Celtic Sea Herring Acoustic Survey Report 2025 (C-PAS), 09 - 29 October 2025

The 2025 Celtic Sea Herring Acoustic Survey (C‑PAS; TC25021) was conducted aboard the RV Tom Crean from 9–29 October 2025 to assess the relative abundance and biomass of small pelagic fish species, including herring, sprat, and sardine, in the Celtic Sea and southern Irish Sea. The survey used systematic acoustic transects supported by targeted trawl sampling, with acoustic data collected primarily during daylight hours to align with co‑occurring regional surveys and species behaviour. Biological sampling provided information on species composition and population structure, with additional herring tissue samples collected for stock‑origin studies. Hydrographic conditions were measured using CTD casts, and zooplankton samples were collected for image‑based analysis. Apex predator surveys were conducted for seabirds throughout the survey and for marine mammals during leg two. Celtic Sea herring biomass was estimated at 1,962 t (14.895 million individuals; CV 0.66), composed predominantly of mature fish and observed mainly offshore. Sprat biomass was estimated at 9,085 t (2,946.6 million individuals; CV 0.24), while sardine biomass was 15,374 t (720.7 million individuals; CV 0.51). No anchovy estimate was produced. Results indicate that the mature component of the Celtic Sea herring stock remains low, with no clear evidence of improved recruitment.

URI

https://oar.marine.ie/handle/10793/2091

Citation

O'Donnell, C., Mullins, E., & Daly, E. (2025). Celtic Sea Herring Acoustic Survey Report 2025 (C-PAS), 09 - 29 October 2025. Marine Institute, Ireland