Download World Fisheries and the Great Lakes

UN-Food & Agriculture Organization statistics
World consumption of fish increasing, especially China
Capture fishery = wild fish & other spp. caught from
Oceans, Lakes & rivers
Aquaculture = domestic fish & other spp. raised in
ponds or floating cages
A few areas eat lots of fish, some almost none
Aquaculture driving big increases in fish
consumption in China
Aquaculture ponds can provide food, but can also
cause pollution that harms natural rivers, lakes and
oceans
Inland fish ponds in China FAO/20044
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 as
Maximum Sustainable Yield (MSY)
Most recent thinking suggests that more holistic view
should be taken…… we’ll talk about why.
 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
Hypothetical fish population responds to
harvest regimes
harvest
assume “s-shaped” population growth
Biomass
growth  K
K
Time
Hypothetical fish population responds to
harvest regimes
Biomass
small harvest
K
Time
slower growth, top
of S curve
Hypothetical fish population responds to
harvest regimes
Biomass
keeps biomass oscillating
around K/2, highest
growth rate, leads to MSY
K
Time
regular harvests
Hypothetical fish population responds to
harvest regimes
Biomass
frequent harvest
K
Time
population drops to
non-viable levelbelow critical number
Hypothetical fish population responds to
harvest regimes
Biomass
recovery takes time
 generation time
 survival
K
Time
borderline between 2 scenarios can be fine line
Biomass
 spatial variability
 temporal variability
 other species
 inaccurate biomass estimate
K
Time
MSY can be risky
borderline between 2 scenarios can be fine line
Biomass
 spatial variability
 temporal variability
 other species
 inaccurate biomass estimate
K
Time
MSY can be risky
Climate= source of uncertainty
Natural year to year variation
Climate change models predict more extreme events
Individual stocks can crash…..
South American
anchovies were
~20% of world
catch at this
time
Heavy fishing
maintained
during El Nino
year.
Normal year
Trade 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 Ecuador
Sea surface temperature ~ 8 C higher in west, w/ cool temperatures off
South America, due to an upwelling of cold water from deeper levels
Cold water is nutrient-rich, supporting high levels of primary productivity,
El Niño
Trade winds relax in the central and western Pacific
Depression 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
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
http://www.fnoc.navy.mil/PUBLIC/
Normal Year
Asia
Trade winds
warm surface water
cold high nutrient water
South America
El Niño
Asia
Trade winds
warm surface water
cold high nutrient water
South America
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
Trade winds
http://www.fnoc.navy.mil/PUBLIC/
Are world fisheries being overfished?
ratchet effect
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…
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.
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.
Crustaceans (lobster, shrimp)
Water column fish
Bottom oriented fish
Not just cod catches down, many species
http://www.sethwhite.org/animals.htm
Despite individual stock crashes, according to world
Food & Agriculture Organization (FAO) total marine
catch is going up.
But…… effort has been increasing
…. the ratchet effect in action?
source FAO
rate of increase slowing
In addition to  # ships, technology (catch
efficiency) has improved
Over fishing effects the target stock and:
 by-catch species
 habitat destruction (reefs)
 trophic relationships
And…. when catch is examined more closely
Bottom fish catches
(demersals)
declining
Small midwater fish
(pelagics) increasing
Discards increasing!
large scale seining
 Bycatch, or the nontargeted 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”)
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
Over fishing effects the target stock and:
 by-catch species
 habitat destruction (reefs)
 trophic relationships
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.
Trawling imperils little known deep reefs; may affect
future catch
Trawl scar
Over fishing effects the target stock and:
 by-catch species
 habitat destruction (reefs)
 trophic relationships
 Trophic level
of catch is
decreasing
 Assume that
fisheries switch
to low trophic
level species in
response to
abundance
North Sea
Increased fishing of pout could
cause trophic cascade, might
eventually feed back to cod!
http://www.fauna.is/Pages/archves/fish4/spaerlingur.html
Norway pout
Cod & other
human food fish
euphausiid krill
http://lifesci.lscf.ucsb.edu/~biolum/organism/pictures/euphausiid.html
copepods
 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
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
Lost Fisheries of the Great Lakes
Superior
Huron
Michigan
Ontario
Erie
Lake Sturgeon
-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 late1800s.
-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 pounds
Lake Michigan, commercial harvest closed in 1929 after catch declined to
only 2000 pounds
Trends in Lake Sturgeon Catches in the Great
Lakes
(from Harkness and Dymond 1961)
-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
Blue Pike (walleye relative)
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
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.
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).
http://www.mbayaq.org/cr/SeafoodWatch/web/sfw_re
gional.aspx?region_id=6
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?