Summer growth reduction: Do epibenthic feeding flatfish suffer less - - PowerPoint PPT Presentation

Royal Netherlands Institute for Sea Research

Summer growth reduction:

Do epibenthic feeding flatfish suffer less from summer growth reduction than benthic feeding flatfish?

A case study of 0-group plaice and flounder in the western Wadden Sea Suzanne S.H. Poiesz, Henk W. van der Veer, Joana F.M.F. Cardoso, Johannes IJ. Witte, Vânia Freitas

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0-group plaice and flounder in the Western Wadden Sea

Life cycle flatfishes

0-group juveniles

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• Decline in activity of benthos after summer

+ growth model

Summer growth reduction

History

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Starting point: Freitas et al. 2012 Observed growth vs max. predicted growth

Summer growth reduction

History

Summer growth reduction

• Various flatfish species
• Various locations

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Summer growth reduction in flatfishes

Explanation for plaice:

Possible causes: Stomach content analysis of plaice Less benthic prey in stomach Supported by De Vlas, 1979, food intake Balgzand

Summer growth reduction

Explanation for plaice – less food available

Spring Summer Autumn

Benthic feeder

Production Activity

Hypothesis:

Test: benthic versus epibenthic feeders

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Spring Summer Autumn

• Decline in activity of benthos after summer

Plaice Growth reduction? Flounder Growth reduction?

YES NO

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Freitas et al 2012: Summer growth reduction

• Various locations
• Various flatfish species
• No difference between plaice and flounder

Summer growth reduction

Hasn’t it already been done?

But: Calculation was based on population growth

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Summer growth reduction

Hasn’t it already been done?

Solution?

(Size-selective migration / mortality ? Growth reduction ?

?

Mean length 60 mm Mean length 80 mm

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Benthic plaice Epibenthic flounder

Individual growth predictions based on otoliths microstructure analysis

Solution:

Individual growth

Oto tolith mi microstru ructure analysis

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Number of daily rings (Age) Plaice or flounder Sampling data Length + Age in days = Settlement date Length - age

• bservations
• Freq. for different cohorts

For each cohort

Growth predictions: DEB model

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DEB model:

• One model for all species
• Species specific parameters
• Temperature
• Size

Water temperature

DEB parameters Growth trajectories Maximum growth predictions F M

Summer growth comparsion:

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F M Otolith readings:

• Length – age relationship
• Various cohorts

DEB simulation (growth trajectories):

• Females and Males

Relative growth ratios:

• Observed / (mean F and M)

+ =

Hypothesis

Results

Benthic (plaice) versus epibenthic (flounder) feeder

Realized growth of flounder

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0.00 0.50 1.00 1.50 60 90 120 150 180 210 240 270

1995

0.00 0.50 1.00 1.50 50 100 150 200 250 300

1995

0.5 1 1.5 50 100 150 200 250 300

1996

Realized growth of Plaice

0.00 0.50 1.00 1.50 60 90 120 150 180 210 240 270

1996

Benthic feeding plaice Epibenthic feeding flounder

Confirming hypothesis

Summer growth reduction

Conclusions

• Hypothesis confirmed:
• Benthic feeder (slight) growth reduction

Epibenthic feeder no growth reduction

• Growth predictions based on individual growth: less prominent
• Summer growth reduction based on population growth: biased

(Emigration, Immigration, Size selective predation??)

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Summer growth reduction

Conclusions

• Possible next steps:
• Use a fully benthic species (Sole)

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Thank you for listening.

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