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
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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
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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
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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
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- 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.
Surplus Production Model
All good and well to replace natural mortality BUT dermersal (near the bottom) fishing catches a range of cohorts for a single species as well as a range of species.
Difficult to set spp MSY bc stochasticity, by catch, discard – problem for fixed quota
MSY and Surplus yield apply to single stocks. But most fisheries don’t just catch one species. Have to set MSY for other spp too- if MSY low once reached quota can move onto other species with same gear. Still going to catch what they have reached the quota on- even if they throw them back not good
EU unions say they’re solving the discard problem by banning discards for 15/20 commercial species. Can still chuck dead back –> huge ecosystem problem.
Draw and effort based and an economic base model of a fishery
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National VS International fisheries
National waters around coastlines (and inland) theoretical autonomous fisheries management. BUT countries share fishing rights through international treaties requiring international cooperation for stock assessment and management.
Nationally managed icelandic cod fishery (cod wars) vs North Sea cod fishery. International waters have no limit apart from international treaty
ICES International Council for Exploration of the Sea (1902). 50x50km grid squares form basis for collection of fisheries data. Demonstrated British boats breaking the law so we kicked out of Icelandic waters where they were over-exploiting cod. Icelandic cod no managed sustainably because unilateral fishery. Unlike N Sea which is a composite of partners. N Sea not doing great in terms of fisheries and consideration.
What information is needed to assess exploited stocks
- Age/Size composition and individual growth- (include age-length + and length weight relationship)
- ‘Birth rate’- actually recruitment- incorporation of a cohort into a fishery at the size at which they become susceptible to capture, after which they are progressively fished. Typically one cohort a year of age class.
- Stock size- absolute or relative measures
- Mortality- total mortality (Z) comprises of natural mortality (M) in the absence of fishery and fishery mortality (F). Some mortality may occur in nets that are lost and not recovered (ghost fishing). Discards add to mortality. Black fish are illegally landed fish. V difficult to measure so data on mortality can often be underestimated.
About 20 yrs ago it was estimated about 1/2 cod in N sea landed illegally - Movement/distribution of stock- if stock moves on a cyclical basis and may be there are fisheries ie 2 areas but assessment only covers one stock may be fished at double intended rate.
Also levels of fishing activity, types of fishing activity, locations of fishing
Match-Mismatch hypothesis
Many species of fish (eg cod, plaice, herring) rely on zooplankton (eg rotifers) as food in larval stage.
Cushing et al suggested that in crucial first few days of life where level of mortality has massive influence on future recruitment matching (good survival) or mismatching (poor survival) of peak larval production with availability in space and time of peak zooplankton.
With CC then maybe timings of key events will changes For fish we know there is a succession of critical stages of food availability liked to environmental conditions for them to do well.
What is the gadoid outburst
A period of good recruitment for cod (and other gadoid fish) between 1960s and early 80s. Unusally cool period in the N sea and much of N atlantic. Beaugrand et al 2003
Southern end of north sea is the edge of their climatic range. Fish grow faster than arctic but suffer risk if water is too warm won’t recruit well. Temperature affects availability of crucial food forms. Cold= good
Incr fishing in 70s and 80s combined with environmental conditions (warmer) meant poor food availability. Do poor recruitment combined with large scale fishing and poor management meant pop of cod declined. Were at a real threat of extinction in the 90s.
Similar pattern in the US however it was too late to put in restrictions. Cod collapsed and ecosystem changed. Passes tipping point.
Spawning stock recruitment relationships
We expect an increase in recruitment with number of eggs released (fecundity) which is directly related to number of spawners up to a maximum therefore recruitment levels off or even declines because of the effects of infraspecific competition. Where density dependent processes are most developed (eg territoriality in brown trout) stock recruitment relationships most apparent - Ricker curves
If small pop of spawners, difficult to recovers pop so biollogist have pushed the idea of stock recruitment curves. Relationship between spawner biomass and amount of eggs produced- eg on essay qs
Catch and effort data and mortality
Can be used to estimate mortality
Total mortality= natural mortality + fishing mortality (F)
F= official landings + illegal landings + discards + non-landed fishing mortality
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With many years of data can put data points on a graph for total mortality. Can put natural mortality estimates in models but it is only a single average value. Loads of variation in natural mortality- so how valid are the things?
Exploitation models
Data can be split by age to assess Fishing mortality, natural mortality and recruitment annually and combined- basis of “cohort analysis” or “virtual pop analysis”
Fishery independent methods
Standard survey transects (eg trawls, direct observations, egg/larval surveys/ hydroacoustics) could pull trawl over same area year after year. can build spawning data into predictions
Underwater hydroacoustics for fish detection
Complex split beam transducers and software can count and size individual targets or aggregate returns (eg shoals). Most fish have a swim bladder made of air and this gives back a different sound to the water so can use it to locate fish. Can tell us relative abundance but not what species they are. Main return is from material with different density
Telemetry
Can be used to tell the difference between fish stocks
Includes satellite telemetry
Can put satellite tags on that pop up to the surface after a period of time and can give info back about fish position on a daily basis
Stock segregation
Are E and W stocks of atlantic bluefin tuna separate?
DNA studies suggest substaintail segregation of spawning. But do they mix widely in the atlantic fishing zones?
Th International Commission for the conservation of Atlantic Tunas (ICCAT) historically managed tuna in 2 separate areas and assumed they didn’t mix.
They tracked movement over 4 years using reconstructed tracks from archival data (data logger) tag. We now know they do mix and this has major implications in terms of double counting, fishery management, and sustainability of management method
Nominal ICCAT management split of stock at 45 degrees west is farcical.
ICCATs website predicts constant catches up to the year 2024 for yellowfin tuna of 120,000t. Using a MSY method. Furthermore, they extrapolated some data for 2014 to produce this report in 2016.
They also noted Overall catches have exceeded TAC (110,000) by 17-37% since 2015. The stock status may have degraded since 2014, and overfishing may be occurring
Very little mention of environmental stochasticity is present .
How can fisheries be regulated and managed
- Technical measures- mesh size (conserve young fish), square mesh panels, Nordmore grates, Turtle Excluder Devices –> doesn’t do much for selectivity of fish
- Quotas of landings (Not the same as catch) and discard reduction
- Regulating fishing effort; number of licenses, boats/gears, days of fishing, location/timing of fishing/temporary closure of fishing grounds, marine PA, no-take zones; need for inclusivity and transparency and ‘fair play’ (ethical and historical needs should be considered
Europeans tend to favour tech rather than socioeconomic methods and provide lots of funding. Quota is what can be caught but is vastly different from mortality. Just because you get rid of some discards doesn’t mean you remove ecosystem damage,.
Also what is the suvivability of the escapees
One tries to separate fish species by swimming/escape behaviour (those that swim up or down to escape)
Protected Marine Areas
People have been fishing historically in areas so can be difficult to set up PA. Tend to have areas of zoned impacts. Some areas can do trawling, some cant do gravel dredging, or restricted shipping, only certain types of fishing gear.
No-take zones from a fishery POV are closest you get to PA. True marine reserves typically have some kind of fishing policy within them
Management top down trends tend not to work. Need to have some init from all stakeholders. Then more likely to work.
TAC
Total Allowable Catch- Eu. Total catch of a given fish stock allowable by entire fishing fleet in a given yea. If fished by several countries TAC is divided between fleets. Doesn’t work well when multiple species caught (eg demersal trawl) or when stock migrates and is ‘double fished’ from 2 assumed TAC
EU uses this. Not v effective bc fisherman transfer to another species when filled the quota on one
Problem of quota- overshoot/selfish behaviour ‘tragedy of commons’. Takes little account of discards of C when quota reached and fishing for stock of Y
In theory annual stock assessment should enable fluctuations in recruitment
ITQ
Individual transferable Quota- licence sold by regulators to individual boat owners who can sell personal quota to others. Can work well when restricted to individuals/small business as value is related to stock quality and potential for future profit (sustainable). Used widely in Aus, Canada, Can also be used to regulate size of boat/gear
Better. Fixed number of licenses. Owner of licence buys in to ensure sustainability of stock. If population crashes their investment would be wasted (risk fishery banned or blocked for few years)
This works
Can limit effort through
- boat/gear or methods used- fisherman don’t like this as these are key ways to improve catches eg banning pair trawling boat sizes to <30m or
“The landings obligation”
Non selective fishing- eg for cod catches many unsaleable/nontarget species (by catch) that are discarded. Big problem in international shared resource eg N Sea, Bay of Biscay, run by EU Common Fisheries Policy TAC
Current EU members manage fisheries and biodiversity in partnership and by compromise through the EU. Common Fisheries Policy (CFP) and Policies such as the EU Habitat and SPp Directive.
Updated CFP will progressively ban discards by 2018, But only discards of saleable ‘fishing quota’ species to be banned, most biota (>50% of spp) will be shovelled back, mostly dying.
Many seabirds rely on discards so banning could affect their numbers
Temporary closure of fishing grounds - Boxes
Closing certain areas for restricted time to safe guard fish eg N Sea. None of the closed areas exclude all fishing activity.
‘boxes’ were established for very different purposes (to allow species to recover and to prevent all accidental by catch, to protect juveniles, to protect seabirds- they’ve had varying success
Ecosystem based Marine Protection- Polunin et al 1983
marine PA- geographic unit designed to protect marine habitats and communities often incorporating provision of reproductive reserves of fish stock that will disperse over wider areas contributing to fisheries outside of MPA. Ecosystem approach to fishery management while sustaining biodiversity (Roberts et al 2005)
They are a continuum for strict reserves (no damaging) to mild restrictions- most are intermediates
Justification
- Protection of diverse structural habitats or communities that are deemed by society to be important for economic, educational, r aesthetic reasons
- Protection of areas crucial for the maintenance of population expansion of exploited fishery resources (‘source’ meta populations)
- Worm et al 2003
Requirements for MPA likely to vary dramatically according to target speies/habiatas and risks to those eg areas for large, transoceanic migrating species such as turtles are difficult to identify and protect. But discrete nesting/nursery areas are more feasible
All fish on coral reef live on the reef so you protect the reef you protect all the biodiversity. Some will disperse to neighbouring reefs –> overflow effect. 1 Fished + 2 protected reef. Protected can refill exploited.
MPA and local stakeholders
Most MPAs are complex structures with multiple zones and multiple restrictions.
Need to be supported by local stakeholders, often with widely varying view points. Most MPA do not include full fishery protection; increasingly MPA with No-take zones or fully protected Marine Nature Reserves or Marine Conservation Zones are being explored. Likely to be successful for sedentary animals. Ideal for rock and coral reefs which are studied widely in temperate and tropical reefs.
Do MPA and No take zones work
Increasing number of studies to carried out to evaluate effect on community structure, production and wider benefits eg adjacent fisheries eg Roberts et al 2001
St Lucia established MPA in 1995. Fish biomass in 5 reserves tripled by 1998 and in adjacent fished areas doubled.
Roberts when in 2000-2001 and found per fishing trip big trap catches increased by 46%, 90% with small traps (compared to 95-96)
Wont work for something like tuna - need to protect half an ocean for beneficial effect
On reefs fish are sedentary and sippers radially as population grows. For wide ranging spp can protect key areas eg historic areas for reproduction
Durban Action Plan
Aimed to protect 20-30% of oceans by 2012
Currently <1% highly protected
compared to 6% land
6% of UK waters protected but only 0.001% highly protected
Coral Reef and Aquarium Trade
Ecological and Socio economic impacts in S Sri Lanka
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Uk Fisheries
Lampreys are a threatened species in EU under Habitat Directive eg Humber Estuary Special Area of Conservation (SAC)
1995 commercial fisherman exploited legal loopholes to take up to 40,000 lamprey per year for recreational angling market (bait) from Humber. Now its regulated
Trade has grown to around 90,000 lampreys per year to anglers (almost all British) supplied from England, Netherlands, and Estonia
Exploitation of threatened species less ethically defendable when done for leisure than for food/income for poor eg Sir Lanka fishermen
Interviewed users/traders of lamprey and they seemed poorly informed or lamprey conservation status. treated as commercial commodity. Education and communication?
