Fisheries harvest marine organisms across habitat types. While fisheries do generate food and profit, they could be doing much more harm than good for underwater ecosystems. The film Cowspiracy makes a convincing case for the deleterious affect that large-scale fishing operations have on aquatic habitats, species variety and species abundance. Cowspiracy paints modern fishing as a largely unsustainable industry that may lead to fishless oceans before 2050.
Fishing As Depicted By Cowspiracy
Fish and other marine life are mostly hunted as food. However, some species are used for other commodities. Sharks, for example, are sometimes hunted for their skin which can be used in the making of leather. Other species like whales and manatees are regularly harmed or killed unintentionally by getting caught in fishing nets. The Cowspiracy Facts page sites a Food and Agriculture Organization (FAO) document which states that in the year 2017, between 51 – 167 billion farmed fishes had been killed for food. That same year an estimated 250 – 600 billion crustaceans were also farmed and killed for food.
Even animals that are not eaten by humans are caught and killed inadvertently because of drift netting or trawling. Susan Hartland of Conservation Society says that animal populations are being extracted from oceans more quickly than they can recover. Marine species are therefore collapsing under the immense pressures of modern hunting. The unintended catches, sharks, sea turtles and dolphins, are referred to as bykill.
Keystone Species and Trophic Cascades
Apex predators often act as keystone species, meaning that they have disproportionately large effects in their natural environments. This makes the removal of sharks particularly concerning. As top predators, many sharks species exert top down influence in their respective food webs. The removal of sharks, and other keystone species increases trophic cascade risks. Trophic cascades are the ecological chain of events triggered by the removal or addition of top predators.
Agriculture, Fishing and Algae Blooms
“Livestock operations on land have created more than 500 nitrogen flooded dead zones around the world in our oceans…” According to Dr. Richard Oppenlander, an environmental researcher featured in the Cowspiracy film. Water pollution comes in the form of pesticides, herbicides, heavy metals, plastics and other waste material. However, animal agriculture is the leading cause of ocean pollution – a fact which is stated explicitly in the Cowspiracy film. Animal agriculture run-off upsets nutrient balances in aquatic ecosystems by introducing phosphorus, nitrogen, manure and potassium from chemical fertilizers. These excess nutrients can cause alae blooms, leading to uninhabitable zones for marine species. Blooms of algae drain sunlight and deplete oxygen levels – making the environment unsuitable for most other lifeforms in the ecosystem.
Bottom trawling contributes to inhabitable zones similarly. Bottom trawling, also referred to as “dragging” involves casting a fishing net to the sea floor. Trawling disturbs sediments along the sea floor which causes carbon to be released. Once carbon dioxide is released from sediments, it is then absorbed by ocean seawater. Elevated carbon levels allow water to trap in more heat and further facilitate algae and plant overgrowth.