Thünen Institute of Baltic Sea Fisheries, Rostock, Germany.
Thünen Institute of Fisheries Ecology, Bremerhaven, Germany.
PLoS One. 2022 Sep 28;17(9):e0274476. doi: 10.1371/journal.pone.0274476. eCollection 2022.
Coexistence of fish populations (= stocks) of the same species is a common phenomenon. In the Baltic Sea, two genetically divergent stocks of Atlantic cod (Gadus morhua), Western Baltic cod (WBC) and Eastern Baltic cod (EBC), coexist in the Arkona Sea. Although the relative proportions of WBC and EBC in this area are considered in the current stock assessments, the mixing dynamics and ecological mechanisms underlying coexistence are not well understood. In this study, a genetically validated otolith shape analysis was used to develop the most comprehensive time series of annual stock mixing data (1977-2019) for WBC and EBC. Spatio-temporal mixing analysis confirmed that the two stocks coexist in the Arkona Sea, albeit with fluctuating mixing proportions over the 43-year observation period. Depth-stratified analysis revealed a strong correlation between capture depth and stock mixing patterns, with high proportions of WBC in shallower waters (48-61% in <20m) and increasing proportions of EBC in deeper waters (50-86% in 40-70m). Consistent depth-specific mixing patterns indicate stable differences in depth distribution and habitat use of WBC and EBC that may thus underlie the long-term coexistence of the two stocks in the Arkona Sea. These differences were also reflected in significantly different proportions of WBC and EBC in fisheries applying passive gears in shallower waters (more WBC) and active gears in deeper waters (more EBC). This highlights the potential for fishing gear-specific exploitation of different stocks, and calls for stronger consideration of capture depth and gear type in stock assessments. This novel evidence provides the basis for improved approaches to research, monitoring and management of Baltic cod stocks.
鱼类种群（= 群体）共存是一种常见现象。在波罗的海，两种遗传上不同的大西洋鳕鱼（Gadus morhua）群体，西部波罗的海鳕鱼（WBC）和东部波罗的海鳕鱼（EBC），在阿尔科纳海共存。尽管当前的种群评估考虑了该地区 WBC 和 EBC 的相对比例，但对共存的混合动态和生态机制了解甚少。在这项研究中，使用经过基因验证的耳石形状分析，开发了 WBC 和 EBC 最全面的年度种群混合数据时间序列（1977-2019 年）。时空混合分析证实，这两个群体在阿尔科纳海共存，尽管在 43 年的观测期间混合比例波动。分层深度分析显示，捕获深度与种群混合模式之间存在很强的相关性，WBC 在较浅水域的比例较高（<20m 时为 48-61%），EBC 在较深水域的比例增加（40-70m 时为 50-86%）。一致的特定深度混合模式表明 WBC 和 EBC 在深度分布和生境利用方面存在稳定的差异，这可能是这两个群体在阿尔科纳海长期共存的基础。这些差异也反映在使用被动渔具的较浅水域（更多 WBC）和使用主动渔具的较深水域（更多 EBC）的渔业中 WBC 和 EBC 的比例存在显著差异。这突出了针对不同群体使用渔具的特定捕捞潜力，并呼吁在种群评估中更加强调捕获深度和渔具类型。这一新证据为改进波罗的海鳕鱼种群的研究、监测和管理方法提供了基础。
