Publication Abstract

Recent studies on the crawfish Palinurus elephas in South Wales and Cornwall

E. Hunter, S.E. Shackley and D.B.Bennett

From May 1993 until January 1994, 788 male and 1604 female crawfish, Palinurus elephas in total, were examined from the South Wales and Cornish fisheries. Mean carapace length (CL) of Cornish crawfish was 125.6 mm for males, 132.4 mm for females and 1350 mm for berried females, while mean CL for Welsh crawfish was 155.8 mm for males, 138.7 mm for females and 1386 mm for berried females. The overall size distribution of male Welsh crawfish differed significantly from that observed in the Cornish population. An analysis of variance gave significant (P<0.05) differences for the factors; Site, Sex and the Sex/Site and Month/Sex interactions. Male crawfish reached greater overall size than female crawfish, but for specimens of equal CL, total lengths (TL) of females were longer than those of males. Males were heavier than females of equal CL or TL.

Females bearing spermatophores were retrieved between August and October. The first freshly berried females were observed in August, with 90% of Cornish females in berry by January. Incubation time was 8-9 months. The smallest berried female measured 90 mm CL. Dissection of 40 females measuring 79-137 mm revealed ovaries typical of those of other palinurids. Only two immature specimens were observed, both measuring 79 mm CL. Six stages of ovarian development were distinguished. Dissection of 20 male crawfish measuring 89-169 mm CL also revealed testes similar to those of other palinurids, and no immature specimens were observed.

Peak moulting was recorded in September for both male and female crawfish from both fisheries. Moult condition was recorded in conjunction with fouling level. Female crawfish outnumbered males in both Cornish and Welsh landings throughout the season at a ratio of ~2:1. A record was also maintained of the occurrence of three distinct colour morphs, normal, sandy and brown. In the laboratory, brittlestars and mussels were eaten more readily than fish. These results are discussed in relation to previous findings and relative to changes in fishing methods employed in the crawfish fishery over the past 30 years.

Reference:

E. Hunter, S.E. Shackley and D.B.Bennett, 1996. Recent studies on the crawfish Palinurus elephas in South Wales and Cornwall. Journal of the Marine Biological Association of the UK, 76: 963-984.