Jones J Brin, Campana Steven E
Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
Ecol Appl. 2009 Sep;19(6):1500-14. doi: 10.1890/07-2002.1.
Changing environmental conditions set against a backdrop of high exploitation can result in severe consequences for commercially harvested stocks. The collapse of the Eastern Scotian Shelf cod (Gadus morhua L.) off eastern Canada was primarily due to overexploitation but may have been exacerbated by a widespread temperature decline. Recent studies have called for accurate determination of ambient temperature (the actual temperature exposure history of the fish) before discarding environmental conditions as a factor in the collapse. We used the stable oxygen isotope composition of otoliths (delta18O(oto)) to reconstruct the ambient temperature history of Eastern Scotian Shelf cod from 1970 to 2000 in order to determine whether the stock experienced the temperature decline or shifted their distribution to avoid it. To correct delta18O(oto) for seawater isotope content (deltaO(w)), we generated a new meta-equation for the relationship between delta18O(w) (per mil) and salinity (S, in psu) on the Eastern Scotian Shelf: delta18O(w) = 0.539 x S - 18.790. The ambient temperature series revealed that the large-scale geographic distribution of mature cod remained constant through the cooling period, although their ambient temperature was cooler than expected in warmer periods and warmer than expected in cooler periods, indicating small-scale thermoregulatory movement. Although the mean hydrographic temperature was 4 degrees C, mature cod usually inhabited the coldest available waters (mean ambient temperature = 3 degrees C), while the juveniles usually inhabited warmer waters (mean ambient temperature = 5.5 degrees C). Length-at-age was significantly related to ambient temperature, especially in the early years of growth, and therefore declining ambient temperatures were at least partially responsible for declines in asymptotic length (up to age 8 yr). The most active thermoregulatory movement occurred during a moderate warming period; therefore extreme warming events (such as those predicted under climate change) may force large-scale northward latitudinal shifts in this historically sedentary stock. Retroactive stable isotope chronologies can be an important tool in sustainable management strategies under the shifting climate conditions predicted for years to come.
在过度开发的背景下，环境条件的变化可能会给商业捕捞种群带来严重后果。加拿大东部沿海的东斯科舍大陆架鳕鱼（Gadus morhua L.）种群崩溃，主要原因是过度捕捞，但广泛的温度下降可能加剧了这一情况。最近的研究呼吁在排除环境条件作为种群崩溃因素之前，准确测定环境温度（鱼类实际的温度暴露历史）。我们利用耳石的稳定氧同位素组成（δ18O(oto)）来重建1970年至2000年东斯科舍大陆架鳕鱼的环境温度历史，以确定该种群是否经历了温度下降，或者是否转移了分布范围以避开低温。为了校正耳石δ18O(oto)中的海水同位素含量（δO(w)），我们得出了东斯科舍大陆架上δ18O(w)（‰）与盐度（S，单位为psu）之间关系的新元方程：δ18O(w) = 0.539 × S - 18.790。环境温度序列显示，在降温期，成熟鳕鱼的大规模地理分布保持不变，尽管它们的环境温度在温暖期比预期的低，在寒冷期比预期的高，这表明存在小规模的体温调节移动。尽管平均水文温度为4摄氏度，但成熟鳕鱼通常栖息在最冷的可用水域（平均环境温度 = 3摄氏度），而幼鱼通常栖息在较温暖的水域（平均环境温度 = 5.5摄氏度）。年龄体长与环境温度显著相关，尤其是在生长早期，因此环境温度下降至少部分导致了渐近体长（至8岁）的下降。最活跃的体温调节移动发生在适度升温期；因此，极端升温事件（如气候变化预测的那些）可能会迫使这种历史上定居的种群大规模向北纬度转移。追溯稳定同位素年代学可能成为未来多年预测气候变化条件下可持续管理策略的重要工具。
