Historical marine ecology has shown that many exploited animal populations declined before their abundance was quantified by scientists. This situation applies for autumn-spawning herring (Clupea harengus) in the Baltic Sea. This stock used to be the dominant spawning group of herring in the early decades of the 1900s and supported several commercially important fisheries, including in the Gulf of Riga (GoR). However, the GoR stock declined during the 1960–1970s and has not recovered. Neither the former biomass nor reasons for its decline are known. Here, we recover and analyse historical fishery and biological data and conduct population development simulations to evaluate the hypothesis that exploitation may have been sufficient to lead the stock towards commercial extinction. We found that the estimated exploitation pattern, including exploitation of juveniles, was unsustainable and led to stock decline. The pattern of exploitation of this stock was consistent with that which caused collapses of other herring stocks, which have since recovered. If autumn-spawning herring in the GoR recovers, our findings indicate that this stock could support sustainable annual yields of ∼4000 t and diversify the fishery resource base, which is presently restricted to a relatively small number of species for essentially local coastal inhabitants.