Overexploitation of Marine Fisheries and Shifting Baselines

1. Overexploitation of Marine Fisheries and Shifting Baselines

2. Marine Fisheries Terms to Know • Fishery – Refers to aspects of harvesting and managing aquatic organisms. Can refer specifically to a species being harvested, the methods of harvesting, or the ecosystem from which the organisms are harvested. • Term is not limited to animals classified as fish • Stocks – Groups of organisms considered to be distinct units, typically distinct populations. From: Beckman 2013

3. Marine Fisheries Terms to Know • Fisheries management – The regulation and monitoring of a fishery, including setting harvest limits, developing management plans, and protecting fish habitat. • Fisheries landings – Common measure to monitor fisheries. Is the amount of fish caught, measured as the biomass or number of individuals caught and brought to shore.

4. Types of Fishers • Recreational (Sport) • Subsistence • Artisanal • Commercial • Small-scale • Mid-sized • Industrial

5. Methods of Fishing • Spears/harpoons • Dredging • Hook-and-line • Includes long-lining • Traps and weirs • Gill and drift nets • Seines • Trawlers (bottom and mid-water)

6. Sustainability in Marine Fisheries • Sustainability = harvesting at levels that allow continued harvest indefinitely • Can be achieved if the population remaining after harvest is able to replenish itself by reproduction • Have to determine the surplus that can be taken without adversely affecting production

7. Overfishing affects Marine Ecology • Major top-down force that has led to large depletions of top predators • By removing species which exert control over lower consumers, there are severe consequences to marine ecosystems through trophic cascades • Paulyet al. (1998) that chronicled fishing down marine food webs

8. Overfishing: Continued • There is great difficulty in sustaining global fisheries production. In response to declines of big, slower growing species, fishers have begun "fishing down the food chain", targeting smaller species of less value, but which can play critical roles in food webs. • Over-capitalization of the industry has led to the buildup of excessive fishing fleets, particularly of the larger-scale vessels, catching too many fish.

9. Pauly, D. et al. 1998. Fishing down marine food webs. Science279: 860-863 Trophic Level 4 Trophic Level 3 Trophic Level 2 Trophic Level 1

10. Overfishing: Impacts on Biodiversity • Fishing can be an agent of selection, affecting age distribution, age and size at maturity, and growth • Fishing can alter species composition and interactions among fished species and their prey. • Fisheries often begin on large predators but their reduced numbers may lead to increased numbers of prey species, which may themselves become fished. • Intense fishing can lead to dominance by r-selected species, which often become major parts of mature fisheries. Other species can also be affected; e.g., fishery discards have caused long-term changes in seabird species composition.

11. Overfishing (= Intense Predation) • The global marine catch has increased more than 4x in the past 40 years. • Overfishing has pushed many fish populations into steep declines. Catches are falling, even though fleets are fishing harder than ever before • The U.N. Food and Agriculture Organization (FAO) reports that ~70% of commercially targeted fish stocks are at least heavily exploited

12. Exploitation of global fisheries

14. Ocean Fisheries • > 109 people (mostly developing nations) depend upon marine fish for primary source of protein • 40 y ‘fishing boom’ has now ended: catch increasing steadily since 1950, but since 1989 world catch has stayed the same • Catch of ‘high value’ fish decreasing; catch of low value fish increasing; Also catching smaller sized fish

15. Essington, T. et al. 2006. Fishing through marine food webs. PNAS103: 3171-3175 • Alternative view is fishing through food webs where continue to fish for upper trophic levels with sequential addition of lower trophic level fisheries. • E.g. Continue to fish for snapper and grouper while concurrently targeting parrotfish and other herbivores

16. A.) Sequential collapse/replacement mode where mean trophic level declines over time and old fisheries are replaced with new ones at lower trophic levels B.) Sequential addition mode of fishing down the food web where continue to fish at all trophic levels and introduce new fisheries as well

17. One success story, Spanish mackerel in the Gulf of Mexico are no longer overfished and, in fact, have become a sustainable fishery. Pompano are also recovering in the Gulf Overfishing: A few success stories

18. Jackson, J.B.C. et al. 2001. Historical Overfishing and the Recent Collapse of Coastal Ecosystems. Science293: 629-638 • Historical overfishing has altered coastal ecosystem structure through targeting of top consumers: • Resulted in losses of previously abundant members of the food web and increases in other members who were once less abundant • Analyzing historical and paleontological data allowed for reconstruction of historical ecosystem structure prior to the impacts of overfishing

19. Shifting Baselines • Diversity & ecosystem structure today may be strongly altered relative to a few human generations ago • We might mistakenly take today’s situation as the baseline for conservation • The baseline for a natural community has shifted over generations because we have forgotten the original natural state