Biological Resources (A2); Aquatic Food Resources (Complete) Flashcards
Marine productivity; how much of the Earth’s surface is covered by oceans and why is this not all productive?
-70%+
-Only a small proportion is biologically productive as limiting factors restrict growth of the most important photosynthetic organisms; algae
Marine productivity; how are there variations in light levels in the ocean and how does this impact organisms?
-Little light penetrates water to a greater depth than 100m, less if water is turbid, so photosynthesis is limited to surface water layers, called the photic zone
-Most life at greater depths, in the aphotic zone, relies on food produced near the surface, eg planktonic algae that’s carried down by water currents/bodies of dead organisms that sink
Marine productivity; how does nutrient availability in the oceans impact organisms + example of this?
-Algae absorb nutrients directly from water as there’s no soil & they don’t have roots. Some nutrients are readily available, such as CO². Others are often the limiting factor on biological productivity when they’re not sufficiently abundant, eg phosphates
-Low solubility of phosphates causes oceans to be deficient in phosphates except where there are processes that cause phosphates to be added
-Phosphate levels in the photic zone are increased by runoff from rivers & in areas in which deep, cold water rises towards ocean surface, a process known as upwelling, but these aren’t found in most areas of open ocean
-In open areas nutrients contained in planktonic organisms are carried to the seabed when they die; may reduce nutrient availability in surface photic layer so future biological productivity is reduced
Marine productivity; what is freshwater productivity like?
-Water bodies on land are often very productive as they receive nutrient runoff from the land & receive high light levels as they’re relatively shallow
-Total productivity is limited by the relatively small total area of rivers & lakes
Fishing; what does fishing include?
The capture of a wide range of species of different taxa, including fish & shellfish (crustaceans + molluscs)
Fishing; what does demersal fishing include?
Fishing for species that live on the seabed
Fishing; what are the two types of demersal fishing?
-Demersal trawling is used for species on the seabed like cod, hadddock, plaice, shrimps & scampi
-Demersal long lines use a line of baited hooks to catch species like cod & haddock
Fishing; what are shellfish traps?
Baited traps that catch crustaceans like crabs, crayfish & lobsters
Fishing; what does pelagic fishing include?
Fishing for species that live in open water above the seabed, often near the water surface
Fishing; what are pelagic trawling and its advantage/disadvantage?
-Used for species that form shoals in mid-water/near the surface like bass, anchovies, herring & mackerel
-Pelagic fish often form single-species shoals so the catch of non-target species is usually low but predator species may also be caught accidentally, eg porpoises & dolphins
Fishing; what are pelagic drift nets?
Long curtain-like nets that are supported by floats & catch pelagic species near the surface eg tuna + herring
Fishing; what is purse seining and how does it work?
-Uses a net that’s laid around a shoal of fish
-The top is held up by floats while bottom is held down by weights then pulled tight underneath the shoal
-It’s used for species like tuna, sardines, herring & anchovies
Fishing; what are pelagic long lines used for?
-Use a line of baited hooks which can be many kilometres in length
-Catch species like tuna & squid
Fishing- environmental impacts; how can fishing have environmental impacts?
-Can have major impacts on target species by reducing their populations but can also have impacts on non-target species
-Some of these impacts are direct, while others are caused indirectly by other ecological effects of fishing
Fishing- environmental impacts; how can fishing cause population decline in fish species?
-Population of any species will decline if mortality exceeds birth rate but some species are more likely to be overfished than others
-K-selected species are more vulnerable to overfishing as they produce fewer young & start breeding at an older age, eg Orange Roughy, Blue Fin Tuna, & all shark speces
-These species may reach a catchable size before they’re sexually mature, so overfishing could remove the entire breeding population
-The survival of the population then relies on immature fish which may be caught before their first chance to breed
Fishing- environmental impacts; what are two species vulnerable to overfishing and why?
-The ‘common’ skate is the biggest skate species reaching a size of 1.9m across its ‘wings’. It has few natural predators, starts breeding around 11 years old, produces few young, & can live to be 100+. It’s not a commercially important species but it’s caught in demersal trawls. Its range includes the NE Atlantic, Mediterranean Sea & Baltic Sea. It’s now extinct in the Baltic sea & Critically Endangered in the Mediterranean Sea + NE Atlantic. The commercial value of demersal trawling makes it likely that fishing will continue & the Common Skate will become extinct. It’s been renamed the Blue Skate/Flapper Skate
-The Greenland Shark was fished commercially for lamp & lubricating oil until 1960s. Its main threat now is bycatch from commercial deep-water trawling. It’s a cold-water species but little is known about its range/populations size. It can live to be 400+ years old but doesn’t start breeding until it’s 100-150 & produces few young so it’s very vulnerable to overfishing
Fishing- environmental impacts; what is bycatch?
-The catch that isn’t wanted
-It’s usually the catch of non-target species but can also include catch of target species where individuals are too small to be legally landed/sold
Fishing- environmental impacts; what are the reasons for by-catch being unwanted?
-Immature fish of the target species that are too small to sell. This may reduce future catches by killing the fish that would’ve grown to reach a saleable size
-Individuals of species which would be saleable but catch quota has already been reached, so they must be discarded. If these species are still being killed during fishing for other species, then having a catch quota will fail to protect them
-Species with no commercial value
-Many of the bycatch organisms will be dead/injured & won’t survive when thrown back into sea
Fishing- environmental impacts; how do drift nets create bycatch?
Are non-selective & will catch any animals swimming near the surface including whales, dolphins, turtles + sharks
Fishing- environmental impacts; how do pelagic long lines cause bycatches?
-Albatross are large seabirds that feed over large areas of the open ocean in the southern hemisphere & North Pacific
-Most species can’t dive deep into the water so collect food like squid, kill & fish near the water surface. Large numbers are caught by long-line fishing where they drown after being caught on the lures put out for squid/fish
-Albatrosses are long-lived birds living up to 50 years, and don’t normally start breeding until they’re 7-10yrs old
-Most species have a low reproduction rate, laying one egg every second year so their populations are seriously affected by any increase in mortality -Other bycatch taxa caught on long lines include sharks & turtles
Fishing- environmental impacts; how does pelagic trawling cause bycatches?
-Pelagic pair trawls for seabass can kill porpoises
-The porpoises are trying to catch the bass but become trapped in the nets where they drown
Fishing- environmental impacts; how does demersal trawling cause bycatches?
Seabed fish often live in mixed-species shoals so chance of catching a mixture of species is high
Fishing- environmental impacts; how does shrimp trawling cause bycatches?
-Uses nets w/ a very small mesh size so few bycatch animals can escape
-These include crabs, sea urchins, molluscs. & starfish
-The by catch of shrimp trawling can make up as much as 99% of catch
Fishing- environmental impacts; what is ghost fishing and how does it cause environmental impacts?
-Fishing gear that’s been discarded/lost may continue to trap & kill marine organisms
-The dead organisms caught in the fishing gear often act as bait + attract more individuals which also become trapped & die
Fishing- environmental impacts (habitat damage); how can different kinds of fishing cause seabed damage?
-To be effective, demersal trawls need to disturb organisms so that they swim upwards & are caught in the net, especially if they normally live in the sediments on the seabed, eg shrimps & scampi (Norway Lobsters)
-Trawl nets often have chains/metal balls to disturb the seabed. This mixes the shallow aerobic surface layer of the seabed w/ deeper anaerobic layers
-The nets also destroy slow-growing organisms like sea fans & deep water corals
Fishing- environmental impacts (habitat damage); how can fishing cause coral reef impact?
-Coral polyps are sensitive to physical damage as can be killed if they’re pressed against the sharp coralite cup to which they’re attached
-Nets, traps, ropes & discarded gear can all cause physical damage
Fishing- environmental impacts (habitat damage); what are seagrass beds and why is their damage from fishing disadvantageous?
-Grass-like flowering plants that grow on shallow sandy areas of relatively protected tropica seas
-They’re important nursery grounds for many species of fish that may live on coral reefs/in deep water as adults
-Disturbance by trawling kills plants so their roots no longer hold sand grains together
-Currents & waves move the sand around, making it more difficult for new plants to colonise + become established
Fishing- environmental impacts (habitat damage); what is dynamite fishing and how can it cause environmental damage?
-The pressure waves released by underwater explosions can stun fish & make them easy to catch
-Use of dynamite is illegal in most countries but it’s still carried out in remote areas, esp where subsistence fishermen are finding it difficult to catch fish w/ other methods
It’s a particularly common method on coral reefs where nets can’t be used to catch fish that live among coral heads
-The explosions destroy coral & kill many other organisms
Fishing- environmental impacts (habitat damage); how can fishing cause food web impacts?
-Reducing the numbers of any species will affect the other organisms that are in the same food web, eg;
-Competitors may become more common
-Their prey may become more common
-Their predators may become rarer
Fishing- methods of reducing environmental impacts; what are catch quotas and how are they successful + unsuccessful in reducing environmental impacts?
-A catch quota sets a limit on total weight of fish that can be landed
-This quota may be divided up amongst all fishing boats in the fleet
-Quotas work best when fish are found in single-species shoals where fishing will stop if quota for that species has already been reached
-In mixed fisheries, many species may be caught in the same net. If the quota for one species has been reached then any surplus must be thrown back even though they’re probably dead, while fishing for other species continues
Fishing- methods of reducing environmental impacts (fishing equipment design & use); how can mesh size reduce environmental impacts?
Net mesh size can be set so that fish below a certain size can escape
Fishing- methods of reducing environmental impacts (fishing equipment design & use); how can mesh design reduce environmental impacts?
-Fishing nets are designed so that mesh direction is diagonal to direction of movement
-This gives net elasticity as it’s pulled through water but mesh closes as it fills w/ fish & drag increases, so smaller fish can’t escape through shrinking gaps
-Panels in net w/ mesh at right angles to direction of movement don’t close up so small fish can still escape
Fishing- methods of reducing environmental impacts (fishing equipment design & use); how can escape panels reduce environmental impacts?
Turtle Exclusion Devices (TEDs) are large spring loaded escape panels in the nets which allow turtles to escape
Fishing- methods of reducing environmental impacts (fishing equipment design & use); how can acoustic deterrent devices reduce environmental impacts?
Dolphin pingers produce high frequency sounds that warn dolphins about the presence of the net
Fishing- methods of reducing environmental impacts (fishing equipment design & use); how can hook shape reduce environmental impacts?
Longline hooks w/ curved points still catch tuna but are less likely to catch albatrosses
Fishing- methods of reducing environmental impacts (fishing equipment design & use); how can decoys reduce environmental impacts?
Attract & distract birds so that they don’t get caught on longline hooks
Fishing- methods of reducing environmental impacts (fishing equipment design & use); how can sinkers reduce environmental impacts?
Weights attached to pelagic longlines hold hooks down in the water so that they still catch fish but don’t catch albatrosses
Fishing- methods of reducing environmental impacts (fishing equipment design & use); how can night fishing reduce environmental impacts?
Using longlines at night when birds aren’t feeding
Fishing- methods of reducing environmental impacts (fishing equipment design & use); how can biodegradable & radio tracked equipment reduce environmental impacts?
-To reduce ghost fishing
-If traps for crabs & lobsters are lost, they may continue to catch more crabs & lobsters as dead trapped individuals act as bait for more to be caught
-Traps that are held together by biodegradable rope will fall apart if they’re lost
-In the USA, traps have radio-transmitters that activate if traps are lost so they can be recovered
Fishing- methods of reducing environmental impacts; how can restricted fishing efforts reduce environmental impacts?
-In some areas around the UK there are limits on the size of fishing boats & power of their engines
-Fishing boats have limits on the number of days each year that a boat may spend fishing
-Where number of fishing boats is so large that overfishing is unavoidable, boat owners may receive compensation for their boats to be de-commissioned
Fishing- methods of reducing environmental impacts (restricted fishing methods); how can the banning of drift nets reduce environmental impacts?
Some areas, drift nets may be banned/their length restricted
Fishing- methods of reducing environmental impacts (restricted fishing methods); how can the banning of demersal trawling reduce environmental impacts?
-In areas where the seabed ecosystem is particularly sensitive/important demersal trawling may be banned
-Demersal trawling is banned on the NW Rockall Bank & Hatton Bank which are large deep water coral reefs off NW coast of Scotland
Fishing- methods of reducing environmental impacts (restricted fishing methods); what are no take zones (NTZs) and how can they reduce environmental impacts?
-Areas where fishing & other activities that exploit wildlife/damage the habitat aren’t permitted, eg Palau in the Pacific Ocean
-This protects the breeding populations of breeding adults, esp larger individuals
-They produce a lot of offspring which can colonise surrounding areas where fishing may have reduced populations of breeding adults
-The communities of wildlife species that live within NTZ can recover once damaging activities stop
Fishing- methods of reducing environmental impacts (restricted fishing methods); how can turtle bycatches be reduced?
-In tropical fishing areas w/ large numbers of turtles, reducing time that net is towed can reduce bycatch mortality
-The survival rate of turtles caught in shrimp trawls depends on length of time they were in the net
If it’s >10 mins the survival rate is 99%+
If the trawls are towed for 1hr then 50 - 100% drown
Fishing- methods of reducing environmental impacts (restricted fishing methods); what are closed-seasons and how can they be successful and unsuccessful in reducing environmental impacts?
-A ban on fishing for part of the year allows the fish to grow to a larger size
-Ideally, the closed-season should include the breeding season to protect future generations, however, many fish species congregate in shoals to breed which makes them easier to catch, so fishermen may oppose this restriction
Fishing- methods of reducing environmental impacts (restricted fishing methods); how can minimum catchable size reduce environmental impacts?
-Banning capture of small fish may not reduce the mass of the catch by much but it may allow large numbers of small fish to grow to a larger size & live long enough to breed
-Eg cod; 35cm & mackerel; 30cm
Fishing- methods of reducing environmental impacts (restricted fishing methods); how can maximum catchable size reduce environmental impacts?
-Protecting large individuals may ensure there’s a surviving population of breeding adults
-Each individual, being large, may produce many young, eg;
-Female lobsters around Outer Hebrides of NW Scotland may not be caught if carapace (shell) is longer than 145mm
-Larger Nassau Grouper in some areas of coral reefs of elize in Central America are protected to conserve population of good breeding individuals
Fishing- methods of reducing environmental impacts (restricted fishing methods); how can protected individuals reduce environmental impacts?
-Future production of young can be increased if adults known to breed are protected
-Female lobsters caught & found to be carrying eggs must be released
-A V-notch is cut in the tail so if it’s caught again it’ll be released. Female velvet crab around Orkney must be released if they’re carying eggs
Fishing- methods of reducing environmental impacts (restricted fishing methods); how can captive rearing and release reduce environmental impacts?
-This is also called population seeding
-The wild populations of some species may be increased by releasing individuals that have been raised in captivity
-They’re usually raised from eggs/larvae until their chances of survival in wild are good so they should increase the size of the adult population, eg lobsters, oysters
-Most marine species spend their first few weeks drifting in the plankton before they settle to the seabed where they may colonise a suitable habitat
-Most individuals are either eaten while they are drifting in plankton/fail to find a suitable habitat
-Population seeding increases the chances of surviving this period
Fishing- population dynamics & monitoring fish populations; what are breeding rates like in fish species and what does this result in?
-All species are adapted via evolution to have a natural breeding rate which exceeds rate that’s necessary to sustain the population
-This breeding surplus won’t increase long-term adult population as carrying capacity of the environment will have been exceeded & surplus individuals will die
-In any population which exceeds carrying capacity, density-dependant factors will increase mortality rate, esp intra-specific competition for food
Fishing- population dynamics & monitoring fish populations; what happens if adult mortality rate in fish increases?
If adult mortality rate increases (eg, due to fishing) then more juvenile fish will survive & be recruited to adult population as more food will be available & intra-specific competition will have reduced. This’ll maintain the population
Fishing- population dynamics & monitoring fish populations; what can lead to a rapid population decline in fish?
-If an excessive number of adults is caught then adult population may decline as there aren’t enough young to replace them
-A reduced adult population will produce fewer young which may further reduce ability of population to recover & lead to a rapid population decline
Fishing- population dynamics & monitoring fish populations; when can fishing not always reduce the total population?
As long as catch doesn’t exceed population’s ability to replace losses
Fishing- population dynamics & monitoring fish populations; how can overfishing affect population dynamics?
-Overfishing isn’t necessarily evident in reduced catches as total catch weight may be maintained by catching a larger number of smaller fish
-If such fishing continues then adult breeding population may be reduced to the point that very few young fish are produced; may result in complete population collapse
-If fish species reaches a catchable size after it’s started breeding then there will always be an adult breeding population, although overfishing may remove all larger fish
-If a fish species reaches a catchable size before it’s large enough to breed then it’s possible to catch all breeding adults & destroy entire population
Fishing- population dynamics & monitoring fish populations; what is the Maximum Sustainable Yield (MSY) and how can it affect population dynamics?
-The greatest biomass that can be removed from the population each year w/out population suffering a long-term decline
-It’s important that fishing rate doesn’t exceed MSY as that’d cause over-fishing & a population decline
Fishing- population dynamics & monitoring fish populations; what are examples of fish that have been exploited above the Maximum Sustainable Yield (MSY) and how?
-Orange Roughy; a deep water fish species found off many coasts like New Zealand, SE Australia, W Ireland & NW Scotland. It was first exploited in the late 1970s but many populations were soon overfished. It’s a k-selected species so it’s very vulnerable to overfishing. The fish live to an age of 150 but don’t start breeding until they’re 30 years old & produce few eggs
-Atlantic Cod; reach a catchable size at age 2 but most don’t reach maturity until age 4 so excessive fishing can remove majority of breeding population
-Tuna; start breeding after they’ve become large enough to be caught so excessive fishing can remove most of breeding population
Fishing- population dynamics & monitoring fish populations; how can Maximum Sustainable Yield (MSY) be estimated?
-Reliable data are needed in to estimate the MSY
-Biomass can be estimated if following information is available to use in the Russell formula;
S1 = biomass of stock at beginning of year
S2 = biomass of stock at end of year
A = biomass of young fish added to stock
G = biomass added by growth of all fish in the stock
C = biomass caught by fishing
M = biomass lost via natural mortality
-Russell Formula; S2 = S1 + (A + G) - (C+M)
Fishing- population dynamics & monitoring fish populations; why might data about fish in the sea be difficult to collect?
-Fish populations are often mobile & can move long distances, often betw the territories of different countries
-The distribution of fish populations is often very uneven
-Collecting representative data of a large enough proportion of total area occupied by population may be impractical
Fishing- population dynamics & monitoring fish populations; how can catch size of fish be measured?
-Total landed catch each year isn’t always a good measure of biomass/population size of species being exploited
-Technological changes may make it possible to maintain catches while the population is declining at an increasing rate, eg bigger boats w/ bigger nets, improved fish detection equipment such as sonar
-The final, sudden population collapse may come as a surprise
Fishing- population dynamics & monitoring fish populations; how can catch per unit fishing effort be measured and why?
This is more difficult to measure but it’s a better measure of fishing sustainability than the actual catch
If it’s becoming harder to maintain catches then population is being overfished
Fishing- population dynamics & monitoring fish populations; how can mean fish size be measured and why?
-Catch biomass may be maintained but this can hide the fact that it includes an increasing number of smaller fish
-However, a reducing mean fish size may indicate that older aduts are being caught faster than they’re being replaced
Fishing- population dynamics & monitoring fish populations; how can mean fish age be measured and why?
-In many species, the age of fish can be determined by growth rings on scales that grow on their skin/from otoliths which are bones in their ears
-If the mean age is declining then overfishing is taking place
Fishing- population dynamics & monitoring fish populations; why is data on catches collected and what can this tell us?
-People fishing generally only have knowledge of fish in the population large enough to be caught in their nets
-If data on catches are collected then current catchable population can be estimated
-The fish in younger year groups are very important as they’ll be recruited to the adult population in the future & would replace those that have been caught/died
-If there are too few fish in the younger year groups, then adult population could suddenly collapse. If the adult population declines but fish catches are not reduced then population decline will accelerate as a greater proportion of the population is being removed
-W/ fewer adult fish, fewer young will be produced
Fishing- population dynamics & monitoring fish populations; why is data on fish eggs and larvae collected and what happens if it isn’t?
-Most fish eggs & larvae die in the first few weeks of life when they’re planktonic. They’re eaten by predators, fail to find food or suffer accidental deaths during storms/by being carried into unsuitable areas by currents
-Survival rates in different years can vary greatly so knowing population of breeding adults isn’t an accurate predictor of number of young fish that’ll be produced
-Collecting data on planktonic fish egg & larval populations can help to predict number of young fish likely to be recruited to adult population in future years
-If this data isn’t collected then it’s possible that several years of poor survival of eggs & larvae may lead to poor recruitment + sudden population collapse as fishing rates weren’t reduced to anticipate lowering in MSY
What is aquaculture and its aim?
-Aquaculture is to fishing what agriculture is to hunting & gathering
-It aims to control aquatic ecosystems so that more food enters the human food chain
Aquaculture- principles; what is extensive aquaculture and its purpose?
-Involves minimal inputs which may simply involve a pond where fish have been introduced to feed on wild food naturally present before being caught when they’ve grown
-Greater inputs may involve feeding w/ wastes, adding nutrients, or control of competitors & predators
-May be for subsistence/commercial purposes
Aquaculture- principles; what is intensive aquaculture and its purpose?
May involve artificial control of all abiotic & biotic limiting factors to maximise productivity + profitability for commercial purposes
Aquaculture- principles (species selection); how do local conditions & species’ adaptations affect the choice of aquaculture species?
-Local conditions will control species that can survive, esp temp & water quality
-Salmon & trout are important in cooler temperate regions while Tilapia thrive in warmer tropical regions
-Marine species are kept in coastal areas
Aquaculture- principles (species selection); how does market demand affect the choice of aquaculture species?
-In MEDCs the main species raised by aquaculture are carnivores like salmon & trout due to their better flavour + popularity w/ customers
-In LEDCs the traditional species raised by aquaculture are herbivores/omnivores, eg carp & tilapia as they can feed on naturally occurring vegetation, phytoplankton & wastes
-They require low food inputs, although productivity is increased if more food is provided
-As international transport has become easier, demand for seafood in MEDCs has stimulated a big expansion in tropical aquaculture
Aquaculture- principles (selection of adults for breeding); what do desirable characteristics selected for breeding include?
-Disease resistance
-Rapid growth rate
-Good appearance, eg bright colour
Aquaculture- principles (selection of adults for breeding); how are adult fish bred?
-Eggs & milt (sperm) are collected from mature individuals
-Hormone injections may be used to induce spawning
Aquaculture- principles (gender control); how can the gender of fish be controlled?
-Gender of fish can be controlled hormonally regardless of their genetics
-Young fish w/ 2 X chromosomes normally become female, while fish w/ 1 X chromosome & 1 Y chromosome normally become male
-However, if young fish are given female hormones they’ll develop into female adults
-If they are given male hormones they’ll all develop into male adults
Aquaculture- principles (gender control); why is the gender often controlled in rainbow trout?
-Meat from female trout has a better flavour than meat from males
-Some female fish are given the male hormone testosterone
-They’re still genetically female but they’re functional males & produce sperm, all of which carry an X chromosome
-When they’re used to fertilise eggs w/ X chromosomes, only female fish are produced
Aquaculture- principles (gender control); why is the gender often controlled in Tilapia?
-Male Tilapia are more energy efficient than fernales & grow larger
-Treating the young fish w/ male hormone testosterone produces all male fish so a bigger & more marketable harvest is produced
Aquaculture- principles (gender control); what are Triploid fish and why are they created?
-Fish that escape from fish farms may prey on local wildlife & compete w/ other fish but ecological impacts of fish that escape from fish farms aren’t serious if they can’t reproduce
-Triploid fish have 3 sets of chromosomes & are infertile
-This is achieved by heat/pressure-treating eggs soon after fertilisation has taken place
Aquaculture- principles (control of pests & diseases); how is disease/infection made more likely in fish?
-Keeping fish at high stocking densities increases risk of spread of disease betw individuals
-High stocking densities increase contact & collisions betw fish. This increases risk of spread of pathogens & parasites
-Injuries that may lead to infections are also more likely
Aquaculture- principles (control of pests & diseases); how are diseases/pests controlled in fish?
-Where water flows betw tanks w/ fish of different ages, the flow is from tanks w/ younger fish to tanks w/ older fish. This reduces risk of continual spread of disease from older fish to new stock
-A lower stocking density reduces these risks
-Pesticides may be used/biological control like wrasse that eat lice that carry disease
-Tanks w/ circulating water currents encourage all fish to swim in the same direction so there’s less contact betw them which could’ve transferred pathogens
Aquaculture- principles (competition and predation); how is competition and predation controlled and why?
-Other competitors/predators species are rarely a problem in closely controlled intensive systems but outdoor large-scale systems are harder to protect
-Fencing, netting & bird scarers can be used to exclude problem species
-Culling may be used to reduce populations of pest species
-Some licences are granted in the UK for killing of seals & cormorants
Aquaculture- principles; why and when is nutrition used in fish species?
-Herbivorous fish are more likely to find natural food in their lagoons, eg phytoplankton/water weeds
-Carnivorous fish are more likely to require artificial feeding
-Artificial control of food supply is more important w/ intensive production systems
Aquaculture- principles (control of abiotic factors); why is temperature controlled in aquaculture?
-Temp requirements depend upon species that are being kept & their natural adaptations
-Warmer temps increase metabolic rates & growth but can reduce levels of dissolved oxygen which may be unsuitable for some species
Aquaculture- principles (control of abiotic factors); why is dissolved oxygen controlled in aquaculture and how?
-Fish w/ a high oxygen requirement like trout must have well aerated tanks, esp if stocking density is high
-Food waste & faecal matter must be removed as this can cause deoxygenation
-Fish that are adapted to feeding in sediments w/ a high dead organic matter content can usually survive w/ a lower dissolved oxygen level, eg carp
-Catfish live in water but breathe air. Low dissolved oxygen levels don’t harm them so they can be kept at very high stocking densities
Aquaculture- principles (control of abiotic factors); why is daylength controlled in aquaculture and how?
-As w/ many terrestrial livestock species, reproduction is affected by length of the day. This is a natural adaptation to match annual reproductive cycle to seasonal changes in abiotic climatic factors & food availability
-Salmon stop growing when they become sexually mature. Having a long daylength delays maturation & increases size they reach so some fish farms extend length of day w/ artificial lighting to produce larger fish
Aquaculture- principles (control of abiotic factors); why is water flow controlled in aquaculture and how?
-Fish often swim against the flow of water
-This can be used to get all fish swimming in the same direction in circular/oval tanks
-This reduces collision damage betw fish which improves the appearance of saleable fish
-It also reduces risk of injuries & allows a higher stocking density in tanks
Aquaculture- extensive & intensive systems; what is extensive oyster aquaculture like?
-Most oyster farms use extensive systems w/ low inputs. Oysters filter planktonic organisms from seawater
-In some systems, young oysters are bred from selected adults
-In other systems, oyster ‘spat’ (planktonic larvae) settle onto cleared areas of seabed & are collected
-The young oysters are spaced out on seabed where they grow until they’re large enough to harvest
-Predators like crabs may be removed
Aquaculture- extensive & intensive systems; what is shrimp aquaculture like and why?
-Most shrimp farms are in tropical areas; SE Asia & Latin America
-The most important species are Giant Tiger Prawn & Pacific White Shrimp
-10% of world’s mangroves have been destroyed to create coastal shrimp farms
-Females in hatcheries lay up to 500,000 eggs each
-Ovary development & egg production are increased by eyestalk ablation where 1/both eyestalks are broken off which simulates low light levels that stimulate breeding, as they’re blind
-The eggs hatch to produce shrimp lavae fed on algae & zooplankton. As they grow, the shrimps are moved to outdoor lagoons up to 100ha in size
Aquaculture- extensive & intensive systems; what are extensive and intensive systems like in shrink aquaculture?
-In extensive systems, shrimps feed on plankton naturally produced in the lagoons
-In intensive systems, nutrients are added to increase growth of algae. Food pellets may also be added, water may be exchanged to remove wastes & aeration may be needed to prevent deoxygenation as wastes decompose
Aquaculture- extensive & intensive systems; what occurs in salmon aquaculture breeding?
-Fish are chosen w/ desirable characteristics eg fast growth rate, shape & brightly coloured scales
-Adult fish in breeding condition are stripped of their eggs (roe) & milt (sperms). These are mixed to allow fertilisation to take place
-Fertilised eggs are raised in aerated freshwater tanks. Dead/diseased eggs are removed daily
-After hatching, young fish are moved through a series of tanks as they grow, being fed on fish meal pellets
-After 12-18 months they become ‘smolts’ & are ready to move to seawater tanks. They continue to be fed on fish & plant meal pellets until they’re ready for harvest, usually at 3-5kg
Aquaculture- extensive & intensive systems; how are limiting factors controlled in salmon aquaculture?
-Salmon are sensitive to low dissolved oxygen levels, so water temp mustn’t be too high. Most salmon farms are in countries w/ cooler climates like Scotland & Norway
-Dissolved oxygen levels are kept high w/ water sprays/weirs (aerate water)
-Water flow rate is kept fairly high to produce more muscular fish as they swim against current
-Water flow direction is constant, often around circular tanks; keeps fish swimming in same direction so there are fewer injuries
-Pests, parasites & diseases are controlled by removing diseased fish + selective use of antibiotics & pesticides. Predators may be excluded/killed
-Light levels controlled to induce smoltification of young fish as they mature
-Food chain is controlled to increase its efficiency. Like most fish raised in aquaculture systems, salmon are carnivores. Fishmeal pellets made from low value fish like sandeels, herring, anchovy & sardines are similar to their natural food. Food chain efficiency is increased by adding food from lower trophic levels eg plant foods & vegetable oils
Aquaculture- extensive & intensive systems; what is polyculture?
-Some aquaculture systems produce food from 1+ species
-Total productivity may be increased by rearing species together that aren’t competitors
-Selective rearing of predators w/ other species can increase production of larger fish by controlling survival of small fish that could compete w/ larger fish
-Bottom feeding fish can disturb sediments & re-suspend nutrients which increase growth of plants & phytoplankton
Aquaculture- extensive & intensive systems; what is an example of a polyculture system?
-Silver carp feed mainly on phytoplankton
-Bighead carp feed mainly on zooplankton
-Grass carp & Tilapia feed mainly on vegetation
-Common carp are bottom feeders & feed on molluscs, insects. They also re-suspend nutrients from sediments
-Catfish & perch eat small fish + prevent over-reproduction of species that breed well, eg Tilapia
Aquaculture- extensive & intensive systems; what is Integrated Multi-Trophic Aquaculture (IMTA)?
-A polyculture system where species in different trophic levels benefit from each other
Aquaculture- extensive & intensive systems; what is fed aquaculture?
Species that are given food, eg shrimps, salmon
Aquaculture- extensive & intensive systems; what is inorganic extractive aquaculture?
Species that absorb inorganic nutrients for growth, eg algae/seaweed
Aquaculture- extensive & intensive systems; what is organic extractive aquaculture?
Species that catch food items such as plankton, eg filter feeding shellfish
Aquaculture- extensive & intensive systems; what is aquaponics and how is it beneficial?
-Combines hydroponic crop production w/ aquaculture
-Water from aquaculture system is used in the hydroponic system
-The drainage water from hydroponic system is returned to aquaculture system
-The productivity of the hydroponic system is increased as the supply of inorganic nutrients & organic matter is increased
-The aquaculture system benefits as nutrients that could lead to deoxygenation are removed
Aquaculture- extensive & intensive systems; what are suitable hydroponics and aquaculture species?
-Hydroponics; leafy salad vegetables like lettuce, spinach, herts
-Aquaculture; Tilapia, carp, catfish
Aquaculture- extensive & intensive systems; what are rice-fish systems?
-Rice is grown in flooded ‘padi’ fields (padi means rice in Malay)
-Fish can also be kept in the fields, increasing overall food production
Aquaculture- extent to which it can replace fishing; how efficient are trophic levels in aquaculture?
-Raising herbivorous fish, like Tilapia, can be very productive as amount of food produced per unit area is high
-Although raising carnivorous fish may be less energy-efficient, they’re often more popular w/ customers, eg salmon is a high-value carnivorous fish
-Fish have very low Basal Metabolic Rates as they don’t use energy to keep warm/for support, so they’ve much higher food conversion ratios than mammal/bird livestock species
-Food conversion ratio= quantity of food required to produce a unit of growth, eg a species that needs 3.5kg of food to produce 1 kg of new growth has an FCR of 3.5
Aquaculture- extent to which it can replace fishing; what are the different food requirements in aquaculture species?
-Herbivorous fish may eat plants & algae that grow naturally in water. Growth may be increased by adding plant nutrients. Supplementary feeding may involve adding plant material eg crop waste
-Carnivorous fish are usually fed on fish that have a lower econ value like salmon fed on fishmeal made sandeels. Overfishing of sandeels has caused population decline in other species that eat sandeels, eg puffins & terns
-Some plant-based foods have been developed but fish meat produced may be less tasty if there’s no fishmeal included
Aquaculture- extent to which it can replace fishing; stock collection in aquaculture
-Some species eg Atlantic Blue Fin Tuna don’t breed well in captivity, so young fish are caught in the sea then raised in large cages in the sea
-Tuna aquaculture can’t continue w/out a wild population
Aquaculture- extent to which it can replace fishing (environmental impacts); how does aquaculture have impacts on food supply and how can this be reduced?
-Overfishing of wild fish to make food pellets. This reduces populations of the fish & species that feed on them like seabirds
-Reduced; use of more plant products in food pellets/cultivation of herbivorous fish, eg Topia
Aquaculture- extent to which it can replace fishing (environmental impacts); how does aquaculture cause habitat loss and how can this be reduced?
-Habitat destruction during construction, esp lagoons in mangroves
-Reduced; careful site selection (difficult for very large scale developments)
Aquaculture- extent to which it can replace fishing (environmental impacts); how does aquaculture cause pesticide pollution and how can this be reduced?
-Pesticides used to control weed & crustacean growth may kill wildlife
-Reduced; mechanical cleaning of cages & biological control w/ crustaceans reduces need for pesticides
Aquaculture- extent to which it can replace fishing (environmental impacts); how does aquaculture cause the development of antibiotic resistant bacteria and how can this be reduced?
-Antibiotics used to prevent/treat diseases may lead to development of antibiotic-resistant bacteria
-Resistance may also transfer to human pathogens
-Reduced; lower stocking densities lower risk of disease so antibiotic use can be reduced
Aquaculture- extent to which it can replace fishing (environmental impacts); how does aquaculture control wild predators and how can this be reduced?
-Culling predators like seals & fish eating birds reduces predator populations so fewer fish are eaten
-Reduced; better cage designs to exclude predators
Aquaculture- extent to which it can replace fishing (environmental impacts); how does aquaculture create environmental impacts from controlling lice and how can this be reduced?
-Parasitic lice reduce fish growth & increase risk of virus + fungus infections
-Lice can spread to nearby wild fish populations. Lice may be controlled w/ chemicals like Hydrogen Peroxide wash, Azamethiphos (organophosphate pesticide) & Pyrethroid pesticides
-Pesticides may kill local wildlife
-Reduced; tanks should hold fish of a single age group so lice aren’t transferred from old fish to young unaffected fish, biological control w/ wrasse (fish) that eat lice. However, this can reduce wild wrasse populations if wrasse are caught & moved to fish farms. Washing fish in warm water
Aquaculture- extent to which it can replace fishing (environmental impacts); how does aquaculture have wild gene pool impacts and how can this be reduced?
-Fish that escape may breed w/ wild fish & introduce disadvantageous characteristics to wild gene pool, eg bright colour
-Reduced; better cage designs to reduce escapes, eggs exposed to high pressure produce triploid fish which are sterile (Sterile fish also grow faster)
Aquaculture- extent to which it can replace fishing (environmental impacts); how does aquaculture cause the introduction of non-indigenous species and how can this be reduced?
-Escaped non-indigenous species may colonise & become predators/competitors
-Reduced; cultivation of species that can’t breed in the wild, eg Japanese oysters in UK (too cold to breed)
Aquaculture- extent to which it can replace fishing (environmental impacts); how does aquaculture create organic waste pollution and how can this be reduced?
-Organic wastes from faeces/surplus food causes deoxygenation as it decomposes
-Reduced; feeding is monitored to prevent over-feeding, cages can be located where currents disperse wastes, freshwater aquaculture systems may have effluent treatment works similar to sewage works, bacteria in reed beds can also be planted to absorb nutrients & break down organic wastes
