Casault, B., Johnson, C.L., Devred, E., and Beazley, L. 2025. Chemical and Biological Oceanographic Conditions on the Scotian Shelf and in the Eastern Gulf of Maine during 2023. Can. Tech. Rep. Fish. Aquat. Sci. 3658: vi + 57 p. https://doi.org/10.60825/4d69-8120
Nutrient and plankton metrics are assessed in the context of physical conditions observed in the Maritimes region in 2023. Sub-surface (50-150 m) nitrate inventories were spatially variable across the region in 2023 but indicated a gradual return toward near-normal levels, except in the Bay of Fundy (i.e., at Prince-5) where a record-low value was observed in 2023. Bottom nitrate concentrations during summer were predominantly below normal across the region in 2023. In situ chlorophyll-a inventories were on average higher than normal in the region in 2023. Surface chlorophyll-a concentrations measured by satellite remote sensing reached record-high values in some sub-regions in 2023. The spring phytoplankton bloom timing was later than normal with a mainly lower-than-normal intensity in 2023. The fall bloom was generally earlier than normal with a higher-than-normal intensity. Diatoms abundance at Halifax-2 indicates increasing levels over the last three years. The abundance of Calanus finmarchicus was on average slightly above normal in the region in 2023, contrasting with the low abundances observed since 2011. Pseudocalanus spp. abundance was on average above normal in the region while zooplankton biomass and the abundance of Arctic Calanus species remained mainly near or below normal levels in 2023.