Nekton

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NektonNektonOrganisms capable of swimming against a current

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

Importance of NektonImportance of Nekton

• Large nekton can profoundly influence marine communities

• Important in current or historical harvests

• Fishes of critical importance to world food supply

Vertical distribution

Epipelagic countershadingCountershading: a nektonic organism is bicolored, dark above and light below

Holoepipelagic: shark, tuna, ocean sunfish

Meroepipelagic: herring, salmon

MesopelagicSeldom exceed 10 cm Equipped with well developed teeth and large

mouthLarge light-sensitive eyes, uniformly blackPhotophores: light-producing organs

Abyssalpelagic Species-specific pattern of photophoresSmall with flabby, soft, nearly transparent

flesh supported by weak bones Oversized mouth

Morphological features of nekton at different vertical zones

Major zones of life in a marine ecosystem

Nektonic CrustaceaNektonic 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

Euphausia superba

Who eats Krill?

Krill & the Antarctic Food WebCritical components of Antarctic food webs

Krill Fishery• Annual consumption by natural predators =

470 million MT• 1972: Japan and Russia began harvesting

krill

Krill Fishery…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

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

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

Squid FisheriesSquid 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

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

Drift-netsDrift-nets

• 1993: UN General Assembly accepted a resolution calling for a moratorium on all high-seas drift-netting

• Some illegal drift-netting continues

Marine turtle

Marine iguana

Saltwater crocodile

Marine ReptilesMarine Reptiles

Sea snake

Marine BirdsMarine Birds

Marine MammalsMarine Mammals

Inquiry

1. What is the difference between nekton and plankton?

2. Describe the krill fishery.3. Why did the krill catch drop in

1984 and 1993?4. What is a drift net?