Predator & Prey

Interactions between marine predator and prey species vary at every trophic level in the surrounding ecosystem. Both the stability of the trophic level and the community depend heavily upon these interactions and the total abundance of all predator and prey species in the food chain. As seen across the seven seas, changes in abundances of species in any trophic levels have a great effect on the ecosystem as a whole. Lower trophic levels are composed of mainly detritivores, who are responsible for recycling nutrients in the ecosystem. Higher trophic levels include consumers and apex predators. The trophic level system as a whole works together and is of utmost importance to community structure and balance among all levels. Changes in abundance of higher trophic level species of predators can impact the profusion of their prey at lower trophic levels, causing a cascade of events that takeover the ecosystem and are detrimental to balance in the community. One example of this effect is shown off the Pacific coast in the 1900s where sea otter populations severely diminished due to overhunting for the fur trade. As the populations of sea otters diminished, the abundance of their main prey source, sea urchins, experienced unrestrained growth. The immense populations of sea urchins devastated local kelp and algal supplies, creating colossal issues for primary production, nutrient recycling, habitat degradation, and coastal erosion in this ecosystem. Subtle changes to predator and prey relationships can cause severe effects that resonate throughout the entire marine community. Consequently, understanding these relationships may provide beneficial information about ecosystem heterogeneity which may aid in protecting and conserving biodiversity in these fragile marine systems.

Ecosystem heterogeneity is controlled by various factors, living and nonliving, throughout marine environments. Although the factors controlling ecosystem heterogeneity fluctuate based on varying locations and conditions, studies have revealed patterns in the processes of marine organisms in maintaining the diversity of ecosystem arrangements. Almost all ecosystems have been modified or controlled by a single species and their existence may be traced back to the dependence upon a single organism. Apex predators are prime examples of organisms that aid in preserving heterogeneity. As the top tier of the food chain, apex predators control the balance and efficiency of the trophic levels underneath them. Sharks are amazing apex predators that act as the doctors of the sea, or the white blood cells of the sea, that kill of the sick, weak, dying, and injured so that the strong individuals have more resources and therefore can survive and reproduce. This removal of the weak and sick species in lower trophic levels helps maintain the ecosystem’s overall health. Shark’s ecological role is to maintain strong and healthy ecosystems and not let sickness and disease overrun the population of species in lower trophic levels. Without sharks in our global ecosystems, there would be a detrimental chain reaction felt in every level of the food chain. Lower trophic level organisms would become uncontrolled and consume too much of their prey, leaving an insufficient amount of food for survival and this cascade of events would eventually reach every level of this complex food chain.

Other than ecosystem balance, health, and population control, sharks also maintain proper nutrient recycling in our oceans. We get 70% of oxygen from the ocean, thus ocean health is vital to human health. Sharks are necessary for ecosystem heterogeneity, healthy fish populations, food webs, trophic level systems, whole ecosystems, and the world’s oxygen supply. Therefore, sharks are a necessity and demand protection and preservation in our oceans.

The Overfishing of Sharks

In order to properly understand and conserve any aspect of marine life, the demographic and diversity of a species or ecosystem must be studied. Sharks are among the top apex predators in the ocean and provide scientists with various outlooks on an ecosystem’s trophic networks, health, and biodiversity. These aspects are associated with shark populations due to the elasmobranch’s importance as keystone species in marine ecosystems, meaning that they protect the diversity of a food chain by maintaining levels of predatory fishes and thus, every organism at every trophic level. Without sharks, food chains would collapse, and biodiversity would be lost. At every trophic level, the consumption by a predator species keeps the populations of prey species in check, but without a top apex predator, such as sharks, each level would be left unrestricted. Thus, the target species of sharks would be plentiful and soon take over their prey species in the trophic level below them, wiping them out and contributing to a cascade of this effect at every level. This trophic cascade, and depletion of shark populations as a whole, has been seen throughout ecosystems across the globe due to finning, overfishing, pollution, and habitat loss.

The oceans’ biodiversity is under immense threat from marine pollution and habitat loss, but the most ominous is arguably the overarching effects of overfishing. Overfishing is detrimental to marine landscapes due to fishing tactics, such as longlining, that ruin fragile habitats. Lines, nets, and other fishing-related debris are also among the top contributors to ocean pollution, contributing to over half of the plastic pollution found in the Great Pacific Garbage Patch. In addition, overfishing noticeably facilitates the immense loss of fish species biodiversity and population sizes and impacts species that interact with those target species in marine ecosystems. Thus overfishing, apex predator or not, is arguably one of the worst contributors to marine community degradation and loss of biodiversity.

The key to protecting against the overfishing of any apex predator is to understand the species at risk. To successfully conserve and protect vulnerable ecosystems and marine organisms from overexploitation and loss of biodiversity, their migrations, reproduction periods, and risk factors need to be understood. For many species of sharks, much research has been done to understand their migratory patterns, where and why they are at risk, and their common reproduction grounds. Migration to warmer waters during autumn and winter seasons is common in several species of sharks in the Pacific waters because most sharks are ectotherms; meaning they need to be in warm temperatures to regulate their body temperatures. Certain nomadic patterns of several species of sharks suggest that some yearly migrations to warmer southern waters might be due to mating tendencies and nursery purposes. Studies suggesting shark migrations to various known nurseries and mating grounds surrounding the Hawaiian Islands by specific species such as the Scalloped Hammerhead Shark and Galapagos Shark have been recorded for several years. These migrations aimed at reproductive purposes are vastly significant for conservation resolves due to the increased risk that the influx of populations of both adult and juvenile sharks face in mating and nursery areas.

Marine Protected Areas are locations in which fishing and hunting are banned so that the species there can mate, reproduce, and live significantly less affected by human life than in other areas around the world. The implementation of MPAs in the Pacific could help the shark population on the mend and create a healthier and more sustainable ecosystem overall. The Hawaiian Islands are home to many small conservation areas such as Hanauma Bay and many restricted fishing areas along the coasts but implementing major MPAs could significantly benefit Hawaii’s local marine life even further. The implementation of Papahānaumokuākea Marine National Monument has helped heal and maintain amazing biodiversity in the remote Pacific region. Conserving and protecting more local waters should be of utmost importance to our local government to help save and heal our local ecosystems and marine life populations that face threatening and injurious factors every day.

How do sharks communicate?

Imagine everyone is armed with a lethal weapon and no one can audibly speak, how would we communicate? For sharks, this is the reality.

Research shows that sharks cannot audibly make noise, and therefore do not communicate through sound. Scientists have not yet found an organ in sharks that is capable of producing sound, thus their communication is limited to other methods. Through extensive research, various ways of interaction have been revealed in shark species. Most species communicate through territorial body language. Territorial body language is defined as using powerful movements and behaviors to convey dominance. Body language is a shark’s way of “talking it out,” (Ocean Ramsey, ‘What You Should Know About Sharks’). They demonstrate various signals and display certain body language to establish dominance in the water column and communicate with one another.

Within the water column, sharks display a strict social hierarchy. This hierarchy poses different levels of dominance based on the structure and place of sharks within the water column. The most dominant individuals assert themselves highest in the water. The more submissive individuals are deeper in the water. The dominant species swim closer to the surface and practice many behaviors to maintain this dominant role. This behavior relays to other individuals by preserving their space as the highest individual in the water column. However, the hierarchy and placement of sharks can change at any given time, and various behaviors can influence and challenge the dominance of individuals.

Some of the displays sharks use to challenge one another and decide dominance in the water include various swimming patterns. For sharks, swimming patterns and behaviors are of great importance to communicate, as they cannot audibly make a sound. Some of the swimming behaviors commonly seen in shark species include Parallel Swimming, following, and piggybacking. Parallel Swimming is the action in which two sharks swim next to each other to size each other up and see who is larger. The larger shark is usually established as being more dominant, but every scenario can vary, and sharks can display more aggressive behavior even if smaller in size. Following is another swimming pattern that includes a more dominant shark following closely behind a more submissive shark to push the shark out of its space. This is similar to tailgating someone on the freeway after being frustrated with driving behind that person. Following happens quite frequently in the water column and can occur out of annoyance or intimidation. The third swimming pattern is called piggybacking. This shark’s behavioral pattern establishes dominance over another shark through physically communicating the established social hierarchy in the water column. The more dominant sharks are higher in the water with more submissive species deeper in the water. Piggybacking refers to this shark hierarchy by intentionally establishing dominance over another shark by physically going on top of the more submissive shark to push that shark deeper into the water and further submit to the above shark in the social hierarchy. These behaviors use space, physical contact, and swimming patterns to maintain the pyramid structure in the ecosystem.

Although some species of sharks may prefer solitude, when seen in schools, they resort to these patterns and behaviors to assert their position in the water with unfamiliar individuals. Again, sharks do not have a sensory organ capable of making sound, thus they cannot speak or communicate through noises. Species-to-species interactions often involve these swimming patterns because they are one of the most resourceful ways to communicate as individuals vary in the ecosystem. Communication through body language is commonplace in shark behavior. Hence the importance of your body language when diving with sharks!