Enhanced data collection in the Canadian Arctic for seabird bycatch information yields highly variable results

Incidental catch of seabirds (bycatch) in fisheries has been identified as a major threat to the conservation of seabird populations globally. Acquiring accurate, detailed data on seabird bycatch is an ongoing challenge to effective integrated ecosystem management of commercial fisheries. This is especially true in the Arctic region where different countries have highly variable reporting and data systems to track and understand seabird bycatch in fisheries. To collect detailed data on seabird bycatch in the Greenland halibut ( Reinhardtius hippoglossoides ) fishery in northern Canada, we applied two methods that asked for more information than standardly reported in the fishery as a voluntary effort with industry partners. We found that the amount of bird bycatch reported in both enhanced datasheets completed by at-sea observers (ASO) and carcass collections yielded different results when compared to the typical seabird bycatch reporting in the fisheries ASO database. Across three years of data collection (2016, 2018, and 2019), the number of seabirds reported using the enhanced data collection methods were 0.5-11-fold the number from typical ASO database values. In a fourth year of observations (2023), enhanced datasheets from the ASO reported no bycaught fulmars (gulls and terns were reported), but the accompanying photographs showed northern fulmars as bycatch, further supporting that seabird identification is hampering accurate reporting. We then used these data to model how the differences between data sources may fluctuate across years. These large discrepancies between the methods highlight the challenges with obtaining accurate and precise seabird bycatch data needed to implement a meaningful ecosystem approach to the management of the fisheries. Future modelling efforts need to take these differing data sources and variability into account to fully understand the potential population level impacts of fisheries on seabird populations.