Dec 03 2009

Dec 03 2009 - Lecture 20: Human impacts (continued)...

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Reading: Text Chapter 18 assigned last time Text Chapter 19 Lecture 20: Human impacts (continued)
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Wasted fshery resources: discarded by-catch in the USA Jennie M Harrington, Ransom A Myers & Andrew A Rosenberg. 2005. Fish and Fisheries 6: 350-361. Abstract Fishery by-catch, especially discarded by-catch, is a serious problem in the world’s oceans. Not only are the stocks of discarded species affected, but entire trophic webs and habitats may be disrupted at the ecosystem level. … Overall, our compiled estimates are that 1.06 million tonnes o± fsh were discarded and 3.7 million tonnes o± fsh were landed in USA marine fsheries in 2002. This amounts to a nationwide discard to landings ratio o± 0.28, amongst the highest in the world. Regionally, the southeast had the largest discard to landings ratio (0.59), followed closely by the highly migratory species ±sheries (0.52) and the northeast ±sheries (0.49). The Alaskan and west coast ±sheries had the lowest ratios (0.12 and 0.15 respectively). Shrimp fsheries in the southeast were the major contributors to the high discard rate in that region, with discard ratios o± 4.56 (Gul± o± Mexico) and 2.95 (South Atlantic). By-catch and discarding is a major component of the impact of ±sheries on marine ecosystems. .
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Some fsheries have excessive bycatch > 8 lbs of discards per lbs of shrimp
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Turtle Excluder Devices (TEDs) Variation on a theme… http://www.afma.gov.au/information/students/methods/images/seal.jpg http://www.afma.gov.au/information/students/ methods/images/ted_4.jpg
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www.marinebuzz.com/. ../turtle_escape_device1.jpg http://marinelife.about.com/od/w atchingandphotography/ig/Sea- Turtle-Images/Turtle-Excluder- Device-Photo.htm Turtle excluder success…
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Longlining -- sea turtle bycatch reduced by changing shape of the hooks and type of bait
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The Tuna-Dolphin Issue [updated from W. F. Perrin, B. Wursig and J. G. M. Thewissen, eds. Encyclopedia of Marine Mammals. Academic Press, San Diego, California., p.1269-1273 (2002)] Fig. 1. Purse seine being set on tuna and dolphins. The net is not yet closed, and four speedboats are driving in tight circles near the opening to prevent the dolphins (and tuna) from escaping. Fig. 2. Backdown procedure in progress. As the tuna vessel moves backwards to the right in this photo, the net is drawn into a long channel. The corkline at the far end is pulled under water slightly, and the dolphins escape. Speedboats are positioned along the corkline to help keep the net open.
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Eastern Spinner Dolphin Stenella longirostris orientalis (mother and calf) creagrus.home.montereybay.com/ETP_cetaceans. html Spotted Dolphin Stenella attenuata www.cascadiaresearch.org/robin/ NovDec2006.htm
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Fig. 3. Estimated annual number of dolphins killed in the eastern tropical Paci±c purse-seine tuna ±shery, total for all dolphins and separately for the two dolphin stocks with the highest number killed.
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Fig. 4. Estimated population size,
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Dec 03 2009 - Lecture 20: Human impacts (continued)...

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