Sheku Sei

1
Ageing and Growth Estimation of Plaice
(Pleuronectes platessa L.), from the Celtic Sea
and the North Sea Stable ?13C and ?18O Isotopes
in otoliths as Validation Check for classical
methods

Sheku Sei Inter University Programme, M.Sc
Ecological Marine Management Promoter Philippe
Claeys ( VUB) Co-promoter Ir Demare, Sea
Fisheries Deparment( Oostende)
2
Sssss
OUTLINE

• INTRODUCTION
• - Rationale
• - Aim
• - Objectives
• MATERIALS AND METHODS
• RESULTS
• DISCUSSIONS
• CONCLUSIONS
• RECOMMENDATIONS
• REFFRENCES
• ACKNOWLEDGEMENTS

3

Ss ss
INTRODUCTION

• This is an ongoing work It is part of a
  project -Fisheries Management Initiative (FMI),
  Co-peration between Sea Fisheries Department,
  Oostende, and Marine Geology Department-VUB
• Rationale
• Saggital Otoliths Are fish ear bones of
  carbonate crystals growing by precipitation of
  ions on its exposed surfaces - they are the
  CD-ROM of fish, made of opaque and translucent
  bands.
• They provide information on age, growth rate,
  life history and taxonomy.ICES advice for
  management of NEA fish stocks is based on
  ageing disagreement on otolith reading for some
  stocks e.g Hake warrants new methods Otolith
  ?18O and ?13C Represent seasonal temperature
  signal and coincides with visible growth bands.

4

• Aim
• -Estimate age and growth of plaice from
  classical methods (length- at- age analysis), and
  test the use of otolith stable isotopes (?18O
  and ?13C) as a validation check .
• Objectives
• 1.Obtain ALKs and estimate growth rates from
  ages and length composition of plaice stock in
  the Celtic Sea
• 2. Develop methods for stable isotope analysis in
  otoliths
• 3. use the method in (2) to analyze stable ?18O
  and ?13C composition in rhythmic banding
  patterns of otolith structure
• 4. Reconstruct retrospective environmental
  regimes of plaice
• 5. Estimate seasonal isotopic signals in growth
  zones of otoliths and link results to
  environmental regimes

5

MATERIALS AND METHODS

• Sampling Samples of Plaice were collected
  during observer trips
• -on board Belgian Beam Trawlers (discards), and
  surveys.
• - periods are January and February 2004 for
  Winter samples, And
• August for summer samples.
• Fishing done in the ICES Division for plaice
  stock (VIIfg) When
• -the fish were assumed to be on or near
  spawning areas
• -discard samples collected by fisheries
  observers and preserved.

S ssssss
Fig.1. ICES division for plaice(VIIfg)
6
MATERIA AND METHODS 2
Ageing The Classical Method Plaice samples
measured-fork length (FL) to the nearest
cm. Saggital otoliths from each fish was
transverse sectioned via nucleus using Beacon
cutting machine 3700Rpm. Slices purified by
alcohol, embedded in black resin and pasted on
slides. Rings counted using stereoscopic
microscope and a computer software, AxiOVision
3.1 The use of stable isotopes Ion probe based
on mass spectrometry- micromill analysis along
transects from center of otoliths to edges to
collect carbonates. Sample aliquots analyzed for
?18O and ?13C by MAT252/Kiel III.
7
Materials and Methods 3

• Growth Rate
• Classical Method
• Ages determined at lengths, used to fit growth
  curves -Von Bertallanfy Growth Model (VBGF).
  ALKs generated for Celtic Sea plaice based on
  the the age estimates. ELLEFAN embedded in
  FAO-ICLARM Fisheries Stock Assessment tool
  (FISAT2) used to generate curvature parameter K
  (growth rate for plaice).
• Use of Stable Isotopes
• Same method for ageing employed to study growth.
  Stable ?18O and ?13C enrichment for juveniles
  and adults compared to age at length, trophic
  levels, metabolic rates and age specific growth
  rates.

8

Materials and Methods 4

Computer controlled micromilling apparatus with
dental drill- permits stage manipulation and
drilling of otoliths
9

RESULTS

10


Results 2
Growth parameter estimates

• Estimated growth parameters from FISAT
• Asymptotic length (L?) 26.87
• K 0.78
• T0 0

Fig. 3. Growth curve for plaice
11
RESULTS 3
Visible growth bands in otolith sections- 3year
old plaice
12
DISCUSSIONS

• The classical approach has produced results for
  the ageing and growth rate of plaice for
  preliminary samples ready for stable isotope
  analysis.
• At this stage, all that can be said is that the
  objective of ageing and growth rate determination
  from classical methods has been met as a start.
• The second phase of analysis will have to be done
  before making any final conclusions on the growth
  of Celtic sea plaice. Another important aspect
  still to be addressed is the development of age
  ALKs from many more samples. Curvature parameter
  is yet to be determined for all samples
  characterizing the two stocks

13
THANKS FOR YOUR ATTENTION!!
Questions?