To prevent the overfishing of marine fish populations, governments often limit access through the allocation of fishing opportunities. While some studies have linked particular systems of fishing opportunities to sustainable outcomes (particularly individual transferable quota (ITQ)), it remains unclear, whether it is the use of exclusive property-rights (individual allocation and secure duration), the use of a market for fishing opportunities (tradability), or the quota limits themselves that underlie these positive outcomes. To determine which system attributes lead to sustainable fishing we developed a novel method to systematically classify how fishing opportunities are allocated for 443 global fish stocks from 1990 to 2018 to produce the longest and most comprehensive dataset and longitudinal study of its kind. Our results revealed that quota limits and individual allocation were associated with a reduced probability of overfishing, with the most robust result for quota limits. The leasing of quota was the only attribute associated with a reduced probability of overfished biomass. Whereas some previous studies have emphasized that market-based systems or those with strong property rights (i.e. a long duration) are associated with sustainable fishing, these benefits are small or not significant once proper controls for other system attributes are introduced. These results highlight the importance of considering all attributes of institutional design in the governance of common pool resources.

Fishers with individual catch quota, but limited control over the mix of species caught, depend on trade and catch-quota balancing al-lowances 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.

The quota market is the instrument through which fishing operations under an individual transferable quota (ITQ) system achieve greater efficiency. It allows fishing companies to optimally configure their quota portfolios to their catches. Globally, fisheries corresponding to ~25% of landings have adopted ITQ systems. However, there is surprisingly little empirical information on quota markets functioning. Here we study the development of quota share and lease markets and assess market activity and functioning for the cod fishery in Iceland. We use a social network analysis to assess changes in four Icelandic quota markets, distinguished by boat size (large versus small) and permanence of transfers (leases versus shares). The quota market for permanent trades in small-boat quota shows a sharp increase in trade and network connectivity between 2004 and 2006, resulting in a high rate of quota concentration. The quota markets for permanent quota shares were the most fragmented and sparse during the years of the financial crash in Iceland and never regain the same activity. Our results suggest that quota systems evolve towards a consolidated state and that their markets are not entirely resilient to financial instability. We also found some evidence that better-connected traders could sell quota at higher prices in the lease markets, though price dispersion was generally low.

Trade in grandfathered fishing quota has been argued to inevitably lead to a Transitional Gains Trap whereby revocation of quota initially gifted becomes politically impossible as the original beneficiaries are eventually succeeded by harvesters who have paid for their quota and would become loss-making in the event of revocation. This paper proposes a quantitative measure of the trap which reflects not only the potential loss faced by individual harvesters due to revocation of purchased quota but also the offsetting effect on these harvesters of accumulated profits due to the initial grandfathered allocations and subsequent investment in quota. Illustrative calculations for Iceland´s ITQ system suggest that the extent of the trap varied considerably by species but remained below 60% under a range of assumptions. Finally, it is shown that the proposed measure may decrease over time, suggesting that the trap may not necessarily be a long-term political barrier to reform.

The Arctic may be particularly vulnerable to the consequences of both ocean acidification (OA) and global warming, given the faster pace of these processes in comparison with global average speeds. Here, we use the Atlantis ecosystem model to assess how the trophic network of marine fishes and invertebrates in the Icelandic waters is responding to the combined pressures of OA and warming. We develop an approach where we first identify species by their economic (catch value), social (number of participants in fisheries), or ecological (keystone species) importance. We then use literature-determined ranges of sensitivity to OA and warming for different species and functional groups in the Icelandic waters to parametrize model runs for different scenarios of warming and OA. We found divergent species responses to warming and acidification levels; (mainly) planktonic groups and forage fish benefited while (mainly) benthic groups and predatory fish decreased under warming and acidification scenarios. Assuming conservative harvest rates for the largest catch-value species, Atlantic cod, we see that the population is projected to remain stable under even the harshest acidification and warming scenario. Further, for the scenarios where the model projects reductions in biomass of Atlantic cod, other species in the ecosystem increase, likely due to a reduction in competition and predation. These results highlight the interdependencies of multiple global change drivers and their cascading effects on trophic organization, and the continued high abundance of an important species from a socio-economic perspective in the Icelandic fisheries.