New findings along Sweden’s west coast challenge the idea that cod populations there were entirely gone. The University of Gothenburg’s press service reported that Atlantic cod (Gadus morhua) comprises multiple ecotypes, each adapted to a distinct environment. These groups can interbreed, but their habitats often keep them apart, reducing practical mixing. One ecotype of interest is the coastal cod, which inhabits shallow nearshore waters rather than the open sea.
For years, researchers believed that this coastal form had vanished from western Sweden. Recent work, however, uncovered young coastal cod individuals in the region, indicating that coastal ecotypes persist alongside offshore populations. To reach this conclusion, scientists collected juvenile cod specimens no longer than about one decimeter from more than 100 sites spanning Skagerrak, Kattegat, and Øresund, and performed genetic analyses on the samples. The results show a mixed cod population in these waters, comprising both offshore and coastal ecotypes. The coastal ecotype was found in higher proportions in the fjord systems of western Sweden, suggesting a broader distribution than previously thought.
The researchers report that in several fjords both offshore and coastal cod occur within the same water bodies, yet they seem to occupy different depth ranges. Offshore cod tends to dwell slightly deeper, while coastal cod concentrates in shallower zones. The reasons behind these distinct vertical distributions remain a topic for future study, as does the question of why mature coastal cod are not observed in some areas where young individuals do appear. Looking ahead, scientists aim to identify management strategies that could help sustain and possibly revive coastal cod populations along the Swedish coast.
In a surprising aside, the historical note of ancient researchers creating faux leather for tracking mosquito bites is mentioned within the broader sweep of scientific curiosity, illustrating how researchers have long experimented with novel materials to observe biological phenomena.