Assessing indirect biodiversity conservation benefits of fisheries closures in the Gulf of St. Lawrence, Canada

Implications for fisheries in the Gulf of St. Lawrence Our results point toward wider implications for associated fisheries that rely on successful spawning and recruitment, as well as historically consistent geographical distribution of the three groundfish species [67, 70]. A prominent example of largely climate-induced changes to a fishery in the region is the recent increase in redfish which has prompted the fishery to be reopened after a ~30-year moratorium [17]. However, given our results, the projections men- tioned above, and a recent DFO study [17], the redfish fishery is unlikely to persist over the long-term, as biomass is likely to decrease, independent of fishing pressure. This is partly due to a reduction in the size-at-maturity and recruitment, possibly as a response to the warming bottom waters in the Gulf (redfish grow slower in warmer waters) [9]. However, there is uncertainty in these patterns, as they also showed persistent survival even at 10 ˚C, indicating that redfish may reside here under future climate change conditions. While recent rising water temperatures have also been linked to increasing abundance of Atlantic halibut [15, 16] suggest a shift in the Atlantic halibut spawning timing due to these temperature changes, potentially leading to an earlier spawning season in the Gulf of St. Lawrence. This, in turn, could have future consequences for larval survival and recruitment, partly due to a mismatch between food requirements and food availability, affecting subse-

quent recruitment to the Atlantic halibut fishery [70, 71]. If this is the case, indirect BCBs for Atlantic halibut in the respective OECMs will likely become weaker or disappear with ongoing climate change. Implications for OECM policy, designation, and monitoring Our analysis of indirect BCBs in the present day and throughout the 21st century can inform OECM policy, including OECM designation and monitoring. OECMs are designed to operate similarly to marine protected areas, but they are not officially or legislatively designated as such. Although biodiversity conservation might not be the primary management goal of an OECM, it must be a primary outcome [8, 9]. We show that the majority of the OECMs in the Laurentian Channel are fulfilling this outcome by providing indirect BCBs; all the described benefits are, however, unlikely to persist under climate-induced changes in bottom tempera- ture, oxygen concertation and pH. Consequently, OECM policy and management needs to adapt to those changes to remain effective and to continue their contribution to Canada’s com- mitment to protect marine biodiversity in the long-term. Further, all the OECMs assessed in our study exist under the Sensitive Benthic Areas Policy [72] which prohibits any form of bottom contact fishing (i.e., bottom trawls, dredges, bottom seining, traps, gillnets, and bottom longlines); however, other fishing practices and industries such as oil and gas are allowed, ultimately questioning actual protection of biodiversity in the

respective OECMs [7]. These concerns are in the context of the fact that systematic assess- ments of OECMs as effective contributors to biodiversity conservation are still relatively spo- radic. By integrating existing knowledge into a more complete picture of current and future BCBs in Canada’s OECMs, our results contribute to fill this knowledge gap. However, our analysis is based on opportunistic, if irregular sampling of adults and/or larvae of Atlantic hali- but, Greenland halibut and redfish to assess their spawning timing and locations. To assess continuing BCBs for these species, and ideally for other species that may indirectly benefit from the OEMCs, non-invasive annual ecological monitoring needs to take place and ecosys- tem indicators need to be developed. When designing new OECMs, an ecosystem-based approach, rather than a single species approach, should ideally being pursued. This is necessary to guarantee that in-situ biodiversity conservation, the main objective of OECMs, is being achieved. To do so, ecosystem indicators, PLOS ONE Indirect biodiversity conservation in the Gulf of St. Lawrence PLOS ONE | https://doi.org/10.1371/journal.pone.0316754 January 9, 2025 12 / 20