Marine Food Webs and Fisheries

OCN 201 Biology Lecture 9

http://archive.wri.org/image.cfm?id=2648&z=?

A series of different species of organisms at different trophic levels in an arrangement such that each species feeds only on organisms one trophic level below and serves as food only for the next level above.

Food Chain

Primary Producer

Primary Consumer

Secondary Consumer

Tertiary Consumer

Trophic Levels

• Much of the biomass consumed by an organism is respired (released as CO2 and heat) or released as waste products

• Typically only 10% is used to make biomass

• This results in the biomass pyramid (or biomass pyramid)

Trophic Efficiency

Biomass Pyramid

e.g., 10,000 kg

1,000 kg

100 kg10 kg

1 kg

Phyto-plankton

Zoo-plankton

Sm. Fish

Med. Fish

Top Consumer

The complex feeding arrangements among all the organisms in a community that takes into account that any organisms may feed on more than one species of prey and on more than one trophic level.

Food Web

Simplified Marine Food Web

BiomassPyramid

• There are many interdependent connections in the marine food web!

• Disturbance of one component of a food web can have unexpected consequences at many other levels

Trophic Cascades

Simplified Marine Food Web

Lots of interdependent

links

Removing one can alter the entire food

web structure

Otters

North Pacific Whale Catch

Overharvesting of Whales

Springer et al 2003 PNAS

Trophic Cascade

Whaling Moratorium

Urchin Barrens

Simplified Marine Food Web

BiomassPyramid

Ocean Fisheries

Global Fishing Watch —map showing locations of fishing activity

NASA

• Seaweed

• Invertebrates

• Fish

• Whales

Food from the Sea

Commercial whaling nominally ceased in 1987 (IWC moratorium)

Subsistence whaling by indigenous cultures is permitted

Whaling resumed by Norway in 1993, Japan never stopped: whales taken for ”scientific purposes”; meat and blubber sold to market. New program (since 2015) 300 Minke whales taken from Antarctic waters every year

Food from the Sea

• Wild caught fisheries

- Hunting and gathering from the ocean

- Ocean fishing is the last example of catching wild animals on large scale for food

• Mariculture

- A form of aquaculture that involves the farming of marine species

Commercial Fishing MethodsGRAB & RUN

Commercial Fishing MethodsHARPOONS AND SPEARS

© WWF-Canon / Morten Lindhard

Commercial Fishing MethodsBAITED LINE

Longlining

Pole and Line

Trolling

Commercial Fishing MethodsNETS

Otter Trawl Purse Seine

http://www.legasea.co.nz/images/commercial-fishing-methods.jpg

Factory TrawlerAlamy Stock Photo Fish caught, processed,

packaged, and frozen all the same ship

We have become EXTREMELY efficient at removing fish from the sea

maximum catch of fish that can be harvested without depleting stocks in the future

Maximum Sustainable Yield

North Atlantic Cod Fishery

Marine Fish Harvest

Global marine fish catch has declined since mid-nineties

Food and Agriculture Organization of the United Nations

Appear to be at or above maximum sustainable yield

Despite increasing effort

EffortgW

24

16

8

0

Current Assessments of Sustainability

Food and Agriculture Organization of the United Nations

30% Overfished90% of fisheries at or above maximum capacity

7.7 Billion

Fisheries Issues

•Overfishing (taking more than m.s.y.)

•Habitat destruction (bottom trawls)

• Bycatch (catch of non-target species)

Super Trawlers

http://coastmonkey.ie/wp-content/uploads/2016/12/Super-Trawlers.png

Huge factory ships with enormous capacity

Bottom TrawlersHabitat destruction

Before After

BycatchBottom Trawl

Mid-water Trawl

Longline

Food from the Sea

• Wild caught fisheries

- We are at the limit of what we can pull from the sea, but human population continues to grow

• Aquaculture

- Marine and freshwater aquaculture are critical areas of growth

MaricultureOyster Farms

Fish Farms

Fish Farm

Mariculture

Oyster Farm

Kona-BlueKona Kampachi

(yellowtail)

Kualoa Ranch Oysters(Moli‘i Fish pond)

Total Fish SupplyFigure from Food and Agriculture Organization

Marine + Inland

Caught

Farmed

Aquaculture is becoming increasingly important

Food and Agriculture Organization of the United Nations

Aquaculture Issues

• Dependence on fish meal/oils

• Waste effluent (pollution of the environment)

• Diseases (and antibiotics used to treat them)

• Escape of non-native species

Research, engineering, and development is helping to mitigate some of these problems

Making Informed Choices

• Both wild caught and farmed food sources have issues

• Some wild caught fisheries and aquaculture operations are better managed and more sustainable than others

• By being informed you can make better choices and minimize damage to the ecosystem

Informed Public

What you can do:

Region-specific Consumer Guides