Inter-cohort growth patterns of pharaoh cuttlefish Sepia pharaonis (Sepioidea: Sepiidae) in Eastern Arabian Sea.

Sepia pharaonis is an important commercial species endemic to the tropical Indo-Pacific region. Despite its commercial significance, only few information on natural populations is available. This study was aimed to describe the aspects of size-composition, length-weight relationship, catch rates, seasonal recruitment and inter-cohort growth patterns of S. pharaonis population (Clade C), distributed along the Eastern Arabian Sea (South-West coast of India). For this, the Dorsal Mantle Length (DML) and weight of cuttlefishes was obtained from commercial trawl catches, from April 2002 to October 2006. Data was analyzed by normal length-weight methods such as von Bertalanffy. A total of 12454 cuttlefishes, ranging in length from four to 41cm were analyzed. Size-composition patterns discriminated two pulses in recruitment to the fishery, discernible by a decrease in the monthly mean size of the population. The DMLs of the two seasonal cohorts were subjected to modal-progression analysis using the Bhattacharya's method for the estimation of growth. The estimated parameters Linfinity and K in von Bertalanffy Growth Function (VBGF) were used to model growth curves in length for the cohorts. The first cohort, (post-monsoon cohort) which supports the major fishery, was composed of medium-sized, fast growing individuals, whereas the second cohort (pre-monsoon cohort), comprised of slow growing and large-sized individuals. There were differential growth characteristics between the sexes and the life span was estimated at less than 2.3 years for males and 2.1 years for females. Negative allometric growth in weight (W) with length (L) was observed for males (W=0.33069.L2.5389) and females (W=0.32542.L26057). The females were heavier compared to males at any given mantle length, and the males were found to attain larger ultimate lengths. The major fishing season for cuttlefish was from May to November, when higher monthly catch rates of 1.67-13.02kg/h were observed in comparison with 0.03-0.85kg/h in December-April. Seasonal catch rates indicated a migratory life cycle ofS. pharaonis between offshore and inshore coastal zones.

Inter-cohort growth patterns of pharaoh cuttlefish Sepia pharaonis (Sepioidea: Sepiidae) in Eastern Arabian Sea

Sepia pharaonis is an important commercial species endemic to the tropical Indo-Pacific region. Despite its commercial significance, only few information on natural populations is available. This study was aimed to describe the aspects of size-composition, length-weight relationship, catch rates, seasonal recruitment and inter-cohort growth patterns of S. pharaonis population (Clade C), distributed along the Eastern Arabian Sea (South-West coast of India). For this, the Dorsal Mantle Length (DML) and weight of cuttlefishes was obtained from commercial trawl catches, from April 2002 to October 2006. Data was analyzed by normal length-weight methods such as von Bertalanffy. A total of 12 454 cuttlefishes, ranging in length from four to 41cm were analyzed. Size-composition patterns discriminated two pulses in recruitment to the fishery, discernible by a decrease in the monthly mean size of the population. The DMLs of the two seasonal cohorts were subjected to modalprogression analysis using the Bhattacharya’s method for the estimation of growth. The estimated parameters L∞ and K in von Bertalanffy Growth Function (VBGF) were used to model growth curves in length for the cohorts. The first cohort, (post-monsoon cohort) which supports the major fishery, was composed of mediumsized, fast growing individuals, whereas the second cohort (pre-monsoon cohort), comprised of slow growing and large-sized individuals. There were differential growth characteristics between the sexes and the life span was estimated at less than 2.3years for males and 2.1years for females. Negative allometric growth in weight (W) with length (L) was observed for males (W=0.33069.L2.5389) and females (W=0.32542.L2.6057). The females were heavier compared to males at any given mantle length, and the males were found to attain larger ultimate lengths. The major fishing season for cuttlefish was from May to November, when higher monthly catch rates of 1.67-13.02kg/h were observed in comparison with 0.03-0.85kg/h in December-April. Seasonal catch rates indicated a migratory life cycle of S. pharaonis between offshore and inshore coastal zones.

Sepia pharaonis es una importante especie endémica comercial del trópico Indo-Pacífico. A pesar de su valor comercial, hay muy poca información de sus poblaciones naturales disponible. En este estudio se describen aspectos como composición de tallas, relación longitud-peso, tasas de captura, reclutamiento estacional y patrones de crecimiento entre cohortes de la población (Clado C), distribuidos a lo largo del Mar Arábigo del Este (costa Suroeste de India). Se obtuvo la Longitud del Manto Dorsal (LMD) y el peso de las capturas de los arrastres comerciales, de Abril 2002 a Octubre 2006. Los datos fueron analizados mediante FiSAT y von Bertalanffy. Se capturó un total de 12 454 sepias, con una longitud entre 4-41cm. Los patrones de composición de tallas discriminaron dos pulsos en el reclutamiento de la pesquería, perceptibles por una disminución en el tamaño promedio mensual de la población. Los LMD de las dos cohortes estacionales se sometieron a un análisis de progresión modal mediante el método de Bhattacharya para la estimación del crecimiento. La primera cohorte (después de los monzones) mantiene la principal pesquería, se compone de individuos medianos de rápido crecimiento, mientras que el segundo grupo (pre-monzón) está compuesto por individuos de crecimiento lento y de gran tamaño. Se encontraron diferencias en las características de crecimiento entre sexos y la duración de vida útil se estima en menos de 2.3 años para machos y 2.1 años para hembras. Se observó crecimiento alométrico negativo entre el peso (W) y la longitud (L) para machos (W=0.33069. L2.5389) y hembras (W=0.32542.L2.6057). Las hembras fueron más pesadas en comparación con los machos en cualquier longitud de manto. La temporada de pesca más importante fue de mayo a noviembre, cuando se tuvieron las tasas de captura mensual más altas, de 1.67-13.02kg/h en comparación con 0.03-0.85kg/h entre diciembre y abril. Las tasas de captura estacional indican un ciclo de vida migratorio de S. pharaonis entre las zonas marinas y costeras de las áreas someras.