Fishers with individual catch quota, but limited control over the mix of species caught, depend on trade and catch–quota balancing allowances to fully utilize their quota without discarding. However, these allowances can theoretically lead to overfishing if total allowable catches (TACs) are consistently exceeded. This study investigates usage of balancing allowances by the Icelandic demersal fleet over 2001–2017, for over 1,900 vessels. When a vessel’s demersal catch exceeds owned and leased quota for a given species, the gap can be bridged by borrowing quota from the subsequent fishing period or transforming unutilized quota in other species, restricted by limits. Conversely, excess quota can be saved or transformed into quota for species where there is a shortfall. We found evidence that balancing behavior is frequently similar across the fleet. Transformations are consistent with indicators of a general quota shortage and potential for arbitrage caused by differences in conversion ratios used for transformation and lease prices. Larger companies contribute more to these patterns. Nevertheless, TAC overages are generally modest especially in recent years—key reasons appear to be the tightening of vessel transformation limits and the central role of Atlantic cod, which is the main target species but cannot be persistently overfished due to a specific prohibition on positive transformations into the species. These results show how the tailored design of the Icelandic catch–quota balancing system has helped in balancing economic and ecological goals of management. We suggest policy changes that could further reduce ecological risks, e.g., prioritizing between-year transfers over transformations.

拥有个人捕捞配额但对捕捞物种组合的控制有限的渔民依靠贸易和捕捞配额平衡津贴来充分利用其配额而不丢弃。然而，如果总允许捕捞量 (TAC) 持续超出，这些限额理论上可能会导致过度捕捞。本研究调查了 2001 年至 2017 年间冰岛底层船队 1,900 多艘船只的平衡津贴使用情况。当船只的底层捕捞量超过特定物种自有和租赁的配额时，可以通过从后续捕捞期借用配额或将未使用的配额转化为其他物种的未使用配额来弥补缺口。相反，多余的配额可以节省下来或转化为短缺物种的配额。我们发现证据表明整个机队的平衡行为通常是相似的。转型符合总体配额短缺的指标，以及转型所用转换率和租赁价格差异导致的套利潜力。较大的公司对这些模式的贡献更大。尽管如此，TAC 过量捕捞总体上并不严重，尤其是近年来，主要原因似乎是船舶改造限制的收紧以及大西洋鳕鱼的核心作用，大西洋鳕鱼是主要目标物种，但由于对积极改造的具体禁止，不能持续过度捕捞进入物种。这些结果表明冰岛捕捞配额平衡系统的定制设计如何有助于平衡管理的经济和生态目标。我们建议可以进一步降低生态风险的政策改变，例如，优先考虑年际转移而不是转型。