Immediate effect of intertidal non-mechanised cockle harvesting on macrobenthic communities: a comparative study


  • Francisco Miguel Sousa Leitão Instituto Nacional de Investigação Agrária e das Pescas (INIAP/IPIMAR)
  • Miguel Baptista Gaspar Instituto Nacional de Investigação Agrária e das Pescas (INIAP/IPIMAR)



Cerastoderma edule, cockle, fishing effect, hand dredging, harvesting knife, Ria Formosa


In Ria Formosa cockles (Cerastoderma edule) have traditionally been harvested with a harvesting-knife (HK). However, over the last six years there has been an increase in the use of a hand-dredge (HD) to exploit cockle beds. A comparative study on the impact of these harvesting methods on the benthic macrofauna was undertaken with the aim of evaluating the possible introduction of the hand-dredge in the fishery. Macrofaunal mortality was very low regardless of the gear. However, the total mortality resulting from using the HK was superior to the one observed for the HD. For the same fishing time the hand-dredge covers an area approximately five times greater that the one covered by the knife, with the former yielding 5 times the catch of the latter. Consequently, the use of hand-dredges increases the fishing effort, which may lead to the overexploitation of the cockle populations. Our results revealed that the immediate effect of both gears on macrobenthic communities was similar and minimal. Therefore, we believe that introducing the hand-dredge in the cockle fishery should only be authorised if other management measures, such as daily quotas, closed areas and limiting the number of fishing licenses, are implemented.


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Agardy, T. – 2000. Effects of fisheries on marine ecosystems: a conservationist’s perspective. ICES J. Mar. Sci., 57(Suppl. 3): 761-765

Beukema, J.J. – 1995. The long-term effects of mechanical harvesting of lugworms on the zoo-benthos community of a tidal flat in the Wadden Sea. Neth. J. Sea Res., 33(Suppl. 2): 219-227

Clarke, K.R. and R.N. Gorley. – 2001. PRIMER (Plymouth Routines In Multivariate Ecological Research) v5: User Manual/Tutorial. PRIMER-E Ltd, Plymouth

Clarke, K.R. and R.M. Warwick. – 1994. Change in marine communities: An approach to statistical analysis and interpretation. Natural Environment Research Council, Plymouth Marine Laboratory, Plymouth

Dayton, P.K., S.F. Thrush, T. Agardy, and R.J Hoffman. – 1995. Viewpoint: Environmental effects of marine fishing. Aquat. Conserv. Mar. Freshw. Ecosyst., 5: 205-232

De Alteris, J., L. Skrobe and C. Lipsky. – 1999. The significance of seabed disturbance by mobile fishing gear relative to natural processes: a case study in Narragansett Bay. In: L. Benaka, (eds.), Fish Habitat: Essential Fish Habitat and Rehabilitation, pp. 224-237. American Fisheries Society, Symposium 22, Bethesda, MD

Eleftheriou, A. and R. Robertson. – 1992. The effect of experimental scallop dredging on the fauna and physical environment of shallow sandy community. Neth. J. Sea Res., 30: 289-299

Ferns, P.N., D.M. Rostron and S.H.Y. Siman. – 2000. Effects of mechanical cockle harvesting on intertidal communities. J. Appl. Ecol., 37: 464-474

Gaspar, M.B., M.D. Dias., A. Campos., C.C. Monteiro., M.N. Santos., A. Chicharo and L. Chicharo. – 2001. The influence of dredge design on the catch of Callista chione (L. 1758). Hydrobiologia., 465: 153-167

Gaspar, M.B., F. Leitão., L. Chicharo., M.N. Santos and C.C. Monteiro. – 2003. A comparison of direct mortality inflicted on macrofaunal organisms by three types of dredges used in the Portuguese clam fishery. ICES J. Mar. Sci., 60: 733-742

Gaspar, M.B and C.C. Monteiro. – 1999. Indirect mortality caused to juveniles of Spisula Solida due to deck exposure. J. Mar. Biol. Ass. UK., 79: 567-568

Gislason, H. – 2003. The effect of fishing on non-target species and ecosystem structure and function. In: M. Sinclair and G. Valdimarsson (eds), Responsible fisheries in the marine ecosystem, pp. 255-274. Rome, Italy and Wallingford, UK

Goñi, R. – 1998. Ecosystem effects of marine fisheries: an overview. Ocean. Coast. Manage., 40: 37-64

Graça, C.M.B.R. – 2001. Contribuição para o estudo do crescimento e reprodução de Ruditapes decussatus (Linnaeus, 1758) e Cerastoderma edule (Linnaeus, 1758) na Ria Formosa. Ph. D. thesis, Univ. do Algarve

Hall, S.J., D.J. Basford and M.R. Robertson. – 1990. The impact of hydraulic dredging for razor clams Ensis sp. on an infauna community. Neth. J. Sea Res., 27: 119-125

Hall, S.J and M.J.C. Harding. – 1997. Physical disturbance and marine benthic communities: The effects of mechanical harvesting of cockles on non-target benthic infauna. J. Appl. Ecol., 34: 497–517

Hall, S.J., M.R. Robertson., D.J. Basford and R. Fryer. – 1993. Pitdigging by the crab Cancer pagurus: a test for long-term, large scale effects on infauna community structure. J. Anim. Ecol., 62: 59–66

Hiddink, J.G. – 2003. Effects of suction-dredging for cockles on non-target fauna in the Wadden Sea. J. Sea Res., 50: 315-323

Kaiser, M.J., D.B. Edwards., P.J. Armstrong., K. Radford., N.E.L. Lough., R.P. Flat and H.D. Jones. – 1998. Changes in megafauna benthic communities in different habitats after trawling disturbance. ICES J. Mar. Sci., 55: 353-361

Kaiser, M.J., G. Broad and S.J. Hall. – 2001. Disturbance of intertidal soft-sediment benthic communities by cockle hand raking. J. Sea Res., 45: 119-130

Kristensen, I. – 1957. Differences in density and growth in a cockle population in the Dutch Wadden Sea. Arch. Néerl. Zool., 12 (suppl. 3): 351-453

Leitão, F.M.S. – 2004. Estudo comparativo da mortalidade inducida pela faca de mariscar e draga de mão na comunidade macrobentónica associada aos bancos de pesca do berbigão (Cerastoderma edule, L. 1758). MSc thesis, Univ. de Coimbra

Lindeboom H.J and S.J. De Groot. – 1998. The effects of different types of fisheries on the North Sea and Irish Sea benthic ecosystems. NIOZ-Rapport 1998-1RIVO DLO report65 c003/98, 404 pp

Moore, J. – 1991. Studies on the impact of hydraulic cockle dredging on intertidal sediment flat communities. A report to the Nature Conservancy Council from the Field Studies. FSC/RC/4/91. Council Research Centre, Pembroke, Wales. Philippart, C.J.M. – 1998. Long-term impact of bottom fisheries on several by-catch species of demersal benthic fish and benthic invertebrates in the South-eastern North Sea. ICES J. Mar. Sci., 55: 342-352

Piersma, T., A. Koolhaas., A. Dekinga., J. Beukema., R. Dekker and K. Essink. – 2001. Long-term indirect effects of mechanical cockle-dredging on intertidal bivalve stocks in the Wadden Sea. J. Appl. Ecol., 38 (suppl. 5): 976-990

Rees, E.I.S. – 1996. Environmental effects of mechanized cockle fisheries: a review of research data. Report to the Marine Environmental Protection Division, MAFF. Scholl of Ocean Sciences, University of Wales, Bangor, UK

Rostron, D. – 1993. The effects of tractor towed cockle dredging on the invertebrate fauna of LLanrhidian Sands, Burry inlet. Subsea survey. Report Countryside Council for Wales

Rostron, D. – 1995. The effects of mechanised cockle harvesting on the invertebrate fauna of LLanrhidian Sands. Burry Inlet and Loughor Estuary Symposium, 111-117

Ruano, F.D.L. – 1997. Fisheries and farming of important marine bivalves in Portugal. NOAA Techical Report NMSF., 129: 191-200

Seed, R and A.R. Brown. – 1978. Growth as a strategy for survival in two marine bivalves, Cerastoderma edule and Modiolus modiolus. J. Anim. Ecol., 47: 283-292

Spencer, B.E. – 1996. Clam cultivation: localised environmental effects. Results of an experiment in the River Exe, Devon (1991-1995). Report Prepared for Directorate of Fisheries Research, Fisheries Laboratory, Conwy

Spencer, B.E., M.J. Kaiser and D.B. Edwards. – 1998. Intertidal clam harvesting: benthic community change and recovery. Aquac. Res., 29(suppl. 6): 429-437

Sprung, M. 1994. – Macrobenthic secondary production in the intertidal zone of the Ria Formosa – a lagoon in southern Portugal. Est. Coast. Shelf. Sci., 38: 539-558

Sprung, M and M. Machado. – 2000. Distinct life histories of peracarid crustaceans in a Ria Formosa salt marsh (S. Portugal). Wetlands Ecol. Manag., 8: 105-115

Zar, J.H. – 1996. Biostatistical analisys. Prentice-Hall International Inc, New Jersey.




How to Cite

Sousa Leitão FM, Baptista Gaspar M. Immediate effect of intertidal non-mechanised cockle harvesting on macrobenthic communities: a comparative study. scimar [Internet]. 2007Dec.31 [cited 2023Jan.28];71(4):723-3. Available from:




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