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MARS2001 Module 7
Module 7
| Question | Answer |
|---|---|
| How have we caught fish over the years? | used to only be capture fisheries but aquaculture has significantly grown over the past 30 years |
| Why have fisheries been static for so long? | marine capture fish stocks are under threat; almost no resources left to enable increase in harvest (resources left for exploitation are depleting whilst demand has increased) |
| What does fishery management entail? | assessing status of stock; setting catch targets , better data and scientific research; making regulations; collecting data; dynamics of fish stocks depends on mortality rate and recruitment rate |
| What factors affect the mortality rate of fish in fisheries? | catch (recorded fish landings, by-catch, illegal fishing, recreational fishing) and natural mortality (age, predation, environmental factors) |
| What factors affect the recruitment rate of fish in fisheries? | maturation rate, habitat, temperature, prey abundance, population size |
| What is maximum sustainable yield size (MSY)? | usually calculated from single-species sotkc assessments; attempt to maintain catch rate at a level lower than or the same as recruitment rate |
| How is maximum sustainable yield (MSY) managed? | using a quote system that includes total allowable catch (TAC) or individual transferable quote (ITQ) |
| What is total allowable catch (TAC)? | defines a maximum total quote for one fishery that the entire fishery fleet may catch in a season |
| What are the disadvantages of TAC? | skippers compete to catch as much of the TAC that they can early in the season, before the quote is fished to limit; high risk of overshooting quotes; concentrates fishing effort at start of season |
| What is individual transferable quote (ITQ)? | allocate defined quotas of a particular fishery to each vessel; may be fished at any time during the season, and un-fished balances sold on |
| What are the advantages of ITQ? | distribute the fishing effort over the season and rarely results in over-fishing; ITQs have high value; can be sold to compensate retiring fishers; aids with fleet reduction |
| Why do quote systems fail? | simplistic models; single species stock assessment models based on incorrect assumptions; missing data |
| What's wrong with simplistic models in quote systems? | unpredictable patterns of stock decline based on single-species stock assessments and catch per unit effort |
| What's wrong with incorrect assumptions of single species stock assessments in quote systems? | assumption that reduced stock numbers reduces competition for mates, habitats, feeding for larvae and juveniles, therefore enhance larval and juvenile survival (compensation effect), but in reality it is depensation |
| What is depensation? | where lower stock densities critically reduce spawning success and larval survival |
| What is the problem with missing data in artisanal fisheries in quote systems? | these fisheries vital in developing countries and use low technology; sheer number of artisanal fisheries have very high impacts, particularly on coastal reef habitats; fish landings often not recorded |
| How is missing data a problem in recreational fishing (quote systems)? | account for 23% of total catch from sensitive populations rising to 64% in certain regions; disproportionately high impact on fishery stock as recreational fishers target fish that are large, long-lived, slow maturing, higher trophic levels |
| How does fishing down the food web affect ecosystems? | overfishing selectively depletes fish at higher trophic levels; depletes species and age/size class; larger more mature females more fecund than young |
| Why do recovery plans often fail? | habitat destruction; based on single species don't account for continued damage to habitats by other fisheries; also don't account for severe changes to dynamics of entire food webs; shifting baselines for planning |
| What is spawning and recruitment affected by? | affected by water temperature; species dependent; e.g. in herring spawn faster and recruitment stronger in warmer oceans; has not yet translated into deeper water fish like cod |
| How is distribution of fish affected by climate change? | as oceans warm, fish are moving into cooler water; species dependent; redistribution away from equator |
| What is the fishing credits system (FCS)? | mixed catch quota; each species caught in a specified fishing region is worth a particular number of 'credits which can be traded; fishers can choose what they catch and in what quantity for each species, as long as not over total credit allowance |
| What are some fishery management solutions? | ecosystem based approaches (e.g. marine protected areas); better data (bycatch - fishing credit systems, big dfata and global information systems) |
| Recruitment ecosystems | often different to where capture fisheries are (in estuaries and rivers rather than continental shelf areas); |
| What can riverbank modifications cause? | destruction of habitat; increased water speed; change in riverbed sediment deposition; loss of refuge; loss of native vegetation |
| What happens when wetland drainage occurs? | have to drain wetland to grow crops; when there is a large tidal area, the pyritic layer stays anoxic; when exposed to oxygen, layer becomes very acidic; rain washes the acidic layer into water and affects water pH |
| What is food demand growth fuelled by? | population growth, income growth, diet changes |
| Why is the feed efficiency of fish so good compared to land stock? | fish don't need to maintain internal body temperature; are buoyant so expend less energy fighting gravity; excrete ammonia whereas terrestrial animals must process to urea |
| What are the three types of approaches to aquaculture? | extensive, semi-intensive, intensive |
| What is extensive aquaculture? | has low input; relies on natural productivity from ecosystem providing food and water quality; low cost enables farming of low value fish; major global source of farmed fish |
| What is semi-intensive aquaculature? | higher input; some feeding input; water may be aerated; ponds may be fertilised to maintain water quality; allows higher stocking density; higher output |
| What is intensive aquaculture? | high input; high feeding rates with expensive formulated diets; ; maximum possible stocking density; established hatchery technology with control over breeding cycle; high production per hectare |
| How is cage farming beneficial? | low land use; can be very efficient; highest value product; greatest potential for expansion |
| What practices have been adopted by many modern farms to reduce impact of organic waste? | precision controlled feeding; high efficiency diets; single point moorings (reducing intensity and distributing waste a bit more); fallowing (allows recovery and reduces long term effect) |
| How do escapes happen in fish farms? | weather - if storm is strong enough, even good quality infrastructure becomes vulnerable; seals can also get into some farms |
| What is the problem with escapes from fish farms? | comes down to difference between wild and domesticat stock; captive animals stressed in wild and vice versa; |
| What are some risks/impacts of escapes from a salmon farm? | invasive species (when fish farmed outside native range); genetic introgression (contaminate wild populations with domesticated genes); competitions for mates, food, habitat; disease risk |
| What are some solutions to mitigate effects of escaped fish? | farming sterile fish (triploidy); consider location of farm with more care; better engineering of cage infrastructure; |
| Why use triploidy in the fish? | triploid fish are sterile and don't waste energy on laying down gonad tissue; triploids should grow faster because they have more energy; prevents early maturation in warm water |
| What is the problem with using antibiotic resistance to treat diseases in fish? | resistance develops or is acquired quickly by fish pathogens after introduction of new antibiotics; generally applied by top-dressing feed; thought to be high chemical use; economic hardship (expensive to make new ones and administer them) |
| What has happened with vaccinations in fisheries? | disease prevention by vaccination has replaced antibiotic use in salmon farming; antibiotic use has significantly dropped |
| What should be considered when using antiparasitic pesticides? | how effective is it at getting rid of parasites; how long it lasts; specificity (if it affects other marine life); cost; half-life in environment; dispersal |
| How are chemicals used in fisheries? | changes overtime because of development of resisstance; has the potential to threaten natural environment; however, compared to other forms of aquaculture, aquaculture uses very low levels of chemicals |
| What are some natural solutions to preventing diseases and parasites? | using cleaner-fish to get rid of lice; using integrated multi-trophic aquaculture by introducing mussels because they take lice out of water; can use behavioural ecology (lice only occur in top 2-10m of water) |
| What is the problem with compound feeds? | synthetic diets contain high contents of fish meal and fish oil; largely derived from the capture fishery; very high demanded by global aquafeed industry for both fish oil and meal |
| What is the all important number in fish feed? | fish in - fish out; how much biomass of capture fishery fish we need to put in to get 1 tonne out; varies with species and feed conversion; as you change diet, feed conversion raatios may also change |
| What influences fish in fish out more, fish oil or fish meal? | get less fish oil from a fish than fish meal so FiFo is greatly influenced by the inclusion level of fish oil |
| What are some potential substitutions for fish meal and fish oil? | can replace with vegetable proteins/oil (proteins for fish meal, oil for fish oil); can use a finishing diet; include more sustainable ingredients that utilise by-products and waste directly (e.g. brewers yeast) and indirectly (soldier fly larvae) |
| What are problems with these fish oil/meal substitutions? | can create health issues for fish due to digestion; reduced quality of fish fed on alternate diets (low omega 3); displacement of food crops by feed crops |
| How to solve the problem of displacing crops for feed? | use more sustainable marine resources (e.g. squid meal), proteins from fungi (tofu for fish), insects or bacterial proteins |
| How to solve nutritional quality issue in feed? | by using partial replacement for most of the life of the animals and then use a finishing diet (a high quality diet fed at the end to improve fish quality) |
| How use sustainable ingredients in fish feeds? | microbial proteins from algae and bacteria are a possible direct source of nutrition for some fish; other fish like salmon can eat these through an intermediate such as mussels |
Created by:
tkeen40
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