Sayer, CD; Copp, GH; Emson, D; Godard, MJ; Zieba, G; Wesley, KJ; (2010) The decline of crucian carp Carassius carassius in its native English range: the example of rural ponds in north Norfolk. (ECRC Research Report 139 ). Environmental Change Research Centre: London, UK.

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Abstract

Small agricultural ponds are important sites for the conservation of freshwater biodiversity, including native fish such as the crucian carp Carassius carassius L., a cryptic, benthic species that is thought to have undergone a significant decline in England over recent decades. To assess the extent and causes of its decline, we focused on a discrete region of north Norfolk, in the heart of the species native range in England (UK). The study area included 29 ponds, 24 of which, were known (from interviews with local anglers and land owners) to have previously contained crucian carp in the 1970s–80s. Fish surveys revealed crucian carp to be present in just six of these ponds representing a 75% decline in its distribution over the last 20–30 years. Non-native carp species or their hybrids with crucian carp were observed in six of the 29 ponds, with common carp Cyprinus carpio L., goldfish Carassius auratus L., crucian carp × goldfish and crucian carp × common carp hybrids occurring in one, two, two and five ponds respectively. Causes of crucian carp extinction were determined for 16 of the ponds: desiccation during the droughts of 1976 (2 ponds) and 1988–1992 (4 ponds); terrestrialisation leading to a virtual loss of open water and/or to deteriorating habitat (5 ponds); hybridisation and/or competition with common carp (3 ponds); infilling for agricultural land reclamation (two ponds) and predation following introduction of pike Esox lucius L. (1 pond). The results of this study have led to the designation of crucian carp as a Biodiversity Action Plan (BAP) species in the county of Norfolk; a major advance in the conservation of this much overlooked species in the UK. This is aimed at halting the decline of crucian carp through conservation measures to protect and/or rehabilitate ponds that contain or used to contain crucian carp populations via collaborative efforts with landowners, anglers and the general public.

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