Marine Food Webs and Fisheries

Transcription

1 Marine Food Webs and Fisheries OCN 201 Biology Lecture 9

2 Food Chain 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. Trophic Levels Primary Producer Primary Consumer Secondary Consumer Tertiary Consumer

3 Trophic Efficiency Much of the biomass consumed by an organism is respired (released as CO 2 and heat) or released as waste products Typically only 10% is used to make biomass This results in the biomass pyramid (or biomass pyramid)

4 Biomass Pyramid 1 kg 10 kg 100 kg 1,000 kg Top Consumer Phytoplankton Zooplankton Med. Fish Sm. Fish e.g., 10,000 kg

5 Food Web 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.

6 Simplified Marine Food Web Biomass Pyramid

7 Trophic Cascades 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

8 Simplified Marine Food Web Lots of interdependent links Otters Removing one can alter the entire food web structure

9 North Pacific Whale Catch

10 Overharvesting of Whales

11 Trophic Cascade Springer et al 2003 PNAS Whaling Moratorium

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13 Urchin Barrens

14 Simplified Marine Food Web Biomass Pyramid

15 Ocean Fisheries NASA Global Fishing Watch map showing locations of fishing activity

16 Food from the Sea Seaweed Invertebrates Fish Whales 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

17 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

18 Commercial Fishing Methods GRAB & RUN

19 Commercial Fishing Methods WWF-Canon / Morten Lindhard HARPOONS AND SPEARS

20 Commercial Fishing Methods Pole and Line BAITED LINE Longlining Trolling

21 Commercial Fishing Methods NETS Otter Trawl Purse Seine

22 Factory Trawler Alamy Stock Photo Fish caught, processed, packaged, and frozen all the same ship We have become EXTREMELY efficient at removing fish from the sea

23 Maximum Sustainable Yield maximum catch of fish that can be harvested without depleting stocks in the future

24 North Atlantic Cod Fishery

25 Food and Agriculture Organization of the United Nations Marine Fish Harvest Global marine fish catch has declined since mid-nineties Despite increasing effort Appear to be at or above maximum sustainable yield Effort gw

26 Current Assessments of Sustainability 30% Overfished 90% of fisheries at or above maximum capacity Food and Agriculture Organization of the United Nations

27 7.7 Billion

28 Fisheries Issues Overfishing (taking more than m.s.y.) Habitat destruction (bottom trawls) Bycatch (catch of non-target species)

29 Super Trawlers Huge factory ships with enormous capacity

30 Bottom Trawlers Habitat destruction Before After

31 Bycatch Bottom Trawl Longline Mid-water Trawl

32 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

33 Mariculture Oyster Farms Fish Farms

34 Mariculture Kona-Blue Kona Kampachi Oyster (yellowtail) Farm Fish Farm Kualoa Ranch Oysters (Moli i Fish pond)

35 Total Fish Supply Figure from Food and Agriculture Organization Marine + Inland Aquaculture is becoming increasingly important Farmed Caught Food and Agriculture Organization of the United Nations

36 Aquaculture Issues Dependence on fish meal/oils Escape of non-native species Waste effluent (pollution of the environment) Diseases (and antibiotics used to treat them) Research, engineering, and development is helping to mitigate some of these problems

37 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

38 Informed Public

39 What you can do: Region-specific Consumer Guides

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