Integrating fisheries independent surveys to account for the spatiotemporal dynamics of spiny dogfish (Squalus acanthias) in US waters of the northwest Atlantic

Abstract

Spiny dogfish (Squalus acanthias) are a ubiquitous shark species found throughout the northwest Atlantic. Understanding their abundance and distribution patterns are paramount for determining stock status and guiding harvest. Previous work describing their abundance and distribution has relied on a single fisheries independent trawl survey and focused on course size groupings, ultimately capturing only a part of their geographic distribution and making such tools unavailable for use as stock assessment inputs, respectively. Here, we develop spatiotemporal models that integrate multiple surveys’ data to provide a more holistic understanding of the species distribution over time. Models were developed to produce predictions in abundance by season (spring and fall), sex (male and female) and size (6 cm length bins) to assess differences across these dimensions. Models also incorporated environmental covariates to assess whether oceanographic conditions allow for explaining distribution patterns or addressing survey catchability concerns. Model results suggest that spiny dogfish spatiotemporal dynamics were influenced by bottom water temperature. Distributional metrics (northings, eastings, effective area occupied) were largely similar between males and females over time, but highlighted seasonal patterns that reflect their seasonal migrations. For both sexes and season, relative abundance estimates have been stable over time; however, male abundance has increased in recent years in both spring and fall. Integrating the surveys into a single index has not changed perception on spiny dogfish abundance trends for this region, but better accounts for the species’ range. Through the development of these models, we provide more holistic, model-based relative abundance indices for future use in stock assessments of northwest Atlantic spiny dogfish.