🌊 Environmental Management (0680) Study Notes 🌊

Topic 5.3: Impact of Exploitation of the Oceans

Hello future Environmental Manager! This section is all about understanding the consequences of humanity’s huge appetite for ocean resources, especially fish. While oceans seem endless, our actions have serious impacts. Understanding these problems is the first step toward finding sustainable solutions!

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Section 1: The Problem of Exploiting Fisheries

When we talk about 'exploitation' of the oceans, we are mainly focusing on commercial fishing—taking fish, crustaceans (like shrimp), and molluscs (like squid) from the wild.

What is Exploitation?

Exploitation means using a resource. If we don't manage this use properly, it leads to significant environmental damage.

Key Impact 1: Overfishing of Marine Species

Overfishing occurs when fish are caught at a rate faster than they can naturally reproduce to replace the stock. Think of it like a bank account: if you withdraw money faster than you deposit it, you will eventually run out!

  • Stock Depletion: The number of fish in the ocean drops drastically. Many commercial stocks (like Atlantic Cod) have collapsed in certain regions.
  • Collapse of the Fishery: Once the stock falls below a certain level, it is no longer economically worthwhile for fishermen to target that species, leading to job losses and economic hardship.
  • Loss of Biodiversity: Removing large quantities of certain species disrupts the entire food web. If a top predator is fished out, its prey species may increase uncontrollably, throwing the ecosystem out of balance.

Quick Review Box: The biggest consequence of uncontrolled fishing is overfishing, leading to stock depletion.

Section 2: Wider Impacts of Fishing Methods

Fishing doesn't just reduce the number of target species; the methods used can harm non-target species and entire ocean habitats.

1. Effect on Target Species

Even when a species isn't completely fished out, overexploitation causes problems for those that remain:

  • Catching Juveniles: Many nets or trawls catch young, small fish (juveniles) before they have had a chance to breed even once. This severely limits the population’s ability to recover.
  • Reducing Size and Age: Fishing often targets the largest and oldest fish (the ones that breed most successfully). By removing the best breeders, we effectively weaken the genetic quality of the remaining population. The fish left are smaller and less resilient.

2. Bycatch and Non-Target Species

This is a massive problem. Bycatch refers to any species that is accidentally caught during the fishing process but is not the target species. These creatures are usually thrown back, often dead or dying.

Common Examples of Bycatch:
  • Marine Mammals: Dolphins, porpoises, and whales often get tangled in large drift nets or gill nets and drown.
  • Sea Turtles: Turtles are frequently caught in trawl nets, especially those used for shrimp fishing.
  • Seabirds: Birds like albatrosses are caught on longlines when they dive for bait.
  • Non-commercial Fish: Small sharks or rays are often caught and discarded because they have no market value.

Imagine catching 100 tuna but accidentally killing 5 sea turtles and 2 dolphins in the process—that’s bycatch in action.

3. Damage to Marine Habitats

Certain destructive fishing practices physically damage the seabed environment.

  • Bottom Trawling: This involves dragging large, heavy nets (trawls) along the ocean floor. The gear scrapes and crushes everything in its path, permanently destroying fragile, slow-growing ecosystems like deep-sea corals and sponge gardens.
  • Dynamite Fishing: (Illegal but still practiced) Explosives are used to stun or kill fish, but this totally obliterates local coral reefs—the 'rainforests' of the ocean.

Memory Trick: Remember the three 'Bs' of destructive impact: Bycatch, Breeding disruption, and Bottom trawling damage.

Section 3: Farming Marine Species (Aquaculture)

One major strategy to reduce the pressure on wild fisheries is to farm marine species, a practice known as aquaculture or mariculture.

How Aquaculture Reduces Exploitation

The core benefit of marine farming is simple: it supplies seafood without relying on catching wild fish.

  • Reduced Catch Effort: By growing species like salmon, shrimp, and mussels in controlled pens or ponds, the need for fishing boats to exploit wild stocks decreases significantly.
  • Market Supply: It meets the high global demand for seafood, stabilizing prices and ensuring food security, while giving wild populations a chance to recover.

Did you know? Over half of all seafood consumed globally now comes from aquaculture, showing its success in supplying the market!

Evaluating Aquaculture: The Trade-Offs

While aquaculture helps stop overfishing, it introduces its own set of environmental challenges. We must weigh the benefit (less pressure on wild fisheries) against the disadvantages:

Environmental Disadvantages of Marine Farming:
  1. Pollution: Fish farms produce large amounts of waste. This includes uneaten food, fish faeces, and chemicals (like antibiotics used to keep the densely packed fish healthy). This waste flows into the surrounding ocean, leading to eutrophication (excessive nutrient enrichment) and damage to local habitats.
  2. Disease and Parasites: Because fish are kept at high densities in pens, diseases and parasites (like sea lice) spread very quickly. These can escape and infect vulnerable wild fish populations.
  3. Habitat Destruction for Siting: Many prawn and shrimp farms are built by clearing sensitive coastal habitats like mangrove forests. Mangroves are vital nursery grounds for many wild fish and act as natural sea defences.
  4. The Feed Problem (Carnivorous Species): This is a critical point. Farming carnivorous fish (like salmon) requires feeding them fishmeal and fish oil, which are made from wild-caught forage fish (like anchovies or sardines). If it takes 3 kg of wild fish to grow 1 kg of farmed salmon, we haven't truly reduced the overall exploitation of the oceans!

Don't worry if this seems tricky at first! Just remember that Aquaculture is a trade-off: it solves the problem of overfishing but creates new problems related to pollution and habitat loss.

Key Takeaways Summary

Impacts of Exploitation:

Overfishing leads to stock collapse and reduced breeding success.
Bycatch kills non-target species like dolphins and turtles.
Destructive methods (like bottom trawling) destroy critical habitats.

Mitigation (Aquaculture):

Farming marine species reduces exploitation of wild stocks.
However, farms can cause pollution, spread disease, and destroy coastal habitats (like mangroves).