionary adaptations and ecological importance in marine ecosystems.