Regional and stock-specific differences in contemporary growth of Baltic cod revealed through tag-recapture data

Abstract

The use of growth estimation methods that depend on unreliable age data has previously hindered the quantification of perceived differences in growth rates between the two cod stocks inhabiting the Baltic Sea. Data from cod tagged in different regions of the Baltic Sea during 2007–2019 were combined, and general linear models were fit to investigate inter-regional (defined as area of release) and inter-stock (assigned to a subset of recaptures using genetic and otolith shape analyses) differences in individual growth. An average-sized cod (364 mm) caught in the western Baltic Sea and assigned to the western Baltic cod stock grew at more than double the rate (145 mm year−1) on average than a cod of the same size caught in the eastern Baltic Sea and assigned to the eastern Baltic cod stock (58 mm year−1), highlighting the current poor conditions for the growth of cod in the eastern Baltic Sea. The regional differences in growth rate were more than twice as large (63 mm year−1) as the stock differences (24 mm year−1). Although the relative importance of environmental and genetic factors cannot be fully resolved through this study, these results suggest that environmental experience may contribute to growth differences between Baltic cod stocks.

Diverse Transcriptome Responses to Salinity Change in Atlantic Cod Subpopulations

“…The results are in accordance with our previous studies using the RT-qPCR method and transcriptome sequencing [13,14,32]. All individuals used in this study have also been measured in length and weight and showed statistically significant differences between the WBC and EBC subpopulations (Figure 3), which is consistent with previous studies [54]. These results showed a poor condition of the EBC, which may cause difficulties in recovery of the stock [55].…”

It’s elemental, my dear Watson: validating seasonal patterns in otolith chemical chronologies

“…Among the elements regulated by physiological processes, P varies consistently over the seasons in both validation samples with minima co-occurring with otolith zones without visible daily increments in DECODE otoliths or, in the case of the TABACOD otoliths, in late winter/early spring. The amplitude in P is considerably larger in western compared to eastern Baltic cod corresponding to known stock-specific differences in growth rate (Bagge et al, 1994;McQueen et al, 2020) and experienced temperature amplitude, apparently with a smaller variation around the mean values in the western Baltic cod. Throughout the Baltic Sea, phosphate concentrations are low from April to September, presumably owing to a combination of increased primary production (Wulff and Rahm, 1988) coupled with a precipitation-related increase in P loading during fall/winter (Rolff et al, 2008) and recycling in the sediments in hypoxic areas ( ViktorssonPage 18 of 57 Canadian Journal of Fisheries and Aquatic Sciences (Author's Accepted Manuscript) et al, 2013).…”

Living apart together: Long-term coexistence of Baltic cod stocks associated with depth-specific habitat use

“…The cod stocks also differ in several other parameters, e.g. the WBC stock has a lower stock size [ 11 ] but cod in the western Baltic Sea have a higher growth rate and reach larger sizes [ 12 , 13 ], their livers are less infested with anisakid larvae [ 14 ] and they have more easily readable otoliths [ 15 ].…”