Impacts of climate change on marine fisheries

Transcription

1 Impacts of climate change on marine fisheries Dr Jim Salinger Principal Scientist, NIWA, Auckland

2 Outline Observed changes in ocean climate Observed changes in fisheries Future ocean climate Impacts on fisheries

3 Fisheries production Global fisheries production, excluding China, from capture fisheries (open squares) and aquaculture (crosses). Marine and inland production in black and red respectively Brander, 2007

4 Observed changes in climate IPCC 2007

5 Observed changes in climate Linear trends ( ) of ocean heat content (Wm -2 ) for the 0 to 700 metre layer. Contour interval 0.25 Wm -2 IPCC 2007

6 Observed changes in climate Blue = cool (>= -1 C) Red = warm(>= +1 C) Oceans are warming in 0 700m layer

7 Observed changes in climate ATLANTIC Surface seawater ph has decreased by 0.1 units in the last 200 years (Orr et al. 2005) PACIFIC

8 Observed changes in climate IPCC 2007

9 Observed changes in fisheries El Niño Ocean Warming Events Catches increase for warm water species normally caught in the warm season in southern California including dolphin fish, yellowtail and California barracuda. California sheephead, bonito, and swordfish, typically found in Southern California, are caught in northern California during warm events and Pacific mackerel, skipjack tuna, Pacific bonito, bluefin tuna, and white seabass are caught off Oregon and Washington. R. Lea

10 Observed changes in fisheries Decadal variability Salmon stocks from Alaska have been highly productive since the 1976 regime change in the North Pacific, 3 times more productive than in the period. These periods correspond to an eastward shift of the Aleutian Low pressure system with more frequent and severe winter storms, and a warming of the surface waters in the Gulf of Alaska. This shift between warm and cold periods is called the Pacific Decadal Oscillation or PDO. The warmer conditions and increased nutrient levels from upwelling in the central Alaska gyre carried northward toward the coast contributed to an increase in plankton, a source of food for young salmon in the ocean. Hare, S.R., Mantua, N.J., and Francis, R.C

11 Observed changes in fisheries Reduced Abundance of Zooplankton and Temperate Fish Off Southern California During Two Decades of Warming. Roemmich, D. and J. McGowan Ocean productivity off southern California has declined during the last 25 years. Zooplankton levels have dropped by 80% from the level to the early 1990s, sea surface temperature increased by 1.4 C. Researchers believe this was because of increased warming of the surface layer reducing the nutrient enrichment of this layer by reducing upwelling of nutrients from below the thermocline

12 Observed changes in fisheries Historical variability of Fish Populations from Sediment Records Sardine and anchovy populations over seventeen hundred years from sediments off Santa Barbara, California. Baumgartner, T. A. Soutar and V. Ferreira-Bartrina. 1992

13 Type of changes Climatic variable Impacts Potential outcomes for fisheries Changes in ph Effects on animals Potential declines in production for through increased CO2 e.g. molluscs, crustaceans calciferous marine resources and acidification corals, Warming upper layers Warm water species Shifts in distribution of plankton, of the ocean replacing cold water invertebrates, fishes birds, towards species the north or south poles, reduced Physical Plankton species moving species diversity in tropical waters Environment to higher latitudes (Indirect Timing of phytoplankton Potential mismatch between prey ecological) blooms changing (plankton) and predator (fish) Changing zooplankton populations and declines in Fish stocks (Indirect Ecological) changes production and diversity Sea level rise Loss of coastal fish Reduced production of coastal and related breeding and nursery fisheries habitats e.g.mangroves, coral reefs Higher water Changes in sex ratios Possible impacts on timing and levels of temperatures Altered time of spawning productivity across marine and fresh Altered time of peak water systems abundance Increased invasive species, Reduced production of target species diseases and algal blooms in marine and fresh water systems Changes in Changes in fish Abundance of juvenile fish affected ocean currents recruitment success and therefore production in marine and freshwater Ecosystems Increased frequency Changes in timing Changes in pelagic fish distribution (Indirect of ENSO events and latitude of upwelling ecological) Coral bleaching and Reduced coral-reef fisheries productivity die-off

14 Observed changes in fisheries

15 Observed changes in fisheries Brander, 2007

16 Observed changes in fisheries Climate change is expected to drive most terrestrial and marine species ranges toward the poles, expanding the range of warmer water species and contracting that of colder-water species, and deepening of assemblages Examples of North Sea fish distributions that have shifted north with climatic warming. Relationships between mean latitude and 5-year running mean winter bottom temperature for (A) cod, (B) anglerfish, and (C) snake blenny are shown (from Perry et al. 2005).

17 Observed changes in fisheries Deepening of North Sea bottom dwelling (dermersal) fish assemblages over 25 years by ~ 3.6 m per decade Brander, 2005

18 Observed changes in fisheries Snapper recruitment year class strength and sea surface temperature ( C), Hauraki Gulf, Auckland, New Zealand Francis, Langley & Gilbert, 1997

19 IPCC 2007 Future ocean climate

20 Future ocean climate Precipitation increases in the equatorial and high latitude oceans water fresher Precipitation decreases across the subtropical oceans increase in salinity

21 Future ocean climate IPCC 2007 Sea Ice Concentration (%)

22 Impacts on fisheries Local extinctions of fish species on edges of ranges Slowing of meridional overturning reduces nutrient upwelling

23 Impacts on fisheries

24 Impacts on fisheries Local extinctions are expected at the edges of ranges In some cases productivity will increase Emerging evidence suggests that meridional overturning circulation is slowing, with serious potential consequences for fisheries; IPCC 2007

25 Impacts on fisheries Annual to Decadal Times Scales Temperature mediated physiological stresses and phenology changes will impact the recruitment success and abundances of many marine populations (high confidence) Impacts most likely to be acute at the extremes of species ranges, and for shorter-lived species. Changes in abundance will alter the composition of marine communities, with possible consequences to the structure & productivity of marine ecosystems Increasing vertical stratification is likely for many areas, and is expected to reduce vertical mixing and decrease productivity (intermediate confidence) These will drive changes in species composition

26 Impacts on fisheries Multidecadal Time Scales Impacts depend upon changes in net primary production in the oceans and its transfer to higher trophic levels Models show high variability in their outcomes so any predictions have low confidence Regional predictions have improved confidence because of better knowledge of the specific processes involved Most models do show decreasing primary production with changes of phytoplankton composition to smaller forms, although with high regional variability

27 Primary production increases 2-5 times Expanded ranges of Atlantic/Pacific species north Reduced ranges of Arctic species & extinctions Arctic Climate Impacts Assessment, 2004 Impacts on fisheries Arctic

28 Impacts on fisheries North Atlantic Northward shifts of all species Expanded ranges of Atlantic species north Reduced ranges of Arctic species & extinctions Southern invaders move into North Sea Species adapted to cool and narrow temperature conditions (Atlantic salmon) may be extirpated from present habitats

29 Impacts on fisheries North Pacific PDO expected to continue on top of upward trend in sea temperatures Pacific Salmon may be restricted to Bering Sea Bering Sea extensive retreat of sea ice, loss of cold water species & increasing abundance of North Pacific species North Pacific becomes more acidic; various species negatively impacted

30 Impacts on fisheries Tropical/subtropical Pacific Likely decline in primary production because of increased stratification and less nutrient supply Tuna habitat conditions east of Date Line could improve with a more El Niño-like climate Benthic and demersal fisheries likely to shift their distributions southward Pelagic species also likely to shift southwards, and may benefit from increased local upwelling

31 Impacts on fisheries South Pacific/Southern Oceans Australian models predict ocean warming, increased stratification, strengthening of poleward coastal currents, increasing acidification Greatest impacts likely on coastal species, temperate species and coastal and demersal species rather than pelagic and deep-sea species Tropical wild fisheries will move southwards Southern fisheries will require reconciliation between non-climatic threats with increasing temperatures and pro-active management

32 Climate and marine fisheries Tropical & subtropical oceans have become warmer & more acidic El Niño drives causes seasonal to annual variability of Pacific fisheries Pacific decadal oscillation causes decadal variability of Pacific fisheries Warming has caused poleward migration of fisheries Ocean climate will warm most at high northern latitudes & least in the southern oceans Tropical & subtropical oceans will become more acidic, polar oceans near ice sheets will become fresher

33 Climate and marine fisheries In Arctic southern species move north, extinctions of Arctic species, dermersal species move deeper Expanded ranges of Atlantic/Pacific species north, reduction in Arctic species In tropical Pacific all species shift south, with primary productivity decreasing with increased stratification Southern oceans, temperature fisheries move south These will require resolving between non-climatic threats with increasing temperatures & pro-active management Reducing mortality in fisheries which are fully or overexploited reduces impacts of climatic change