The ocean covers more of the Earth's surface than anything else.

71% of the planet is covered in water and 74% of the planet's species are aquatic. (Universe Today)
 

Healthy, balanced oceans are essential to all life on Earth.

Phytoplankton are the basis of the marine food web, producing at least half of the world's oxygen. (Nat Geo)
 

Our oceans are currently in peril.

Of the seventeen primary fishing stocks worldwide, all are either overexploited or on the verge of collapse. (UN FAO)


Sec. 1

How does fishing harm our oceans & environment?

Fishing greatly interferes with the delicate balance of the marine food web, impacting the ocean's ability to act as a climate-healing carbon sink.

This interference affects phytoplankton, the basis of the marine food web that produces 80% of the world's oxygen.

2006 research extrapolates that there may soon be no more so-called commercial fish stocks left in the sea, with the last due to be lost by 2048. What would that mean for humanity?:

But the issue isn't just having seafood on our plates. Ocean species filter toxins from the water. They protect shorelines. And they reduce the risks of algae blooms such as the red tide. (CBS News)

The marine animals people want to eat are not the only victims:

  • Bycatch - Around the world, "animals including sea birds, dolphins, penguins and sea lions are routinely ending up in commercial fishing nets along with the intended catch." Also: "The fisheries do not deny there is bycatch and that endangered animals do fall victim." (BBC)
     
  • Additional carnage - And just like wild animals viewed as threats to/competition for "livestock" are deliberately killed, so are marine animals viewed as competitors for our target fish, some even driven to extinction for this reason such as the Caribbean monk seal. This carnage adds to that of the trillions of captured target and bycatch marine animals. (Encyclopedia.com)
     
  • Cattle of the sea - Did you know that "sustainably" caught tuna has a worse climate impact than any other animal protein except beef? (New Scientist)
     
  • Great Pacific Garbage Patch - A study published in Scientific Reports finds the most of the 79,000 metric tons of plastic in the humongous patch is actually abandoned fishing gear (nets, ropes, traps, crates, baskets and more)—as opposed to plastic bottles or packaging. (National Geographic)
 

Scientists estimate the following figures:

  • 160 million – tons of fishes (amounting to many trillions of individual animals) pulled from the oceans in 2012 (The World Bank)
     
  • 90% – amount of all large predator fish that have been wiped out by fishing
    (Research published in the journal Nature)
     
  • 650 thousand - number of whales dolphins and seals killed by fishing vessels (Ocean report "Wasted Catch")
     
  • 100 million – number of sharks caught and killed each year globally due to bycatch, illegal fishing and the persistent demand for shark fins (Ocean report "Wasted Catch")
     
  • 2.7 trillion – number of fish taken from the seas every year (UN FAO, 2012)
     
  • 40% – percentage of those fish that are discarded as bycatch (Davies et al, 2009) 
     
  • 37 - 50%+ - percentage of those fish that are used to feed so-called livestock (see below)
     
  • 140 - amount of ocean species listed as endangered, threatened, or near threatened by extinction (Ocean Preservation Society)
     
  • 100% - percentage of the world's major "fishing stocks" that are either overexploited or on the verge of collapse (UN FAO)
 
 
...animals are being pulled from our oceans faster than ever before. Dropping shark populations could spell big trouble for the ocean ecosystems so crucial to life on Earth.
— National Geographic, "Sharks Falling Prey To Humans' Appetites"
 
Massive extraction of fish species from our oceans is taking place in order to supply our ever-increasing demand to eat them.
— Richard Oppenlander, researcher
 

Large predator fish in the ocean

90% of all large predator fish have been wiped out by fishing and only 10% remain. Source: The cover story of the May 15, 2003 issue of the international journal Nature

The fate of aquatic animals killed by fishing

40% of the fish snatched from their ocean habitats are then discarded as (dead) bycatch. Source: Davies et al, 2009
 
I think the point is there is nowhere left in the ocean not overfished.
— Ransom Myers, a fisheries biologist at Dalhousie University in Halifax, Nova Scotia

Sec. 2

Is fish farming better?

 

Fish farming threatens freshwater and ocean health, marine life, and human biosecurity in the following ways:

  • Threats to marine life: 
     
    • Pollution of surrounding water by concentrated waste and uneaten food pellets occurs, smothering plants and animals on the seafloor.
       
    • Diseases and parasites—common occurrences in crowded pens—can be spread to wild fish.
       
    • Pesticides and antibiotics used to control those diseases and parasites can be discharged into the environment, also impacting local species.
       
  • Threats to human biosecurity

    Frequent application of chemical treatments add to the emergence of antibiotic-resistant bacteria can affect our ability to treat human diseases.

    (Source for above facts: Monterey Bay Aquarium)

As one example of biosecurity threats, Oceana reports that Chile's salmon farms may use more antibiotics than any other meat industry, while Bloomberg reports of a massive "spill" on such a farm of nearly a million salmon. Marine Harvest recorded 15 farmed fish escape incidents worldwide in 2017, totaling 23,223 fish.

Fish farming is also inherently inefficient because it relies on secondary consumption of food.

It takes a lot of input in the form of other fish to farm the kind of fish people prefer to eat directly. For example:

  • It takes more than 4 times the amount of smaller pelagic or open-ocean fish to create just 1 kg of high-protein fishmeal, which is then fed to farmed fish (along with fish oil, which also comes from other fish).
     
  • It takes about 20 kg of such feed to get 1 kg of tuna ready for a sushi bar near you.

(Source for above facts: TIME magazine)

 

Pounds of fish used to make fishmeal to feed farmed fish

Per TIME Magazine, it takes 4.5 kg (10 lbs.) of smaller pelagic, or open-ocean fish to create 1 kg (2.2 lbs.) of high-protein fishmeal, which is then fed to farmed fish (along with fish oil, which also comes from other fish). It takes about 20 kg (44 lbs.) of such feed to get 1 kg of tuna ready for a sushi bar near you.
Factory fish farming — also known as aquaculture — is generally big, dirty, and dangerous, just like factory farming on land. Around half of the seafood eaten in the entire world comes from these types of facilities as producers attempt to produce fish as cheaply as possible.
— Food and Water Watch
 

Not surprisingly, the most comprehensive analysis to date of the damage farming does to the planet found that freshwater fish farming has a much larger environmental impact than often assumed:

You get all these fish depositing excreta and unconsumed feed down to the bottom of the pond, where there is barely any oxygen, making it the perfect environment for methane production [a potent greenhouse gas].
— Jospeh Poore, Oxford University (lead researcher of above study)

Sec. 3

How does land-based animal agriculture affect the oceans?

In an extra bizarre unnatural food chain that results in a negative feedback loop, both ocean and farmed fish are now fed to farmed land animals that would normally never set foot in the ocean, and the runoff from those land animals then pollutes the oceans and other bodies of water.

As noted above, fish are fed to farmed fish, but they're also fed to animals farmed on land as well. Like all secondary consumption, feeding animals and then eating the animals is an inefficient way to produce food and accounts for significant losses of calories, protein and more. Yet the percentage of fish fed to farmed land animals appears to be somewhere between 37% (UBC Fisheries Centre) to more than 50% (Endangered Wildlife Trust). Somewhere in the middle:

  • 45% – Approximate percentage of the global production of fishmeal and fish oil going to the world's so-called livestock industry, mostly pigs and so-called poultry. (TIME)

The waste from the land animals who are fed fish, in turn, negatively impacts the oceans and their sealife.

Per iconic marine biologist Sylvia Earle's project Mission Blue, animal waste doesn't stay on farms, and animal production contributes directly to sea temperature rise and ocean acidification.

  • Manure lagoons - Huge open-air waste lagoons ("manure lagoons") often as big as several football fields, are prone to leaks and spills.
     
  • Algal blooms - Nutrients in animal waste (including ammonia, a toxic form of nitrogen) cause algal blooms, which use up oxygen in the water, contributing to ocean “dead zones.”
     
  • Ocean acidification - Animal agriculture is a large source of GHG emissions, which raise global ocean temperatures and lead to coral bleaching and reef die-off. Additionally, these emissions in the atmosphere increase ocean acidity.
 
The largest marine predator on earth is now the cow, with over half the fish catch serving as fish meal feed for domestic livestock.
— Endangered Wildlife Trust director Dr. Nick King
 

What about "sustainable" and "sport" fishing?

Like land animals, the flesh and eggs of marine animals are not nutritional requirements for human beings (and vegan options for fish oil bypass the fish and use the algae the fish eat). The list of fish species considered sustainable is always changing, because the species on those lists then of course become overfished. Additionally, the certification bureaus for fish sustainability are essentially a money-generating sham. Plus, from an ethical perspective, "many fish are long-lived, have complicated nervous systems and are capable of learning complicated tasks." They don't deserve to be torn from their habitats and killed for no vital reason. The solution is not to look for a better way to do the wrong thing, but to stop eating marine animals and agitate for an end to fishing and fish farming.

This world-renowned marine biologist agrees:

 

Make better choices. I personally have stopped eating ocean wildlife because I think they’re more important alive than dead. And I think now is the time to make a serious issue of this.
— Dr. Sylvia Earle, a marine biologist, explorer, author, and lecturer who has been a National Geographic explorer-in-residence since 1998
 
I don’t eat fish because I am an ecologist and I have seen the diminishment of fish in the seas all of my life… people must stop eating fish and stop eating meat that fish are fed to. Our position is based solely on the ecological reality that commercial fishing is destroying our oceans… The problem is that we are in absolute denial and we refuse to acknowledge that by stripping life from the seas, we will be undermining the foundation for our survival on land.
— Captain Paul Watson, Sea Shepard
 

Summary

Our oceans are in peril largely due to consumer demand to eat fishes. Staggering amounts of marine animals are killed both as a direct and indirect result of fishing. This interferes with trophic cascades, which has far-reaching impacts on both land and sea. Fish farming is no better because it poses threats to marine life and human biosecurity while relying on inherently inefficient secondary consumption. Finally, additional damage is caused by feeding wild and farmed fishes to animals farmed on land, whose runoff then pollutes oceans causing dead zones and whose emissions cause ocean acidification. There is no need to consume land or sea animals. Delicious plant-based options use plant protein flavored with kelp powder, and vegan sushi is out of this world.