Emptying the oceans

1. Emptying the oceans Overharvesting is the worst marine problem We are putting unprecedented pressure on marine resources Half the world’s marine fish populations are fully exploited and can’t be fished more intensively 28% of fish population are overexploited and heading to extinction Total fisheries catch leveled off after 1988 Despite increased fishing effort The maximum wild fisheries potential has been reached

2. The global fisheries catch has increased • It is predicted that populations of all ocean species we fish for today will collapse by 2048

3. We have long overfished People began depleting sea life centuries ago Species have been hunted to extinction: Caribbean monk seal, Steller’s sea cow, Atlantic gray whale Overharvesting Chesapeake Bay oyster beds led to its collapse, eutrophication, and hypoxia Decreased sea turtle populations cause overgrowth of sea grass and can cause sea grass wasting disease Overharvesting nearly exterminated many whale species People never thought groundfish could be depleted New approaches or technologies increased catch rates

4. Fishing has industrialized Factory fishing = huge vessels use powerful technologies to capture fish in huge volumes Even processing and freezing their catches at sea Driftnets for schools of herring, sardines, mackerel, sharks, shrimp Longline fishing for tuna and swordfish Trawling for pelagic fish and groundfish

5. Fishing practices kill nontarget animals Bycatch = the accidental capture of animals Drift netting drowns dolphins, turtles, and seals Fish die on deck Banned in international waters But it is still used in national waters Longline fishing kills turtles, sharks, and over 300,000 seabirds/year Methods (e.g., flags) are being developed to limit bycatch

6. Dolphins and tuna Dolphins are trapped in purse seine nets used to catch tuna Hundreds of thousands of dolphins were killed The 1972 Marine Mammal Protection Act forced fleets to try to free dolphins Bycatch dropped dramatically Other nations fished for tuna, and bycatch increased The U.S. government required that nations exporting tuna to the U.S. minimize dolphin bycatch Dolphin-safe tuna uses methods to avoid bycatch

7. Dolphin deaths have declined, but … Other animals (e.g., sharks) are still caught Dolphins have not recovered Too few fish to eat Rules and technology have decreased dolphin deaths

8. Bottom-trawling destroys ecosystems Heavy nets crush organisms and damage sea bottoms It is especially destructive to complex areas (e.g., reefs) It equals clear-cutting and strip mining Georges Bank has been trawled three times Destroying young cod as bycatch The reason the cod stock is not recovering

9. Modern fleets deplete marine life rapidly Grand Banks cod have been fished for centuries Catches more than doubled with industrial trawlers Record-high catches lasted only 10 years George Bank cod fishery also collapsed

10. Industrialized fishing is destroying fisheries Worldwide, industrialized fishing is depleting marine populations with astonishing speed 90% of large-bodied fish and sharks are eliminated within 10 years after fishing begins Populations stabilize at 10% of their former levels Communities were very different before modern fishing Removing animals at higher trophic levels allows prey to proliferate and change communities Oceans today contain only one-tenth of the large-bodied animals they once did

11. Several factors mask declines Industrialized fishing has depleted stocks But global catch has remained stable for the past 20 years How can stability mask population declines? Fishing fleets travel farther to reach less-fished areas Fleets fish in deeper waters (now at 250 m) Fleets spend more time fishing and set more nets Improved technologies: faster ships, sonar mapping, satellite navigation, thermal sensing, aerial spotting Fleets expend more effort to catch the same number of fish

12. Purchasing choices influence fishing practices Buy ecolabeled seafood Dolphin-safe tuna Consumers don’t know how their seafood was caught Nonprofit organizations have devised guides for consumers Avoid: Atlantic cod, wild-caught caviar, sharks, farmed salmon • Best choices: farmed catfish, mussels, oysters, tilapia

13. Diversity loss erodes ecosystem services Factors that deplete biodiversity threaten ecosystem services of the oceans Systems with reduced species or genetic diversity show less primary and secondary production They are less able to withstand disturbance Biodiversity loss reduces habitat for nurseries for fish and shellfish Less diversity leads to reduced filtering and detoxification Resulting in algal blooms, dead zones, fish kills, beach closures

14. Fisheries management Based on maximum sustained yield to maximize harvest While keeping fish available for the future Managers may limit the harvest or restrict gear used Despite management, stocks have plummeted It is time to rethink fisheries management Ecosystem-based management shifts away from species and toward the larger ecosystem Considers the impacts of fishing on habitat quality, species interactions, and long-term effects Sets aside areas of oceans free from human interference

15. We can protect areas in the ocean Marine protected areas (MPAs) = most are along the coastlines of developed countries They still allow fishing or other extractive activities 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 Be sensitive to concerns of local residents

16. Reserves work for both fish and fisheries Marine reserves: Increased densities of organisms by 91% Increased biomass by 192% Increased organism size by 31% Increased species diversity by 23% Benefits inside reserve boundaries include: Rapid and long-term increases in abundance, diversity, and productivity of marine organisms Decreased mortality and habitat destruction Decreased likelihood of extirpation of species

17. Areas outside reserves also benefit A “spillover effect” occurs when individuals of protected species spread outside reserves Larvae of species protected within reserves “seed the seas” outside reserves Improved fishing and ecotourism Local residents who were opposed support reserves once they see their benefits Once commercial trawling was stopped on Georges Bank: Populations of organisms began to recover Fishing in adjacent waters increased

18. How should reserves be designed? 20–50% of the ocean should be protected in no-take reserves How large? How many? Where? Involving fishers is crucial in coming up with answers