Southern North Sea and Eastern Channel Seasonal Aggregation IMMA

Size in Square Kilometres

33,849 km2

Qualifying Species and Criteria

Harbour porpoise – Phocoena phocoena

Criterion B (2), C (2)



The Southern North Sea and Eastern Channel Seasonal Aggregation Area IMMA holds an important aggregation of harbour porpoises (Phocoena phocoena) in spring. The very diverse habitat, including a series of sandbanks and reefs and a front system supports an abundance of harbour porpoise prey species such as sole, goby, herring and sandeel.

Description of Qualifying Criteria

Criterion B: Distribution and Abundance

Sub-criterion B2: Aggregations

Following a historical decline and near extirpation in the southern North Sea and English Channel, harbour porpoise (Phocoena Phocoena) occurrence in the southern North Sea, including the area of the IMMA, has been increasing since the mid-1990s (Camphuysen, 2004; Hammond et al. 2002). Harbour porpoises were almost absent in the English Channel two decades ago but are now regularly seen in this region (Hammond et al., 2013, 2021; Bouveroux et al., 2020; Blanchard et al., 2023). A comparison of harbour porpoise distribution between the SCANS and SCANS-II surveys showed a marked difference in summer distribution of harbour porpoises within the Greater North Sea, with a shift towards the south in the main concentrations of animals between 1994 and 2005 and decreasing numbers in the northern North Sea (Hammond et al., 2013). This southward shift in distribution is supported by data from smaller scale surveys in the southern North Sea which show increasing numbers of porpoises and aggregations in French, Belgian, Dutch and German waters (e.g., Gilles et al., 2009, 2011; Haelters et al., 2011; Scheidat et al., 2012; Peschko et al., 2016; Laran et al., 2017; Nachtsheim et al. 2021). This shift in harbour porpoise distribution is probably related to changes in prey distribution and abundance (Hammond et al., 2013). Data from SCANS-III in 2016 and the recent SCANS-IV survey in 2022 confirm that the shift to the south has been maintained (Hammond et al., 2021; Gilles et al., 2023).

A recent aerial survey conducted mid-May 2023 recorded a high encounter rate of the species in the southern limit of the IMMA, with encounter rates up to 0.1 sightings/km of aerial effort (Blanchard et al., 2023).  Aggregations of porpoises in spring in the northern part of the IMMA were also previously reported by ship surveys in 2012-2014 (Bouveroux et al., 2020) and aerial surveys in 2017-2018 (Virgili et al., 2018). In the Belgian part of the IMMA the density is highest in spring with a mean estimated density of 2.78 ind/km2 over aerial surveys in the years 2009 to 2022 (Haelters et al., 2023 in press). In the Dutch part of the IMMA, aerial surveys in 2010-2011 showed that spring densities of porpoises were threefold higher than in summer (Geelhoed et al., 2013). The occurrence in summer has also increased over time and densities reach the same order of magnitude as in spring (0.70-1.44 animals/km2, Geelhoed and Scheidat, 2018).

Analysis of harbour porpoise stranding records from 1990 to 2017 support the evidence of increasing abundance in the southern North Sea with a steep increase in strandings reported since 2005 (Ijsseldijk et al., 2020, Blanchard et al., 2023).

Criterion C: Key Life Cycle Activities

Sub-criterion C2: Feeding Areas

The high porpoise densities and aggregations that occur in this IMMA in spring and summer are likely due to the abundance of prey fish species. Indeed, the diverse and abundant benthic community forms a rich food base for the fish fauna. A variety of flatfish, goby species and other bottom-dwelling fish can be found there, but also pelagic fish species. Prey species such as sole, goby (multiple species), herring (Clupea harengus) and sandeel (Family Ammodytidae) that are a regular part of the porpoise diet are known to be abundant in the area.

Supporting Information

Blanchard A., Laran S., Williams G., Van Canneyt O., Genu M., Sanchez T., Doremus G., Gamelin P.-L. (2023). Synthèse des données de l’Observatoire PELAGIS au sein du PNM des estuaires picards et de la mer d’Opale. Rapport pour le PNM EPMO (OFB-22-0565). 61 pp. Availaible from

Bouveroux, T., Waggitt, J. J., Belhadjer, A., Cazenave, P. W., Evans, P. G. H., Kiszka, J. J. (2020). Modelling fine-scale distribution and relative abundance of harbour porpoises in the Southern Bight of the North Sea using platform-of-opportunity data. J. Mar. Biol. Assoc. United Kingdom 100, 481–489. doi: 10.1017/s0025315420000326

Camphuysen, C.J. (2004). The return of the harbour porpoise (Phocoena phocoena) in Dutch coastal waters. Lutra 47, 113-22.

Geelhoed, S.C.V., Scheidat, M., van Bemmelen, R.S.A., Aarts, G. (2013). Abundance of harbour porpoises (Phocoena phocoena) on the Dutch Continental Shelf, aerial surveys in July 2010-March 2011. Lutra 56 (1): 45-57.

Geelhoed, S.C.V., Scheidat, M. (2018). Abundance of harbour porpoises (Phocoena phocoena) on the Dutch Continental Shelf, aerial surveys 2012-2017. Lutra 61(1): 123-132.

Geelhoed, S., Authier, M., Pigeault, R., Gilles, A. 2022. Abundance and Distribution of Cetaceans. In: OSPAR, 2023: The 2023 Quality Status Report for the North-east Atlantic. OSPAR Commission, London. Available at:

Gilles, A., Adler, S., Kaschner, K., Scheidat, M., Siebert U. (2011). Modelling harbour porpoise seasonal density as a function of the German Bight environment: implications for management. Endangered Species Research 14: 157-169

Gilles, A., Viquerat, S., Becker, E.A., Forney, K.A., Geelhoed, S.C.V., Haelters, J., Nabe-Nielsen, J., Scheidat, M., Siebert, U., Sveegaard, S., van Beest, F.M., van Bemmelen, R., Aarts, G. (2016). Seasonal habitat-based density models for a marine top predator, the harbor porpoise, in a dynamic environment. Eco-sphere 7(6):e01367. 10.1002/ecs2.1367

Gilles, A., Authier, M., Ramirez-Martinez, N.C., Araújo, H, Blanchard, A., Carl-ström, J., Eira, C., Dorémus, G., Fernández-Maldonado, C., Geelhoed, S.C.V., Kyhn, L., Laran, S., Nachtsheim, D., Panigada, S., Pigeault, R., Sequeira, M., Sveegaard, S., Taylor, N.L., Owen, K., Saavedra, C., Vázquez-Bonales, J.A., Unger, B., Hammond, P.S. (2023). Estimates of cetacean abundance in Eu-ropean Atlantic waters in summer 2022 from the SCANS-IV aerial and ship-board surveys. Final report published 29 September 2023. 64 pp.

Haelters, J., Kerckhof, F., Jacques, T. G., Degraer, S. (2011). The harbour porpoise Phocoena phocoena in the Belgian part of the North Sea: trends in abundance and distribution. Belgian J. Zool. 141, 75–84.

Haelters, J., Paoletti, S., Vigin, L., Rumes, B., 2023 (in press). Seasonal distribution of harbour porpoises (Phocoena phocoena) and response to operational offshore wind farms in the Belgian North Sea. In: S. Degraer et al. (Eds). Winmon report, Chapter 4, in press. Institute of Natural Sciences, Brussels, Belgium.

Hammond, PS, Macleod, K, Berggren, P, Borchers, DL, Burt, ML, Cañadas, A, Des-portes, G, Donovan, GP, Gilles, A, Gillespie, D, Gordon, J, Hedley, S, Hiby, L, Kuklik, I, Leaper, R, Lehnert, K, Leopold, M, Lovell, P, Øien, N, Paxton, CGM, Ridoux, V, Rogan, E, Samarra, F, Scheidat, M, Sequeira, M, Siebert, U, Skov, H, Swift, R, Tasker, ML, Teilmann, J, Van Canneyt, O, Vázquez, JA. (2013). Cetacean abundance and distribution in European Atlantic shelf waters to inform conservation and management. Biological Conservation 164: 107-122

Hammond P, Lacey C, Gilles A, Viquerat S, Börjesson P, Herr H, Macleod K, Ridoux V, Santos MB, Scheidat M, Teilmann J, Vingada J, Øien N. 2021. Estimates of cetacean abundance in European Atlantic waters in summer 2016 from the SCANS-III aerial and shipboard surveys – Revised version (June 2021). sign-based_estimates_final_report_revised_June_2021.pdf

Lacey, C., Gilles, A., Börjesson, P., Herr, H., Macleod, K., Ridoux, V., Santos, M.B., Scheidat, M., Teilmann, J., Vingada, J., Viquerat, S., Øien, N., Hammond, P.S. (2022). Modelled density surfaces of cetaceans in European Atlan-tic waters in summer 2016 from the SCANS-III aerial and shipboard surveys. Final report.

Laran, S., Authier, M., Blanck, A., Doremus, G., Falchetto, H., Monestiez, P., Pettex, E., Stephan, E., Van Canneyt, O., Ridoux, V. (2017). Seasonal distribution and abundance of cetaceans within French waters- Part II: The Bay of Biscay and the English Channel. Deep Sea Research Part II: Topical Studies in Oceanography 141, 31-40.

Nachtsheim, D., Viquerat, S., Ramirez-Martinez, N.C., Unger, B., Siebert, U., Gilles, A. (2021). Small cetaceans in a human high-use area: Trends in harbour por-poise abundance in the North Sea over two decades. Frontiers in Marine Science. Frontiers in Marine Science 7:606609. doi: 10.3389/fmars.2020.606609

Peschko, V., Ronnenberg, K., Siebert, U., and Gilles, A. (2016). Trends of harbour porpoise (Phocoena phocoena) density in the southern North Sea. Ecol. Indic. 60, 174–183. doi: 10.1016/j.ecolind.2015.06.030

Scheidat, M., Verdaat, H., Aarts, G. (2012). Using aerial surveys to estimate density and distribution of harbour porpoises in Dutch waters. J. Sea Res. 69, 1–7. doi: 10.1016/j.seares.2011.12.004

Virgili A., Authier, M., Dars, C., Dorémus, G., Laran, S.,Van Canneyt, O, Spitz, J. (2018). Levée des risques pour l’appel d’offres éolien au large de Dunkerque par observation aérienne. Programme DUNKRISK – Campagne LEDKOA. Rapport d’analyses. Observatoire Pelagis / Agence Française pour la Biodiversité. 49 pp + annexes (available on request from

Waggitt, J.J., Evans, P.G.H. , Andrade, J., Banks, A., Boisseau, O., Bolton, M., Brad-bury, G., Brereton, T.; Camphuysen, K.C.J.; Durinck, J.; Felce, T.; Fijn, R.C., Garcia-Baron, I.,Garthe, S., Geelhoed, S.C.V., Gilles, A., Goodall, M., Haelters, J., Hamilton, S., Hartny-Mills, L., Hodgins, N., Jessopp, M., Kavanagh, A.S., Le-opold, M.,  Lohrengel, K., Louzao, M., Markones, N.,  Martinez-Cadiera, J.,  O’Cadhla, O.,  Perry, S.L., Pierce, G.J., Ridoux, V., Robinson, K., Santos, B., Saavedra, C., Skov, H., Stienan E.W.M., Sveegaard, S., Thompson, P., Vaner-man, N., Wall, D., Webb, A., Wilson, J., Wanless, S., Hiddink J.G. (2020). Distribution maps of cetacean and seabird populations in the North-East Atlantic. Journal of Applied Ecology 57: 253-269. DOI: 10.1111/1365-2664.13525


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