Aquatic food resources Flashcards
What abiotic factors can influence marine productivity?
Temperature, dissolved CO2 level, turbidity and light levels
What is the aphotic zone and what does it rely on?
Area of water where light does not reach, it relies on the food produced near the surface, e.g. planktonic algae that is carried down by water currents, or the bodies of dead organisms that sink
What are the different types of fishing?
Demersal (organisms that live near or on the bottom of the water body), shellfish traps and pelagic (organisms that live in open water) fishing
What is demersal trawling?
Demersal involves fishing for species on the seabed, such as cod, haddock, plaice, shrimps and scampi
What are demersal long lines?
Use of line of baited hooks to catch species e.g. cod and haddock
What animals do shellfish traps catch?
Baited traps that catch crustaceans e.g. lobsters, crabs and crayfish
What is pelagic trawling?
Used for species that form shoals in mid-water or near the surface e.g. bass, anchovies, herding and 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 e.g. porpoises and dolphins
What is drift net?
Long curtain-like nets that are supported by floats and catch pelagic species near the surfaces e.g. tuna and herring
What is purse seining?
A net that is laid around a shoal of fish, the top is held up by floats, the bottom is held down by weights then pulled tight underneath the shoal, used for sardines, herring, anchovies and tuna
What are pelagic long lines?
These use a line of baited hooks which can be many kilometres in length, used for squid and tuna
What are the environmental impacts of fishing?
Overfishing, bycatch, ghost fishing and habitat damage
How is the common skate impacted by fishing?
K-selected species, it’s not commercially important, however, it is often caught in by catch of demersal trawls. It has become extinct in the Baltic Sea and Critically Endangered in the Mediterranean Sea and NE Atlantic
How is the Greenland Shark affected by fishing?
K-selected species that was fished commercially for lamp and lubricating oil until the 1960s, it’s main threat now is by catch from commercial deep water trawling
Why may a species be considered by-catch?
If the catch quota has already been reached, immature fish of the target species that are too small to sell and species that have no commercial value
What species are commonly caught as by-catch in shrimp trawling?
Crabs, sea urchins, molluscs and starfish
How are albatross birds impacted by fishing?
K-selected species that are commonly caught in pelagic long line fishing, they dive into surface waters for their food where they may get caught on the lure put out for squid or fish and drown
What’s a common pelagic trawling by-catch?
Porpoises are trying to catch the bass when they become entangled
What is ghost fishing?
Fishing gear that has been discarded or lost may continue to trap and kill marine organisms, the dead organisms in the gear often act as a bait and trap more animals
What habitats are affected by fishing?
Coral reefs, seagrass beds and seabed damage
Why are seagrass beds important?
Nursery grounds for many species of fish that may live on coral reefs or in deep water as adults
How does trawling impact seagrass beds?
Kills the plants so their roots no longer hold the sand grains together, currents and waves move the sand around, making it more difficult for new plants to colonise and become established
How does dynamite fishing work?
The pressure waves released by underwater explosions can stun fish and make them easy to catch, the use of dynamite is illegal in most countries but it is still carried out in remote areas, it is particularly common method on coral reefs where nets cannot be used to catch the fish that live among the coral heads , the explosions destroy coral and kill many other organisms
How does the mesh impact fishing?
Size can be set so certain smaller fish can escape, the design can be modified by adding the mesh pattern at right angles so they do not close up and smaller fish can escape
What are acoustic deterrent devices?
AKA Dolphin pingers, produce high frequency sound to warn dolphins that nets are nearby
How can hook shape be changed to save albatross?
Long line hooks with curved points still catch tuna but less likely to catch albatross
What are Turtle Exclusion Devices?
Large spring loaded escape panels in the nets which allow turtles to escape
What are sinkers?
Weights attached to pelagic longlines hold the hooks down in the water s they still catch fish, but not birds
Why is biodegradable and radio tracked equipment desired?
Reduces ghost fishing
What equipment design can be changed to prevent birds getting caught?
Hook shape, night fishing, decoys and sinkers
What are NTZs?
No Take Zones are areas where fishing and other activities that exploit wildlife or damage the habitat are not permitted. This protects the breeding populations, especially larger individuals,
How is turtle by-catch reduced by restricted fishing methods?
Reducing time a net can be trawled, if the trawl is less than 10 minutes, survival is 99%, if it is over an hour it’s 50-100%
What are some other restricted fishing methods?
Closed seasons, minimum and maximum catchable size, captive rearing and release and protected individuals
What is captive rearing and release?
Wild populations can be increased by releasing individuals that were raised in captivity
How is the Atlantic cod impacted by fishing?
They reach a catchable size at 2 but don’t mature until 4, so excessive fishing can remove the majority of the breeding population
How is the Orange Roughy impacted by fishing?
K-selected species, they live for 150 years, but only reach maturity at 30 years and produce few eggs
Why can collecting data on fish be difficult?
Populations can move long distances, distribution of populations is very uneven or it may be impractical to collect representative data
What data can be collected from catches?
Catch size (population estimation), mean fish size or age and catch per fishing expedition is an estimate of decline in populations
What is extensive aquaculture?
Minimal inputs which may simply involve a pond where fish have been introduced to feed on the wild food naturally present before being caught when they have grown e.g. oysters
What is intensive aquaculture?
Involves artificial control of all abiotic and biotic limiting factors, to maximise productivity and therefore profitability e.g. salmon, cod, trout and prawns
What are some desired characteristics of fish for selective breeding?
Rapid growth rate, disease resistant and good appearance e.g. bright colour
How is breeding impacted by gender?
Gender can be controlled hormonally, regardless of their genetics, each species can be changed by hormone injections
When may different genders be more desired?
Males can be more energy efficient and grow larger (tilapia), whereas females sometimes have better taste (rainbow trout)
What are the problems with aquaculture?
Disease and pests spread rapidly, competition and predation and nutrition
What abiotic factors need controlling in aquaculture?
Day length, dissolved oxygen, temperature and water flow
What is inorganic extractive aquaculture?
Desired species absorb inorganic nutrients to allow growth, an example is seaweed
What is organic extractive aquaculture?
Organisms (usually filter feeding shellfish) that catch their food such as plankton
What are some of the methods of aquaculture?
Polyculture, integrated multi-trophic, aquaponics and rice fish systems
What are the methods of reducing environmental impacts of fishing?
Catch quotas, improved design of fishing nets, restricting fishing effort and restricting fishing methods
What are examples of improvements to fishing methods?
Larger mesh size, mesh design so nets are at right angles to the direction of movement and smaller species can escape, acoustic deterrent devices, hook shape, decoys, sinkers, night fishing (reduce bird harm) and biodegradable and radio tracked equipment
What factors impact the choice of species for aquaculture?
Local conditions and species adaptations and market demands
What abiotic factors need to be controlled in aquaulture?
Temperature, dissolved oxygen, day length and water flow
How does day length impact aquaculture?
Some fish like salmon stop growing once they reach sexual maturity, extending the day length delay maturation and increase growth of fish
Intensive vs extensive in shrimp production
Shrimp feed on plankton naturally produced in the lagoons of extensive systems
Intensive systems add nutrients to increase the growth of algae, food pellets may also be added, water may be exchanged to remove wastes and aeration may be needed to prevent deoxygenation as wastes decompose
What’s the breeding process for salmon aquaculture?
Fish are chosen with desirable characteristics and adult fish are stripped of their eggs and milt, these are mixed to allow fertilisation and the young fish are moved through a series of tanks from 12-18 months before being placed in seawater, they are fed food pellets and then harvested at 3-5kg
What controls are in place for limiting factors in salmon aquaculture?
Lower temperature, water sprays or weirs to aerate the water, high flow rate to produce muscular fish, constant flow direction to minimise injury, removal of diseased fish and selective antibiotics and pesticides used
What is fed aquaculture?
Species in a IMTA that are given food
What is aquaponics?
Combination of hydroponics from agriculture and aquaculture, Aquaculture water is used in hydroponics and then drained back into aquaculture
What are suitable hydroponic and aquaculture species for aquaponics?
Lettuce with carp
What is food conversion ratio?
The quantity of food required to produce a unit of growth, if 3.5kg of food is needed for 1kg of growth the FCR is 3.5
