Food Webs and Fisheries OCN 201 Biology Lecture 10 Steward 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 Primary Secondary Tertiary Producer Consumer Consumer Consumer Trophic Efficiency • 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 trophic pyramid (or biomass pyramid) Trophic Pyramid 1 kg Top Consumer 10 kg Med. Fish 100 kg Sm. Fish Zoo- 1,000 kg plankton 10,000 kg Phyto- plankton 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. Simplified Marine Food Web Biomass Pyramid Trophic Cascades • There are may interdependent connections in the marine food web! • Disturbance of one component of a food web can have unexpected consequences at many other levels North Pacific Whale Catch Trophic Cascade Whaling Moratorium Springer et al 2003 PNAS Healthy Kelp Forest Urchin Barrens Ocean Fisheries Food from the Sea • Seaweed • Invertebrates • Fish • Whales Commercial whaling ceased in 1987 (IWC moratorium) ! Resumed by Norway in 1993, Japan never stopped: Minke whales taken for ”scientific purposes”; meat and blubber sold to market. In 2000, extended to blue and Bryde’s whales Commercial Fishing Methods • Harpoon - whales, swordfish, bluefin tuna • Pole and Line - tuna, mahi-mahi • Longlining - swordfish, tuna (pelagic); cod, halibut (bottom) • Trolling - salmon, albacore, mahi-mahi • Drift (gill) netting - various pelagic fish • Trawling - anchovies (pelagic); cod, halibut (bottom) • Purse Seine - Sardines, herring, mackerel, tuna • Traps and Pots - Crabs, lobster, rock fish Mariculture Kona-Blue Kona Kampachi (yellowtail) Some Problems • Many farmed fish fed fish meal - inefficient! • High concentrations of fish - lots of waste water, diseases, antibiotic resistance • Shrimp farms often built at the expense of mangroves - destroy important fish habitat Some Solutions • Farm vegetarian fish (Carp, Tilapia) • Farm shellfish (filter feeders--clean water) • Better nutrition and better engineering to minimize waste Fisheries Production • Maximum Sustainable Yield: maximum number of fish that can be harvested without depleting stocks in the future • Present harvests remain < 100 mmt; cannot sustainably increase • Estimated 45% of fisheries overfished at present Fisheries Model Catch Value MSY Cost Money Max Profit Amount of Effort Ratchet Effect • Overcapitalization: when fishing is good, more boats built, more people employed • When yields decline, much more difficult to scale back (protect capital investments, jobs) Marine Fish Harvest Data from Food and Agriculture Organization. Data for all countries, for marine and anadromous fish only. 80 16 60 12 40 8 Millions of Tons Millionsof 20 4 kg of fish per person per fish of kg 0 0 1950 1960 1970 1980 1990 20002010 1950 1965 1980 1995 2010 Year Year Marine Fish Harvest Data from Food and Agriculture Organization. Data for marine and anadromous fish only, all countries. Capture Mariculture 80 60 40 Millionsof Tons 20 0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Year Total Harvest Data from Food and Agriculture Organization for ALL capture and aquaculture sources (marine and freshwater fish and other species) Food supply from all sources is keeping up with population, thanks to dramatic expansion of aquaculture ! But wild marine fish populations still in trouble. Trend in Fisheries Collapses http://news.bbc.co.uk/2/hi/science/nature/6108414.stm .