| How has fisheries scinence developed over time? | Began in norway to understand way cod catches fluctuated in 19th century
Early development based on early life-history knowledge and ability
to age fish (mainly otoliths)
Single-species assessment and management (tool: single-species
models)
Now developing into ecosystem based management (tool: ecosystem
models) |
| How can you determine the age of a fish | Ortholites baby - count the rings |
| How much is fished around the world? | Excluding china in 2005 it was about 70-100 million tons. It is pretty stable |
| How has wild catch fisheries vs aquaculture evolved over time? | Check the statistics
Now there is more aquaculture than wild fisheries |
| Where is fish cunsomption pr capita the highest? | High in norway southern europe and different places in asia like china |
| How do fisheries usually develop over time? | If unregulated!:
Fish abunca high in the beginng but goes down as number of vessels and cathings are rising. In the beginning profits are rising until they start the fisheries become overexploited and collapse. After that you see a recovery and number of ctaches and profits go up.
Unexploited -> development of fisheries -> fully exploited fishery -> over exploited fishery -> fishery collapse -> fishery recoery |
| What are the largest fisheries? | In areas with high primary production!!
Generally along coasts.
Not in order:
West africa,europe, West south america, east asia |
| What is recruitment in relation to fisheries? | Amount of fish that enter the fishable stock each year.
It is very variable from year to year. One reason is because of a lot of egss and high mortality for the fish larvae. |
| How does the relationship between spawners and recruitment look like | Generally the recruitment increases with spawning until a certain point where recruitment actually starts to decrease or flatten out with to many spawners. |
| Name some different methods to catch fish and how they are used and for what type of fish and ecological impact | Pole and line
- Tuna fisheries or other large pelagic fish
- Small bait fish put in waters to create illusion of fish school
- low bicatch - can be sustainable
Longline: Trail a long line behind boat
- Baited hooks attached to nets to attract target fish
- Used for pelagic or demersal(bottom) fish
- Can have bycatch and uninteded impact on nontarget fish, birds and other marine life
Pots and traps:
- used for crustatians - lobster and crabs
- Cone shaped - get in but not out
- On bottom for ca 24 hours |
| Name some more different methods to catch fish and how they are used and for what type of fish and ecological damage | Dredging:
- rigded structures towed along bottom
- Bar dislodges shellshelfish as it drags over sediment - bivalves, oisters, clams
- High ecological damage depending on sediment type
Purse Seine:
- vertical net sourrounds school of fish the bottom is closed
- used for dense single species schools like makerel or tuna
- low bicatch and no contact with seabed
Gillnets - A net that hangs in the water
- Size of fish depend on mesh size
- High bycatch
- little contact with sea bed - low impact |
| Name some more different methods to catch fish and how they are used and for what type of fish and ecological damage | Bottom trawl
- cone shaped pulled just above or on seabed
- Very efficient to catch many fish
- can have high ecological damage - bycatch and seabed damage
Pelagic trawl
- as bottom trawl but in the pelagic
- use echosounders to locate fish position and depth
- can have bycatch but methods are used to avoid |
| How do fisheries affect exploited populations? | Population biomass is decreased beacause of fisheries effect on growth and recruitment |
| When is population biomass highest for fish?
What is a cohort? | with age size and mortality both increase. Therefor the population biomass is highest at a intermediate age for cohort.
Cohort: a batch of fish of all of approximately the same age and belonging to the same stock |
| How might trawls affect bottom invertebrates? | Trawling may affect large
long-lived benthic
invertebrates negatively! |
| What characteristiscs do fish share as a group? | -wide range of modes for feeding, reproduction, life-histories and habitats
-fish grow all their life
-many fishes have high fecundity and high recruitment variability
-often ontogentic (skift fra ung til voksen) shifts in feeding and habitat |
| Where are fish placed in food webs and chains?
Trophic levels? | Se billedet |
| What is a trophic cascade? | changes in biomass of one trophic level propagates to other trophic levels
Top down:
see picture
Bottom up:
Could also be increased primary production increases biomass on all other levels.
Wasp waist:
environmental effect on intermediate level
propagates.
Eksempel:
Decline in capelin will have negative effect in cod population, positive in copopod and negative in phytoplankton. |
| Explain wasp waist trophic cascade | environmental effect on intermediate level
propagates.
Eksempel:
Decline in capelin will have negative effect in cod population, positive in copopod and negative in phytoplankton. |
| What is trophic control?
Which different forms excist? | Trophic control: regulation or influence exerted by one trophic level over another within a food chain or food web
top-down - (will expect negative correlation between predator and prey in a time serie)
bottom-up - (will expect positive correlation between predator and prey in a time serie)
wasp-waist - (induce top-down for lower trophic levels and bottom-up for higher trophic levels) |
| Explain top down control: | top-down - (will expect negative correlation between predator and prey in a time serie) |
| Explain bottom up control | bottom-up - (will expect positive correlation between predator and prey in a time serie) |
| Explain wasp waist control | wasp-waist - (induce top-down for lower trophic levels and bottom-up for higher trophic levels) |
| How is species richness and latitude correlated? | negatively |
| How are growth patterns and lattitude corelated? | At high temp:
- faster individual growth
-lower age-at-maturity
-higher natural mortality rate |
| How have anthropogenic effects in marine changed the environment | Climate change
Species introduction
Mechanical habbitat destruction
Pollution
Fishing
All above have Altered the ecosystems |
| How is production and production/biomass (P/B) calculated? | For a population in the long run the growth production = death or loss production
Production = Biomass x (Production/biomass)
Production/Biomass = P/B, unit per year or year-1
In most cases: P/B = Z (total instantaneous mortality rate * (year-1) |
| How do you know the diet of functional groups? | -stomach/gut examination
-stable isotopes (d15N, d13C) (to sea trophic level)
-fatty acid markers
-literature |
| Can ecopath predict trophic positions of species? | Yep it is pretty good. |
| How do cold and warm fjord foodwebs differ? | Cold:
Cod dominated system
Warm:
less cod dominated, more biomass of small fish groups. |
| How will arctic foodwebs change with increasing temperatures? | -fish species richness increase with increasing temperature
-more species means more alternative «channels» or pathways for the energy to
flow between trophic levels ?
-change from topdown to bottom-up trophic control ? |
