1. Land Use Part 3: Food from the Sea

2. Where does our food come from?
Croplands
Mostly grain
Provide 77% of the world’s food
Rangelands
Meat
Provide 16%
Oceanic fisheries
Fish and shellfish
Provide 7%
These 16 groups supply around 65% of the commercial marine catch

3. Emptying the oceans
Humans are placing unprecedented pressure on marine resources
Half the world’s marine fish populations are fully exploited
25% of fish populations are overexploited and heading to extinction
Total fisheries catch leveled off after 1998, despite increased fishing effort
Some predictions state that populations of all ocean species we fish for today will collapse by the year 2048
No nation lays claim to open ocean
Resource susceptible to overuse and degradation
Tragedy of Commons

5. Several Factors Mask Declines
Fishing has depleted stocks, but global catch has remained stable for the past 20 years
Fishing fleets travel longer distances to reach less-fished portions of the ocean
Fleets spend more time fishing and have been setting out more nets and lines
Increasing effort to catch the same number of fish
Improved technologies:
Faster ships
Sonar mapping
Satellite navigation
Thermal sensing
Aerial spotting
Hard to obtain reliable data
Information supplied to international monitoring agencies may be and often is false

6. Overharvesting Overharvesting
Is the catching or removing from a population more organisms than the population can replace
Many species are at point of severe depletion
Cod
62% of world’s fish stock are in need of management action
Created no-fishing zones, so that fish populations can recover

7. Overharvesting Is Not New
People began depleting sea life centuries ago
Some species hunted to extinction
Steller’s sea cow
Atlantic gray whale
Caribbean monk seal
Overharvesting of Chesapeake Bay oyster beds
Led to the collapse of its fishery
Eutrophication
Hypoxia

9. Oceans today contain only one-tenth of the large-bodied animals they once did

10. Causes of Overharvesting – Industrialization of Fishing Fleet
Factory fishing
Highly industrialized, huge vessels use powerful technologies to capture fish in huge volumes
Even process and freeze their catches while at sea
Driftnets
Large nets set and allowed to drift
Used for schools of herring, sardines, mackerel, sharks
Longline fishing
Hooks on a line
For tuna and swordfish
Bottom Trawling
Large net dragged along bottom
For pelagic fish and groundfish

12. A comparison between typical trawl catch and a typical gillnet catch associated with the pre-industrial fishing. Note that the cod end of the net on the factory trawler is bigger than the entire boat housing the traditional fisher.

13. How Have Industrial Techniques Effected Harvests?
Grand Banks Cod Example:
Have been fished for centuries
Catches more than doubled with immense industrial trawlers
Record-high catches lasted only 10 years
Even protected stocks are not recovering
Prey may now be competing with, and eating, young cod

15. What Happens After Industrial Fishing?
Catch rates drop precipitously with industrialized fishing
90% of large-bodied fish and sharks are eliminated within 10 years
Populations stabilize at 10% of their former levels
Marine communities may have been very different before industrial fishing
Removing animals at higher trophic levels allows prey to proliferate and change communities
Leads to “Fishing Down the Food Chain”
As fishing increases
The size and age of fish caught declines
10-year-old cod, once common, are now rare
As species become too rare to fish, fleets target other species
Shifting from large, desirable species to smaller, less desirable ones
Entails catching species at lower trophic levels

17. Many Industrial Fishing Techniques Kill Nontarget Animals
By-catch
The accidental capture of animals
It is estimated that 27 million tons of by-catch are caught each year
25% of the annual world catch
Shrimp nets are even worse
For each pound of shrimp caught, there are 10 pounds of by-catch
While some of these animals survive, many have been dragged through the water in nets for hours before they are released
These do not survive
Drift-netting
Drowns dolphins, turtles, and seals
Fish die from air exposure on deck
Banned or restricted by many nations
Long-line fishing
Kills turtles, sharks, and albatrosses
300,000 seabirds die each year
Bottom-trawling destroys communities
Likened to clear-cutting and strip mining

18. Effects of Bottom-Trawling

19. By-catch solutions Use nets with the largest holes possible
The larger the holes, the fewer unwanted animals will be caught
Use exclusion devices
Turtle Exclusion Devices (TED’s) are trap doors to let turtles out of nets
Use pingers to warn away whales and dolphins
Use harpoons and hook-and-line methods to catch one fish at a time
Takes longer, but more fishermen can be employed
Reward fishers that catch less by-catch

20. Managing Fisheries Based on maximum sustained yield
Maximal harvest while keeping fish available for the future
Managers may limit the harvest or restrict gear used
Despite management, stocks have plummeted
New techniques must be used
Ecosystem-based management
Shift away from species and toward the larger ecosystem
Consider the impacts of fishing on habitat and species interactions
Set aside areas of oceans free from human interference
Set up protected areas
Marine protected areas (MPAs)
Established along the coastlines of developed countries
Still allow fishing or other extractive activities, but with limits
Marine reserves
Areas where fishing is prohibited
Leave ecosystems intact, without human interference
Improve fisheries, because young fish will disperse into surrounding areas
Many commercial, recreation fishers, and businesses do not support reserves

22. Reserves Work for Both Fish and Fisheries
Found that reserves do work as win-win solutions
Overall benefits include…
Boosting fish biomass
Boosting total catch
Increasing fish size
Benefits inside reserve boundaries included…
Rapid and long-term increases in marine organisms
Decreased mortality and habitat destruction
Lessen the likelihood of local extinction of species
Also called extirpation
Areas outside reserves also benefit
A “spillover effect” when individuals of protected species spread outside reserves
Larvae of species protected within reserves “seed the seas” outside reserves
Improved fishing and ecotourism