Marine Science (0697) | Fisheries

Marine Science (0697) Study Notes: Fisheries

Introduction: Why do we study Fisheries?

Hello Marine Scientists! This chapter is all about how humans interact with the ocean to get food—specifically, through fishing. As the global population grows, the way we fish has huge impacts on marine environments, making this one of the most critical topics in the "Human Influences" section.
We will look at the tools we use, the harm they can cause, and, most importantly, the smart strategies we can use to make fishing sustainable so future generations can also rely on the ocean.

6.3 The Importance and Methods of Fishing

6.3.1 Social and Economic Importance

Fishing, or the harvesting of marine organisms, is essential globally for two main reasons:

• Social Importance (Food): Marine organisms are a crucial source of food for billions of people worldwide, providing necessary protein and nutrients.
• Economic Importance (Income): Fisheries provide income and employment for coastal communities and entire countries, from the fishers themselves to processing plants and distributors.

6.3.2 Different Methods of Fishing and Their Environmental Impacts

Fishing methods range from simple lines to massive nets. While efficient, many methods have severe environmental consequences, mainly through bycatch (catching unintended species) and habitat damage.

A. Netting and Trapping Methods

These methods generally use large nets or enclosed structures to capture fish in bulk.

• Cast Netting:

  Method: A circular net is thrown by hand and pulled back.
  Impact: Generally low impact as it is small scale, but can target juveniles if mesh size is too small.

• Trawling (Pelagic and Beam):

  Method: A large net shaped like a cone is dragged through the water (pelagic, or midwater) or along the seabed (beam/bottom).
  Environmental Impacts (Crucial!):

  • Bottom Trawling: This is highly damaging. Think of it like a giant underwater bulldozer. It physically destroys sensitive habitats like coral reefs and seagrass beds, and disrupts sediment, harming benthic (seabed) organisms.
  • Bycatch: Trawling often results in high levels of bycatch, catching non-target species like dolphins, sea turtles, and juvenile fish, which are usually discarded.
• Seine Nets (Purse Seine):

  Method: A large net is deployed around a school of fish. The bottom of the net is then cinched shut, like pulling the drawstring on a purse, trapping the entire school.
  Impact: Very effective at catching schooling fish (like tuna), but can trap large amounts of bycatch, especially when used near Fish Aggregating Devices (FADs).

• Tangle Nets (Gill Nets, Drift Nets):

  Method: Vertical nets set in the water column. Fish swim into the net and get caught by their gills (gill nets) or tangled (drift nets). Drift nets are massive nets allowed to drift freely.
  Impact: Known for extremely high levels of bycatch, including marine mammals, birds, and turtles. Drift nets are sometimes called "walls of death" due to their indiscriminate killing power.

• Basket Traps:

  Method: Static structures (cages or baskets) used to trap bottom-dwelling species like lobsters or crabs.
  Impact: Generally low impact, provided they are not lost (becoming "ghost gear") and are species-specific.

B. Angling Methods

These methods use lines and hooks and tend to be more targeted than nets.

• Line Fishing (Trolling, Longlining):

  Method: Longlining uses a main line that can be tens of kilometres long, studded with thousands of baited hooks. Trolling drags several lines behind a slow-moving boat.
  Impact: Longlining has severe bycatch issues, especially affecting seabirds (who dive for the bait) and sea turtles.

• Rod Fishing (Pole and Line, including Bait Fishing):

  Method: Fishers use poles or rods to catch fish individually.
  Impact: Very selective and has minimal bycatch or habitat damage, making it one of the most sustainable methods.

6.3.3 Navigational Aids in Modern Fishing

Modern fishing vessels use technology to maximize efficiency. These navigational aids help boats locate fish, find their way, and avoid hazards.

• Chart / Compass / Compass Rose: Used for basic direction, plotting courses, and knowing the vessel's location relative to land or fishing grounds.
• GPS (Global Positioning System): Provides highly accurate location (latitude and longitude coordinates), essential for navigating and returning to rich fishing spots.
• Sonar: Uses sound waves to detect objects underwater, primarily used to locate schools of fish or map the seabed (especially important for bottom trawling).
• Radar: Uses radio waves to detect objects above the water surface, helping vessels navigate safely, especially in fog, and avoid collisions with other boats.

Did you know? While navigational aids increase safety and efficiency, they also contribute to the problem of overfishing, as fishers can find and track smaller and smaller populations of fish with ease.

6.3.4 & 6.3.6 The Crisis of Unsustainable Harvesting

The Threat of Over-harvesting

The core problem facing marine fisheries is unsustainable harvesting. As the human population increases, so does the demand for seafood. This pressure means fisheries are in danger of being over-harvested.

A resource or activity is sustainable if we can continue to use it at the current rate without:
1. Causing damage to the environment.
2. Causing the resource to run out.

If we fish unsustainably, fish stocks decline sharply and eventually collapse, meaning future generations will not have fish.

Impacts on Food Chains

Sustainable harvesting is essential to maintain fish stocks at levels that do not affect food chains.

If we remove too many fish (especially those high up in the trophic levels, like sharks or tuna), it destabilizes the entire ecosystem (a process called trophic cascade). For example, if we remove all the predators, the population of their prey (say, smaller fish) explodes, which in turn wipes out the primary consumers (zooplankton), affecting the producers (phytoplankton).

Key Takeaway: Sustainable fishing protects the harvested species AND the whole ecosystem it belongs to.

6.3.5 Strategies for Sustainable Harvesting

To combat overfishing and ensure marine resources last, governments and international organizations implement various strategies. These aim to manage the *what*, *when*, and *where* of fishing.

1. Restricting Boat Size, Net Types, and Mesh Size:
   • How it helps: Limiting net mesh size ensures that juvenile (small) fish can escape and reproduce before being caught. Limiting boat size restricts the amount of gear a boat can carry, reducing fishing effort.
   • Evaluation: Effective locally, but difficult to monitor globally, and fishers may use nets illegally.
2. Quotas and Licences:
   • How it helps: A quota is a limit on the total weight or number of fish that can be caught in a season (the Total Allowable Catch). Licences control who is allowed to fish and where.
   • Evaluation: Directly controls the *volume* of fish removed. However, quotas can lead to "discarding" (throwing dead fish overboard once the quota is reached) if rules are poorly enforced.
3. Closed Seasons:
   • How it helps: Fishing is banned for a specific period, usually during the species’ peak breeding or spawning season. This ensures that the fish can reproduce, replenishing the stock.
   • Evaluation: Very effective for species with clear, predictable breeding cycles.
4. Marine Protected Areas (MPAs):
   • How it helps: These are specific ocean zones where fishing is restricted or banned entirely. They serve as nurseries and refuges, allowing fish populations to recover and grow larger. These bigger, healthier fish then spill out into surrounding waters.
   • Evaluation: Highly effective for conservation and habitat protection, but can cause conflict with local fishers who rely on those specific areas for income.
5. International Agreements:
   • How it helps: Because fish migrate across international borders, countries must cooperate. These treaties set shared quotas and management rules for species like tuna and whales, ensuring global effort toward conservation.
   • Evaluation: Essential for species that migrate long distances, but success relies entirely on countries keeping their promises and enforcing the rules.

6.3.7 Fish Aggregating Devices (FADs)

What are FADs?

A Fish Aggregating Device (FAD) is simply a man-made or natural floating object placed in the ocean to attract fish. It could be a raft, a buoy, or even old netting.

The Principle of FADs

The principle is based on marine ecology: many open-ocean fish (like tuna, dorado, and sharks) naturally gather around floating objects (like logs or debris) for shelter, food, or navigation. FADs mimic this natural aggregation point, making it easier for fishers to locate and harvest large schools.

Ecological Impacts of FADs (The Discussion)

While FADs make fishing hyper-efficient, they come with significant ecological drawbacks:

• Negative Impacts:
  • Increased Bycatch: Because FADs attract *all* types of marine life—not just the target species—the use of purse seine nets around FADs results in very high bycatch of non-target fish, turtles, and juvenile sharks.
  • Targeting Juveniles: Often, the fish that aggregate under FADs are juveniles (young fish) that have not yet reached reproductive age. Catching them before they reproduce harms future stock recovery.
  • Ghost Fishing: If FADs are abandoned, they can continue to trap and kill marine life, becoming a form of marine pollution.
• Mitigation (How to make them better):
  • Using FADs that are biodegradable (made of natural fibres) to reduce plastic pollution.
  • Using electronic tags to track the FADs so they don't get lost.