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Lecture 3

OCEAN 320 Lecture Notes - Lecture 3: Marine Protected Area, Shifting Baseline, Continental ShelfPremium

5 pages48 viewsSummer 2018

Department
Oceanography
Course Code
OCEAN 320
Professor
K.Robinson
Lecture
3

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Unit 3B: How Much Has the Ecosystem Changed?
Daniel Pauly’s TED Talk: The ocean’s shifting baselines
Charles Darwin
o Wrote that the Galapagos fish was “common;” now it is on the IUCN Red List
Field work in Sakumo Lagoon, Ghana
o Lagoon had black chin tilapia, but was overfished; fish species shrunk to 5 cm
RV Mutiara 4 in Semarang (Java), Indonesia
o Europeans impose industrial fishing on other smaller countries
o Caught mostly fish and animals from the bottom of the sea: 90% sponges and
other reef fish
o When we overfish, the reefs turn muddy and cannot stay fixed on the bottom of
the ocean; other animals were retrieved already dead from related complications
o Way of adjusting a baseline
The shifting baseline syndrome (1995)
o Want to sustain “what is left” as best as possible; as baseline decreases, we hold
onto what little is left
Fishing down marine food webs
o Baseline shrinks because what once was abundant becomes rare, and then we lose
rare species, so it doesn’t seem like a huge loss
o We don’t know past and we don’t trust non-scientific evidence (ie: sailor’s
observations)
o Marine protected areas can recreate the past; we can see the baselines (which has
shifted very very low)
Simulating Visual Oceans
o Use movies/film to explain these shifting baselines to people who have no access
to marine protected areas
Counting the Last Fish
Nova Scotia, Canada: used to have huge variety of fish, bow fishermen scrape the bottom
clean, often bringing up supporting substrates (sponges)
o Also catch last sharks, swordfish, tuna
o Population sizes are dwindling, many fish are captured before maturity
o Fishers must work farther off shores and in deeper waters to make quota
1982 UN’s Convention on the Law of the Sea: allows countries bordering the ocean to
claim exclusive economic zones reaching 200 nautical miles into open waters; includes
the highly productive continental shelves of ~200 m in depth where most fish live
o Ended fighting over fishing grounds, but placed responsibility for managing
marine fisheries on maritime countries
o US and Canadian governments have subsidized the growth of domestic fishing
fleets to supplant excluded foreign countries
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Canada build new off-shore fleets to replace those nations pushed out by
convention; fleets are even larger and more modern than domestic, in-
shore fleets; fish year round, rather than seasonally
Demand for fish makes countries seek agreements to allow foreign fleets
in waters that don’t belong to them; creates overfishing, as foreign fleets
have no incentive to preserve local marine resources long-term
o Convention and technological advancements (acoustic fish finder) temporarily
boost fish catches; by 1980’s, trend reversed despite China overreporting (trying
to meet political productivity increases)
2001: examine where catches differed significantly from those taken from similarly
productive waters at same depths and latitudes elsewhere
o Figures from Chinese waters much higher than predicted; 40% of deviations from
the statistical model
o When readjusted to include misrepresentations: concluded that world fish
landings have declined slowly since the late 1980’s, by ~700,000 metric tons a
year
o Other countries over/underreport too, but they usually cancel each other out
Nations gather data in variety of ways (surveys, census, logbooks)
o In some countries (China) data is forwarded to national government offices;
throughout the processes, officials manipulate statistics to meet production
targets, which creates the huge gap
o Other countries have systems for cross-checking fish landings against
import/export data and info on local consumption
“Fishing down the food web”
o Occurs when fishers deplete large predator fish at top of food chain (tuna,
swordfish) until they become rare and then target smaller species that would
usually be eaten by fish
o Position on food web is determined by size, anatomy of mouth parts and feeding
preferences
o Layers of food web (trophic levels) ranked according to how many steps they are
removed from primary producers at base of web (phytoplanktonic algae, TL 1)
o Phytoplankton eaten by zooplankton (TL 2); small fishes (sardines, herring,
anchovies) between 20-50 cm are TL3; table fish (cod, snapper, tuna, halibut) are
predators of small pelagics and have TL of 3.5-4.5 (not whole numbers bc they
consume prey on several trophic levels)
o First evidence of fishing down: in North Atlantic, off Patagonian coast of South
America, near Antarctica, Arabian Sea, parts of Africa and Australia; experienced
TL declines of 1 or greater between 1950-2000
o Conclusions based on analysis of global database of marine fish landings created
& maintained by UN Food & Ag Org; information is often inaccurate or not well
differentiated, so use global distribution of fish from FishBase and knowledge
about fishing patterns
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