Abundance and trophic interactions in North Sea fishes

Transcription

1 Abundance and trophic interactions in North Sea fishes Georgi M. Daskalov and Steven Mackinson CEFAS, Lowestoft Laboratory, Lowestoft, Suffolk, NR33 OHT, UK Tel/fax: +44 () ,

2 Objectives Construct a comprehensive Ecopath model of the North Sea based on the best available information Fit to time-series of biomass and fishing effort Explore ecological indicators Explore scenarios of temporal and spatial simulation Explore environmental change hypotheses Evaluate alternative fisheries management policies Evaluate the effects of Marine Protected Areas Projects: UK DEFRA MO323, EU INCOFISH, EU UNCOVER, EU RECLAIM

3 Data Biomass: Target species: Stock assessments (e.g. MSVPA), Non-target species associated to target species by proportionality (catchability/availability) between biomass from assessments and survey (IBTS) catch (using the approach of Sparholt, 199) Temporal and spatial biomass data for EwE validation Production rate P/B =Z, (MSVPA and literature, FishBase) Consumption rate Q/B consumption rate (MSVPA and literature, FishBase)) Diet composition: 1991 year of stomach data (Hislop et al. 1996, Niels Daan unpublished) and literature Catches (landings and discards) and fleet structure (1991 Scientific Technical Committee for Fisheries data, UK Fishing activity database, Trio Discards database, Mickleburgh 23).

4 68 functional groups 12 fishing fleets North Sea model (1991) CEFAS technical report Fishing (12 fleets) Birds Sharks & Rays (8) Marine Mammals (3) Fish (36) Zooplankton (3) Meiofauna Fisheries Discards Squids & Cuttlefish Benthos (8) Microflora & Bacteria (2) Primary producers Detritus (2)

5 -1-2 Seals Cetaceans Halibut/turbot /brill Other predatory Other prey fish Mean All Sole Plaice Sandeel Sprat Herring Horse mackerel Mackerel Norway pout Saithe Halibut, turbot, Other predatory Other prey fish Sole Plaice Sandeel Sprat Herring Horse mackerel Mackerel Norway pout Haddock Whiting Cod 188 Saithe Haddock Whiting Rays and Skates 5 Cod Sharks Rays and Skates 1 Seabirds % Change Sharks Seabirds Seals 2 Cetaceans Biomass (' tons) Results: Biomass comparisons with Mackinson S 22. Fisheries Centre Research Reports 9(4):

6 Structure of Biomass Biomass 1% Other prey fish Other predatory fish 8% Target flatfish Sandeels 6% Clupeids Mackerel and horse mackerel 4% Norway pout 2% % Target gadoids Elasmobranchs s 1991

7 Large flatfish Small gadoids 1 Small demersal fish Squid & cuttlefish Long-rough dab Plaice Horse mackerel Mackerel Saithe (adult) Juvenile saithe Haddock (adult) Juvenile haddock Whiting (adult) Juvenile whiting 2 Small flatfish Mackerel/horse mackerel MSVPA gadoid predators Norway pout Clupeids Sandeels ' t m Quantity of fish consumed by predators and fished -2 Cod (adult) Juvenile cod Elasmobranchs Seabirds Seals Toothed whales Baleen whales ' t m-2 3 Invertebrates Fish Consumption fish and invertebrates by the main predators Fished Consumed

8 Small demersal fish Miscellaneous filterfeeding pelagic fish % Small demersal fish Miscellaneous filterfeeding pelagic fish 2% Large demersal fish 4% Large demersal fish 6% Small flatfish 8% Small flatfish 1% Large flatfish Fishery (F) Large flatfish Sandeels Mackerel & Horse mackerel Clupeids Predation (M2) Sandeels Predation (M2) Mackerel & Horse mackerel Clupeids Natural (M) Small gadoids Large gadoids Norway pout Adult MSVPA gadoids Juvenile MSVPA gadoids Elasmobranchs Juvenile Elasmobranchs Natural (M) Small gadoids Large gadoids Norway pout Adult MSVPA gadoids Juvenile MSVPA gadoids Elasmobranchs Juvenile Elasmobranchs Mortality year -1 4 Structure of mortality Fishery (F) 3 2 1

9 Partial mortality of some prey groups: How prey is affected by different predators or by fishing.4 Norway pout.3 Sprat & Juvenile Herring Sandeels.2.1 Fishery Cephalopods Other demersal fish Flatfish Mackerel & Horse mackerel MSVPA gadoid predators Elasmobranchs Seabirds Marine mammals Relative Mortality MSVPA Juvenile Gadoids

10 .8.6 All Mackerel & Horse mackerel Dab Plaice & Sole All Sandeel.2 Sandeel.4 Clupeids Predation 1974 Predation 1991 Fishery 1974 Fishery 1991 Clupeids Mackerel & Horse mackerel 1 Dab Plaice & Sole Norway pout 15 Norway pout 2 Adult MSVPA gadoids Juvenile MSVPA gadoids ' t m-2 25 Adult MSVPA gadoids Juvenile MSVPA gadoids Relative Mortality Consumption & Mortality comparison with V. Christensen 1974 model: Predation mortality decreased, F increased 3 Consumed 1974 Consumed 1991 Catch 1974 Catch

11 Comparing UK marine food webs PPR to support Catch Finn's cycling index Omnivory Index Western Channel Connectance Index Average organism size (B/P) English Channel Thermodynamic order (R/B) Ecotrophic efficiency Irish Sea Utilisation of detritus Utilisation of primary production Mean trophic level Fishery gross efficiency Total biomass Flow to detritus Ascendency System throughput Primary production % Difference from the North Sea 35 4

12 Fitting Biomass dynamics to survey data with Ecosim

13 Sandeel (adult) 2.5 Sandeel biomass Sandeel MPA Season close Biomass (t/km2 ) Biomass (t/km2 ) 2 Multispecies effects of sandeel fisheries: application to the EAF mill TAC 1.5 Status quo TAC 1 mill t TAC.5 mill t Close N.Sea Season close MPA Months Competitor biomass Sandeel MPA 1 mill TAC 2 Landings (t/km ) mill TAC Status quo TAC.5 mill t Season close Months 8 TAC 1 mill t Close N.Sea MPA Fish(3a) Predator Landings Fish Predators Landings

14 Spatial dynamics with Ecospace Observed distribution, based on ICES bottom trawl survey catches Haddock (all) E6 E8 F F2 F4 F6 F8 G G2 G Predicted distribution maps for 72 ecosystem components E4 6 E G

15 Effect of fisheries closure in the North Sea: difference in biomass compared to no closure Sandeel box Plaice box

16 Summary The model integrates the best available information (subject to upgrade!) on the North Sea food web and allows various ecological analyses It allows to consider many factors, some of which beyond control by management, but rather important for the state and dynamics of the ecosystem and its resources It reveals significant changes in fish community in recent years comparing to historical data: decrease in predators and increase in prey fish Thanks to Brian Rackham, Nils Daan, John Pinnegar, Jim Ellis, Paul Eastwood, Paul Mickleburgh. Funding by UK DEFRA and EU INCOFISH