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Aquaculture practices in irrigation reservoirs of the Western Cape Province of South Africa in relation to multiple resource use and socio-ecological interactionSalie, Khalid 04 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Aquaculture has proven to be a viable operation in multi-used irrigation reservoirs (also referred to as farm
dams) in the Western Cape province (WCP) of South Africa. Many studies found that the fitness-for-use of
these reservoirs for both net cage culture of fish and irrigation of crops is feasible. However, practising
intensive fish farming in existing open water bodies can increase the nutrient levels of the water through
organic loading, originating from uneaten feeds and fish metabolic wastes. Under such conditions the
primary (irrigation) and secondary (drinking water and recreation) usage of the dam could be compromised
by deteriorating water quality. Rainbow trout (Oncorhynchus mykiss) farming is done in Mediterranean
climatic conditions of the WCP. This type of climate presents short production seasons with fluctuating water
quality and quantity. The study investigated the dynamics of water physico-chemical parameters and
assessed the long term impact of rainbow trout farming on irrigation reservoirs. Furthermore, associated
land-use in the catchment of such integrated aqua-agriculture systems is described, and mitigation to
minimise the impact of fish farming evaluated. The investigation concluded with assessing the contribution of
aquaculture to rural and peri-urban communities. The aim is to present an integrated, socio-ecologically
balanced farming system for irrigation reservoirs with associated aquaculture activities. A total of 35 reservoirs, including both fish farming and non-fish farming ones, were selected as research
sites. They were located in three geographical regions namely, Overberg (Grabouw/Caledon), Boland
(Stellenbosch/Franschhoek) and Breede River (Ceres/Worcester). Reservoirs were <20 ha in surface area
and the volume ranges from 300 000 to 1 500 000 m3. Water samples were collected monthly and
seasonally for the different investigations and analysed for a range of water quality parameters, including:
transparency (Secchi disc), temperature, dissolved oxygen (DO), pH, sodium (Na), potassium (K), calcium
(Ca), magnesium (Mg), iron (Fe), chloride (Cl), carbonate (CO3), bicarbonate (HCO3), manganese (Mn),
copper (Cu), zinc (Zn), boron (B), total phosphorous (TP), orthophosphate (PO4), total ammonia nitrogen
(TAN), nitrate-nitrogen (NO3-N), nitrite-nitrogen (NO2-N), aluminium (Al), total suspended solids (TSS), total
dissolved solids (TDS), alkalinity, hardness and sulphate. Phytoplankton samples were also collected,
genera identified and biomass calculated. The water quality data were analysed in terms of surface and
bottom strata in both fish farming and non-fish farming reservoirs based on repeated measurements at the
same site location at different times using the procedure General Linear Models of Stastical Analysis System
(SAS, 2012). Values p<0.05 were considered as statistically significant. A Principal Component Analysis
(PCA) biplot was used to graphically depict all the sites and measured water quality variables with the
purpose of trying to see whether the fish farming and non-fish farming ones showed any groupings and how
the sites were related to the measured variables. Structured questionnaires and informal discussions were
used to collect additional information on the water use, production data and socio-economic effects on fish
farmers. Categorical data gathered from the interviews (21 aquaculture projects) were analysed for
frequency of occurrence using the Statistical Product and Service Solutions (SPSS) computer programme
(SPSS Systems for Windows, Version 12.0). Results are presented in publication form with research
chapters focusing on the subject areas of water quality impact, catchment land-use, potential mitigation
measures and aquaculture contribution.
Results for the water quality analyses indicated that as a collective, the farm reservoirs’ overall minimum, mean and maximum values for the physico-chemical parameters were fit-for-use for trout farming. The depth
of the reservoirs ranged from 1.2 - 21.6 m with the low value taken during the summer season. Values lower
than 5.0 m can cause management problems for floating cages that require a minimum of 4.0 m for net
suspension and 1.0 m of free space below for adequate lateral flow. The Secchi disc reading of the
reservoirs ranged from 10 – 510 cm. Higher transparencies were recorded after the winter rains when sand,
silt and clay settled. Trout feeding is dependent on visibility and transparencies of more than 50 cm are
required for good feeding conditions. The dissolved oxygen (DO) ranged from 0.3 – 16.4 mg/L with values
below 5.00 mg/L recorded during summer when extraction and temperatures were high and provided
conditions unable to sustain trout farming. The situation reverses with the onset of winter when the dams fill
and DO rises above 5.00 mg/L as required for trout farming. The phosphorous (P) levels ranged from 0.001
– 0.735 mg/L. Higher concentrations were recorded during the winter turnover phase when bottom and
surface waters mixed. Concentration above 0.01 mg/L can cause eutrophication of the water bodies. Total
ammonia nitrogen (TAN) ranged from 0.015 - 6.480 mg/L. Higher concentrations were recorded during
summer when temperatures were high and depths were low. TAN can be toxic to fish when the pH and
temperature are high. The generally low least square means (LSM) for TAN were indicative of minor environmental impact of trout
farming operations conducted during the colder, winter rainfall months. Trout farming coincided with
conditions where the water temperatures were low, dam levels were high and dams were overflowing. The
difference in bottom and surface water quality of reservoirs and the site location were found to be more
important than the absence or presence of fish farming. The difference in bottom and surface water is
directly linked to the ecological status of the sediment, which serve as nutrient sinks. In monomictic dams
found in Mediterranean areas, mixing occurs during the winter turnover phase. Nutrients are released due to
surface and bottom water mixing, brought about by torrential rains and wind turbulence. The concentration of
organic material in the sediment and bottom waters is a function of the nutrient loading over time,
irrespective whether the non-point sources were fish farming or agricultural activities and therefore it is
difficult to partition causes and effects. In cases where reservoirs were already eutrophic due to past
agricultural practices, implementing aquaculture could exacerbate the poor water quality status of the
reservoir. There was a statistically significant difference between fish farming and non-fish farming for
phosphorous, Secchi disc, total suspended solids and nitrite-nitrogen (p<0.05) and no statistically significant
difference between fish farming and non-fish farming for dissolved oxygen, total ammonia nitrogen and
nitrate-nitrogen (p>0.05). There was a statistically significant difference between surface and bottom waters
for P and TAN (p<0.05). One reason for higher P and TAN concentrations in bottom waters is the
accumulation of both in the sediment and subsequent release in the water column when the water mixes. A
two-dimensional scatter plot was generated using the score for the first two principal components. The first
two principal components accounts for 40 and 17 % of the total variance respectively, and the two groups of
fish farming and non-fish farming did not separate well based on the first two principal components.
The occurrence and distribution of phytoplankton biomass fluctuated with dam water levels and nutrient
concentrations. The prevailing phytoplankton communities are important to fish farmers for two reasons: 1. It
leads to fluctuations in dissolved oxygen concentrations via users (respiration and decomposition) and
producers (photosynthesis). 2. It could lead to algal taint of fish flesh when geosmin-producing phytoplankton species are present. The frequency of occurrence indicated that the Group Chlorophyta (including genera,
Chlamydomonas, Closterium, Oocystis, Scenedesmus, Staurastrum, Tetraedron, etc) had the most
occurrences (n=371) with Chrysophyta (including genera, Dinobryon, Mallomonas, Synura, etc) the least
(n=34). There was a statistically significant difference between genera occurrence and season (p<0.05). The
geographical location of sites had no significance influence on the frequency of phytoplankton occurrence.
There was no direct link between water quality and production yield (p>0.05). The fish yield of farms were
linked mainly to the quality of fingerlings and the feed conversion ratio (FCR) achieved (p<0.05).
Land-use patterns in the catchment where fish farming dams were located have shown that the dams are
multiple-used systems. The ecological integrity of the farm dam ecosystem is dependent on the base
volume. The dam is primarily for irrigation and fish farming can be compromised when higher demand for
water is required during the dry season. The dams receive about 20 % of its water from rainfall and the rest
from runoffs. Farmers could not provide accurate extraction rates making it difficult to predict water levels for
future fish production.
Four potential mitigation measures to reduce nutrient loading were described namely, feed management
(quantity, frequency, type, etc.), feeding method (demand feeders, hand feeding), feed ingredients
(formulation) and floating gardens. Both feed management procedures and demand feeders were evaluated
as to the efficiency of reducing feed wastage and optimising FCR’s. The small-scale fish farmers were
producing approximately 6 tons and had an average FCR of 1.96:1 ± 1.15. If farmers could improve their
FCR’s by 0.1 (i.e. from 1.96 to 1.86), it would translate into a reduction of 100 kg feed for every ton of fish
produced and result in 5% decrease in nutrient loading. The results of the water analysis and visual
assessment of faecal length and colour showed no statistically significant difference between treatments for
the guar-gum based binder (p>0.05). In addition, the level of binder did not influence digestibility of the
experimental diets.
The floating garden study indicated that it was feasible to construct a low cost raft system that is easy to
manage and can produce plant crops as a hydroponic system in conjunction with fish farming cages. The
lettuces grown on farm dam water provided support for the premise that the water quality can be improved
via extraction of nutrients for crop production. For the production of 3.5 kg/m2 lettuce, a ratio of 1.09
plants/fish equal to 1.84 g feed/day/plant would reduce the accumulation of soluble nutrients around floating
net cage farming system. The socio-economic evaluation of the contribution of fish farming to the welfare of rural and peri-urban
farming communities supported the notion that aquaculture can lead to the upliftment of participating
communities. Seventy-one percent (71%) of the respondents indicated that their motivation for exploring
aquaculture is to supply fish to the wholesale market in order to generate income. Sixty-one percent (61%) of
the respondents conducted the sales themselves or co-opted family members to assist them. The
contribution of aquaculture provided direct benefits through improvement in household income, subsistence
food supply and skills development. Indirect benefits included providing an information hub for other
emerging farmers, elevation of the fish farmer’s status in the community through greater wealth and
knowledge creation and promoting sector diversification through new products and technology. The three main constraints to the promotion and growth of aquaculture were listed as lack of government support,
insufficient market intelligence and access, and limited choice in the availability of suitable candidate
aquaculture species.
Irrigation reservoirs in the WCP have a history of enrichment through external sources supplying water via
agricultural runoff (fertilisers and pesticides), catchment runoff (leaf litter and organic debris) and stormwater
effluent (grey and black water). The incorporation of aquaculture into such dams adds extra nutrients to the
water column and management is crucial to limit the nutrient loading and ensure environmental
sustainability. Such an approach will ensure that commercial land-based crop farmers’ irrigation regime and
water distribution operations would not be negatively affected. Therefore future research needs should focus
on; firstly the prevention and minimisation of pollution deriving from aquaculture through improved production
management and technology transfer, secondly the monitoring and evaluation of the catchment ecosystem
as a continuum with all the external factors affecting the ecology of farm dams and thirdly, evaluating the
sediment processes and dynamics as sinks for nutrient accumulation. / AFRIKAANSE OPSOMMING: Akwakultuur het getoon dat dit ‘n lewensvatbare inisiatief is vir meerdoelige-gebruik van besproeiingsdamme
(ook genoem plaasdamme) in die Wes-Kaap provinsie (WKP) van Suid-Afrika. Vele studies het bewys dat
die geskiktheid-vir-gebruik van die reservoirs haalbaar is vir beide visproduksie sowel as besproeiing van
landbougewasse. Nieteenstaande, die beoefening van intensiewe visboerdery in bestaande buitelug
watersisteme kan lei tot ‘n toename in nutriëntvlakke van die water as gevolg van organiese belading
afkomstig van ongevrete voere en metaboliese afvalstowwe van die vis. Onder sulke omstandigthede kan
die primêre- (besproeiing) en die sekondêre (drinkwater en rekreasie) gebruik van die dam in gedrang kom
weens ‘n afname in waterkwaliteit. Reënboogforel (Oncorhynchus mykiss) boerdery word beoefen in die
omliggende Mediterreense klimaat van die WKP. Die tipe klimaat verskaf kort produksie-seisoene met
wisselvallige water kwaliteit en kwantiteit. Die studie het die dinamika van water se fisies-chemiese
parameters ondersoek en het die impak van forelboerdery op besproeiingdamme oor die langtermyn beskryf.
Verder het die studie die geassosieerde landgebruik in die opvangsgebied met geïntegreerde akwa-landbou
sisteme beskryf, asook moontlike toetrede (mitigasie maatreëls) geëvalueer wat die impak moontlik kan
verlaag. Die ondersoek is afgesluit deur die bydrae wat akwakultuur lewer aan landelike en semi-stedelike
gebiede, te beskryf. Die hoofdoel is die daarstelling van ‘n geïntegreerde, sosio-ekologiese gebalanseerde
sisteem vir besproeiingdamme met gesamentlike akwakultuuraktiwiteite. ‘n Totaal van 35 besproeiingsdamme, insluitend die met visboerdery en nie-visboerdery, is gekies as
navorsingspersele. Dit is hoofsaaklik geleë in drie geografiese gebiede naamlik, Overberg
(Grabouw/Caledon), Boland (Stellenbosch/Franschhoek) en Breederivier (Ceres/Worcester). Die reservoirs
is almal < 20 ha in oppervlakarea en die volumes het gewissel van 300 000 – 1 500 000 m3. Watermonsters
is maandeliks sowel as seisoenaal versamel vir die onderskeie ondersoeke en ontleed vir ‘n reeks van
parameters, insluitend: sigbaarheid (Secchi disc), temperatuur, opgeloste suurstof (OS), pH, natrium (Na),
kalium (K), kalsium (Ca), magnesium (Mg), yster (Fe), chloor (Cl), karbonaat (CO3), bikarbonaat (HCO3),
mangaan (Mn), koper (Cu), sink (Zn), boor (B), totale fosfor (TP), ortofosfaat (PO4), totale ammoniak stikstof
(TAN), nitraat-stikstof (NO3-N), nitriet-stikstof (NO2-N), aluminium (Al), totale gesuspendeerde vaste stowwe
(TGV), totale opgeloste vaste stowwe (TOV), alkaliniteit, hardheid en sulfate. Phytoplanktonmonsters is ook
versamel, genera geïdentifiseer en die biomassa bepaal. Die waterkwaliteitsdata is ontleed in terme van
oppervlak- en bodemstrata vir beide visboerdery en nie-visboerdery reservoirs en was gebaseer op
herhaalde metings by dieselfde perseel op verskillende tye deur gebruik te maak van die Algemene Liniêre
Model van Statistiese Analitiese Sisteem (SAS, 2012). Waardes p<0.05 is oorweeg as statisties beduidend.
‘n Hoofkomponentanalise bi-stipping (HKA) is toegepas om die persele en veranderlikes grafies voor te stel
en te bepaal of die visboerdery en nie-visboerdery s’n enige groeperinge vorm asook hoe die persele
assosieer met die veranderlikes. Gestruktureerde vraelyste en informele besprekings is onderneem om
inligting in te samel op watergebruik, produksie-data, en die sosio-ekonomiese invloed wat akwakultuur bied
aan visboere. Kategoriese data wat deur die onderhoude (21 akwakultuurprojekte) ingesamel is, is ontleed
vir die frekwensie van aanwesigheid deur die gebruik van Statistiese Produk en Dienste-oplossings (SPDO)
rekenaarprogram (SPSS Systems for Windows, Version 12.0). Die resultate vir die verskeie ondersoeke is
beskryf en saamgestel in publikasie-vorm met die navorsingshoofstukke wat gefokus het op die areas van
waterkwaliteitsimpak, opvangsgebied landgebruik, toetrede-meganismes en die bydrae van akwakultuur. Die resultate vir die waterkwaliteitsanalises het getoon dat gesamentlik die reservoirs se oorhoofse
minimum, gemiddelde en maksimum waardes vir die verskillende fisies-chemiese parameters geskik is vir
forelboerdery. Die diepte van die reservoirs het gewissel van 1.2 - 21.6 m, met die laagste waarde
aangeteken gedurende die somermaande. Waardes laer as 5.0 m kan bestuursprobleme vir drywende
hokstelsels versoorsaak want ‘n minimum van tenminste 4.0 m vrye spasie onder die hokke word benodig vir
voldoende laterale vloei. Die Secchi-skyf lesing (sigbaarheid) van die reservoirs het gewissel van 10 – 510
cm. Hoër sigbaarheidswaardes is aangeteken na winterreëns wanneer sand-, slik- en klei deeltjies uitgesak
het. Forel voer op sig en sigbaarheid van > 50 cm word benodig om goeie voeding te handhaaf. Die OS het
gewissel van 0.3 – 16.4 mg/L met waardes onder 5 mg/L aangeteken gedurende somer wanneer
wateronttrekking en temperature hoog was. Dit het gelei tot ongunstige toestande vir forelboerdery. Die
situasie swaai om met die begin van winter wanneer die damme vol reën en die OS bo 5 mg/L styg soos
benodig vir forelboerdery. Die P-vlakke het gewissel van 0.001 – 0.735 mg/L. Hoër waardes is aangeteken
gedurende die winteromkeerfase wanneer die bodem en oppervlak se water meng. Konsentrasies bo 0.01
mg/L kan tot eutrofikasie van watersisteme lei. TAS het gewissel van 0-015 – 6.480 mg/L. Hoër
konsentrasies is aangeteken gedurende die somer wanneer temperature hoog is en damvlakke laag. By hoë
pH’s en temperature kan TAS toksies wees vir vis. The algemene lae kleinste kwadaat gemiddelde (KKG) waarde vir TAS het getoon dat daar ‘n klein impak op
die omgewing was wanneer forelboerdery bedryf word gedurende die koue, winter reënvalmaande.
Forelboerdery val saam met omstandigthede wanneer die watertemperature laag is, damvlakke hoog en die
reservoirs oorloop. Die verskil in die bodem- en oppervlak water in die besproeiingsdamme en die ligging
van die perseel is vasgestel om meer belangrik te wees as die teenwoordigheid of afwesigheid van
visboerdery. Die verskil in die bodem en oppervlak is toe te skryf aan die toestand van die sediment waar
nutriënte kan opgaar. In monomiktiese damme soos gevind in Mediterreende areas, vind vermenging plaas
gedurende die winteromkeerfase. Nutriënte word vrygestel a.g.v. die vermenging van die oppervlak en
bodem se water wat dan veroorsaak word deur harde reën en windturbulensie. Die konsentrasie van
organiese materiaal in die sediment en bodem water is ‘n funksie van die nutriëntlading met tyd, ongeag of
dit afkomstig was vanaf visboerdery of landbou-aktiwiteite. Dit is dus moelik om die spesifieke oorsaak van
besoedeling af te baken. In gevalle waar die reservoirs alreeds eutrofies is a.g.v. aangewese landbouaktiwiteite,
kan die toestand van die waterbron vererger indien akwakultuur toegepas word. Daar is ‘n
statistiese noemenswaardige verskil tussen visboerdery en nie-visboerdery vir P, Secchi-skyf, totale
gesuspendeerde vaste stowwe en nitrite-stikstof (p<0.05), en geen statistiese noemenswaardige verskil
tussen visboerdery en nie-visboerdery vir OS, TAS en nitraat-stikstof (p>0.05). Daar is ‘n statistiese
noemenswaardige verskil tussen oppervlak- en bodem water vir P en TAS (p<0.05). Een moontlike rede vir
hoër P en TAS konsentrasies in die bodemwater, is die akkumulasie van beide parameters in die sediment
en gevolglike vrystelling in die waterkolom wanneer die water gemeng word. ‘n Twee dimensionele
spreidingstipping is geprodueer deur die waardes te gebruik van die eerste twee hoofkomponente. Die
eerste twee hoofkomponente dra by 40 % en 17 % van die totale variansie onderskeidelik, en die twee
groepering van visboerdery en nie-visboerdery het nie duidelik getoon nie.
Die voorkoms en verspreiding van phytoplankton biomassa het gewissel met die verandering in damvlakke
en nutriëntkonsentrasies. Die aanwesige phytoplanktongemeenskappe is belangrik vir die visboer vir twee redes: 1. Dit kan wisselende OS-vlakke versoorsaak deur die verbruik (respirasie en dekomposisie) en
produksie (fotosintese) daarvan. 2. Dit kan lei tot alge na-smake van vis wanneer geosmin-produserende
phytoplankton spesies aanwesig is. The frekwensie van voorkoms het getoon dat die Groep Chlorophyta
(insluitend die genera, Chlamydomonas, Closterium, Oocystis, Scenedesmus, Staurastrum, Tetraedron,
ens.) die meeste voorkom (n=371), met Chrysophyta (insluitend die genera, Dinobryon, Mallomonas,
Synura, ens.) die minste (n=34). Daar is ‘n statistiese noemenswaardige verskil tussen genera voorkoms en
seisoen (p<0.05) vir phytoplankton. Die geografiese ligging van die perseel het geen noemenswaardige
invloed op die frekwensie van phytoplankton voorkoms nie. Daar is geen statistiese noemenswaardige
verbintenis tussen waterkwaliteit en visproduksieopbrengste nie (p>0.05). Die visopbrengste by plase is
hofsaaklik afhangende van die kwaliteit van die vingerlinge en die voeromsettingsverhouding (VOV) wat
bereik is (p<0.05).
Die landgebruikspatrone in die opvangsgebied waar visboere gesetel is, het aangedui dat die
besproeiingsdamme meeldoelige sisteme is. Die ekologiese integriteit van die plaasdam-ekosisteem is
afhanklik van die basisvolume. Die dam is hoofsaaklik daar vir die besproeiing en visboerdery kan in
gedrang kom wanneer daar ‘n hoër aanvraag vir water gedurende die droë seisoen is. Die damme het
omtrent 20 % van die water vanaf reënval ontvang en die res van aflope. Boere kon nie akkurate inligting
verskaf van waterontrekking nie wat dit moeilik gemaak het om te voorspel wat die beskikbare watervlakke in
die toekoms sou wees vir visproduksie.
Vier potensiële toetrede meganismes om die nutriëntlading te verminder, is beskryf naamlik
voedingsbestuur, (kwantiteit, frekwensie, tipe, ens.) voermetodes (aanvraagvoeder, handvoeding),
voerbestandele (formulasies) en drywende tuine. Beide voedingsbestuur prosedure en aanvraagvoeders is
geëvalueer as ‘n metode om die voervermorsing te verminder en die VOV te verbeter. Die kleinskaalse
visboere het ongeveer 6 ton produseer met ‘n gemiddelde VOV van 1.96:1 ± 1.15. Indien die visboere hul
VOV’s met 0.1 kan verbeter (bv. van 1.96 tot 1.86), sal dit beteken dat daar ‘n vermindering van 100 kg voer
bewerkstellig word vir elke ton vis geproduseer. Dit kan ook lei tot ‘n vermindering van 5 % in die
nutriëntlading. Die resultate van die wateranalises en die visuele waarneming van faeceslengte en kleur het
geen statistiese noemenswaardige verskil tussen die behandelinge vir die guar-gom binder getoon nie
(p>0.05). Verder, die hoeveelheid van die binder het nie die vertering van die eksperimentele diëte beïnvloed
nie. Die studie op die drywende tuine het getoon dat dit haalbaar is om ‘n lae-koste sisteem te bou wat maklik is
om te bestuur en gewasse kan produseer soos in ‘n hidroponiese sisteem tesame met visproduserende
hokstelsels. Die kropslaaie se groei het getoon dat die waterkwaliteit van besproeiingsdamme kan verbeter
word deur die opname van nutriënte wanneer plante verbou word. Vir die produksie van 3.5 kg/m2
kropslaaie, sal ‘n verhouding van 1.09 plante/vis of 1.84 g voer/dag/plant die akkumulasie van opgeloste
nutriënte rondom die hokstelsels verminder.
Die sosio-ekonomiese evaluasie van die bydrae van visboerdery tot die welvaart van die landelike en semistedelike
plaasgemeenskappe ondersteun die feit dat akwakultuur verbetering kan bewerkstellig, veral onder
deelnemende gemeenskappe. Een-en sewentig persent (71 %) van die respondente het getoon dat hul oorweging vir die bedryf van akwakultuur is om vis te voorsien aan die grootmark en daarvolgens geld te
maak. Een-en-sestig persent (61 %) van die respondente het aangedui dat hulself die vis verkoop of vir
familie-lede vra om met die verkope te help. Die bydrae van akwakultuur het direkte voordele aan die
deelmers voorsien deur ‘n verbetering in huishoudelike inkomste, voedselvoorsiening vir selfgebruik en die
ontwikkeling van vaardigthede. Indirekte voordele sluit in dat die deelmers ‘n bron van inligting geword het vir
opkomende boere, hul status in die gemeenskap het verbeter omdat hul kennis verbreed het en dit het
verder gelei tot diversifisering in die sektor a.g.v. die skepping van nuwe produkte en tegnologie. Die drie
hoof struikelblokke wat die groei en bevordering van akwakultuur belemmer is o.a., ‘n tekort aan
staatsondersteuning, onvoldoende markinligting en toegang en ‘n beperkte keuse in spesies vir boerdery.
Besproeiingsdamme in die WKP het ‘n geskiedenis van verryking deur eksterne bronne wat water voorsien
vanaf landbou-afloop (bemestingstowwe en pesbestrydingsmiddels), opvangsgebied-afloop (blare en ander
organiese debris) en stormwateruitlaat (gruis- en swart water). Die implementering van akwakultuur in sulke
damme voeg addisionele nutriënte tot die waterkolom en bestuur is krities om die lading te verminder en te
verseker dat omgewingsvolhoubaarheid behou word. Indien die regte praktyke en bestuur toegepas word,
sal dit beteken dat die kommersiële boer se besproeiing en waterverspreiding nie negatief beïnvloed word
nie.
Vervolgens moet toekomstige navosingsbehoeftes fokus op eerstens, die voorkoming en vemindering van
besoedeling afkomstig van akwakultuur deur verbeterde produksie-bestuur en tegnologie-oordrag,
tweedens, die monitoring en evaluering van die opvangs-ekosisteem as ‘n kontinuum met al die eksterne
faktore wat die ekologie van die plaasdam kan beïnvloed en laastens, die ondersoek en evaluering van die
sediment se prosesse en dinamika as ‘n sisteem wat nutriënte ophoop.
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Development and application of dynamic models for environmental management of aquaculture in South East AsiaMunro, Lynn I. January 2014 (has links)
With the world’s population set to reach 9 billion by the mid 21st century food security has never been more important. Increased competition regarding land for agricultural use and over fished seas means it falls to aquaculture to meet the global demands for protein requirements. The largest supply of aquaculture products are cultivated in South East Asia where the industry has seen rapid expansion, particularly of pond production in the past 50 years. This initial expansion has come at a cost with mangrove losses and eutrophication of natural water sources resulting. The impact of these not only affects other stakeholders, including domestic users, but effects will be felt by the aquaculture industry. Indiscriminate release of effluents to the surrounding water reduces the water quality for other users and may impact on the farm discharging the water originally. Poor water quality can then result in poor growth rates and increased mortalities reducing the profitability of the farm and endangering the livelihood of the farmer. If aquaculture is to meet the global food demand it is important that current and future enterprises are developed with sustainability at the fore front. This study investigates the nutrient dynamics in pond culture in South East Asia, focussing initially on four countries outlined by the SEAT (Sustainable Ethical Aquaculture Trade) project, including Thailand, Vietnam, China and Bangladesh. Within the four countries the main species cultured for export were identified resulting in tilapia, shrimp, pangasiid catfish and prawn. Following a farmer survey designed to collect a large volume of data over a range of topics including, water management, social, economic and ethical perceptions, dynamic models were developed, using Powersim Studio 8© (Powersim, Norway), for a generic fish and shrimp ponds separately. The models draw on data from the survey combined with other literature sources to provide outputs for Total Nitrogen and Total Phosphorus in water and sediment as well as dissolved oxygen in the pond water. One of the biggest challenges facing this study was the objective selection of relevant sites for case studies to apply the models to. With such a large preselected set of sites (200 per species per country) it was important that the method be capable of handling such large datasets. Thusly it was decided that a multivariate method be used due to the removal of any pre judgement of the data relevant to the study. In order to investigate the nutrient dynamics water management data was used in the multivariate analysis to identify any similarity between the practices occurring on farms. The case studies in this project focus on Thailand and Vietnam, covering tilapia, shrimp and pangasius. Prawn farms were disregarded as, through the survey, it was discovered most production was for domestic trade. The models were adapted to each farm case study expanding the boundary from pond level to farm level, providing an output for each pond in terms of nutrients in the water and production levels and the farm as a whole for dissolved oxygen and sediment accumulation. The results of the models suggest the culture species to be taking up much of the TN added followed by the accumulation in sediments in shrimp ponds, while TP is mostly taken up by sediments. The fish case studies suggest that most of the TN is discharged to the environment followed by uptake. While Total phosphorus shows similar results to shrimp, accumulating in the sediment. The models presented in this study can be used to estimate outputs from farms of similar water management strategies and can assist in the determination of where improvements can be made to reduce the potential for eutrophication of natural water sources.
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Identificação e análise de vantagens competitivas em empresas de aquicultura / Identification and analysis of competitive advantages in aquaculture companiesPaseto, Luísa Amélia, 1964- 25 August 2018 (has links)
Orientador: Marco Túlio Ospina Patino / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola / Made available in DSpace on 2018-08-25T12:09:17Z (GMT). No. of bitstreams: 1
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Previous issue date: 2014 / Resumo: A problemática ambiental ocupa importante papel nas discussões sobre os rumos da economia e as políticas públicas. O conhecimento científico para um desenvolvimento econômico sustentável confronta-se com a necessidade de encontrar soluções capazes de integrar as diversas características e as relações de interdependência dos processos ambiental, produtivo e econômico. O objetivo deste trabalho foi de identificar e analisar os indicadores de boas práticas de gestão ambiental e seu grau de influência na formação de vantagem competitiva na cadeia de valor dos empreendimentos aquícolas de Capitólio/MG. Duas correntes econômicas sobre estratégias empresariais nortearam o estudo na evidência de vantagem competitiva. A primeira corrente utiliza o posicionamento como um atributo de desempenho interior e exterior das organizações e a segunda reconhece as capacidades coletivas como cadeia de valor dinâmica e inter-relacionada para a inserção e reconhecimento pelo mercado. Os métodos aplicados nesta pesquisa para determinação da geração de competitividade e seu aproveitamento, integram as dimensões biofísicas, políticas, culturais e econômicas, com uma visão multidisciplinar dos indicadores na cadeia de valor. As análises determinaram os pontos fortes e fracos necessários para o direcionamento das intervenções na cadeia de valor, de acordo com o potencial de criação de vantagem competitiva, sob a ótica do capital social. Os pontos fortes e fracos analisados se inter-relacionam nas atividades produtivas com a quantidade de ração administrada, minimização do estresse e mortalidade dos peixes e deficiências nutricionais que prejudicam a qualidade final do pescado e sua inserção no mercado. As respostas e análises apontam à necessidade do produtor associado e individual, perceberem que sua produção pode melhorar em custos, desempenho alimentar e qualidade nos tanques-rede, a partir de ajustes comportamentais, culturais e ou de gestão nas atividades que integram os stakeholders e os elos de inter-relacionamento na cadeia de valor. Uma simulação de custos e receitas de produção, com intervenção na cadeia de valor, demonstrou uma possibilidade de aumento do lucro de até 267%, permitindo ao produtor a inserção em um mercado consumidor que considera boas práticas de produção como valor agregado / Abstract: Environmental issues occupy an important role in discussions about the direction of the economy and public policy. Scientific knowledge for a sustainable economic development is faced with the need to find solutions capable of integrating the various characteristics and relationships of interdependence of environmental, productive and economic processes. The aim of this study was to identify and analyze good practice indicators of environmental management and their degree of influence in the formation of competitive advantage in the value chain of the aquaculture ventures of Capitólio/MG. Two current economic on business strategies guided the study on evidence of competitive advantage. The first uses the current positioning as an attribute of indoor and outdoor performance of organizations and the second recognizes the collective capabilities as interrelated and dynamic value chain for insertion and recognition by the market. The methods used in this research to determine the generation of competitiveness and their use, integrate biophysical dimensions, political, cultural and economic, with a multidisciplinary vision of the indicators in the value chain. The analysis determined the necessary strengths and weaknesses to the targeting of interventions in the value chain, according to the potential of creating competitive advantage, from the perspective of social capital. The strengths and weaknesses analyzed interrelate in productive activities with the ration quantity administered, minimizing the stress and mortality of fish and nutritional deficiencies that affect the final quality of the fish and its insertion in the market. The answers and analyses indicate the necessity of the associate and individual producers, realizing that their production may improve in costs, food and quality performance in tank-nets, from behavioral, cultural and/or management adjustments in the activities that integrate stakeholders and the related links in the value chain. A simulation of production costs and revenues with intervention in the value chain, demonstrated a possibility of profit increase of up to 267 percent, allowing the producer to insertion into a consumer market that considers good manufacturing practices as added value / Mestrado / Gestão de Sistemas na Agricultura e Desenvolvimento Rural / Mestra em Engenharia
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Building Integrated AquacultureWoodin, Erik A 01 January 2011 (has links) (PDF)
Exploratory research into a fresh concept, building integrated aquaculture, has found new information on the topic. Motives indicating building integrated aquaculture is important for sustainable development were identified. A review of the literature found relatively little in the way of experiments, aquaculture operations, and case studies which documented or demonstrated a deep understanding of the interactions between building and aquaculture systems. A simple experiment was conducted observing thermal energy and moisture interactions in simulated aquaculture facilities, some with tank covers and insulation. Two different retrofit programs were developed in a case study of building integrated aquaculture for an existing structure on the campus of the University of Massachusetts.
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The Inactivation of Pathogens in Aquaculture SystemsGonzalez-Alanis, Pablo January 2007 (has links)
As aquaculture has become a significant provider of the human diet, the interest to have better quality of sea and fresh products has been increasing. However the potential hazards associated with pathogenic agents resulting in losses to the industry are major concerns that provided the motivation for this study.The use of ultraviolet irradiation is an alternative to disinfect water in inlet and outlet water sources. However the ultraviolet disinfection method has some drawbacks including no disinfectant residuals and high cost of lamp fouling and replacement. The ultraviolet system needs to be calibrated according with the life time of the ultraviolet lamps.The MS-2 coliphage in this study is an approach to determine a good indicator for determining if an ultraviolet system can be effective in an aquaculture recirculation system. The susceptibility of this system can provide an indication if WSSV can be inactivated and possible other pathogenic agents.The WSSV experiment was successful in reducing mortality. Further studies have to be completed and analyzed before recommending for control of other pathogens.
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Possible limiting factors for a sustainable crappie fishery in the Salt River chain of reservoirs, ArizonaHorton, Christopher Michael, 1973- January 1997 (has links)
The dynamics of crappie populations in southwestern reservoirs are not well documented. In order for managers to enhance a crappie fishery, they need to understand the factors that control populations. I examined potential limiting factors for black crappie in 4 sequential reservoirs on the Salt River, Arizona. Only in Roosevelt Reservoir, the uppermost reservoir, were crappie relatively abundant. I identified 3 possible limiting factors. Apache, Canyon, and Saguaro reservoirs lacked sufficient spawning substrates. All 4 reservoirs lacked sufficient cover. Finally, the lower 3 reservoirs are less productive during the fall according to chlorophyll a levels than Roosevelt Reservoir. Low productivity may have resulted in fewer zooplankton and possibly a limited forage base for juvenile crappie. Options such as spawning platforms, artificial cover, fertilization, and stocking are discussed as ways to improve the crappie fishery in these reservoirs.
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Cormorants and the Loch Leven trout fisheryWright, Gordon Alan January 2002 (has links)
Perceived conflicts between piscivorous birds and commercial freshwater fisheries are common, and such a perception exists at Loch Leven, a wetland of international importance for nature conservation and a famous commercial brown trout Salmo trutta fishery, where Great Cormorants Phalacrocorax carbo have been shot in large numbers. This thesis describes the foraging behaviour of cormorants wintering on Loch Leven. It summarises changes in wintering numbers over a 32 year period, and reviews data on fish populations, fish stocking rates, angling catches and angling effort in order to seek evidence of detrimental impacts of cormorants on the fishery, and beneficial effects of large-scale cormorant shooting. Finally, this thesis considers turnover within the wintering cormorant population, and its implications for cormorant control. Cormorants spent most of the time roosting, and a single peak of feeding activity occurred early in the morning. Compared to early or late winter, cormorants showed higher foraging activity during mid-winter. Both solitary feeding and flock feeding were recorded, with flock feeding predominating. Solitary feeding was distributed over a wide area. The intensity of flock feeding was less evenly distributed, with 36% of grid squares not used. Overall, 78% of flock feeding activity took place in 23% of grid squares and 59% took place in 13% of grid squares. The best predictor of both solitary feeding and flock feeding intensity of use was mean water depth. Mean water depth was also the best predictor of winter brown trout distribution, although winter brown trout distribution was not a predictor of either solitary feeding or flock feeding intensity of use.
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Sea turtle ecology and conservation on the North Coast of Trinidad, West IndiesLivingstone, Suzanne Rachel January 2006 (has links)
Five species of sea turtle are known to nest on the north and east coast beaches of Trinidad, West Indies. In descending order of abundance: the leatherback (Dermochelys coriacea), the hawksbill (Eretmochelys imbricata), the green (Chelonia mydas), the olive ridley (Lepidochelys olivacea) and the loggerhead (Caretta caretta). This thesis investigates a number of aspects of the ecology and conservation of the sea turtles nesting and foraging on the north coast. Prior to this project, little research had been carried out on the north coast region, largely due to the difficulties of accessing the nesting beaches. The main aims of the project include making reliable estimates of the annual nesting population size of each species, to identify the main threats to the turtles at various life stages, and to make recommendations on how best to conserve the sea turtles in Trinidad. Overall, this thesis offers an up-to-date overview of the status of the sea turtle populations nesting on the north coast of Trinidad. The results presented here highlight Trinidad’s importance as a region for turtles, especially for nesting leatherbacks, foraging greens and nesting and foraging hawksbills. This study will be useful in assisting the Trinidadian Government to meet their obligations under the Biodiversity Convention, and in facilitating the assessment of the remaining leatherbacks in the Atlantic. Recommendations are made for future conservation and management.
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Post-harvest physiology of the scallop Pecten maximus (L.)Duncan, Peter Fergus January 1993 (has links)
Experiments were carried out to identify the environmental factors influencing survival during emersion with the aim of suggesting modifications to present transit conditions in order to minimise physiological stress, thus improving scallop condition and survival. Results showed that increasing the emersion temperature from 5 to 20oC caused a reduction in maximum survival time of 62%. Similarly, reduction in relative humidity, from 95 to 70% saturation, resulted in 27% reduction in maximum survival time. Scallops exposed to a fine sea-water mist showed a 13% improvement in survival and the survival of scallops tested in December was 67% better than those tested in July. This seasonal effect appeared to be correlated with tissue glycogen concentrations which decreased by 29% over the same period. Maximum survival of any emersed scallop was 166 hours, although the animals were not in an edible condition after this time. Experimental factors which were found not to influence survival directly were packing orientation, enforced shell-valve closure and hypertoxic conditions (˜100% oxygen). These results implicated aspects of energy metabolism as the primary causes of scallop death during emersion and therefore this area was investigated in more detail. Further work showed that, heart rate had a positive linear relationship with temperature until ˜19oC. Thereafter, heart rate became irregular and uncoordinated, suggesting that poorer survival at high temperature is caused by loss of physiological integration and difficulty in meeting increased metabolic demands. The oxygen consumption rate of Pecten maximus in air is reduced to only 50% of the aquatic rate within 8 hours of emersion. This decline in respiration rate continued and was typically between 25 and 30% of the aquatic oxygen consumption rate after 60 hours in air. In addition, heart rate, haemolymph PO2, haemolymph pH and mantle cavity fluid PO2 and pH all decreased during emersion, implying that respiratory and circulatory systems were deteriorating.
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Coping styles and learning in fish : developing behavioural tools for welfare-friendly aquacultureMesquita, Flavia de Oliveira January 2011 (has links)
During the course of this programme of work, two related studies were carried out in collaboration with colleagues in the Division of Ecology & Evolutionary Biology. Together with Hussein Jen-Jan, we explored some hidden costs of an aggressive, proactive life style by examining respiratory function in relation to coping strategy in common carp (chapter 6). Morphometric analysis of the fine structure of the gills was used to estimate respiratory area and histological analysis of sections through the gill filaments was used to measure the extent to which the secondary lamellae were obscured by epithelial cells. There was a significant relationship between risk-taking phenotype and both the size of the respiratory surface and the extent to which this is exposed as opposed to covered with epithelial cells. Risk-taking fish had larger and more exposed respiratory surfaces than did risk-avoiding fish, with fish with intermediate risk-taking phenotype having intermediate scores. These differences are interpreted as an adaptation to the known high resting metabolic rate of risk-taking fish (Chapter 6). Together with Priyadarshini, we look at social interactions and growth in relation to risk-taking phenotype in goldfish. Within the social groups, though most goldfish showed no aggressive behaviour, some of the fish attacked their companions at least once per minute of observation and some individuals showed as many as 8 attacks per minute. These levels are surprisingly high for what is usually seen as a non-aggressive species. In groups comprising 3 goldfish of each risk-taking category, the risk-avoiding fish showed relatively little aggression. Overall, fish that showed any aggression within social groups gained preferential access to a restricted food supply (Chapter 6). There were no differences in weight, length or condition between risk-taking and risk-avoiding goldfish at the point of initial screening, but by the end of the experiment the risk-avoiding fish held in groups with other risk-avoiders had gained less weight and had strikingly lower condition factors compared to the other categories of fish (i.e. all risk-avoiders and risk-takers held in mixed groups). It is suggested that some sort of social facilitation of fear keeps levels of stress high in groups composed entirely of risk-avoiding fish (Chapter 6). The implications of all these results are considered in a final general discussion (Chapter 7).
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