Eikeset Anne Maria, Dunlop Erin S, Heino Mikko, Storvik Geir, Stenseth Nils C, Dieckmann Ulf
Department of Biology, University of Oslo, N-0316 Oslo, Norway;
Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, N-0316 Oslo, Norway.
Proc Natl Acad Sci U S A. 2016 Dec 27;113(52):15030-15035. doi: 10.1073/pnas.1525749113. Epub 2016 Dec 9.
The relative roles of density dependence and life history evolution in contributing to rapid fisheries-induced trait changes remain debated. In the 1930s, northeast Arctic cod (Gadus morhua), currently the world's largest cod stock, experienced a shift from a traditional spawning-ground fishery to an industrial trawl fishery with elevated exploitation in the stock's feeding grounds. Since then, age and length at maturation have declined dramatically, a trend paralleled in other exploited stocks worldwide. These trends can be explained by demographic truncation of the population's age structure, phenotypic plasticity in maturation arising through density-dependent growth, fisheries-induced evolution favoring faster-growing or earlier-maturing fish, or a combination of these processes. Here, we use a multitrait eco-evolutionary model to assess the capacity of these processes to reproduce 74 y of historical data on age and length at maturation in northeast Arctic cod, while mimicking the stock's historical harvesting regime. Our results show that model predictions critically depend on the assumed density dependence of growth: when this is weak, life history evolution might be necessary to prevent stock collapse, whereas when a stronger density dependence estimated from recent data is used, the role of evolution in explaining fisheries-induced trait changes is diminished. Our integrative analysis of density-dependent growth, multitrait evolution, and stock-specific time series data underscores the importance of jointly considering evolutionary and ecological processes, enabling a more comprehensive perspective on empirically observed stock dynamics than previous studies could provide.
密度依赖和生活史进化在导致渔业快速引发的性状变化中所起的相对作用仍存在争议。在20世纪30年代，东北极鳕鱼（Gadus morhua），即目前世界上最大的鳕鱼种群，经历了从传统产卵场渔业向工业拖网渔业的转变，在该种群的觅食场加大了捕捞力度。从那时起，成熟时的年龄和体长急剧下降，这一趋势在全球其他被开发的种群中也有体现。这些趋势可以通过种群年龄结构的人口统计学截断、密度依赖生长导致的成熟表型可塑性、有利于生长更快或成熟更早的鱼类的渔业诱导进化，或这些过程的组合来解释。在这里，我们使用一个多性状生态进化模型来评估这些过程再现东北极鳕鱼74年成熟年龄和体长历史数据的能力，同时模拟该种群的历史捕捞方式。我们的结果表明，模型预测关键取决于所假设的生长密度依赖性：当这种依赖性较弱时，生活史进化可能是防止种群崩溃所必需的，而当使用根据近期数据估计的更强的密度依赖性时，进化在解释渔业诱导的性状变化中的作用就会减弱。我们对密度依赖生长、多性状进化和特定种群时间序列数据进行的综合分析强调了联合考虑进化和生态过程的重要性，与之前的研究相比，能够对实际观察到的种群动态提供更全面的视角。
