Gadus morhua
The Baltic Cod
A Stock in Collapse
The Atlantic Cod (Gadus morhua) in the Baltic Sea is not the iconic North Atlantic giant — it is a brackish-water dwarf form, evolutionarily adapted to the Baltic's low salinity (4–10 PSU) and historically distinct in two populations: the western stock (around Bornholm and the Sound) and the once-vast eastern stock (the Gulfs of Finland, Bothnia and the central Baltic). In Finnish waters this is Turska, a fish that for centuries underpinned Baltic fishing communities and arrived on Finnish tables as the staple winter protein.
The story is now one of collapse. By 2019 the eastern Baltic cod stock had crashed so severely — driven by hypoxic dead zones in the deep spawning basins, parasite loads, food-web shifts and overfishing — that the EU imposed an indefinite ban on the directed eastern-stock fishery. Recreational targeting is sharply constrained. Bycatch must be released. Finnish anglers encountering cod in the western archipelago today are catching the survivors of an ecological emergency, and the framing of any cod page must reflect that.
Where small populations persist, Baltic cod are still recognisable: olive-bronze backs with darker mottling, white belly, the prominent chin barbel, the three dorsal and two anal fins typical of the gadid family. They are demersal, cold-stenothermic and oxygen-demanding — ironic, because oxygen depletion in the Gotland and Bornholm basins is exactly what is killing them. Adult diet is dominated by sprat and herring; juveniles work the benthos for crustaceans.
Seasonal Data
Activity patterns of Baltic Cod in Finnish waters — peak activity in cold months when oxygen-rich water reaches the basins, near-dormancy in stratified summer.
Diet Spectrum
Adult Baltic cod feed almost entirely on sprat and herring; juveniles work the benthos. Diet shifts sharply with prey-fish availability — itself a casualty of the same ecosystem changes affecting cod.
Growth by Age
The modern eastern Baltic cod is a dwarf form: maturity at 18–25 cm and rarely exceeding 70 cm even in older fish. These growth values reflect the contemporary collapsed stock, not the historic ICES Atlantic baseline.
| Age (Years) | Length | Weight | Relative Size |
|---|---|---|---|
| 1 | 12 cm | 18 g | 16% |
| 2 | 20 cm | 80 g | 27% |
| 3 | 28 cm | 220 g | 37% |
| 4 | 35 cm | 450 g | 47% |
| 5 | 42 cm | 750 g | 56% |
| 6 | 48 cm | 1.1 kg | 64% |
| 8 | 58 cm | 2.0 kg | 77% |
| 10+ | 68 cm | 3.2 kg | 91% |
Habitat Requirements
Water Temperature
Cold-stenothermic. Retreats from summer-warm surface water into deeper basins where oxygen is the binding constraint.
Oxygen
The single most critical limit. Baltic deep-basin hypoxia (Gotland, Bornholm) excludes cod from their historic spawning grounds.
Structure
Demersal — adults hold near rocky reefs and basin edges. Juveniles work shallower benthic habitat.
Substrate
Spawning requires neutrally buoyant eggs to hold in oxygenated mid-water — increasingly rare as deep layers go anoxic.
Water Depth
Driven into a narrowing oxygen-temperature window; outside this band the fish simply cannot survive.
Water Type
Adapted to Baltic brackish salinity. Cannot tolerate freshwater inflows or full North Sea salinity.
Cod Fishing in Finland: A Conservation-First Framing
Recreational cod fishing in Finnish Baltic waters is sharply constrained. The directed eastern-stock fishery has been EU-banned since 2019 due to stock collapse, and the only realistic recreational windows are limited western-archipelago opportunities in late autumn and early spring, on a strict catch-and-release basis where any encounters occur. Anglers should consult Eräluvat and ICES advisories before targeting cod and treat every fish as a survivor of an ecological emergency.
Where fishing is permitted, traditional methods are vertical jigging (pirk) over deeper rocky bottoms, slow-trolling diving plugs, and ice fishing in the very limited brackish-coast scenarios where cod still wander shallow.
Vertical Jigging (Pirk)
Late autumn - Early springHeavy pirk lures dropped to the bottom over rocky reefs. Slow lift-drop. Catch-and-release strongly recommended.
Bottom Bouncing
Limited windowsNatural bait (herring strip) drifted along the bottom. Effective but exposes cod to deep-hooking — release with care.
Ice Fishing (Niche)
Jan - Mar (very limited)Rare opportunity in the western archipelago when cod move shallow under ice. Strict release-only ethics.
Slow Trolling
Late autumnSlow-pulled diving plugs over basin slopes. Highly variable — modern stock means many blank days.
Where Cod Are Still Found in Finland
Cod encounters in Finnish waters are increasingly rare and concentrated in a few residual western-archipelago areas. Northern Bothnian waters are now essentially cod-free.
Outer Turku Archipelago / Åland Fringe
60.0°N, 21.5°ELast residual western refuge
The deeper outer-archipelago waters at the boundary with the Baltic Proper still hold occasional cod — the last reliable Finnish encounter zone, and even here fish are scarce.
Southern Bothnian Sea (Selkämeri)
61.5°N, 21.4°EMarginal — declining
Once a productive area, now sees only occasional fish. Encounters are increasingly accidental rather than targeted.
Hanko / Tammisaari Outer Coast
59.8°N, 23.2°ERare Gulf of Finland encounters
The Gulf of Finland eastern stock was historically productive but is now collapsed. Rare encounters along the deeper outer coast.
Bothnian Bay Southern Fringe
63.5°N, 22.6°ENorthern limit (essentially gone)
Cod are essentially absent from the Bothnian Bay today — salinity and oxygen conditions exclude them from this northern reach.
