The Biology ofCrangon VulgarisL. in the Bristol Channel and Severn Estuary

Abstract

Collections of some 22,000 female and 6000 male Crangon vulgaris were made throughout the year from the shrimp fisheries of the Severn Estuary and Bristol Channel. All animals were measured.The habits of the species are described; it can withstand a wide range of temperature but, though euryhaline, resembles other Decapoda in the inability to withstand low salinity combined with low temperature.Osmo-regulation is apparently largely inhibited at low temperatures and to a greater extent in the males than the females.Growth rate decreases with increasing age; in the female there is no increase in length when moulting from the ' neuter' to the egg-carrying intermoult. The duration of this intermoult, if spawning is successful, is about double that of the normal intermoult under the same temperature conditions. Growth almost ceases in the winter.Secondary sexual characters are described, especially the differences between the endopodites of the pleopods in the two sexes.Females become mature at a minimum length of 45 mm. in the Channel and seldom less than 50 mm. in the Estuary. The effect of the female sexual cycle on the size of the ovary and the form of the pleopods is described. The process of copulation is described; it can occur in the brackish waters of the estuary. Egg-laying always follows within two days of moulting into the egg-carrying condition but eggs are not retained if copulation has not occurred.The females lie on their sides during the act of spawning and the eggs are firmly attached within thirty minutes to the egg-carrying setae on the basipodites of the first to fourth pair of pleopods, then to those on the endopodite of the first pleopod, finally to those on the coxopodites of the last two pairs of pereiopods.

Sex-ratio, seasonality and long-term variation in maturation and spawning of the brown shrimp Crangon crangon (L.) in the German Bight (North Sea)

“…Two reasonably discrete spawning periods within the annual breeding season had been reported to occur in C. crangon (Lloyd andYonge 1947 andHenderson andHolmes 1987 for the Bristol Channel, Meredith 1952 for the Liverpool Bay) with some latitudinal modifications (Kuipers and Dapper 1984). Indications for two broods (winter and summer) were also found by Oh and Hartnoll (2004) in the Irish Sea.…”

The biology of the common prawn,Leander serratusPennant

“…However, since the males were found to penetrate well into the estuaries during the summer (1950), it appears that they tended to leave them in the autumn before the females. Lloyd & Yonge (1947) found that Crangon vulgaris behaved in much the same way, and showed that the males were more susceptible to combined low temperature and salinity (i.e. winter conditions) than the females.…”

“…Prawn trawling usually started near Saltash and moved downstream to Torpoint, West Muds and Drake's Island, finishing in Jennycliff Bay and inside the Breakwater. Thus there would appear to be, as the fishermen believe, a migration of the prawns away from estuarine conditions; this would be expected from the wellestablished fact that tolerance of low salinity decreases markedly with temperature in most decapods (Lloyd & Yonge, 1947). Several trawls were made in the Hamoaze during winter with, as might be expected, negative results, but there was always the possibility that the prawns managed to hide away in places inaccessible to the trawl.…”

Feeding ecology of the sand shrimpCrangon hakodateiRathbun, 1902 (Decapoda: Crangonidae) in the East Sea of Korea

“…Stomach fullness is affected by both extrinsic (season) and intrinsic (sex) factors (Lloyd & Yonge 1947;Meredith 1952;Henderson & Holmes 1987). In this study, males had lower values for stomach fullness, food quality indices, and evenness than females.…”

“…A number of studies have investigated the feeding behavior of crangonid shrimp including C. affinis by Kosaka (1970) and Hong and Oh (1989); C. allmani by Allen (1960); C. crangon by Lloyd and Yonge (1947); Tiews (1970), and Oh et al (2001); C. franciscorum and C. nigricauda by Wahle (1985); C. septemspinosa by Price (1962) and Wilcox and Jeffries (1974); and C. uritai by Nakaya et al (2004). However, despite its ecological and economic importance, there is no information on the diet of C. hakodatei.…”