Pitchford Steven C, Smith Brian E, McBride Richard S
Northeast Fisheries Science Center NOAA Fisheries Milford Connecticut USA.
Northeast Fisheries Science Center NOAA Fisheries Woods Hole Massachusetts USA.
Ecol Evol. 2020 Sep 30;10(20):11022-11030. doi: 10.1002/ece3.6694. eCollection 2020 Oct.
Conventional observations show spiny dogfish ( Linnaeus) rarely eat Atlantic cod ( Linnaeus; 0.02% of stomachs) in the northwestern Atlantic Ocean. Critics express concern that digestion may limit species-level prey identification, and with recovery from overfishing, dogfish populations may be suppressing cod by competition or predation. This study applied a real-time PCR TaqMan assay to identify cod in dogfish stomachs collected by cooperating fishing boats during normal trawling operations (May 2014-May 2015; Gulf of Maine, Georges Bank). Conventional methods observed 51 different prey taxa and nearly 1,600 individual prey items, but no cod were observed. Cod DNA was detected in 31 (10.5%) of the dogfish stomachs, with a higher percentage of these from the homogenate of amorphous, well-digested prey and stomach fluids (20 stomachs or 65%) than from discrete animal tissues (11 stomachs or 35%). Re-examination of photographs of these 11 tissue samples revealed one whole, partially digested fish that could be recognized in hindsight as cod. Cod DNA was observed in dogfish stomachs year round: in January (1 of 1 trip), February (1 of 1), May (1 of 3), June (0 of 1), July (3 of 4), August (1 of 2), and October (3 of 3). Although these data suggest higher interaction rates between dogfish and cod than previously observed, addressing the population consequences of this predator-prey relationship requires a robust sampling design, estimates of digestion rates by dogfish to account for complete degradation of DNA sequences, and consideration for dogfish scavenging during fishing operations.
传统观察表明，在大西洋西北部，白斑角鲨（林奈）很少捕食大西洋鳕鱼（林奈；仅占胃样本的0.02%）。批评者担心消化作用可能会限制物种层面的猎物识别，并且随着过度捕捞后的种群恢复，角鲨种群可能通过竞争或捕食抑制鳕鱼数量。本研究应用实时荧光定量PCR TaqMan分析方法，对在正常拖网作业期间（2014年5月至2015年5月；缅因湾、乔治斯浅滩）合作渔船采集的角鲨胃样本中的鳕鱼进行识别。传统方法观察到51种不同的猎物分类单元和近1600个个体猎物，但未观察到鳕鱼。在31个（10.5%）角鲨胃样本中检测到鳕鱼DNA，其中来自无定形、消化良好的猎物匀浆和胃液的样本（20个胃样本，占65%）中鳕鱼DNA的比例高于离散动物组织样本（11个胃样本，占35%）。重新检查这11个组织样本的照片发现一条完整的、部分消化的鱼，事后可以识别为鳕鱼。全年在角鲨胃样本中均观察到鳕鱼DNA：1月（1次航行中的1个样本）、2月（1个样本）、5月（3个样本中的1个）、6月（1个样本中的0个）、7月（4个样本中的3个）、8月（2个样本中的1个）和10月（3个样本中的3个）。尽管这些数据表明角鲨与鳕鱼之间的相互作用率高于先前观察到的，但要阐明这种捕食者 - 猎物关系对种群的影响，需要稳健的抽样设计、对角鲨消化率的估计以考虑DNA序列的完全降解，以及考虑捕捞作业期间角鲨的 scavenging行为。 （注：scavenging在文中可能是指角鲨在捕捞作业时的某种类似清理、搜寻食物等行为，但因没有更多背景信息，暂无法准确翻译，保留英文供参考）
