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.厘清海洋物种对温度变动的响应机制，是预测未来海洋气候变化影响的关键基础。绝大多数变温动物（ectotherms）可通过调整自身行为规避极端温度，并尽可能降低体温的剧烈波动。然而，在野外环境中量化这类行为可塑性仍颇具挑战。本研究整合了4年来基于遥测（telemetry）技术获取的幼龄及成体（体长30~80 cm）大西洋鳕鱼（Gadus morhua）行为数据，以及原位海洋温度观测数据，结果显示，在沿海斯卡格拉克海域，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，鳕鱼会向更深水域栖息。此外，温度对体型更大的鳕鱼影响更为显著。昼夜垂直迁移（diel vertical migration）指夜间向浅海觅食生境移动的行为，该行为在体型更小的鳕鱼中表现得更为强烈。当海表温度升高至约15℃以上时，它们的昼夜垂直迁移活动会被限制在更深水域。除昼夜垂直迁移幅度更大外，体型更小的鳕鱼相较于成体更为活跃，移动距离也更远。但冬季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，未来持续升高的海表温度可能会逐步压缩该海域鳕鱼夏季的浅海觅食生境，这对该区域鳕鱼本地种群或造成不利影响。