Food Chain. Marine Food Webs and Fisheries

Transcription

1 Marine Food Webs and Fisheries OCN 201 Biology Lecture 10 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

2 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 trophic pyramid (or biomass pyramid) Trophic Pyramid 1 kg 10 kg 100 kg 1,000 kg Top Consumer Phytoplankton Zooplankton Med. Fish Sm. Fish 10,000 kg

3 Food Web The complex feeding arrangements among all the organisms in a community that takes into account that organisms may feed on more than one species of prey and on more than one trophic level. Simplified Marine Food Web Biomass Pyramid

4 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 A trophic cascade involves food web perturbations at more than 1 trophic level Trophic Cascade Springer et al 2003 PNAS Whaling Moratorium Sequential collapse

5 Urchin Barrens

6 And the top predator is... Biomass Pyramid How much fish do we take from the sea? LA Coliseum seats 94,000 people ~2 mmt capacity (2 million metric tons)

7 Units: mmt (FAO 2016) Ocean Fisheries

8 Food from the Sea Seaweed Invertebrates Fish Whales fertilizers, cosmetics, animal & human food, vitamins, pharmaceuticals, biotech Commercial whaling ceased in 1987 (IWC moratorium) Resumed by Norway in 1993, Japan never stopped: whales taken for scientific purposes ; meat and blubber sold to market In 2000, extended to blue and Bryde s whales Walleye Pollock is : A: in imitation crab meat. B: in McDonald s fillet-o-fish sandwiches. C: the largest commercial fishery in US waters. D: the primary prey for Stellar s sea lions. E: all of the above.

9 Food from the Sea Peruvian anchoveta was largest commercial fishery in the world for decades 12 species provide up to 40-50% of the world marine catch

10 WWF-Canon / Morten Lindhard Fishing Methods HARPOONS AND SPEARS Pole and Line Fishing Methods BAITED LINE Longlining Trolling Bigeye tuna swordfish

11 Commercial Fishing Methods NETS Otter Trawl Purse Seine Mid-water Trawl Gill Net Fishing Methods POTS AND TRAPS

12 Fishery Harvest - temporal trends Total (Million Tons) Fish Catch Per person (kilograms) 18 What Happened? Fish Catch Human Population Explosion Billions of People Year Year

13 State of global marine fish stocks (FAO, 2016) Majority of stocks are fully or overexploited (~90%) Trend in Fisheries Collapses What are the consequences?

14 Bycatch, Discards, Illegal/Unreported Bycatch and discards make up ~ 35% of the total catch Fisheries Production Maximum Sustainable Yield: maximum number of fish that can be harvested without depleting stocks in the future Objective: maximize fisheries yield Single-species stock assessment & management

15 Simple Fisheries Model: Bioeconomics of fisheries C MSY Yield Population biomass Simple Fisheries Model: Bioeconomics of fisheries Yield = Revenue Yield = $ Costs = $ MSY net = 30 Max Profit Cost break-even point Amount of Effort Gordon model (1954)

16 Bioeconomics of Fisheries Gordon model suggests: If the costs of entering the fishery are low, the fishery will develop well beyond its biological limits and the stock becomes depleted. Fishery becomes economically inefficient, because too many fishers are chasing too few fish. Overcapitalization: when fishing is good, more boats built, more people employed When yields decline (exceeding MSY), much more difficult to scale back (protect capital investments, jobs) Ratchet Effect Tendency is to fish more to get the little extra money needed to stay employed.

17 Tragedy of the Commons For resources held in common (i.e. free ): Use provides direct benefit to the individual, but the costs are shared by everyone Individuals acting in self-interest lead to ruin of the resource International waters Source: Maritime boundaries geodatabase National boundaries Exclusive economic zone = 200 nautical miles

18 Management 1. Control Catch - control fishing mortality by limiting weight of catch fishers can take (target species). F. x., Total allowable catch (TAC), individual transferable quotas (ITQ). 2. Control Effort - control the number of boats/fishers that work the fishery, the amount or size of gear, the time the gear can be left in the water, periods open to fishing. 3. Marine Protected Areas - fishing is limited or prohibited in time (seasonal), or only by local people. Used to protect habitats, non-target species, as well as increase fishery yield. Management one of the largest marine protected areas on the planet

19 Individual Transferable Quotas (ITQs) Limited Access Privilege Programs Fishers own share of total allowable catch Can buy and sell shares Can lead to more responsible and more efficient use of resources Environmental impacts of fishing Over-exploitation of commercially harvested (target) species Reduced genetic diversity of wild populations, increasing susceptibility to natural perturbations Habitat destruction in the benthos - disturbance of bottom communities, sediment environments Fishing down marine food webs - shifting ecosystem function, removal of top predators Effects on non-target species - bycatch of birds, mammals, sea turtles, other fish species.

20 Capture fisheries vs Aquaculture Mariculture/Aquaculture

21 Fishery & Aquaculture Harvest Total (Million Tons) 140 Fish Catch Aquaculture Fish Catch Per person (kilograms) Aquaculture Some Problems Many farmed fish fed fish meal - inefficient! High concentrations of animals - lots of waste water, diseases, antibiotic resistance Shrimp farms often built at the expense of mangroves - destroy important fish habitat

22 Some Solutions Farm vegetarian fish (Carp, Tilapia) Farm shellfish (filter feeders--clean water) Better nutrition and better engineering to minimize waste What you can do:

23 Questions?