in the offshore pelagic community Maxium length (ML) of fish in the - - PowerPoint PPT Presentation

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in the offshore pelagic community Maxium length (ML) of fish in the - - PowerPoint PPT Presentation

Aug 06, 2023 26 likes •211 views

HELCOM Workshop on Fish Indicators HaV, Gteborg, 10 May 2016 Proportion of large fish (LFI) in the offshore pelagic community Maxium length (ML) of fish in the offshore pelagic community Michele Casini Swedish University of Agricultural

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Swedish University of Agricultural Sciences www.slu.se

Michele Casini

HELCOM Workshop on Fish Indicators HaV, Göteborg, 10 May 2016

Proportion of large fish (LFI) in the offshore pelagic community Maxium length (ML) of fish in the offshore pelagic community

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Swedish University of Agricultural Sciences www.slu.se

  • LFI: proportion in weight of fish above a certain size (W>size/Wtotal)
  • LFI tracks the size composition in the fish community
  • Estimated in biomass (weight), to reduce the effect of recruitment

fluctuations

  • Community with relatively high biomass of large fish: higher functional

diversity than community dominated by small fish

  • Fishing has a direct effect on the structure of fish communities:

decrease of relative abundance of large fish, decrease of mean body size in population LFI maps the fishing pressure

  • In the Baltic Sea, the main predatory fish (cod) is affected also by low
  • xygen levels at the bottom  LFI can also map eutrophication

LFI in the offshore pelagic community

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Swedish University of Agricultural Sciences www.slu.se

Primary importance Secondary importance BSAP Segment and Objective Viable populations of species none stated MSFD Descriptors and Criteria 4.2. Proportion of selected species at the top of food- webs. none stated

Legislative linkage:

Stage of development Indicator type Core State

Used in OSPAR

M Casini, N Larson, F Käll, J Olsson, H Wennhage (SWE) O Thurid, C Pusch, R Froese (GER) A Lappalainen, J Raitaniemi (FIN)

LFI in the offshore pelagic community

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Swedish University of Agricultural Sciences www.slu.se

  • LFI is a food-web indicator (at least in the MSFD)
  • Strongest links in the Baltic Sea: cod, sprat and herring
  • The fishery exploiting large species is mainly targetting cod

Important points considering the offshore LFI

Cod Sprat Herring Flounder Benthos

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Swedish University of Agricultural Sciences www.slu.se

  • The offshore communities are

constituted by very motile species

  • The indicator should not be

estimated in too small areas (or within national boundaries)

  • Particularly true for the pelagic LFI

Important points considering the offshore LFI

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Swedish University of Agricultural Sciences www.slu.se

  • Based on pelagic control hauls in

acoustic surveys (BIAS)

  • 4 species included: sprat, herring,

sticklebacks and cod (> 99% of the biomass)

  • CPUEs modelled by GAMs
  • Length threshold = 38 cm
  • Currently limited to Swedish/German

data (no international catch database available)

LFI in the offshore pelagic community: estimation

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Swedish University of Agricultural Sciences www.slu.se

  • 2
  • 1

1 2 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 LFI Year

Assessment area 31

  • 3
  • 2
  • 1

1 2 3 4 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 LFI Year

Assessment area 33

  • 8
  • 6
  • 4
  • 2

2 4 6 8 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 LFI Year

Assessment area 34

LFI in the offshore pelagic community: results

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Swedish University of Agricultural Sciences www.slu.se

  • 3
  • 2
  • 1

1 2 3 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 LFI Year

Whole Baltic Proper

  • Decrease in large species
  • Decrease in the mean size of each species
  • Increase in small species

LFI in the offshore pelagic community: results

Assessment areas 31,33,34

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Swedish University of Agricultural Sciences www.slu.se

  • Baseline approach
  • Prerequisites of the baseline:
  • stable
  • long enough to be at least 2 times the generation time of the

most representative species (in our case, the cod)

  • decide if the baseline represent GES or sub-GES
  • 3
  • 2
  • 1

1 2 3 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 LFI Year

Whole Baltic Proper

LFI in the offshore pelagic community: GES

Eero et al. 2008

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Swedish University of Agricultural Sciences www.slu.se

LFI in the offshore pelagic community: GES

Subjective choice and biased by the lack of data from before the initiation of extensive fishing

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Swedish University of Agricultural Sciences www.slu.se

Maximum length of fish in the pelagic community (ML)

  • ML: largest fish in the community
  • ML tracks the size-structure in the fish community
  • Fish community with larger fish: higher functional diversity than fish

community dominated by small fish

  • Fishing has a direct effect on the structure of fish communities:

decrease of relative abundance of large species  ML maps the fishing pressure

  • Good complement of LFI
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Swedish University of Agricultural Sciences www.slu.se

Primary importance Secondary importance BSAP Segment and Objective MSFD Descriptors and Criteria 3.3. Proportion age and size distribution 3.3.2 Mean maximum length across all species found in research vessel surveys (wrongly placed?) none stated

Legislative linkage:

Stage of development Indicator type Candidate State

Used in OSPAR

ML in the offshore pelagic community

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Swedish University of Agricultural Sciences www.slu.se

ML in the offshore pelagic community: estimation

  • Based on pelagic control hauls in

acoustic surveys (BIAS)

  • CPUE modelled by GAMs
  • 4 species included: sprat, herring,

sticklebacks and cod (> 99% of the biomass)

  • Currently limited to Swedish/German

data (no international catch database available)

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Swedish University of Agricultural Sciences www.slu.se

  • No GES proposed so far

ML in the offshore pelagic community: results

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Swedish University of Agricultural Sciences www.slu.se

How to move on

Short-term goals (meet HOLAS_II)

  • Continue the development of the pelagic LFI
  • Agree on the GES boundaries (or other methods of assessment)
  • Include data from other countries performing the BIAS survey, if possible:

Estonia, Finland, Latvia, Lithuania, Poland, Russia (process started)

  • Hinder: lack of an international database

Long-term goals

  • Include data from all the other countries performing the BIAS survey
  • Integrate the demersal habitat in the indicator (if considered necessary),

using ICES DATRAS database

  • Ensure data-flow from international databases to indicator processing, for

both pelagic and demersal habitat (transparency and automatization)

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Swedish University of Agricultural Sciences www.slu.se

Discussion points

Short-term goals

  • Decide on GES
  • Set of GES is problematic. Is the use of LFI as sourveillance indicator

an option (ex. for HOLAS_II)? Long-term goals

  • Do we need to integrate the demersal habitat?
  • In this case, how?
  • How to assure an efficient data-flow?
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Swedish University of Agricultural Sciences www.slu.se

THANK YOU!

Contact: michele.casini@slu.se

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Swedish University of Agricultural Sciences www.slu.se

5 10 15 20 25 30 35 500 1000 1500 2000 2500 3000 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013

Pelagic (CPUE) Demersal (CPUE) Year Demersal Pelagic

Cod from pelagic and demersal surveys