13.5 What issues affect marine fisheries?

fisheries have provided billions of people around the world nearly 20% of protein intake, with developing countries relying on fish for 27% of their dietary protein

Marine Ecosystems and Fisheries

world marine fishery drawn from five ecosystems:

(1) nontropical continental shelves

(2) tropical continental shelves

(3) upwelling areas

(4) coastal and coral systems

(5) open ocean

largest proportion of marine fishery found in highly productive shallow shelf and coastal waters, whereas low-productivity open ocean areas comprise only 3.8% of total. nearly 21% of world’s total catch from very highly productive upwelling areas, which represent only about 0.1% of ocean surface area

Overfishing

fisheries harvest from standing stock of a population = mass present in an ecosystem at a given time. successful fisheries leave enough individuals from standing stock to repop ecosystem after fisheries have made their harvest

overfishing occurs when harvesting of fish stocks takes place so rapidly that majority of population is sexually immature and therefore unable to reproduce

• can occur in any size or body of water including ponds, rivers, lakes, or oceans when fish or shellfish are harvested beyond sustainable level

• overfishing results in decline of marin efish populations and overall size of fish in a population

• fisheries biologists determine sustainable levels of a fishery by calculating maximum sustainable yield (MSY) = max amt of fish biomass that can be removed yearly from a stock and still allow the population to be sustained indefinitely

  • MSY must be determined yearly for each fishing stock and in addition to harvesting, is affected by several factors including:

    • # of predators

    • food availability

    • fish’s reproductive success

    • water temp (affected by human caused climate change)

**important to accurately estimagte fish stocks’s MSY to avoid exceeding it and overfishing

according to report by UN FAO, 80% of 523 world marine species classified as fully exploited, overexploited, or depleted/recovering from depletion

• these trends can be reversed: Ex. 85 fish stocks in US waters declared overfished or approaching being overfished between 1997-2012, 41 stocks no longer classified as overfished

Ecosystem Effects of Overfishing Large Predators

large predatory fish = keystone species/top predators = vital part of healthy marine ecosystems:

• prevent smaller fish from overrunning and destroying ocean ecosystems

• increase ecosystem healthy by culling sick and old populations of marine herbivores

Yet, modern fishing practices have harvest 90% of large predatory fish species from world ocean

removing large predators from marine environment often has unintended consequences:

• Ex. mid 1990s, cod was overfished and #s greatly reduced —> american lobster population increased to record numbers disturbing ocean’s ecological balance

• Ex. overfishing large predatory sharks —> explosion of their prey species: rays, skates, small sharks

• Ex. removal of sharks in reefs reduced predation and competition —> smaller fish proliferate

• Ex. removal of large fish from reefs —? increases # of smaller nonherbivore fish, algae can overgrow and cover coral reefs, blocking sunlight, denying nutrients for corals, and suppressing coral growth

with reduction of large fish, fishing industry has concentrated on smaller fish that occupy successively lower trophic levels, now low-trophic level species account for >30% of global fisheries production

• danger is that removing large #s of individuals from lower trophic levels can cause unwanted cascade of effects on other parts of marine ecosystems, particularly for fish, seabirds, and marine mammals that rely on these small prey for food

The End of Fish

scientists are predicting oceans w/out fish

• overall, selective removal of larger fish by comercial and recreational fishers leaves fish populations w/ fewer and smaller individuals

• when smaller pops of individuals reproduce, their offspring have less genetic variability, which can cause genetic changes that cut the avg growth rate, time to mature, and size of fish from generation to generation —> sever implications for health and sustainability of fisheries

**scientists determined that negative effects of pollution, habitat loss, and overfishing will deplete current marine fishing stocks by 2048

• if wasteful practices continue, scientists predict that fish will no longer live in oceans damaging marine ecosystems

actions being taken to solve this:

Ex. Seikai National Fisheries Research Institute in Japan and University of Maryland in US started raising bluefin tuna in large tanks to reduce fishing pressure on wild tuna pops while at same time supplying tuna for sushi

Ex. tuna being raised in enclosed ocean pens in coastal waters of Mexico

Ex. in Carlsbad, CA, white seabass being raised in a hatchery w/ millions being released into ocean to repopulate local waters

Recreational Fishing

recreational fishing has impact on fish populations

for some threatened sportfishing species i.e. red drum, bocaccio rockfish, and red snapper, recreational fishing poses more of a threayt than commercial fishing bc of size and # of fish taken by recreational fishers

new fishing regulations that target recreational fishers are needed as well

**commercial fishers blame recreational fishing for decline in some species and vice versa

World Fish Production

world marine fisheries catch in 1950 = 25M metric tons per year, hitting peak in 1996 at 130M metric tons per year —> steadily declining since then, in 2010 was 108M metric tons

• worldwide catch has decreased bc many marine fish tocks have been severely depleted by overfishing

• marine aquaculture has increased a lot, now accounting for >25M metric tons of fish to offset this

Incidental Catch

incidental catch / bycatch = marine organisms caught accidentally by fishers seeking commercial species

• on avg, ¼ of catch is discarded, but for some fisheries i.e. shrimp, incidental catch may be 8x larger than catch of target species

• incidental catch = birds, turtles, sharks, dolphins, species of noncommercial fish

in most cases these animals die before they’re thrown back overboard

**estimated 19M metric tons of bycatch per year in 1989, declined to 10M metric tons, still 10% of world’s total marine fish catch

Tuna and Dolphins

schools of yellowfin tuna commonly found swimming beneath spotted and spinner dolphins in eastern Pacific —> fishers commonly use dolphins to locate tuna and set a purse seine net around entire school

• when underwater line is drawn tight, net traps tuna underwater as well as dolphins at surface —> dolphins need to breathe and get stuck below water’s surface so they drown

1988 - biologist Samuel F. La Budde presented problem of dolphin deaths —> boycott on tuna —> US tuna canning industry said it wouldn’t buy or sell tuna caught using methods that kill/injure dolphins —> 1992 special addendum added to Marine Mammals Protection Act, protecting dolphins

• purse seine nets were modified so dolphins could be released alive

• dolphin populations still haven’t rebounded well

Driftnets

way of getting tuna and other species = driftnets/gill nets, involves capturing fish by their gills

driftnets made of crisscrossed monofilament fishing line that’s virtually invisible and can’t be detected by most marine animals as they swim into them

• depending on size of holes in net, it’s highly effective at catching anything large enough to become entangled —> high amounts of bycatch

until 1993, Japan, Korea, and Taiwan had largest driftnet fleets,

driftnetting was supposed to be restricted to certain fisheries but some fishers who claimed to be fishing for squid were involved in illegally taking large quantities of salmon and steelhead trout

driftnetters also targeting immature tuna in S Pacific —> resulting in reduced abundance of S Pacific tuna

tens of thousands of birds, turtles, dolphins and others killed annually in these nets as bycatch

efforts to reduce wasteful practice:

• US signed international treaty in 1989 prohibiting driftnets greater than 2.5km in S Pacific and includes clause prohitibing import of any fish caught in driftnets

Ghost Fishing

ghost fishing = describes any lost or discarded fishing gear that continues to catch fish, marine mammals, or other organisms after it’s been abandoned

Examples include:

• longlines

• gill nets

• entangling nets

• trammel nets

• traps

• crab and lobster pots

detrimental to enviornment bc anything caught by ghost fishing is killed and wasted. it’s so deadly bc abandoned fishing gear continues to entangle and kill marine organisms as long as it remains intact

Solution: use of biodegradable panels for crab and lobster pots that decompose w/in a few months after pots are lost, allowing captured animals to escape

Fisheries Management

fisheries management = organized effort directed at regulating fishing activity w/ goal of maintaining a long-term fishery. practices include:

• assessing ecosystem health

• determining fish stocks

• analyzing fishing practices (including recommending gear modification)

• establishing areas closed to fishing

• setting and enforcing catch limit

unfortunately fisheries management has historically been more concerned w/ maintaining human employment than preserving a self-sustaining marine ecosystem

one of most pressing problems faced results from fact that some fisheries encompass waters of many diff countries and involve a variety of ecosystems

Ex. many species of commercial fish reproduce in coastal estuaries along world and migrate long distances across international waters to preferred environment. fishing limits very difficult to envorce internationally and if human interference occurs at any location where fish reproduce or migrate to, these species can be severely reduced in #

another problem = degradation of many ecosystems sustaining fisheries

Ex. efforts in US to increase populations of once-abundant Gulf sturgeon are hampered by fact that 4/7 major river systems used by sturgeon are at or exceed capacity for breeding bc of reduction of available habitat

to be successful, fisheries management also has to take into account a wide range of factors

other issues inhibiting good fishery management:

• limited scientific analyses

• lack of regulations enforcement (particularly illegal, private, and international fishers)

• poaching

• misreporting of catch and bycatch

• seafood fraud and mislabeling

• political barriers

• inadequate guidance for minimally regulated new fisheries

Regulation of Fishing Vessels

major regulatory failure = absence of restrictions on # of fishing vessels

increase in fishing vessels = increased fishing effort = overfishing

• commercial fishers use tech i.e. GPS, depth finders and spotter airplanes to locate fish populations

• in some locations, fish becoming so scarce that the fishing effort costs more than the catch is worth

  • governments compound the issue by maintaining an unsustainable # of fishing vessels

Case Study: Fisheries in NW Atlantic

under management by international commission for NW Atlantic fisheries, fishing capacity of international fleet increased 500% from 1966 to 1976 but total catch only rose by 15% = overexploitation

• difficulty of enforcing regulations by the international commission was largely responsible for canada’s unilateral decision to extend its right to control fish stocks in this area, US did same thing later

• claiming coastal waters has limited effectiveness

canadian government had to shut down Grand Banks fishery resulting in loss of 40,000 jobs

Deep Water Fisheries

one result of depleting and/or banning certain fish stocks is that the fishing industry then expands its efforts into deep sea where there are few regulations

• most deep water species have low metabolic and reproduction rates —> severely impacted by fishing

• deep-sea ecosystems are beginning to feel effect of this increased fishing effort as well:

  • tall seamounts rise precipitously from deep-sea floor providing a unique environment that harbors many species of fish and deep0water coral —> to effectively catch fish here, fishers use large bottom-dragging trawl nets the size of football fields with two large steel doors that each weighs several tons. as these nets are dragged along the sea floor, they do long-lasting damage and have proven to negatively affect these slow-growing ecosystems

Ecosystem-Based Fisheries Management

ecosystem-based fisheries management: employs more comprehensive approach to understanding fish stocks indluing analysis of such variables as:

• fish habitat

• migration routes

• predator-prey interactions

ecosystem-based management reverses order of mgmt priorities, starting w/ ecosystem rather than a target species. focuses on rebuilding fisheries on a global basis

• sustainable fisheries can be achieved if mgmt strategies are adpoted that remove subsidies and give individual fishers a right to a proportion of the total catch

  • by removing competition, fishers of all types would be encouraged to act to sustain the entire fishery because, as the common fish stock improves, each individual’s quota will increase. in this way, fishers will have the incentive to manage the stock sustainably, thus avoiding overfishing and the eventual collapse of the fishery

RECAP

for fisheries to be sustainable, they must employ ecosystem-based fisheries management, which considers variables in marine ecosystems and not just individual species. in addition, fishing limits must be upheld despite political factors, unwanted bycatch must be reduced, and critical fish habitats must be protected.

Effectiveness of Fisheries Management

scientists analyzed 6 key parameters:

• scientific quality of mgmt recommendations

• transparency of converting recommendations into policy

• enforcement of policies

• influence of subsidies

• fishing effort

• extent of fishing by foreign entities

results show fisheries management remains largely ineffective

how can fisheries in danger of collapse be brought back? these three things need to be implemented:

1. set scientifically established quotas or limits on amt of fish caught and enforce those limits

2. reduce wasteful and unwanted bycatch

3. protect vital habitats that fish use as spawning and nursery areas

**humans have understanding and tech to do this but all 3 needed to accomplish bringing back fisheries

Effect of Global Climate Change on Marine Fisheries

human-caused global climate change impacting fisheries in many areas

researchers used temperate preferences of fish and other marine species as “biological thermometers” to assess effects of ocean warming on marine species

marine fish normally found in specific regions of ocean related to specific water temp to which they’re adapted

• if same species now found in weird area not normal —> indicates water temp in this region has changed

global climate change having severe impact on over-exploited fisheries

• likely will cause collapse of several depleted fish stocks

• even healthy fisheries can be affected

  • west coasts of continents where populations dependent on upwelling, warming of oceans and reduction in upwelling could devastate salmon, tuna, and mackerel

• climate change will likely result in a global-scale redistribution of nutrients in the ocean w/ net transfer of nutrients from surface waters to deep ocean

• rising sea level will inundate low-lying coastal areas such as mangroves and marshes which are important breeding grounds and nurseries for many commercial fish species

RECAP

higher ocean temps are driving species away from where they normally exist into cooler waters, deeper into oceans, or to high-lat regions. species that prefer warmer water, in turn are population areas vacated by cool-water species.

Seafood Choices

consumers can help by making wise choices in fish they consume by purchasing only fish from healthy, thriving fisheries. some types of seafood carry less environmental impact than others bc of differences in abundance, how they[re caught, and how well fishing is managed.

help by purchasing seafood w/ “sustainable” label

RECAP

marine fishing industry suffers from overfishing, wasteful practices that produce a large amt of unwanted bycatch, and a lack of effective fisheries mgmt.

CONCEPT CHECK 13.5

(1) Define overfishing. When a species is overfished, what changes are there in the standing stock, the size of individuals in the remaining fish population, and the maximum sustainable yield?

• overfishing = occurs when catching of fish takes place so rapidly that the majority of the population is sexually immayture and unable to reproduce, resulting in depleted populations

• stock goes down, smaller size of individuals, and max sustainable yield decreases

(2) What impact do lost or abandoned traps, nets, and fishing gear have on the environment?

• they continue to entangle, entrap, and kill marine species until they biodegrade but this can take very long periods of time

• as long as they’re still in the water, they hurt animals

(3) Describe three unintended consequences that have occurred in marine ecosystems when top predators are removed.

• population explosion - disturbs ecological balance

• population explosion of certain animals can cause their prey to be completely depleted bc there’s too many of them and then they eat other things

• coral reefs reduce competition, increaseing # of nonherbivore fish —> algae overgrows and covers coral reefs, blocking sunlight and denying nutrients for coral, suppressing coral growth

(4) As an environmentally conscious consumer, what factors should you take into consideration before purchasing seafood at a restaurant or grocery store?

• look for “sustainability” logo

• purchasing only fish from healthy, thriving fisheries

• different types of seafood have diff environmental impacts