Fishing Flashcards
marine productivity relies on…
nutrient availability + variations in light levels
what is the difference between the aphotic and the photic layer?
ap: light doesn’t penetrate, no photo.
ph: light penetrates, photo.
some nutrients are ________ factors on biological _______ i.e. phosphates
limiting, productivity
define upwellings
where colder and more nutrient rich H2O come to the surface and increase biological productivity
name the 2 places where upwellings occur
continental margins + open ocean
what is a continental margin upwelling?
wind blows parallel to coastline, pushes coastal surface H2O out to sea
define thermal stratification
warm H2O less dense so floats on cooler H2O
place these in order of low to high productivity:
upwellings, open ocean, coastal areas
open ocean, coastal area, upwellings
describe the productivity in the open ocean
- low primary productivity cus of stratification (nutrients remains at depth)
- death of planktonic organisms sink to sea bed
describe the productivity in coastal areas
- shallow H2O = more light = more photo
2. nutrient runoff from land/rivers
describe the productivity of upwellings
- seamounts change elevation and push H2O to surface
2. storms cause nutrients to distribute
what is the difference between pelagic and demersal trawling?
pelagic: towing of nets in surface H2O
demersal: weighted nets dragged along sea floor
advantages of pelagic trawling
- can be quite selective (single species shoals)
2. fast + efficient as catch large volumes
disadvantages of pelagic trawling
bycatch of porpoises, dolphins, seabirds etc.
advantages of demersal trawling
fast/efficient as catch large volumes (make more money)
disadvantages of demersal trawling
- destroys seafloor habitats i.e. corals/seagrass
2. bycatch high as demersal fish in mixed species shoals
what is purse seining?
large wall of netting to encircle fish then gathered
advantages of purse seining
- no contact with seabed
- more species selective
- efficient as can catch large shoals
disadvantages of purse seining
- bycatch of vulnerable species i.e. sharks/turtles
2. accidental catch of juvenile fish below catch size (thrown back dead/dying)
what is drift netting?
long nets suspended vertically in H2O (pelagic)
advantages of drift netting
- cost effective
- nets placed by low powered vessels (fuel efficient)
- large amount of fish in 1 catch
disadvantages of drift netting
lots of bycatch as its non-selective
what is longlining?
weighted line of baited hooks
advantages of longlining
- no contact with seabed
2. quicker harvesting times (less compression = better quality fish)
disadvantages of longlining
- used for pelagic = seabirds caught on hooks i.e. albatross
- not very selective, bycatch
what are shellfish traps?
baited traps that sit on the seabed
advantages of shellfish traps
- fewer environmental impacts
2. another opening allows for the release of crustaceans below catch size
disadvantages of shellfish traps
ghost fishing = shellfish trapped
name the 6 impacts of fishing
- pop. decline
- bycatch
- ghost fishing
- habitat damage
- food web impacts
- changed age structure
describe pop. decline
deliberate exploitation of a species
effect of pop. decline?
- effects K species the most as have fewer young etc. (i.e. Orange Roughy + sharks)
- catching before sexually matured = no chance to breed
how to reduce pop. decline? (5)
- no take zones
- fishing quotas
- minimum size of fish caught
- closed seasons
- square mesh panels in trawl nets (allow small fish to escape)
what is bycatch?
any catch that is unwanted. 2 types:
- catch of non-target species
- catch of target species that are too small to be legally landed/sold
what is the effect of bycatch?
- many bycatch dead/injured won’t survive
- reduces biodiversity
- impacts food webs
how to reduce bycatch? (4 ways)
- turtle excluder devices/escape panels
- acoustic deterrent devices
- leaving longlining nets for 15 mins not an hour
- change J hooks to circle hooks
what is ghost fishing?
lost/discarded fishing gear (deliberate or storms)
what are the effects of ghost fishing?
- traps/kills
- smother corals
- spread parasites
- juvenile fish hide = get trapped
how to reduce ghost fishing?
- use biodegradable nets
2. radio tracked equipment
what are the effects of habitat damage?
- seabed damage
- coral damage
- loss of seagrass meadows (loss of nursery grounds + roots no longer bind sand)
how to reduce habitat damage?
ban/reduce methods that damage habitats i.e. demersal trawling
describe the food web impact
reducing any species will have an impact on the interspecies relationships
effect of food web impacts?
- bycatch reduces predators
- competitors could be common
- fishing/bycatch could reduce pop. of prey i.e. turtles eat jellyfish so increase bycatch of turtles = increase jellies
describe the effect on age structure
if haven’t reached sexual maturity, hasn’t bred = cannot replenish the pop. (no breeding pop.)
describe factory fishing and its effects
as fish pop. decrease ships travel further
- use large amounts of fuel
- waste effluent deoxygenates H2O = dead zones
name the 8 ways to reduce environmental impacts of fishing
- catch quotas
- restricted fishing effort
- net design
- no take zones
- minimum catch size
- maximum catch size
- captive rearing/release
- biodegradable/radio tracked nets
what are catch quotas?
- upper limit on total no./mass of a species that can be caught + legally sold
- works best in single species shoals
what is restricted fishing effort?
limits the size of fishing boats/power of their engines/ no. of days out fishing
what is minimum size of individuals caught?
- banning capture of small fish
2. allows them to grow/reproduce = replenish pop.
what is maximum catch size? + example
- protecting large species
- allows for surviving pop. of breeding adults
- female lobsters around scotland not caught if shell longer than 145 mm
what is captive breeding and release?
- eggs/larvae raised in optimum conditions = increase survival
- released to boost wild pop.
what is an issue with captive breeding/release?
may not be resistant to local diseases
give an example of captive breeding and release
lobster hatchery in Cornwall (fishing pressure decreased pop.)
what are no take zones?
- provide safe breeding area
2. lots off offspring leds to fish migrating out of NTZ to areas which can be fished
what are closed seasons?
ban on fishing during that time of year = allows fish to breed/grow
give 3 different types of net design that reduces bycatch
- excluder devices
- mest size set (allows fish below quota to escape)
- square mesh panels (can’t close under pressure) = small fish escape
give 3 different ways to reduce bycatch NOT TO DO WITH THE NET
- dolphin pingers/acoustic deterrent
- streamer lines
- J hooks to Circle hooks
- line weighting for pelagic longline
define the Maximum sustainable yield for a fish pop.
the greatest biomass that can be removed from pop. each year without pop. suffering long term decline
fishing rate should not exceed…
birth, growth and mortality rate
give 2 examples of fish that have been exploited about the MSY
- orange roughy (k selected species)
2. atlantic cod (catchable size age 2 but reach maturity age 4)
name the 4 pieces of data you get from fishing catches
- catch size
- catch per unit fishing effort
- mean fish size
- mean age
why is catch size not good to measure biomass/pop.?
better fishing technology maintains catches as pop. declines i.e. better sonar
Catch per unit fishing effort: harder to maintain catches…
pop. decreasing
how can mean fish size see if there’s overfishing?
reducing mean fish size = caught faster than reproduction
how can mean age of fish see if there’s overfishing?
age declining = not allowed to reach maturity/breed
collecting data on __________ fish egg/larvae pop. predicts no. of young likely to reach _________
planktonic, adulthood/maturity
