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

Inland fish ponds in China FAO/20044

Aquaculture ponds can provide food, but can also cause pollution that harms natural rivers, lakes and oceans

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.

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

harvest

growth K

Hypothetical fish population responds to harvest regimes

Time

Bio

mas

s K

assume “s-shaped” population growth

Hypothetical fish population responds to harvest regimes

small harvest slower growth, top of S curve

Time

Bio

mas

s K

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

Time

Bio

mas

s K

Hypothetical fish population responds to harvest regimes

frequent harvest

population drops to non-viable level- below critical number

Hypothetical fish population responds to harvest regimes

Time

Bio

mas

s K

recovery takes time generation time survival

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

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

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 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

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

South AmericaAsia Trade winds

warm surface water

cold high nutrient water

Normal Year

South AmericaAsia Trade winds

warm surface water

cold high nutrient water

El Niño

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

Are world fisheries being overfished?

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

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.

Bottom oriented fish

Water column fish

Crustaceans (lobster, shrimp)

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?

rate of increase slowing

source FAO

In addition to # ships, technology (catch efficiency) has improved

Over fishing effects the target stock and:

by-catch species habitat destruction (reefs) trophic relationships

Bottom fish catches (demersals) declining

Small midwater fish(pelagics) increasing

Discards increasing!

And…. when catch is examined more closely

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

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

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!

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

Ontario

Superior

Michigan

Huron

Erie

Lost Fisheries of the Great Lakes

-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

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

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)

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_regional.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?