Data from: Behavioural responses of Atlantic cod to sea temperature changes

Understanding responses of marine species to temperature variability is essential to predict impacts of future climate change in the oceans. Most ectotherms are expected to adjust their behavior to avoid extreme temperatures and minimize acute changes in body temperature. However, measuring such behavioral plasticity in the wild is challenging. Combining 4 years of telemetry-derived behavioral data on juvenile and adult (30–80 cm) Atlantic cod (Gadus morhua), and in situ ocean temperature measurements, we found a significant effect of sea temperature on cod depth use and activity level in coastal Skagerrak. During summer, cod were found in deeper waters when sea surface temperature increased. Further, this effect of temperature was stronger on larger cod. Diel vertical migration, which consists in a nighttime rise to shallow feeding habitats, was stronger among smaller cod. As surface temperature increased beyond ~15°C, their vertical migration was limited to deeper waters. In addition to larger diel vertical migrations, smaller cod were more active and travelled larger distances compared to larger specimens. Cold temperatures during winter tended, however, to reduce the magnitude of diel vertical migrations, as well as the activity level and distance moved by those smaller individuals. Our findings suggest that future and ongoing rises in sea surface temperature may increasingly deprive cod in this region from shallow feeding areas during summer, which may be detrimental for local populations of the species.

解析海洋物种对温度波动的响应，是预测未来海洋气候变化影响的核心前提。绝大多数变温动物（ectotherms）会调整自身行为，以规避极端温度、减缓体温的剧烈波动。然而，在野外环境中量化此类行为可塑性颇具挑战。本研究整合了4年间针对幼年及体长30~80 cm的成年大西洋鳕鱼（Gadus morhua）的遥测行为数据，以及原位海洋温度观测数据，结果发现：斯卡格拉克海峡沿岸海域的海水温度，对鳕鱼的栖息水层选择与活动水平存在显著影响。夏季时，随着海表温度升高，鳕鱼会栖息于更深水层。此外，温度对体型更大的鳕鱼的该行为影响更为显著。小型鳕鱼的昼夜垂直迁移行为（夜间上浮至浅水区觅食）更为显著。当海表温度超过约15℃时，它们的垂直迁移活动会被限制在更深水层。除了昼夜垂直迁移幅度更大之外，小型鳕鱼的活动水平也更高，移动距离也远大于体型更大的个体。但冬季的低温环境，会削弱小型鳕鱼的昼夜垂直迁移幅度，同时降低其活动水平与移动距离。本研究结果表明：未来持续上升的海表温度，将逐步使该区域的鳕鱼在夏季丧失浅水区觅食栖息地，这对当地鳕鱼种群或造成不利影响。