Data from: Oxygen depletion in coastal seas and the effective spawning stock biomass of an exploited fish species

Environmental conditions may have previously underappreciated effects on the reproductive processes of commercially exploited fish populations, for example eastern Baltic cod, that are living at the physiological limits of their distribution. In the Baltic Sea, salinity affects neutral egg buoyancy, which is positively correlated with egg survival, as only water layers away from the oxygen consumption-dominated sea bottom contain sufficient oxygen. Egg buoyancy is positively correlated to female spawner age/size. From observations in the Baltic Sea, a field-based relationship between egg diameter and buoyancy (floating depth) could be established. Hence, based on the age structure of the spawning stock, we quantify the number of effective spawners, which are able to reproduce under ambient hydrographic conditions. For the time period 1993–2010, our results revealed large variations in the horizontal extent of spawning habitat (1000–20 000 km2) and oxygen-dependent egg survival (10–80%). The novel concept of an effective spawning stock biomass takes into account offspring that survive depending on the spawning stock age/size structure, if reproductive success is related to egg buoyancy and the extent of hypoxic areas. Effective spawning stock biomass reflected the role of environmental conditions for Baltic cod recruitment better than the spawning stock biomass alone, highlighting the importance of including environmental information in ecosystem-based management approaches.

此前人们可能低估了环境条件对商业捕捞鱼类种群繁殖过程的影响，例如处于分布范围生理极限的波罗的海东部鳕鱼种群。在波罗的海海域，盐度会影响鱼卵的中性浮力，而鱼卵浮力与存活率呈正相关——唯有远离耗氧主导的海底的水层才拥有充足的溶解氧。鱼卵浮力与雌性产卵亲体的年龄/体型呈正相关。基于波罗的海的实地观测，我们可建立鱼卵直径与浮力（漂浮深度）之间的野外实测关联。因此，我们可基于产卵种群的年龄结构，量化能够在当前水文条件下完成繁殖的有效产卵亲体数量。在1993至2010年的研究时段内，我们的结果显示产卵栖息地的水平范围（1000~20000平方千米）与依赖氧气的鱼卵存活率（10%~80%）均存在显著波动。若繁殖成功率与鱼卵浮力及低氧区范围相关，那么有效产卵种群生物量（effective spawning stock biomass）这一全新概念会将后代存活情况取决于产卵种群的年龄/体型结构这一因素纳入考量。相较于单纯的产卵种群生物量，有效产卵种群生物量能更好地反映环境条件对波罗的海鳕鱼种群补充量的影响，凸显了在基于生态系统的管理框架中纳入环境信息的重要性。