Humans have been exploiting resources from the sea for millennia

What is "good" for humans is generally bad for marine organisms and their environment:

Three examples of negative human impacts: Resource exploitation, Pollution, Habitat degradation

Exploitation: "harvesting" resources from the sea (food, fertilizer, etc...)

The term "stock" is often used by fishery's biologists to characterize a subset of the total population

"stock" is typically a very general (non-rigorous) term used to describe a regional population that is isolated from other conspecific populations during some period of life history

Defining a stock: geographic range, age/size distribution, life history variables

Recognizing stocks is important for understanding their health and management

Tags, molecular markers, otoliths, and census techniques may all help quantify fish stocks

Landings (number of fish harvested) are influenced by fishing effort (number of fishermen and number of hours spent fishing)

Catch/unit effort measures generally provide the best estimates of stock size

Landings are useful for managing harvest levels when stocks become over exploited.

Models of "Maximum Sustainable Yield" are often used to predict maximum harvest rates

Here is a good review of the challenge and approaches of stock assessment

Lack of data on stock size, demography, etc., combined with low levels of enforcement generally leads to severe over exploitation.

Capture methods commonly include hooks, nets, and traps.

Gill nets, pound nets, and seine nets either entangle fish or surround them with nets

Open ocean drift nets up to 30 miles long are sometimes released to capture squid and fish

Long line sets may be 20-80 miles long, with many thousands of hooks

When used intensively, long lines can be very effective:

US harvest of yellowfin tuna in the Gulf of Mexico in 1984: 35,000 lb.. In 1988: 12 million lb..

Cyanide sulfate and dynamite are often used to collect fish from coral reefs for food and the aquarium trade.

As a general rule, the most efficient harvesting methods are also the least selective and, thus, the most wasteful

"By-catch" describes the organisms that are captured, but discarded.... these are often smaller fish and invertebrates, but can include turtles, sharks, bill fish, and whales

Total global by-catch is currently estimated to be about 27 million metric tons per annum.

Shrimp trawling generates high levels of by-catch: 2-8 lb./1 lb. of shrimp

By-catch levels are highest in the western Pacific: 9 million metric tons/year

Most exploitable marine fisheries are characterized by cycles of boom and bust.

Aspects of supply and demand suggest a reduction in harvest levels as species become rare...

Even when stocks are severely depleted, economics can drive species closer to extinction. Three case histories:

Bluefin tuna

Bluefin tuna were originally considered trash fish... in 1934 they were sometimes collected for their livers and fish sold for ~ $0.15/lb.

As traditionally harvested fish stocks and other species of tuna became more rare, bluefin became commercially profitable

Today, blue fin tuna are prized for sushi and auctioned at special fish markets.

Japanese bidders can drive prices very high for fish of high quality:

A 715 lb. bluefin tuna was sold for $83,500 (~$117/lb.).

This fish produced ~ 2,400 sushi meals worth $75: total final worth of fish: ~ $180,000!

With such demand, fishermen employ planes and electronic harpoons to track down a single fish.

Sharks, once considered a menace to humans, are rapidly disappearing from our oceans

Today, sharks are harvested for meat, skin, cartilage, and fins

Shark fins are prized by Asian markets for their use in soups (they add no flavor, only texture).

They sell for up to $200/lb.

Many shark fins come from US waters.

Only 3 of 26 countries with shark fisheries have any management or research programs.

With long gestation periods and small clutch sizes shark populations do not rebound rapidly

Whales were targeted primarily for their oil until WW II... then they were used for pet food.

The advent of factory ships that processed whales greatly increased the rate of harvest.

Seasonal regulations were imposed in 1937, however, no limit was placed on how many whales could be killed, and the number of vessels hunting whales increased.

Species such as blue whales declined rapidly for several decades, and by the time hunting was banned in the 60s, they were already too rare to harvest commercially.

Japan continues to do limited whaling for "research" purposes.

Mariculture: mythical cure or salvation for over harvested fisheries?

Mariculture practices seek to rear marine organisms under controlled environmental conditions.

Given high levels of fecundity and low levels of recruitment, many mariculture attempts focus on juveniles

Providing substrate can promote settlement (e.g. mussels and oysters), however, local abundances of certain species can deplete local resources or produce high levels of organic waste.

Most mariculture attempts have failed to prove economically feasible. Rearing of salmon in pens is becoming more popular as wild stocks continue to decline.

Pollution: For years, humans have used the ocean as a dumping ground for waste:

Characterizing the intensity of pollution in time and space:

Chronic vs. acute pollution (time)

Point vs. non-point pollution (space)

Assessing the effects of pollution:

Population level declines in abundance and/or diversity

Bioassays that detect the presence of toxins or other chemicals

Some examples of marine pollution:

Toxic compounds used to control "pests" are often harmful

These can harm other species via bio-amplification (e.g. DDT)

Resistance to these compounds often develops quickly in the target species.

Anti-fouling paints inhibit settlement onto ship bottoms and docks.

Copper denatures protein and impairs the function of blood pigments

Tributyl tin (TBT) influences the reproduction of mollusks.

Polychlorinated biphenyls (PCBs) are used as lubricants

These can be highly carcinogenic and can bio-amplify into food-fish

Oil pollution is usually confined to surface waters and shorelines (oil floats)

Petroleum products typically harm sea birds and marine mammals that rely on insulation from feathers and fur.

Detergents used to clean up oil often harms other species

Effects can cascade through an ecosystem as one community after another in affected by a spill.

As in aquatic systems, eutrophication can occur where nutrients are overabundant.

This commonly occurs at the mouths of rivers, in estuaries, and in bays

Acid rain can contribute to eutrophication through the addition of nitrates (sulfur components also decrease pH... sometimes to toxic levels).

What about Carbon pollution in the atmosphere?

CO₂ levels are rising: currently atmospheric concentrations [CO₂]_atm = 380 ppm

projected: 2050: [CO₂]_atm= 480 ppm; 2100: [CO₂]_atm = 560 ppm

While concerns about climate change are valid and frightening, changes in the oceans are also alarming

Sea temperature rise

Sea level rise

Acidification

25% of atmospheric CO₂ is absorbed by the oceans

This causes acidification that changes the balance between the amounts of bicarbonate and carbonate

carbonate is necessary for the accretion of CaCO₃

Accretion is zero at carbonate concentrations of ~ 200µmol/kg ([CO₂]_atm~ 480 ppm)

Is this the end of coral reefs?

 

Habitat degradation is often found in coastal areas

Jetties alter the flow of sediment along coastlines.

Run-off and sedimentation can build bars that restrict flow

Use of marine substrate for building

Dynamite is used to kill fish and break up hunks of coral reef

Dams may be the most important reason that salmon stocks are declining in the Pacific NW

 

Related issues to discussions of sustainable take from marine habitats:

Marine Protected Areas (MPAs) and some examples:

Oceana: a non-profit marine conservation group

California Marine Life Protection Act

California's Channel Islands

Monterey Bay National Marine Sanctuary

Gulf of Maine

Seafood Consumption and the role of consumers in determining what species are bought at what prices.

Marine Stewardship Council

Monterey Bay Aquarium's Seafood Watch Site

 

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