Northern cod spawning sites in 2015

<b>Abstract</b><br/><p>A decade ago, in 2015, a paper in this journal heralded the “comeback” of Canada’s iconic Northern cod some 25 years after its collapse in the early 1990s. In this paper, the stock status determined by current and past models and recent management is reviewed, 10 years later. Summarily, surplus production and growth have stalled, some years being negative, although the stall point biomass is controversial (and well below historical norms). Structural equation models indicate the main correlate of production is spawning stock biomass (positive), whose correlates are abundances of capelin (<em>Mallotus villosus</em>) (positive) and harp seals (<em>Pagophilus groenlandicus</em>) (negative), with net production (enabling SSB growth) further reduced by fisheries. Reductions in the SSB thought necessary to avoid impairing recruitment, from 1.3 to 0.25 million t, have led to increases in harvest allocations and reopened commercial Canadian and foreign fisheries, despite advice by the Department of Fisheries and Oceans and independent science to keep removals low. Management objectives are opaque; if rebuilding, then SSB growth must remain the main objective, otherwise the Northern cod will be restrained to a shadow of its historical abundance and socio-economic and cultural importance.</p>

**摘要**<br/>十年前的2015年，本期刊登的一篇论文宣告，加拿大标志性的北部鳕鱼在20世纪90年代初种群崩溃约25年后，迎来了“复苏”。时至十年后的今日，本文对基于当前与既往模型及近期管理措施所判定的种群现状展开回顾。概而言之，种群剩余产量与增长已陷入停滞，部分年份甚至出现负值；尽管停滞点的生物量存在争议，且该数值远低于历史常规水平。结构方程模型结果显示，种群产量的核心相关因素为产卵种群生物量（spawning stock biomass，SSB，呈正相关）；而产卵种群生物量的相关因素则为毛鳞鱼（*Mallotus villosus*）的丰度（正相关）与竖琴海豹（*Pagophilus groenlandicus*）的种群数量（负相关），且渔业捕捞进一步降低了净产量——即支撑SSB增长的产量。原本为避免损害种群补充而设定的SSB阈值，从130万吨下调至25万吨；尽管加拿大渔业及海洋部与独立科研团队建议维持较低的捕捞移除量，但这一调整仍推动了捕捞配额的提升，并重新开放了加拿大本国与外国的商业捕捞作业。当前的渔业管理目标尚不透明：若以种群恢复为核心目标，则SSB增长仍需作为首要管理目标；否则，北部鳕鱼将只能留存于其历史丰度、社会经济与文化价值的残影之中。