The importance of habitat for differences in condition
The importance of habitat for differences in condition of Atlantic cod (Gadus morhua) in Greenland waters Karl-Michael Werner, Marc H. Taylor, Heino O. Fock Thünen Institute for Sea Fisheries, Bremerhaven, Germany Slide 1/7 Karl-Michael Werner ICES ASC Hamburg 2018
Why is fish condition important? 1. Impact on reproductive output 2. Low condition linked to increased mortality 3. Reflection of habitat suitability (? ? ? ) ? ? ? Objective: Relate variation of diet to fish condition Slide 2/7 Karl-Michael Werner ICES ASC Hamburg 2018
Methodology Data collection: - Stomachs and condition data from 2006 -2011 & 2015 -2016 - Dissection in the lab 7 2 6 3 Analysis: - 3380 individuals - Hepatosomatic index (HSI): Liver weight/Body weight - Multivariate approach: Hierarchical Clustering, Redundancy Analysis - Use of length-corrected HSI residuals (GAM, r²=0. 22, p<0. 001) Slide 3/7 1 Karl-Michael Werner ICES ASC Hamburg 2018 4 positive 5 Residuals negative
Results Diet clusters & condition All habitats Length classes: 20 -40 cm 40 -60 cm 60 -80 cm 80 -100 cm - Inf Slide 4/7 Karl-Michael Werner ICES ASC Hamburg 2018
Results Diet clusters & condition All habitats Length classes: 20 -40 cm 40 -60 cm 60 -80 cm 80 -100 cm - Inf Slide 4/7 Karl-Michael Werner ICES ASC Hamburg 2018
Results Diet clusters & condition All habitats Length classes: 20 -40 cm 40 -60 cm 60 -80 cm 80 -100 cm - Inf Slide 4/7 Karl-Michael Werner ICES ASC Hamburg 2018
Results Diet clusters & condition All habitats Length classes: 20 -40 cm 40 -60 cm 60 -80 cm 80 -100 cm - Inf Slide 4/7 Karl-Michael Werner ICES ASC Hamburg 2018
Results Diet clusters & condition All habitats Length classes: 20 -40 cm 40 -60 cm 60 -80 cm 80 -100 cm - Inf Slide 4/7 Karl-Michael Werner ICES ASC Hamburg 2018
Results RDA modeling (All habitats) Redundancy analysis Formula: Diet composition ~ length*HSI Adjusted r²: 0. 03 Significance of terms (Pseudo-F (p-value)): length = 64. 4 (0. 001***) HSI = 23. 0 (0. 001***) length: HSI = 16. 9 (0. 001***) Poor condition is linked to… - Gadoids (Cannibals) - Redfish - Benthic organisms (Crabs, Briddle stars…) - Euphausiids Healthy condition is linked to… - Mesopelagic fish - Hyperiids ~ „Oceanic deep scattering mixture“ Slide 5/7 Karl-Michael Werner ICES ASC Hamburg 2018
Conclusions & Outlook -> Diet has strong influence on fish condition -> Observation of interannually stable diet – condition patterns -> Trophohabitat „Particular area in which the feeding regime causes interannually stable levels of fish condition “ Slide 6/7 Karl-Michael Werner ICES ASC Hamburg 2018
The importance of habitat for differences in condition of Atlantic cod (Gadus morhua) in Greenlandic waters There are only cannibals on a sinking ship Karl-Michael Werner, Heino O. Fock, Marc H. Taylor Thünen Institute for Sea Fisheries, Hamburg, Germany Bonus Karl-Michael Werner ICES ASC Hamburg 2018
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