fishing Flashcards
what is meant by marine productivity
the amount of food that can be harvested- limited by factors such as light and nutrients
list the different types of fishing methods
1) Demersal- fishing for species that live on the sea bed
2) pelagic- fishing for species that live in the open waters above the sea bed, often near the surface of waters
outline demersal trawling
- used for species on the seabed such as cod or haddock
- involves the dragging or a weighted net along the sea bed which catches fish in its path
what are the disadvantages of demersal trawling
- high bycatch
- disturbed habitat on the sea bed
- increased turbidity from dislodged sand particles
- decarded nets allow ghost fishing
outline demersal long lines
- the use of a long line with baited hooks which catch species such as cod and haddock
- the hooks can be made a specific shape complementary to a certain species gills reducing by catch
outline pelagic trawling
- used for species which form shoals in mid-water or near the surface such as bass
- a net is hung between two boats and dragged through the water collected fish in the shoal s
compare by catch rates of demersal and pelagic trawling
pelagic- pelagic fish tend to form single species shoals so the catch of non-target species is usually low but predator species may also be caught such as dolphins
demersal- higher bycatch rate
outline drift nets as a form of pelagic fishing
- long curtain-like nets which are supported by floats and catch pelagic species near the surface
- nets can be kilometres long
outline purse seining
- a net is laid around a shoal of fish
- the top is supported by floats while the bottom is held by weights the pulled tight underneath the shoal
outline pelagic long lines
lines of baited hooks which may be kilometers in length which catch species in mid or surface waters such as tuna or squid
list the environmental impacts of fishing
1) Bycatch
2) population decline
3) Ghost fishing
4) habitat damage
what is bycatch
the non-target organisms which are caught when fishing such as
- immature fish too small to sell
- individuals of a catch quota that has already been filled
- species with no commercial value
many species will be returned too injured to survive of be dead already
amount of bycatch depends on fishing methods
outline drift net bycatch
- the catch of species near swimming near the surface such as dolphins
what is ghost fishing
fishing gear that has been disregarded or lost may continue to trap and kill marine organisms
dead organisms caught act as bait attracting more individuals who also become trapped and die
list the forms of habitat damage
1) sea bead damage
2) coral reef impact
3) seagrass beds
4) dynamite fishing
5) food web impacts
outline sea bed damage and coral reef impact
1) demersal trawling nets often have metal balls to disturb the sea bed mixing shallow aerobic surface layers with deeper anaerobic layers as well as destroying slow-growing organisms
2) coral polyps are sensitive to physical damage so can be killed if pressed against the cup they are attached
outline habitat damage to seagrass beds
- grass-like plants on shallow sandy areas which act as an important nursery ground for many species in coral reefs of deep water
- disturbance from trawling kills plants so roots no longer bind sand so currents move sand around
outline dynamite fishing
pressure waves released by underwater explosions stun fish making them easier to catch
commonly used in coral reefs where nets cant be used but explosions kill coral and other organisms
outline food web impacts
reducing the number of species will cause
- increased competitors
- increased prey
- predators may become rarer
why might population decline
- if mortality exceeds birth rate species are likely to become overfished
- K select species are more vulnerable to overfishing as they produce fewer young and reach sexual maturity ad a later age
- R select species populations are lily to recover faster
