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Do eggs collected in surveys

accurately reflect adult fecundities?

Hannes Höffle 1 , Frode B. Vikebø 1 , Olav S. Kjesbu 1

Johan Hjort Symposium, Bergen; NO 07 October 2014

1

Institute of Marine Research and Hjort Centre for Marine Ecosystem Dynamics, Bergen, NO

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• Spawning stock biomass (SSB)

• Population fecundity

• Stock reproductive potential (SRP)

Measurments of fecundity

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• Potential: Number of maturing oocytes

• Realized: Number of eggs in the Sea

How well do they match?

Population fecundity

(4)

• Sampling error

• Size and age structure

• Atresia

• Egg mortality

• Movement between different batches

Sources of Error

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North East Arctic cod

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Spawning migration survey

Mar. – Apr., since 1985 Acoustics

CTD

Bottom Trawls (N=902)

Ichthyoplankton (N=2114)

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Temperature at 30 m

•Offshore: Warm Atlantic water

•Inshore: Cool runoff influenced water

•Cooling in Vestfjorden

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Models of Stage I egg distribution

Generalized additive mixed models (GAMMs)

Separate for areas 00 (Vestfjorden) and 05 (Yttersida) Models for presence/absence and non-zero abundance Fixed Factors

•Local temperature at 30 m

•Bottom Depth

•Proportion of old fish (age-9+)

•Regional temperature index (Kola transect)

Random Factors

•Autocovariate

•Median Year Day

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Models of Stage I egg distribution – 00 Vestfjorden

Höffle et al. 2014

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Models of Stage I egg distribution – 05 Yttersida

Höffle et al. 2014

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Real and modeled egg distribution

Höffle et al. 2014

Survey Data Model

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Scaling to annual egg production

σ .... Standard Deviation t .... Day of the Year

N (t) .... No. eggs at day t

Peak spawning: Days 93 and 98 (>69°N)

Standard Deviation: 15

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Potential fecundity – NEA cod

•Gonad samples

•Winter and Lofoten cruise

•191 fish

•Number and size of oocytes

•Image analysis (auto-diametric)

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Potential fecundity vs. length

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Potential fecundity vs. weight

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Scaling to population fecundity

• Length and Weight based formulae

Data from Stock assessment and survey

• Length, weight, maturity and numbers at age

• Sex ratio

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Potential and realized fecundity

-38 % vs. Length

-52 % vs. Weight

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Conclusion and outlook

• Highly variable relationship of realized and potential fecundity

What next?

• Include atresia, mortality and drift

• Resolve spatial distribution of fecundities

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Acknowledgements

Captains and crews of the ships involved.

ICES for additional CTD data.

AFWG for stock data.

Dr. Svein Sundby Dr. Per Solemdal Dr. Arved Staby

Thank you!

hannes.hoeffle@imr.no

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