L14-Fisheries failures,MPA's Flashcards
What drives recruitment?
Total Egg Production (TEP) is what drives recruitment
What is bi catch?
catching fish from other species
What is Total Egg Production (TEP) modified by?
TEP is modified by the stock recruitment relationship
What is recruitment?
TEP x SRR = recruitment
What do managers assume?
linear relationship between fish size and body mass
size structure is irrelevant
What does scaling describe?
how non-linear a function is
How does reproductive output scale with size?
hyper allometric
reproductive output increases disproportionately with size
bigger fish produce more eggs with more energy per egg
How does frequency of spawning change with size?
bigger fish spawn more
What determines Total fecundity?
Batch fecundity x Spawning
Frequency
Why does reproductive hyper allometry
matter to management?
- Fish reproduction scales hyperallometrically
- Biomass is not interchangeable
- Size structure is highly relevant
Why is size structure being important such a problem?
bigger fish are fished preferentially
how bigger proportion of pop would fish 3 years
and older will constitute Assuming a 20% harvest? How much of egg production assuming both isometry and hyper allometry?
just 0.4% of the population.
8% of egg production.
68% of
egg production.
How often are fishing morality too high? by how much?
33 of world’s largest fisheries
2.4x too high on average
5x in some cases
What proportion of fisheries models assume
isometry?
- 95%
- ~half are SPR models, half are MSY models
- Almost all MSY models just assume steepness values
How much do we have to reduce catches?
30-40%
What is happening to fish weight?
fish are getting smaller
evolving to mature at earlier age
How much bigger are fish in mpa’s?
28% longer
twice as heavy
What are the Concerns about MPAs as fisheries
management tools?
- They might not enhance replenishment
- They shift exploitation to elsewhere
- The carry no additional benefit beyond what good management would already provide
How much more eggs are produced inside MPA?
140% more than twice number of eggs
What is difference in reproductive output inside and outside mpa?
3 fold
and more fish
total egg production in an outside mpa?
224 times higher
How much do mpas enhance fishery?
two fold
What are harvest slots
only target fish within a certain size range
if reproductive scaling above 1.5 can be effective
Which of these assumtions from MAXIMUM SUSTAINABLE YIELD is liekly wrong? • Stock spawner biomass • Growth • Natural mortality • Fishing mortality • Fishing selectivity • Steepness • Stock recruitment relationship
- Stock spawner biomass - Wrong
- Growth – Probably right
- Natural mortality – Probably wrong
- Fishing mortality – Probably wrong
- Fishing selectivity – Probably right enough
- Steepness – Almost certainly wrong
- Stock recruitment relationship - Almost certainly wrong
What deo most fishery models assume about size?
Models assumed smaller fish are MORE
productive
