| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 4543226 | Fisheries Research | 2013 | 11 Pages |
The following two hypotheses, using several years of data collected for Barents Sea and Irish Sea cod (Gadus morhua), are scrutinized: (1) potential fecundity closely reflects realised fecundity, and (2) that realised fecundity or associated properties such as spawning duration or egg weight are not dependent on maternal size or condition. Pre-spawning relative fecundity was dependent on stock, fish length and declined by 27 and 30% in Barents Sea and Irish Sea cod, respectively, due to atresia during maturation from 500 to 750 μm mean follicle diameter. A further decline of 4% in the relative fecundity was found in Barents Sea cod when their relative condition was low. No significant change in the standard deviation of follicle diameter during maturation from 500 to 750 μm could be demonstrated, but fish length and condition were positively correlated. We consider that the standard deviation of vitellogenic follicles moderates an individual fish's spawning duration following experiments with captive Barents Sea cod where spawning duration increased with fish length (5 and 11 days in 52.5 and 96 cm females, respectively at 8.8 °C). For the first time we report on spawning atresia where all components of the process are included in the estimate. In Irish Sea cod potential fecundity would make a close approximation (97–98%) to realised fecundity but this assumption was not valid for Barents Sea cod where spawning atresia accounted for a 14–18% fall in relative fecundity depending on the fish length. Batch fecundity was positively related to fish weight and declined as spawning progressed in both stocks especially in the Barents Sea but addition of fish length to the model was not significant. Relative condition declined in both stocks during spawning at the same rate but dropped by a greater proportion in Irish Sea cod. Individual egg dry weight was related to fish length and also declined during spawning. Overall fish size significantly affects some aspects of realised fecundity.
► We show that potential fecundity is a proxy of realised fecundity in Irish Sea but not Barents Sea cod. ► The standard deviation of vitellogenic follicles was proportional to fish length and condition and maybe related to spawning duration. ► Spawning period depended on fish length. ► Prespawning atresia was higher during maturation compared to spawning. ► Egg size and batch fecundity depended on body length and condition.
