What Is Bycatch?
Bycatch refers to the unintended capture of non-target marine species—like dolphins, turtles, seabirds, and juvenile fish—by commercial fishing gear such as trawls, longlines, gillnets, and drift nets [oai_citation:0‡oceana.org](https://oceana.org/wp-content/uploads/sites/18/bycatch_final1.pdf?utm_source=chatgpt.com).
How Much Marine Life Dies?
- Up to 40% of global catch—around 63 billion pounds of fish—is discarded annually .
- Shrimp trawling alone discards 5.7 kg of bycatch per kg of shrimp on average, and up to 20:1 in some tropical fisheries .
- Over 650,000 marine mammals die each year due to bycatch globally .
- 300,000 whales and dolphins drown annually entangled in fishing gear .
- 100,000 seabirds (e.g., albatrosses) die yearly on longlines .
- 100 million sharks killed each year from fishing and bycatch .
- Drift nets discard 27 million tons of fish annually .
Damage to the Fish We Eat
When so much non-target fish is killed and discarded, it undermines wild fish stocks. Bycatch reduces recruitment of younger fish and skews population structures—making fisheries less sustainable and forcing people to rely on fewer species or farmed fish .
Ocean Oxygen and Air Quality
Oceans generate nearly 50% of Earth’s oxygen and sequester carbon. Destructive fishing like bottom trawling releases 370 Mt CO₂ annually—about Germany’s emissions—and destroys sediment-based carbon sinks . Decomposing discarded life also consumes oxygen in localized “dead zones,” reducing marine productivity and, indirectly, global oxygen output.
Why It Matters for Us
Less oxygen production and more CO₂ emissions from the ocean worsen air quality and climate change. Meanwhile, dwindling fish stocks threaten global food security and marine ecosystems that filter pollutants and support coastal communities.
What Can Be Done?
- Use bycatch reduction devices (e.g., turtle excluders, bigger mesh nets) [oai_citation:1‡sciencedirect.com](https://www.sciencedirect.com/science/article/pii/S0308597X23000490?utm_source=chatgpt.com).
- Establish no-trawling zones—especially in marine-protected areas .
- Use best practices: streamer lines, night setting of longlines, and no discard policies .
- Adopt ecosystem-based fishery management to balance catch and conservation.
Key Data at a Glance
| Metric | Annual Estimate | Source |
|---|---|---|
| Bycatch (global) | 40% of total catch (~63 billion lb) | turn0search11 |
| Shrimp trawl bycatch ratio | 5.7 kg per 1 kg shrimp (up to 20:1) | turn0search13 |
| Marine mammals killed | ≥650,000 | turn0search6 |
| Whales & dolphins drowned | ≈300,000 | turn0search5 |
| Seabirds killed | ≈100,000 | turn0search2 |
| Sharks killed | ≈100 million | turn0search0 |
| Fish discards (drift nets) | 27 million tons | turn0search12 |
| Bottom trawl CO₂ emissions | 370 million tonnes | turn0search14 |
References
- Bycatch definition & impacts: IFAW, NOAA, Wikipedia. (turn0search0, turn0search1, turn0search13)
- Species death estimates: FAO, IWC, Center for Biological Diversity, CounterPunch. (turn0search3, turn0search5, turn0search6, turn0search2)
- Global bycatch & shrimp ratios: Wikipedia. (turn0search11, turn0search13)
- CO₂ from bottom trawling: Wikipedia. (turn0search14)
- Mitigation & no-trawl zones: Science Direct, IFAW, news report. (turn0search7, turn0search13, turn0news10)