Fishing and Aquaculture Flashcards
Aphotic zone
Deeper layers of water that receive no sunlight because they are absorbed by shallower layers.
Photic layer
The water layer into which light can penetrate.
Marine productivity is driven by:
light availability and nutrient availability
Where is marine productivity high?
in the photic layer of the oceans near to continental land masses
Why is there high nutrient availability near continents
upwelling of nutrients from the ocean floor as deep ocean currents reach continental shelf, runoff of nutrient rich water from land.
Where is marine productivity low?
In the centre of large oceans away from land
Demersal
Living on the seabed eg cod, plaice.
Demersal fishing methods
Demersal trawling, demersal longlining, pots
Demersal trawling
a cone shaped net is towed on the seabed to target demersal fish species. The mouth of the trawl is held open by a pair of trawl doors/boards
Demersal long lines
Longline fishing uses a line of baited hooks to catch fish. Demersal longlines are typically used in coastal areas on, or close to, the ocean floor and are generally anchored in place. Demersal longlines can be set anywhere from shallow coastal waters to over 1000 metres depth.
Shellfish
All the aquatic animals that are caught or grown to be eaten that have shells or an exoskeleton eg crustaceans and molluscs.
Shellfish trap/pots
Stationary traps, or pots, typically made from wood, wire netting or plastic, are used to catch crustaceans such as lobsters and crabs. Though the size and shape of traps may vary, all feature a cone-shaped entrance tunnel through which a crab or lobster is enticed with bait, but cannot escape through.
Pelagic
Living midwater or near the water surface eg herring, tuna
Pelagic trawling
involves towing a large net through the water column to catch pelagic (midwater) fish species. The net has a cone-shaped body and a closed ‘cod-end’ that holds the catch. The trawl net is deployed from the back of the vessel with floats at the top and weights at the bottom to maintain its opening vertically. Angled boards, known as otter boards or trawl doors, attached to the sides hold the net open.
Drift net
A net which hangs vertical in the water (like a curtain). The top is held at the surface by floats, with the bottom being held down by weights.
Purse seining
A fishing method where a net is used to encircle a shoal of pelagic fish. The bottom of the net is held down by weights and then drawn tight at the bottom
Long lining
A fishing method with many hooks attached to a main fishing line that is trailed behind the fishing boat. They can be used to catch pelagic or demersal fish.
Environmental impacts of fishing
Overfishing (above the MSY), Bycatch, Ghost fishing, Habitat damage
Overfishing
Fishing above the Maximum Sustainable Yield of a population.
Bycatch
The non-target organisms that are caught when fishing.
Ghost fishing
The capture and death of organisms that get caught in lost or discarded fishing gear.
Habitat Damage
Damage/destruction of habitats such as coral reefs, seagrass meadows by destructive fishing methods such as demersal trawling and dynamite fishing.
Dynamite fishing
A destructive fishing method that uses explosives to kill fish. It’s illegal worldwide.
Reducing the environmental impacts of fishing
Bans/restrictions on destructive fishing methods, designations, no take zones, catch quotas, specific mech size matched to target species, escape panels, acoustic deterrents (pingers), hook shape, decoys, sinkers, night fishing, biodegradable equipment, radio tracked equipment, reduced net tow time, closed seasons, minimum catch size, maximum catch size, protected individuals, captive rearing and release.
Marine designations
MCA, MCZ, MPA
Catch quota
A limit on the quantity/weight of fish that can be caught
Mesh size
the mesh size is set so that fish below a certain size can escape. These fish may be smaller non-target species, or juveniles of the target species.
Mesh design
Mesh is designed so that diamond shaped openings become elongated and closed as the net is dragged through the water. Panels of a different shape, that remain open can be incorporated into the net to allow smaller fish to escape
Escape panels
A spring-loaded part of a fishing net through which large by-catch organisms can escape e.g. turtles.
Acoustic deterrent devices
A device that deters mammals by using sound. They are used to deter small cetaceans from fishing nets, or seals from fish farms, for example.
Dolphin pingers
A type of acoustic deterrent device used to deter small cetaceans so they don’t get caught in fishing nets.
Hook shape
different hook shapes can target or avoid different species. Hooks with curved points are more likely to catch tuna but less likely to catch albatrosses
Decoys
Attract/Distract birds away from longlines
Sinkers
Weights that are attached to pelagic longlines to hold the hooks further down in the water to avoid albatross deaths.
Night fishing
In particular for longline fishing to avoid bird feeding times.
Biodegradable equipment
Pots held together with biodegradable rope so they will degrade and fall apart if lost/abandoned and avoid trapping individuals which will then act as bait for more.
Radio Tracked equipment
radio transmitters fitted to equipment that can be activated and recovered if lost.
Ban on specific fishing methods
Worldwide or area bans on specific fishing methods that are harmful to important ecosystems. Eg demersal trawling banned off NW coast of scotland to protect deep water corals, dynamite fishing banned worldwide, has been particularly destructive in warm water corals.
No take zone
An area in which harvesting or fishing is prohibited.
Reducing net tow time
Reducing the amount of time the net is dragged through the water reduces harm to bycatch species, particularly turtles e.g. 99% of turtles survive 10 minutes in a net whereas most die if left for 60 minutes.
Closed seasons
ban on fishing a particular species for part of the year which usually includes the breeding season to boost fish populations
Minimum catch size
Banning the capture of small fish to allow the fish to grow to a larger size and breed
Maximum catch size
Banning the capture of larger individuals to protect the population of breeding adults
Protected individuals
Some individuals are marked and then protected from future catches. For example if a female lobster is caught and is carrying eggs, a notch is cut out of the tail so that if it is caught again it will be released to continue to boost the population.
Captive rearing and release/population seeding
Eggs/larvae raised in captivity past the point where most would be predated upon and then released.
Maximum sustainable yield (MSY)
The greatest amount that can be harvested sustainably.
Data required to estimate the MSY
biomass of stock at the beginning of the year, biomass of stock at the end of the year, biomass of young fish added to stock, biomass added by growth of all fish in the stock, biomass caught by fishing, biomass lost through natural mortality
Difficulties in calculating the MSY
Fish are mobile and travel long distances and between different populations, distribution of fish is uneven, collecting large amounts of data is impractical, timeconsuming and expensive
Assumptions around MSY
The MSY is difficult to calculate so it is often assumed that a fish population can be reduced to down to 30% of the original size and still be able to recover
Getting the MSY wrong, The Orange Roughy
The 30% rule assumes all fish are similar to those that we have good data for. Some species are unusual in that their lifespan, age of maturity, reproduction rate differs from the mean. The orange roughy lives for more than 100 years and does not reproduce until 30, this meant that the population recovery rates were much slower than expected and caused both ecological and economic problems.
European Union Common Fisheries Policy (EU CFP)
This is a set of regulations intended to ensure the sustainable management of fish stocks within the EU.
Cetaceans
Marine mammals including whales, dolphins and porpoises.
Aquaculture
The artificial production of aquatic organisms, including fish farming.
Principles of aquaculture
Species selection, Selection of breeding adults, Gender control, Control of pests/disease, Exclusion of competition/predation, Control of food supply/nutrition, Control of other abiotic factors (eg temp, light, oxygen, water velocity)
Aquaculture species control
species is selected based on demand, value and ease of production
Aquaculture selection of breeding adults
The adults which produce eggs/offspring are controlled to produce specific characteristics usually associated with rate of growth, disease resistance and appearance (marketability)
Aquaculture gender control
Fish gender can be controlled by giving hormones to young fish. In some species one gender is preferable due to flavour (female trout) or adult size (larger male Tilapia)
Aquaculture control of pests/disease
high stocking densities increases risk of pests and disease. Pesticides are used for fish lice. Biological control eg using wrasse to control lice. Water flow is controlled from young fish to older fish to reduce the transfer of established disease.
Aquaculture exclusion of competition/predation
Fencing, netting is used on fish cages. Bird scarers are used, culling of predator populations is sometimes authorised eg seals and cormorants in the UK
Aquaculture control of food supply/nutrition
Carnivorous fish require artificial feed. Herbivorous fish may require less supplementary feeding.
Aquaculture control of abiotic factors
Abiotic factors such as temperature, dissolved oxygen, daylength and water flow are controlled
Aquaculture - why control temperature?
Warm temperatures can increase metabolic rate and growth, too warm may reduce dissolved oxygen levels below that required.
Aquaculture - why control dissolved oxygen?
required for aerobic respiration, must be high for high stocking densities, decomposition of food waste and faecal matter depletes oxygen so must be removed, some fish can breathe air so less important
Aquaculture - why control daylength?
influences reproductive cycle, long daylength delays maturation in salmon and they continue to grow
Aquaculture - why control water flow?
fish swim against the flow of water, all fish swimming in the same direction reduces collision/injuries
Common aquaculture species
salmon, shrimp, trout, tilapia, scallops, mussels
Triploid fish
are a sterile fish with three sets of chromosomes instead of the usual two, resulting in infertility and potentially faster growth rates eg rainbow trout
Aquaculture and mangroves
one of the biggest threats to mangroves has been clearance for shrimp aquaculture. Over 10% of mangroves have already been lost to farm species such as Pacific white shrimp and Giant tiger prawns.
Aquaculture in Scotland
Scottish salmon farming is a major industry, producing a significant amount of farmed Atlantic salmon, provides both economic opportunities and environmental challenges
Extensive agriculture/aquaculture
Agriculture/aquaculture where the yield is achieved with low levels of inputs, often over a large area. Productivity is usually low (yield per unit area) but efficiency is usually high (yield per unit input).
Intensive agriculture/aquaculture
Agriculture/aquaculture where the yield is achieved with high levels of inputs. Productivity is usually high (yield per unit area) but efficiency is usually low (yield per unit input).
Integrated multi-trophic aquaculture
a sustainable aquaculture approach that mimics natural ecosystems by farming multiple aquatic species from different trophic levels together, utilising waste and byproducts from one species as resources for another eg. shellfish feed upon the waste produced from fish species
Impacts of aquaculture
Overfishing of wild fish for feed, habitat loss (mangroves), pesticide pollution, antibiotic resistance, culling wild predators, increase of fish lice transferred to wild populations, escaped fish non-indigenous effects, escaped fish breeding with wild populations, organic waste pollution
More sustainable aquaculture
herbivorous rather than carnivorous fish, cage cleaning reduces pesticide use, low stocking density reduces disease and antibiotic use, biological control of lice (wrasse), better cage design to prevent escapes and deter predators, cultivation of species that cannot survive in the wild and become invasive, reduce organic waste by introducing multi trophic feeding.
Aquaponics
Aquaponics is a food production system that combines aquaculture with hydroponics, creating a symbiotic relationship where fish waste provides nutrients for plants, and plants filter the water for the fish eg. combining a good hydroponic species like spinach with good aquaculture species like catfish
Rice-fish systems / integrated rice-fish farming
a sustainable agricultural practice that combines rice cultivation with aquaculture, it is mutually beneficial for both species. It typically involves freshwater fish and rice and offers benefits like increased yields, diversified production, and reduced reliance on chemical inputs.
