Module 4. Egg production in marine fish

Participants:
Olav Kjesbu (IMR)(Module leader), Ørjan Karlsen (IMR-Austevoll Aquaculture Station), Knut Korsbrekke (IMR), Tara Marshall (IMR), Per Solemdal (IMR), Anders Thorsen (IMR).

Objective:
Develop egg production models for the key fish species, with special focus on Arcto-Norwegian cod, Arcto-Norwegian haddock and Norwegian spring-spawning herring, based on the combined effects of food abundance and temperature on gonad production and maturation.

Based on general principles in biology, increasing temperatures at no food shortage will increase somatic growth up to optimal physiological temperature (which is often quite high), but thereafter act negatively. Surprisingly such growth responses under controlled situations have yet not been established for sexually mature Atlantic cod.

Based on the above shortcoming in the present knowledge this module will:

• Study time series of total egg production of Arcto-Norwegian cod from 1946 to today based on existing ICES and IMR data bases to clarify to which extent environmental temperature influences absolute and relative changes in egg production and acts together with other cofactors (food abundance, age structure, growth etc.). Similar studies will be undertaken on haddock (1950-) and herring (1938-). Comparative analysis between the three stocks will be performed.
  
• Undertake 2 yr laboratory studies at the Institute of Marine Research keeping adult cod of normal condition at various experimental temperatures ranging from 2 up to 8 °C (which is within the range of. ambient temperature for cod in the Barents Sea) (n = 300) to measure effects on specific growth rate and fecundity. This part will take advantage of the long experience at the Institute in fish husbandry and the excellent experimental facilities. A pilot study on haddock will be included.
  
• Contrast weighted egg size and length of spawning period in cod females of similar size and condition but held at different temperatures during spawning. As the cod is a multiple batch spawner (each female liberating 10-20 egg batches per season) this set-up requires continuous monitoring; limited to 10 naturally spawning females at 2 and 8 °C, respectively, held in separate spawning tanks together with one male.

In addition, historical field data on spawning period and spawning locations will be used as input in the particle tracking/individual-based models in Module 3