Stock identification of sword prawn Parapenaeopsis hardwickii in the East China Sea and Taiwan Strait inferred by morphometric variation

ABSTRACT:   Morphometric differences were used to elucidate the stock structure of sword prawn Parapenaeopsis hardwickii in the East China Sea and Taiwan Strait. Six samples were collected separately from the north of the East China Sea (NECS-02) and waters off Tamsui (Tamsui-10), Taichung (Taichung-11 and Taichung-02), Putai (Putai-02) and Cheding (Cheding-02). Eleven measurements made for each individual were size-standardized by allometric methods and the resulting measurements were analyzed by cluster analysis and canonical variate analysis (CVA). Randomization tests were used to test the morphometric variation between groups derived from cluster analysis and CVA. The results of cluster analysis and CVA indicated that the six samples were clustered into three groups: the first group included the NECS-02 sample; the second included the Tamsui-10 and Taichung-11 samples; and the third included the Taichung-02, Putai-02 and Cheding-02 samples. Randomization tests showed that morphometric differences among the three groups were significant. Animals with the same morphometric measurements are often assumed to constitute a stock, so there appear to be at least three morphologically distinguishable stocks of this species in the East China Sea and Taiwan Strait. The first stock is in the north of the East China Sea, the second is in the waters adjacent to Tamsui and Taichung, and the third is in the waters adjacent to Cheding, Putai and Taichung.     

Distribution of albacore (Thunnus alalunga) in the Indian Ocean and its relation to environmental factors

The distribution pattern of albacore, Thunnus alalunga, in the Indian Ocean was analyzed based on catch data from the Taiwanese tuna longline fishery during the period 1979–85. The Taiwanese tuna fishery began operating in the Indian Ocean in 1967. We used a geographic information system to compile a fishery and environmental database and statistically explored the catch per unit effort (CPUE) distribution of albacore. Our results indicated that immature albacore were mainly distributed in areas south of 30°S although some displayed a north–south seasonal migration. Mature albacore, which were mainly concentrated between 10°S and 25°S, also showed a north–south migration. Within 10°S and 30°S, the separation of mature, spawning, and immature albacore life history stages roughly coincided with the boundaries of the three oceanic current systems in the Indian Ocean. The optimal environmental variables for CPUE prediction by stepwise discriminant analysis differed among life history stages. For immature albacore, the sea surface variables sea surface temperature (SST), chlorophyll concentration and surface salinity were significant. For mature albacore, SST was significant, while for spawning albacore, the sub‐surface variables temperature at 100 m and oxygen at 200 m were significant. Spawning albacore evidently prefer deep oceanographic conditions. Our results on the oceanographic conditions preferred by different developmental stages of albacore in the Indian Ocean were compatible with previous studies found in the Pacific Ocean.     

American eel, Anguilla rostrata, growth in fresh and salt water: implications for conservation and aquaculture

Abstract  Growth of American eels, Anguilla rostrata (Lesueur), sampled in saltwater bays and adjacent freshwater ponds in the southern Gulf of St. Lawrence, Canada, was estimated by otolith annulus back-calculation, and related to salinity of growth habitat as determined using otolith strontium:calcium ratios. Eels resident in salt water grew on average in length 2.2 times faster than freshwater residents and increased in weight 5.3 times faster than freshwater residents. Previous findings of superior American eel growth rate in brackish water are thus extended to full-strength salt water. Freshwater residents took an estimated 2.4 times longer than saltwater residents to reach the silver eel stage. The extended time to maturation of eels reared in fresh water increases their vulnerability to fisheries and to bio-accumulation of contaminants. Freshwater eel populations should be managed more conservatively than those in saline waters. The increase in eel growth with salinity suggests that rearing in brackish or salt water could improve growth rates in eel aquaculture.