Impacts of Fishing on Ecosystems & Trophic Structure

Impacts of Fishing on Ecosystems & Trophic Structure

1. Changes in fish communities (inc. benthic)

   • Changes in community structure - k vs r selected
   • Changes in diversity - some species more vulnerable to fishing

2. Large size top piscivorous predators more valuable - lower value smaller herbivorous species

   • Reflected in global landings statistics
   • Fishing down the food web

3. Reduction in predatory pressure leads to increase in prey populations (if top down)

   • Spiny lobster couldn't control urchins anymore due to being heavily fished. Explosion of urchins, so doesn't allow kelp to regrow after winter storms.
   • Keystone species - ecosystem forming species - potential loss of whole ecosystem

4. Reduction in competitive pressure

   • Increase in competitive species
     • E.g. Jellyfish population in Black Sea
   • Dramatic shifts in community structure

5. Local organic enrichment - discards and trawler damaged animals

   • Increases in scavenging species
     • E.g. crabs
   • Anoxia - not a massive issue
   • Increase in seabird numbers
     • Some species benefit by feeding on discards