Climate and current anthropogenic impacts on marine fisheries

Transcription

1 Art: Glynn Gorick Climate and current anthropogenic impacts on marine fisheries Keith Brander - DTU Aqua

2 Structure of the talk History of human impacts on marine fisheries Signs of improvement Ecosystem approaches and balance of objectives Climate impacts on marine productivity (+ distribution) Managing under uncertainty

3 Climate is one of many pressures

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5 World marine capture fisheries are declining

6 Biomass relative to Bmsy (Hutchings et al 2010 CJFAS 67) All 159 fish stocks All 159 fish stocks Demersal green, pelagic red Australia and New Zealand High Seas

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8 Average fishing mortality on ~50 stocks in the NE Atlantic is going down Mean F Std F Year

9 K Brander

10 K Brander Resolving objectives that pull in different directions

11 Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora

12 MSFD contains 11 qualitative descriptors for determining good environmental status 8 descriptors relate to specific pressures (fishing, pollution, habitat disturbance, introduced species, eutrophication, litter, noise) 1 deals with biodiversity 1 deals with ecosystem functioning 1 deals with alteration of hydrographical conditions

13 Climate change is shifting the goalposts Altered biomass and F reference levels for fisheries There is no fixed healthy ecosystem state Is more biodiversity always a good thing? How far will acidification and hypoxia alter marine ecosystem states and productivity? What about the role of marine ecosystems in carbon sequestration?

14 Ocean climate (not just temperature) Wind Cloud cover Waves Sea level Temperature Salinity ph Oxygen Currents Stratification Turbulence Upwelling Frontal processes Monsoon seasonality ENSO, NAO, PDO

15 Trends in Atmospheric CO 2 and Ocean ph 1000 Lowest ph over past 600, years pco ph Year Observed and projected under a business as usual scenario. (source Fernand and Brewer, 2008) Highest CO 2 over past 600,000 years

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17 What about fisheries predictions?

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19 Regional fisheries productivity t*km^2/year

20 Fisheries productivity depends on primary productivity Relationship between annual average phytoplankton production (gc*m 2 y 1 ) in the numbered FAO fishing areas and average fish catch per unit area. The line shown here is forced through the origin; the correlation coefficient is 0.57 with 13 df. Phytoplankton production was estimated from SeaWiFS chlorophyll data (

21 Why is it difficult to make credible predictions of fisheries productivity? Ocean climate forecasts are inadequate We don t live in the sea We don t control the production systems We harvest many species, not just a few plants We have virtually no experimental basis Even if we could predict primary production, the transfer to harvested species is long and uncertain

22 More difficulties in making credible predictions... Climate is only one of many human impacts There is a lot of natural climate variability Food chains may be altered There are wildcards such as falling ph and O 2 There are non-linear effects such as regime shifts

23 the pressures often interact Risk that cod will disappear from the Baltic

24 NCEAS group has constructed a global database using 269 marine studies, containing 2153 data series, published from 1991 to the end of June Data series spanned up to 430 years, with a median length of 37 years. The recent accumulation of climate change knowledge for marine ecosystems is apparent with 57% of the studies published after 2006.

25 Velocity of Climate Change (from surface temp )

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28 What consequences can we expect from warming climate? Changes in distribution of plankton and fish are already occurring Changes in biodiversity (is this good or bad?) Problems for fish farms (which may have to switch to warm adapted species) Possible changes in plankton production (due reduced vertical mixing) Invasive species e.g. through the opening Arctic

29 How urgent is it to tackle climate impacts on fisheries? Depends on how quickly climate changes over next 20 to 50 years (and on sensitivity of biota to change) Tackling excess fishing is much more urgent pressures of fishing and climate interact so the issues are interrelated [Mitigation actions are very urgent]

30 Reduce fishing pressure A triple-win, no regret strategy More resilient populations and ecosystems (enhances adaptation) Lower use of fuel (mitigation of GHG emission) Higher yields (most stocks overfished)