The intensified expansion of the Baltic Sea’s hypoxic zone has been proposed as one reason for the current poor status of cod (Gadus morhua) in the Baltic Sea, with repercussions throughout the food web and on ecosystem services. We examined the links between increased hypoxic areas and the decline in maximum length of Baltic cod, a demographic proxy for services generation. We analysed the effect of different predictors on maximum length of Baltic cod during 1978–2014 using a generalized additive model. The extent of minimally suitable areas for cod (oxygen concentration ≥ 1 ml l⁻¹) is the most important predictor of decreased cod maximum length. We also show, with simulations, the potential for Baltic cod to increase its maximum length if hypoxic areal extent is reduced to levels comparable to the beginning of the 1990s. We discuss our findings in relation to ecosystem services affected by the decrease of cod maximum length.

波罗的海缺氧区的加剧被认为是波罗的海鳕鱼（ Gadus morhua ）目前状况不佳的原因之一，并对整个食物网和生态系统服务产生了影响。我们研究了缺氧区域增加与波罗的海鳕鱼最大长度下降之间的联系，波罗的海鳕鱼是服务产生的人口指标。我们使用广义相加模型分析了 1978 年至 2014 年期间不同预测因素对波罗的海鳕鱼最大长度的影响。鳕鱼的最低适宜区域范围（氧气浓度≥ 1 ml l ^-1 ）是鳕鱼最大长度减少的最重要预测因素。我们还通过模拟表明，如果缺氧面积减少到与 20 世纪 90 年代初相当的水平，波罗的海鳕鱼有可能增加其最大长度。我们讨论了与鳕鱼最大长度减少影响的生态系统服务相关的发现。