Condition indices of Atlantic cod (Gadus morhua) biased by capturing method

In studies evaluating the condition and general health status of fish stocks, the method used for catching the fish is seldom considered as a factor of importance. In this study, condition indices were compared between cod caught in pots, gillnets, and on hooks in the same geographical area. The results showed that cod (Gadus morhua) caught on baited gear types (pots and hooks) generally displayed a lower condition and an older age (i.e. suggesting a lower growth rate) compared to cod caught in gillnets. It is unclear whether these results merely illustrate divergent behavioural responses in fish originating from one single population, or if these divergent behavioural components represent distinct subpopulations displaying different mean conditions and growth rates. Regardless of the underlying causes, the results not only show that parts of the Baltic cod stock are in extremely poor condition, they also indicate that different gear types used in the same area could target similar-sized conspecifics exhibiting large differences in condition and size-at-age. The potential impact of the difference in condition between the pots and other gear types could hamper the implementation of the cod pot as a potentially seal-safe and sustainable fishing method.