1. Recruitment variation in Icelandic summer spawning herring: Is it best explained by ocean environment or by the spawning stock? Guðmundur J. Óskarsson and Christopher T. Taggart Marine Research Institute Reykjavik, Iceland Bergen, May 14, 2004 Oceanography Department Dalhousie University, Canada

2. Environmental factors might influence recruitment in a fish stock through: 1. Female body condition  egg quantity (fecundity)  egg quality (egg size) 2. Spawning time  when offspring are exposed to environment 3. Spawning site  where offspring are exposed to environment 4. Effects on egg, larval and pre-recruit survival.

3. Schematic: environment  recruitment variation: Egg production (number and size) Recruitment Body condition Environment (temperature, mixing, advection etc.) Survival Spawning When Where

4. Objectives: Determine how much of the recruitment variation in Icelandic summer spawning herring can be explained by environmental factors and how much by stock-related factors by considering:  Variation in spawning time  Egg or larval (pre-recruit) survival

5. Life history of Icelandic summer spawning herring Over-wintering Nurserygrounds Spawninggrounds Feedinggrounds Hydrographic stations

6. Spawning Time Analyses: Logistic regression Dependent variable 0 (unspawned) 1 (spawning or recently spawned) Independent variables day of the year, 1-365 (the basic model)day of the year, 1-365 (the basic model) Fish size, age, K, spawning experience and locationFish size, age, K, spawning experience and location SSB, mean annual K of pre-spawning femalesSSB, mean annual K of pre-spawning females Sea temperature (S-Iceland), NAO (Hurrell 1995)Sea temperature (S-Iceland), NAO (Hurrell 1995) deviance Χ 2 test (Ramsey and Schafer 1997).

7. Where: F P potential fecundity where F P ~ L + K N A,Y annual ( Y ) number ( N ) at age ( A ) Mat A,Y proportion of females mature at age Fem A proportion of females at age Total egg production estimates:

8. Repeat spawner total egg production estimates:

9. Recruitment variation (number-at-age-3; VPA- based) during 1963-1999 analysed using GAM and GLM with various: stock (E rep. sp.,E rec.sp., K of pre-spawning females) ecological (Zooplankton of N-Icel.; Anon.2003) environmental (NAO, T S-Icel., T N-Icel. ; Anon.2003) covariates

10. Spawning time simple environmental measures have no influence on spawning time n = 11,370

11. GLM total egg production of repeat spawners & influence on age-3 recruitment ( R ): r 2 =0.538 p<0.001

12. GLM effects of NAO on recruitment r 2 =0.036 p<0.05

13. r 2 =0.575 n=37 p<0.0001 Observed R vs Fitted R using GLM

14.  Spawning in Icelandic summer spawning herring is primarily a function of stock structure and not a function of the local environment  (also consistent with a time series analyses of ovary weight development (In: "Spawning time variation in Icelandic and Scotia-Fundy herring (Clupea harengus)", Oskarsson et al., in preparation).  Together, total egg production of repeat spawners (54%) and NAO (4%) explain 58% of the recruitment variation in the stock SUMMARY

15. Positive impacts of sea temperature (off the north coast of Iceland) on R (Jakobsson et al. 1993) should not be quickly dismissed when 42% of the variation in R remains unexplained. Final remark:

16. Answer to the original question: Recruitment variation in Icelandic summer spawning herring: is best explained by the spawning stock!

17. Thank you to All! Acknowledgements: Marine Research Institute, IcelandMarine Research Institute, Iceland Canada Department of Fisheries and Oceans, St. Andrews Biological StationCanada Department of Fisheries and Oceans, St. Andrews Biological Station Dalhousie University, Faculty of Graduate StudiesDalhousie University, Faculty of Graduate Studies Icelandic Research Fund for Graduate StudentsIcelandic Research Fund for Graduate Students The Fishery Ministry, IcelandThe Fishery Ministry, Iceland NATO Science FellowshipsNATO Science Fellowships NSERC “Discovery Grant” to CTTNSERC “Discovery Grant” to CTT