Fisheries Flashcards
What was the total value of fisheries in 2016
110.2 million tonnes
estimated at $243.5 billion
4.6 million fishing vessels- very intense
Production trends are upwards but only because of aquaculture
Why are inland fisheries less favoured
Many are declining, lots o big rivers being dammed and losing natural production potential eg Yangtze
Such as 2 spp of sturgeon are both seriously threatened
Chinese paddlefish (one of th biggest freshwater fish (about 7m) hasn’t been recorded in the wild since 2007
What is a fin fish
True fish and whales
Shell fish
Molluscs, lobsters, clams etc
How is climate change effecting ecosystem
Decline in sand eels and other small fish species is CC driven at least partly. Caused by interactions between fisheries and sea bed. V difficult to revert back to a pre 20C ecosystem
Puffins are having to feed their pufflings armoured fish because the fish they’d normally eat aren’t there (fisheries)
How much of the worlds fish stocks are being fully exploited, or over exploited, or recovering (2012)
87%
Chinas contribution
one-third of the world’s reported fish production.
as well as two-thirds of the worlds reported aquaculture production. - FAO 2011
How is stock defined
A stock is a group of organisms of a species that will react independently to exploitation from other such groups and can be managed as an entity, Usually self sustaining though there may be immigration and emigration.
Some say the part of the population that can be exploited
other say the part that can be managed
Estimate of the size of the spawning stock. At this size can be caught and are valuable but don’t want to overfish because then nothing will reproduce.
Often length of fish measured to get a length frequency of the stock. Independent surveys. Subsamples for age, weight sex fecundity, age-length relationship
Different methods eg
Peterson- plot length against frequency. Not great because rarely catch youngest fish stochastic, slow down in growth rate- what might be true model may grow age classes together. Often only useful for short lived fish. Can relate age to length.
Scales and otoliths- more useful ageing method. Scales grow at different rates according to different opportunities. In temperate environments rate of growth reduces in winter. Can also do this with ear bones in fish that are often better for showing growth patterns because scales can be replaced
Peruvian anchoveta
Stock is reported in landings
Just because high landings does not mean population is stable
There are dramatic changes over time.
Difficult to census fish so managers often rely on what is caught.
Terrible weather = no landings = no fish in sea?
Was the largest in the world until it collapsed in 1972 during an El Nino event. In spite of reduced fishing, it took 20 years for recovery.
El Nino caused many to die/move. Events difficult for commercial fisheries to manage
What are the general fish trends
Pretty much all declining
Fisheries often have long term data and we can see CPUE declining throughout. Changes in all ecosystems (top and bottom of water) that is having huge effects.
International waters have no regulations so as stocks get really low fisheries just move on
Declines seen and described by fisherman may be a rose tinted specs sort of thing. Or is may be true. Overtime there may have been shifting base levels. So what we regard today as low levels may be historically negligible.
Compensatory fisheries
Start with most prized spp then as they decline move n to next less desirable species –> won’t leave an ecosystem alone. Altering competitive interactions
Leads to flux of responses in communities. Higher trophic levels targeting first. Dramatic reductions in mean trophic index of fisheries/fish communities over 40 years
We are fishing down the food web- removing predatory fish. Most fisheries rely on primary and secondary consumers–> changing the ecosystem.
Aquaculture
Eg farmed salmon–> disease, escapees?
Most of aquaculture of carnivorous fish, need to catch fish to feed the fish. Settlement of faeces on seabed= anoxia
Altered genetic pool of captured stock
Wider ecosystem impacts
Kaiser et al 2005
- Accidental capture/injury eg seabirds captured with long lines, ghost fishing, non target species caught eg dolphins
- Mortality of discarded biota eg turtles, fish, cetaceans, many invertebrates
- physical impact on habitat during fishing process eg damage to benthic habitats during trawling damage to fragile coral, eel grass habitats etc
Some areas are trawled 8 times a year in north sea imagine if you ploughed a field that much. couldn’t even attempt to harvest 8 times a year
- ornamental fish caught from coral reefs. do it because they need money
Types of fisheries
Industrial, commercial, artisanal, recreational (can have impact on the env but not to the same extent)
Major commercial fishing methods
- Purse seine: like a big net purse you can draw the strings together on. Tends to be pelagic (near top). Can catch entire shoal of fish using echolocation
- Benthic trawl- just along the bottom. Big boulder reefs are less impacted because they damage the equipment. Moves at higher speed than fish can escape. Net along the bottom
- Gill net- passive. relies on fish encountering the gear and getting entangled. Like a tube thing.
- Long line- attract fish by baiting - passive. Big hook string
Can have quotas for all.
Artisanal much simpler have traps, nets, spears, baited lines (sometimes explosion and poison but they are bad)
Draw a comparison between major commercial and minor artisanal fisheries
picture on phone
Stakeholders in the exploitation of fish
- Artisanal- provide enough food for family, sell surplus, low demand for intensification of fishing activity
- Commercial- maximise profit by maximising yield of harvestable (and saleable fish). Necessitates opportunistic and selfish behaviour.
However, also have high capital investment in vessel and gear, requires some sustainability go income (but, can switch fish?). They discard- if a commercial fisherman is allowed to land a certain amount of fish and they catch some smaller cod then on the way back find bigger. They will throw the smallest cod back which may be dead.
Also about costs, how long can they sit in port costs (weather could be bad, could have limited fishing days to conserve stocks) may have to pay back boat - Fish processors- sustainable profit bc of high capital investment (sustained and predictable source of right size and type of fish). Canning factory, shelling, filleting. They need a long term supply at a reasonable buying rate because they need to pay off costs over a long time too. Certain types of fish to supply market. Needs predictability of source.
- Fish marketers- relatively sustained source and magnitude of landings. Big dips and peaks not ideal. Similar to the processors. Direct linked to market.
- Environmentalist- long term sustainable use of resources favouring local pops and minimising environmental damage. They would acknowledge that there is reasonable exploitation of the environment. If it is truly sustainable and limiting environmental damage that will be the approach they want to take. Any type of fishery has the potential to cause some sort of damage.
- Fishery managers- sustain fish stocks for broad community and provide for all interests, while seeking to limit environmental damage. Have to try and integrate all these demands.
Have to estimate size of stock, see how its changing, what species are being caught, what are the interactions between these species?
Increasingly fishery managers are expected to put in regulations to limit secondary impact eg by catch or damage to seabed. Normally have a legal mandate to do this - Politicians- votes! Trade offs. Eu marine water (including north sea) fisheries are managed by quotas (amount of each stock of fish that a country and its constituent fisherman can take in a given year). Because it is international mens all the scientists the are going o come up with recommendations. Then meetings of the government representatives for the countries that then take a vote. They tend to compromise and dilute scientific suggestions bc polliticians need to consider other stake holders values such as jobs
Irish and North Sea Herring
Clupea harengus
Both exploit herring.
Fish in the north sea migrate up coat.
Off W coast of scotland migrate quite widely.
Herring in N sea are two different stocks. Some of the populations interchange as they grow more in summer. These are partially isolated from a fisheries perspective and so they are regarded as different entities for management.
Recruitment
The fish large enough to be caught - can depends on mesh and net size
Abundance of target fish that become susceptible to fishery (at certain size). Relative strength of recruited cohorts (Year Class Strength) assessed through regular sampling and ageing. Recruitment often highly variable in fish populations. Adult pop may be strongly influenced or dominated by one strong year class- many poor year classes in a row can put viability of stock at risk
Hjort and Lea 1914 recorded the % of spring herring ages 2-18. Advancement of peas percentages from year to year and low % of other classes demonstrated the persistence of herring from 1904. If stock failed to recruit for 6 years = problem,
This is
Draw the growth of a fish stock
on phone
growth of pop is fastest at half the carrying capacity. As pop goes further towards K intraspecific competition slows population growth.
Cropping back from k reduces competition and keeps pop near fastest growth rate. Especially effective for pops with high reproduction (near the r end of the rk spectrum) but in a steady state (constant env)
Below K per capita individuals are more likely to survive and grow. Degree of risk bc if you crop too much could collapse to 0. Not a sustainable solution.
What is the surplus yield model
Picture on phone
Very easy to overshoot and tip population to extinction.
Even if you overfish for a few years by a little bit could be too much. A lot of management is around MSY even in the EU
Safer to harvest at surplus production yield- more conservative than MSY. So if mortalities for other reasons you risk less- massive stochasticity in the wild. Precautionary. ^ fails to take this into account.
What are the 5 typical stages of evolution of a commercial fishery
Picture of phone
- Exploration- usually little or no monitoring of population size. When it becomes important people might start to monitor.
- Rapid exploitation- more individuals get involved so effort increases. Improved technologies may come with this. Start to monitor at the end of this period as it is starting to be seen as valuable
- Saturation- appears to be stable catch. Falsehood of interpretation. Just because landing stock doesn’t mean population is stable. Bc modern tech people can spend a day to find and catch an entire shoal. 5 years down the line may take 3 days but still catch entire shoal.
- Crash/decline- exploitation and bad reproduction years can cause landings to decline even more
- Recovery- usually only partial
Historic examplesSkate and ray catches: (a) combined for the United Kingdom fleet in the Irish Sea and Bristol Channel (1952–1993 including skates-
we examined two time series of species-specific surveys of a relatively stable skate fishery in the northeast Atlantic. These surveys revealed the disappearance of two skate species, long- nose skate ( Dipturus oxyrhinchus) and white skate ( Rostroraja alba) and confirmed a previously documented decline of the common skate ( D. batis). Of the remaining five skate species, the three larger ones have de- clined, whereas two smaller species have increased in abundance. The increase in abundance and biomass of the smaller species has resulted in the stability of the aggregated catch trends. Because there is significant di- etary overlap among species, we suggest the increase in abundance of the smaller species may be due to com- petitive release as the larger species declined.
Early fisheries science
Thomas Huxley- “Probably all the great sea fisheries are inexhaustible” 1883
Many problems associated with economic and technological advances: rapid mechanisation, steam power, steel hulled boats, power block, diesel engine, sonar –> can uninvent something. Can try and regulate it.
Banning echolocation would be a brilliant form of regulation. But would reduce efficiency too and people want to incr efficiency
Contrary to Huxleys belief- they started to experience a decline in plaice catches in Firth of Forth and N Sea. Despite huxleys views he insisted on an experimental approach
Experimental fishing to measure stock characteristics in areas open and closed to commercial fishing. Collection of fishery stats. Subsequent analysis contradicted Huxley- Garstang 1900
Grimsby- catch of fish per standardised vessel declined by 33% as fishing effort incr by 150% (Garstang 1900)
Despite realising this in 1900 little has changed. Today talking about marine protection areas as saviours of the environment. We knew this in 1918
Great (War) Fishing Experiment
Fishing activity in increased in the N Sea through late 19th century (more demand, apparent depletion of larger target fish). Areas of fishing widened and ‘refuge’ areas reduced.
IN WW1 fishing greatly reduced- marked affect on post-war catches. Greater lengths of plaice caught in 1919 and higher catch rates. Population recovering. Increased survival and older fish = larger fish
Replicated in WW2 with the same result.
