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Understanding Nekton: Importance, Distribution, and Ecology

Explore the characteristics, vertical distribution, and ecological impact of nektonic organisms like squid, krill, and marine reptiles. Learn about squid fisheries, krill fishery, and the issues associated with drift-nets.

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Understanding Nekton: Importance, Distribution, and Ecology

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  1. 015d Nekton

  2. Nekton Organisms capable of swimming against a current

  3. General characteristics of nekton • Larger body size • Greater swimming power • Most nekton animals are vertebrates, and most vertebrates are fish • Only the squid and a few species of shrimps are truly nektonic invertebrates • Few reptiles (turtles and sea snakes), birds (penguin) and mammals

  4. Importance of Nekton • Large nekton can profoundly influence marine communities • Important in current or historical harvests • Fishes of critical importance to world food supply

  5. Vertical distribution • Epipelagic countershading • Countershading: a nektonic organism is bicolored, dark above and light below • Holoepipelagic: shark, tuna, ocean sunfish • Meroepipelagic: herring, salmon

  6. Morphological features of nekton at different vertical zones • Mesopelagic • Seldom exceed 10 cm • Equipped with well developed teeth and large mouth • Large light-sensitive eyes, uniformly black • Photophores: light-producing organs • Abyssalpelagic • Species-specific pattern of photophores • Small with flabby, soft, nearly transparent flesh supported by weak bones • Oversized mouth

  7. Major zones of life in a marine ecosystem

  8. Nektonic Crustacea • Pelagic crabs and shrimp • Larger euphausiids • Antarctic Krill (Euphausia superba) • 5-6 cm long • Dominant food of baleen whales • Increased fishery for livestock and poultry feeds

  9. Euphausia superba

  10. Who eats Krill?

  11. Krill & the Antarctic Food Web Critical components of Antarctic food webs

  12. Krill Fishery • Annual consumption by natural predators = 470 million MT • 1972: Japan and Russia began harvesting krill

  13. Krill Fishery… • Potential harvest = 25-30 million MT/yr • Economic cost of fishery high • Patchy distribution complicates location • Depths may be 150-200m • Single net haul may collect 10 MT • Ecological consequences of removal poorly understood

  14. Squids • Large size range: cm … > 20 m • Giant squid (Architeuthis): largest invertebrate • Water jet propulsion • Highly maneuverable and agile • Up to 10 m/s • Predators consuming 15-20% body mass per day

  15. Giant Squid (Architeuthis dux) • One of the largest marine predators • Little is known about their ecology • Diet: deep-sea fishes, orange roughy, hokie • Rapid growth: full size in 3-5 years with a life span of ~7 years • Predators: fishes when squid are young, then sperm whales http://evomech7.blogspot.com/2006/12/japan-researchers-film-live-giant.html

  16. Squid Fisheries • ~70% of present catch of cephalopods • Major source of human food • Driftnet fishery began in N. Pacific in 1981 • Driftnets: monofilament panels 8-10 m tall and up to 50 km long • Set at night and allowed to drift while entangling prey

  17. Driftnets • 1989: Japan, Korea, & Taiwan were deploying 800 driftnet vessels in N. Pacific • Harvested 300,000 T squid annually • Salmon and tuna also captured as by-catch • 750,000-1,000,000 seabirds killed annually • 20,000-40,000 marine mammal deaths • Destruction to zooplankton not quantified

  18. Drift-nets • 1993: UN General Assembly accepted a resolution calling for a moratorium on all high-seas drift-netting • Some illegal drift-netting continues

  19. Marine Reptiles Saltwater crocodile Marine iguana Sea snake Marine turtle

  20. Marine Birds

  21. Marine Mammals

  22. Inquiry • What is the difference between nekton and plankton? • Describe the krill fishery. • Why did the krill catch drop in 1984 and 1993? • What is a drift net?

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