INLAND FISHERIES: PAST, PRESENT AND FUTURE R. Welcomme

Transcription

1 INLAND FISHERIES: PAST, PRESENT AND FUTURE.

2 Catch (tonnes 10 6 ) Inland fish catch by year Based on FAO Statistics Quantity (tonnes) Asia - Inland waters Africa - Inland waters America, South - Inland waters Europe - Inland waters America, North - Inland waters Oceania - Inland waters Former USSR area - Inland waters 0 Year

3 Recreational fisheries Recreational fishermen Match fishermen Specimen fishermen Removal fisheries Catch and return Put and take fisheries Changing patterns away from rural fishing to urban put and take 6 billion UK 25 billion Europe (2004) $ Canada 8.3 billion $ 34 billion USA Concealed subsistence fisheries Growing importance in countries such as Brazil, Argentine, South Africa

4 The Capitoline sturgeon

5 Mills and fisheries listed in the UK Domesday Book 1086 River Thames

6 If you take a stick and stir well The good old River Irwell Sick of this occupation you will very soon become Cos foetid bubbles rise and burst And really this is not the worst For little birds can hop about dry footed on the scum

7 Eutrophication oligotrophic mesotrophic eutrophic hypereutrophic P concentration Increased biomass of phytoplankton Toxic or inedible phytoplankton species Increases in blooms of gelatinous zooplankton Increased biomass of benthic and epiphytic algae Changes in macrophyte Decreases in water transparency (increased turbidity) Colour, smell, and water treatment problems Dissolved oxygen depletion Increased incidences of fish kills Loss of desirable fish species Reductions in harvestable fish and shellfish Decreases in perceived aesthetic value of the water body or river Eutrophication downstream occurs as part of the natural processes in rivers

8 Historical changes to the Rhine

9 Location of international and bilateral inland fisheries projects in Africa Niger Central Delta Senegal R. Gambia R. Niger R. Niger L. Kossou Volta L. Oueme R. L. Kainji L. Chad Chari Logone R. L. Nasser/Nubia L. Victoria Rivers L. Victoria L. Kivu L. Tanganyika L. Mweru/ L. Bangweulu L. Malawi Kafue R. L. Kariba Barotse floodplains

10 Migration patterns of river fish A Longitudinal migration in river channel with downstream drift of fry (whitefish pattern) B Lateral migration of adults and fry to floodplain C Migrations of adult fish into and out of tributaries D Lateral migrations between main river channel and floodplain lakes E Lateral migrations from floodplain lakes onto floodplain (blackfish pattern) F Migrations of adult to spawn at river margin with movements of fry onto floodplain and return movement of young-of-the-year to main channel (grey fish pattern) G Internal movements within lakes H Anadromous/catadromous migrations into system from the sea

11 Catch (t) Indexes of catch Lakes Mei = Conductivity/mean depth Rivers Basin area main channel length Basin area (km2)

12 Relationship between area of floodplain area flooded and catch. Catch of fish in same year or following years depending on size and age of fish caught Area of floodplain flooded

13 River continuum and flood pulse concepts River continuum Serial degradation of organic material entering system upstream by invertebrates as matter moves downstream Coarse organic matter Fine particulate organic matter Very fine particulate organic matter Flood pulse River channel Floodplain Ultrafine particulate organic matter Mobilisation of nutrients during flood events creates rich environment on floodplain

14 Catch The fishing down process Large, long-lived species and individual fish Small, short-lived species and individual fish Effort

15 Number of species Number of species recorded as being caught in FAO statistics Year

16 Yield (kg/ha) Yield from stocked reservoirs of different areas Mexican reservoirs Y = D r 2 = S.E Asia - Thailand and Vietnam y = x R² = Area (ha) Area (Ha) 1800 Chinese reservoirs 1600 Y = D r 2 = Area (ha) Sri Lankan reservoirs Y = 10329D r 2 = Area (ha)

17 Functions for governance at various administrative levels Fishermen groups, landing committees, lake management committees District authorities; lake or river management committees Regulate access, effort, closed seasons, permissible gear. Collect catch data Set local objectives for river or lake. Negotiate environmental conditions Set up local reserves Central Government Devolve authority and supervise day-to-day management Set overall objectives for fisheries Negotiate agreements on water quality and quantity between users Fisheries Research Interpret and report national statistics. Establish and oversee national parks and reserves. International lake or river International conservation agreements basin commissions International conservation International collaboration. organizations International conservation agreements

18 Ln Species richness (No of species) Ln Species richness (No of species) Number of species by river and lake basin area 6 (a) 4 Ln River basin area (Km 2) Ln Lake area (Km 2 )

19 yield (tones x 10 6 ) Inland and brackish water aquaculture production Brackishwater Freshwater TOTAL year

20 Intensity of human inputs Yields from various types of culture and enhancement Raceways Cages Completely fed and aerated ponds Fertilized and fed ponds Fertilized ponds Brush parks and pens Heavily stocked fertilized( /ha) Extensive stocked unfertilized ( /ha) Natural production with stocking (<500/ha) Natural production with removal of predators Tropical natural production Warm temperate natural production Cold temperate natural production Yield kg/ha/y