Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
A decade in the doldrums: depressed size-structure in the Celtic Sea fish community IRL UK UK FR Effects of fishing on community size-structure • Fishing is selective and directly removes large individuals/species • Removal of large piscivores leads to predation release which indirectly enhances small fish biomass Shift from large to small fish dominated community Percentage Frequency 5 4 1998-2004 1984-1997 3 2 1 0 0 10 20 30 40 50 60 70 80 Length (cm) 90 100 110 120 131 145 Size-based indicators Direct and indirect effects of fishing can be integrated by metrics like the Large Fish Indicator (LFI): Proportion by weight of ‘large’ fish = LFI B Xcm BTotal Where ‘large’ is derived from the data • LFI responds to F (lag). Sustained F in the Celtic Sea until 2002 • Peak LFI in 1990 - low levels throughout the 2000s WCGFS 0.7 IGFS 1.4 0.6 1.2 0.5 1 0.4 0.8 0.3 0.6 0.2 0.4 0.1 0.2 0 1985 1990 1995 2000 Year 2005 0 2010 F LFI F Fishing (+ discarding) of ‘recruits’ prevents recovery (Monkfish, Hake, Cod, Haddock) 43000 R R R M+G 38000 0.35 0.30 33000 R M+G 0.25 23000 0.20 18000 0.15 LFI Biomass 28000 13000 0.10 8000 G+F G+F G+F 0.05 3000 -2000 2004 2005 2006 Small Fish 2007 Large Fish 2008 LFI 2009 0.00 Models suggest a multi-decadal recovery period, asymptote depends on F history • Perturbed system with LFI well below 1990 • No recovery during 2000s due to sustained F • Some good recruitments but low survival • Recovery depends on F history • Decadal process - full recovery not guaranteed