High Post-Capture Survival for Sharks, Rays and Chimaeras Discarded in the Main Shark Fishery of Australia?

Most sharks, rays and chimaeras (chondrichthyans) taken in commercial fisheries are discarded (i.e. returned to the ocean either dead or alive). Quantifying the post-capture survival (PCS) of discarded species is therefore essential for the improved management and conservation of this group. For all chondrichthyans taken in the main shark fishery of Australia, we quantified the immediate PCS of individuals reaching the deck of commercial shark gillnet fishing vessels and applied a risk-based method to semi-quantitatively determine delayed and total PCS. Estimates of immediate, delayed and total PCS were consistent, being very high for the most commonly discarded species (Port Jackson shark, Australian swellshark, and spikey dogfish) and low for the most important commercial species (gummy and school sharks). Increasing gillnet soak time or water temperature significantly decreased PCS. Chondrichthyans with bottom-dwelling habits had the highest PCS whereas those with pelagic habits had the lowest PCS. The risk-based approach can be easily implemented as a standard practice of on-board observing programs, providing a convenient first-step assessment of the PCS of all species taken in commercial fisheries

Distribution and diet of juvenile Patagonian toothfish on the South Georgia and Shag Rocks shelves (Southern Ocean)

The distribution and diet of juvenile (<750 mm) Patagonian toothfish are described from 4 annual trawl surveys (2003-06) around the island of South Georgia in the Atlantic sector of the Southern Ocean. Recruitment of toothfish varies inter-annually, and a single large cohort dominated during the four years surveyed. Most juveniles were caught on the Shag Rocks shelf to the NW of South Georgia, with fish subsequently dispersing to deeper water around both the South Georgia and Shag Rocks shelves. Mean size of juvenile toothfish increased with depth of capture. Stomach contents analysis was conducted on 795 fish that contained food remains and revealed that juvenile toothfish are essentially piscivorous, with the diet dominated by notothenid fish. The yellow-finned notothen, Patagonotothen guntheri, was the dominant prey at Shag Rocks whilst at South Georgia, where P. guntheri is absent, the dominant prey were Antarctic krill and notothenid fish. The diet changed with size, with an increase in myctophid fish and krill as toothfish grow and disperse. The size of prey also increased with fish size, with a greater range of prey sizes consumed by larger fish

Effects of temperature on the rate of embryonic development of cephalopods in the light of thermal time applied to aquaculture

The temporal description of the embryonic development in ectothermic animals and the speed of development depends on environmental temperature. The concept of thermal time helps in solving this problem by making it possible to define a linear model of development linking developmental rate and temperature. The model has been scarcely applied to cephalopods in spite of being useful for programming embryonic development and hatching events. The potential application of the linear model of development would have particular interest in the case of emerging species for aquaculture such as Octopus vulgaris or Sepia officinalis. Therefore, the main goal of this work is to review the effect of temperature on the rate of embryonic development in cephalopods in relation to the linear model of development and to discuss its potential applications and limitations to cephalopod aquaculture. As a result, a good fitting of the model has been proven not only for the total time of development, but also for the time of the organogenesis phase, in nine species of cephalopods. Usually, threshold temperatures for different developmental phases, pre-organogenesis, organogenesis and growth, are the same. In addition, the potential use of anisothermic protocols for egg incubation, as well as the problems connected with the asynchronicity of egg laying within a single spawning are also discussed. In consequence, the linear model of development seems to be useful for basic and applied research on cephalopod embryonic development and particularly for the advancement of cephalopod aquaculture