un-food & agriculture organization statistics world consumption of fish increasing, especially...
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UN-Food & Agriculture Organization statistics
World consumption of fish increasing, especially China
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Capture fishery = wild fish & other spp. caught from Oceans, Lakes & rivers
Aquaculture = domestic fish & other spp. raised in ponds or floating cages
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A few areas eat lots of fish, some almost none
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Aquaculture driving big increases in fish consumption in China
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Inland fish ponds in China FAO/20044
Aquaculture ponds can provide food, but can also cause pollution that harms natural rivers, lakes and oceans
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Goal of Capture Fisheries
Determine maximum harvest that can be taken without impairing the prospects of exploiting the fishery in the future
How many fish can be taken without destroying the stock?
traditionally thought of asMaximum Sustainable Yield (MSY)
Most recent thinking suggests that more holistic view should be taken…… we’ll talk about why.
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Fisheries science began in it’s modern form between WWI & WWII
Much work by fishery scientists estimating how much can be taken. Many methods & models.
Many technical aspects derived from basic population biology
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harvest
growth K
Hypothetical fish population responds to harvest regimes
Time
Bio
mas
s K
assume “s-shaped” population growth
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Hypothetical fish population responds to harvest regimes
small harvest slower growth, top of S curve
Time
Bio
mas
s K
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Hypothetical fish population responds to harvest regimes
keeps biomass oscillating around K/2, highest growth rate, leads to MSY
regular harvests
Time
Bio
mas
s K
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Time
Bio
mas
s K
Hypothetical fish population responds to harvest regimes
frequent harvest
population drops to non-viable level- below critical number
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Hypothetical fish population responds to harvest regimes
Time
Bio
mas
s K
recovery takes time generation time survival
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Time
Bio
mas
s K
borderline between 2 scenarios can be fine line
spatial variability temporal variability other species inaccurate biomass estimate
MSY can be risky
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Time
Bio
mas
s K
borderline between 2 scenarios can be fine line
spatial variability temporal variability other species inaccurate biomass estimate
MSY can be risky
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Climate= source of uncertainty
Natural year to year variation
Climate change models predict more extreme events
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Individual stocks can crash…..South American anchovies were ~20% of world catch at this time
Heavy fishing maintained during El Nino year.
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Normal yearTrade winds blow west across Pacific.Warm surface water end up in the west Pacific, sea surface is about .5 m higher at Indonesia than at EcuadorSea surface temperature ~ 8 C higher in west, w/ cool temperatures off South America, due to an upwelling of cold water from deeper levelsCold water is nutrient-rich, supporting high levels of primary productivity,
El Niño Trade winds relax in the central and western PacificDepression of the thermocline in the eastern Pacific, and an elevation of the thermocline in the west. Reduced upwelling to cool the suface and cut off the supply of nutrient rich
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http://www.fnoc.navy.mil/PUBLIC/
Normal year
Warm surface water pushed west, sea surface ~ .5 m higher at Indonesia than at Ecuador
Surface temp ~ 8 C cooler off South America, due to an upwelling of cold water from deeper levels
Cold water is nutrient-rich, supports high levels of primary productivity,
Trade winds
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South AmericaAsia Trade winds
warm surface water
cold high nutrient water
Normal Year
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South AmericaAsia Trade winds
warm surface water
cold high nutrient water
El Niño
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http://www.fnoc.navy.mil/PUBLIC/
Trade winds
El Niño
Trade winds relax in the central and western Pacific
Warm surface water not pushed west
Reduced upwelling of cool nutrient-rich water to surface
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Are world fisheries being overfished?
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Fisheries scientists give their best information to managers, who must weigh this against sociopolitical consequences. If the scientists say “we are overfishing! stop!!”, but the community says “you’ll cause economic ruin and collapse!” what does the manager do?
There is rarely political pressure for lower harvest rates, and often scientists have some doubts about their estimates…
ratchet effect
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One of the most infamous recent collapses, caused by the ratchet effect, was the loss of the great cod stocks around Newfoundland and Nova Scotia.
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Despite the repeated warnings of Canadian fisheries scientists, some of whose voices were quelled by their superiors, catches were allowed to exceed the biomass of the spawning stock.
Bottom oriented fish
Water column fish
Crustaceans (lobster, shrimp)
Not just cod catches down, many species
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http://www.sethwhite.org/animals.htm
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Despite individual stock crashes, according to world Food & Agriculture Organization (FAO) total marine catch is going up.
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But…… effort has been increasing…. the ratchet effect in action?
rate of increase slowing
source FAO
In addition to # ships, technology (catch efficiency) has improved
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Over fishing effects the target stock and:
by-catch species habitat destruction (reefs) trophic relationships
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Bottom fish catches (demersals) declining
Small midwater fish(pelagics) increasing
Discards increasing!
And…. when catch is examined more closely
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Bycatch, or the non-targeted fish that also get taken, may constitute far more biomass than the targeted species.
Bycatch is often composed of juvenile individuals of target species – so they’re being removed before they can mature and reproduce (“like eating your seed corn”)
large scale seining
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Total discarded catch is ~25% of all catch and much more for some fisheries
How much do you like shrimp?
Crab are an exception to this-gear very targeted
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Over fishing effects the target stock and:
by-catch species habitat destruction (reefs) trophic relationships
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A scraped benthic habitat stands in stark contrast to an undisturbed area
Demersal fish, like cod and haddock, depend on there being benthic organisms on which to feed.
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Trawling imperils little known deep reefs; may affect future catch
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Trawl scar
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Over fishing effects the target stock and:
by-catch species habitat destruction (reefs) trophic relationships
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Trophic level of catch is decreasing
Assume that fisheries switch to low trophic level species in response to abundance
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North Sea
http://lifesci.lscf.ucsb.edu/~biolum/organism/pictures/euphausiid.html
euphausiid krill
copepods
Norway pouthttp://www.fauna.is/Pages/archves/fish4/spaerlingur.html
Cod & other human food fish
Increased fishing of pout could cause trophic cascade, might eventually feed back to cod!
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Toward an “ecological holism”: can fisheries be managed from an ecosystem perspective??
“Holistic” means considering the (eco)system and its complexity
Fisheries management has historically ignored the ecosystem – focus on single species management
New atmosphere for (a) multi-species management, (b) ecosystem conservation (ex. Marine Protected Areas)(c) backing away from MSY and that thinking(d) empowerment of the fisherman – understanding what
their impact is, long-term sustainability is best
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Other threats exist on the land:
Dams keep migratory fishes from their spawning grounds Deforestation has many effects on aquatic ecosystems – affects the fish! Cannot forget that many fish spp. are “land-ocean linkers” – need healthy terrestrial ecosystems
All of these things will affect freshwater fisheries too
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Ontario
Superior
Michigan
Huron
Erie
Lost Fisheries of the Great Lakes
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-Pre-1850 fisherman perceived lake sturgeon as a nuisance because they destroy fishing gear
-Wide-spread slaughter
-Economic importance recognized, commercial fishery by mid- to late-1800s.
-In 1885, 8.6 million pounds harvested, 5.2 million pounds from Lake Erie.
-By the late 1900's, 80% of the lake sturgeon were removed from Lake Erie.
-Commercial harvest reported until 1977, but very low after 1956.
-Late 1970's, Canadian fishery Lake Erie harvest 3 to 5 thousand poundsLake Michigan, commercial harvest closed in 1929 after catch declined to only 2000 pounds
Lake Sturgeon
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Trends in Lake Sturgeon Catches in the Great Lakes
(from Harkness and Dymond 1961)
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-Only a remnant population remains today in most Great Lakes areas.
-Recognized by the American Fisheries Society as threatened in North America and, listed as Endangered, Threatened, or Special Concern in 19 of 20 states throughout its range.
-Habitat loss also contributing factor
-Damming of tributaries prevented access to historical spawning groun
-Siltation on spawning areas (from deforestation, agriculture, and dredging)
-Pollution from nutrients and contaminants
-Interest in the restoration has increased greatly.
-Zebra mussels may be a food source
-Lake sturgeon throughout the Great Lakes appear to be on the rebound.
-Sign that natural reproduction is occurring
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Once an important part of the ecosystem of Lake Erie and a significant catch for the commercial fishing industry.
One of the few fish in Lake Erie to spawn in deep clear water, (primarily the eastern two-thirds) and chose deeper,
Annual commercial catch that often exceeded 20 million pounds (an estimated $150 million today)
Unable to tolerate the pollution of and over-fishing
Last successful spawning occurred in 1954, and the fishery collapsed entirely within three years
Declared extinct in September of 1983
Blue Pike (walleye relative)
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Possible that a few were transferred to smaller lakes
But……… no DNA from a real blue pike to compare to
Angler named Jim Anthony had a fish in his freezer for the past 37 years, a possible blue pike
Offspring of a female blue pike and a male walleye so DNA is not that of an authentic blue pike.
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Health concerns due to contaminants if fish & seafood
Metals and metal-like elements such as arsenic, cadmium, lead, mercury, & others
Persistent organic pollutants such as polychlorinated biphenyls (PCBs), dioxins, and some insecticides. These substances tend to accumulate and persist in the environment.
Processing-related compounds such as sulphites (used in shrimp processing), and residues of drugs used in aquaculture (e.g., antibiotics and hormones).
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http://www.mbayaq.org/cr/SeafoodWatch/web/sfw_regional.aspx?region_id=6
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Discussion Questions
What do you do if your favorite fish/seafood is on the “avoid” list?
Are you willing to pay more for products that are sustainably harvested?