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

Abstract

Aspects of the reproductive and maturation biology of the brown shrimp Crangon crangon (L.) were studied in various subareas of the German Bight (North Sea). The size-specific sex ratio of C. crangon was examined based on length frequency distribution data. The sex ratio for the smallest size groups at which sex was determined was typically around 0.5, indicating an even ratio between males and females. The proportion of females decreased in the 30-45 mm size range. In length classes larger than 50 mm, the proportion of females constantly increases to 100% at around 60 mm total length. We concluded that sex reversal from male to female may not occur in C. crangon. Size at sexual maturity was determined from the proportion of ovigerous females. Size at maturity (L 50 ) was estimated as 55.4 and 62.0 mm total length for spring and winter data, respectively. The seasonal spawning cycle was studied over the period . Between mid February and late June and for size classes larger than 65 mm ovigerous shrimps exceeded 80% and reached up to 100% of the females in the population. This period can be seen as the core spawning season. From early August to early December the proportion of ovigerous shrimps in the female population is very low. Interannual differences in the seasonal process are obvious with a dramatic decline in C. crangon reproductive success in the late 1980s. Various options are discussed for the reasons of the decline and recovery of the reproductive performance.

Estructura de tallas, talla media de madurez sexual y razón sexual de camarones de aguas profundas de importancia comercial en el Caribe colombiano

“…Además, las hembras presentan una alta tasa de crecimiento y la mortalidad natural es mayor en los machos que en las hembras (Papaconstantinou & Kapiris, 2003). La explicación de la relación de la razón sexual con la talla puede responder a las diferencias sexuales en el crecimiento, a la mortalidad o a la migración (Siegel, et al, 2008). De hecho, las diferencias en la mortalidad natural entre los sexos es un factor que contribuye potencialmente a la desigualdad de la razón sexual (Wenner, 1972).…”

“…En este sentido, si las tasas de crecimiento y mortalidad de machos y hembras fueran las mismas, la razón sexual debería permanecer constante; por el contrario, para que haya aumentos y reducciones en ciertas clases de talla debe haber diferencias en las distribuciones de frecuencia de talla entre hembras y machos con altas tasas de crecimiento en un sexo comparado con el otro. Por lo tanto, el patrón de la razón sexual es un resultado de los efectos mezclados de las diferencias en la tasa de crecimiento entre machos y hembras, de las tasas de mortalidad y de la composición de las edades (Siegel, et al, 2008).…”

Seasonal variations in larval biomass and biochemical composition of brown shrimp, Crangon crangon (Decapoda, Caridea), at hatching

“…High larval carbon content during late winter may improve the tolerance of fasting, when poor nutritional conditions coincide with prolonged duration of larval development at cold temperatures (Criales and Anger 1986;Paschke et al 2004;Daewel et al 2011). Hence, the production of larger ''winter larvae'' seems to be an adaptive reproductive trait of C. crangon, allowing for an extension of the period of reproduction (Siegel et al 2008;Urzúa et al 2012), which is in most other decapod crustaceans in temperate regions restricted to late spring and summer (Anger 2001). At higher temperatures and planktonic food concentration, during late spring and summer (Wiltshire et al 2008), smaller shrimp larvae hatch in the southern North Sea.…”

“…This species is very common and abundant in the shallow areas of the German Bight (Siegel et al 2008), plays an important role in the energy transfer within marine food webs (Pihl and Rosenberg 1984;Campos et al 2009) and sustains an important fishery with annual captures exceeding 35,000 tons (ICES 2010). The complex life cycle of C. crangon comprises a benthic juvenile-adult and a pelagic larval phase (Tiews 1970;Hufnagl and Temming 2011), which are tightly linked (Daewel et al 2011;Viegas et al 2012).…”

Shell disease in Crangon crangon (Linnaeus, 1758): The interaction of temperature and stress response

“…Shell disease can also be lethal due to secondary invading pathogens into the epidermis and underlying tissues causing sepsis of the host or impairments of locomotion and feeding functions (Dyrynda, 1998;Hoenig et al, 2017;Smolowitz et al, 1992). In all ectothermic organisms such as C. crangon, temperature determines and interacts with embryogenesis, growth, molting frequencies and also the reproduction and survival (Caudri, 1939;Hufnagl and Temming, 2011a;Lloyd and Yonge, 1947;Siegel et al, 2008;Tiews, 1954). Hence, increasing water temperatures can result in physiological stress and therefore decreased defense mechanisms, which in turn lead to more susceptibility to shell disease as has been shown in the American lobster (Homarus americanus) (Dove et al, 2005;Glenn and Pugh, 2006;Tlusty et al, 2007).…”