Bioenergetics Model for Eastern Baltic Cod

Many of the parameters in the original model made for Northeast Arctic stock of Atlantic cod were updated to better describe the biology of the Eastern Baltic cod stock (Supplementary
Table S1). In terms of energy intake, we tested the difference in the amount of surplus energy when using two different feeding levels. There have been considerable historical changes in food availability for the Eastern Baltic cod, resulting in different satiation levels in different periods. We therefore ran the model first with the historic and then with a more recent satiation level by using different values for . These were parameterised based on two feeding regimes identified by Neuenfeldt et al. (2020) (link).
Minimum liver weight in relation to length was parameterized with data from 828 post-spawned non-infected Western Baltic cod caught between 1996 and 2018. We used data from the western stock instead of the eastern stock to avoid any bias related to infections on the estimated minimum liver weight. The minimal liver weight in relation to length was estimated by using a power law function. This resulted in an exponent of 3.17 for Western Baltic cod (ICES, 2019a ), which yielded unrealistic liver weights compared to observations for Eastern Baltic cod, and an exponent of 3.4 was used instead, based on better agreement between observed and modelled liver weights (Table 1).
The relationship between the modelled weight and length from the bioenergetics model was validated by fitting a weight-at-length relationship using monitoring data from the Eastern Baltic cod stock from 2010 to 2020 (N = 828, ICES, 2019a ).