Age and growth of the blue shark (Prionace glauca) in the northeast Atlantic Ocean

.Abstract: In the Atlantic Ocean, several pelagic elasmobranch species are commonly caught as bycatch in pelagic longline fisheries targeting mainly swordfish and tunas. The natural mortality rates of these species are usually low, so increased fishing mortality may have severe consequences for their populations, with declines occurring even at relatively low levels of fishing mortality. In recent years, elasmobranch fishes have become relatively important fisheries resources, with a substantial increase in fishing effort worldwide coupled with game fishing and an increased commercial interest for shark products, particularly for the fins that are exported to the oriental markets. Furthermore, sharks are particularly vulnerable to fishing mortality and therefore this increased by-catch is a major cause of concern to several pelagic species. Most elasmobranch fishes are predators at, or near, the top of the marine food chains. These animals are thus extremely important for the entire ecosystems balance, by regulating not only their direct main preys, but also second and third degree non-prey species through trophic linkages. The effect of the removal of such predators from the marine ecosystems is difficult to predict, but may be ecologically and economically significant, and may persist over long time periods or without former natural population recovery. Even though there are fisheries directly targeting elasmobranchs there is still limited information about these fishes’ life cycles and biological parameters. The highly migratory nature of the oceanic pelagic species poses particular difficulties for fisheries management and conservation issues, and it has been estimated that some populations may have already declined by 80% over recent decades. Those values have to some extent been challenged and may be overestimated, but still there is currently scientific consensus that elasmobranch species are extremely vulnerable to fishing pressure, with overexploitation occurring even at relatively low levels of fishing mortality. Prionace glauca (blue shark) is a pelagic shark species commonly caught as by-catch in commercial fisheries that operate in the North and South Atlantic. Some previous studies have been carried about the fisheries biology of this species, but still there are significant uncertainties in some of the biological parameters of this species. The study will focus in the dynamics of growth and biology aspects of P. glauca caught in longline fisheries, in particular in their life history parameters, such age and growth, in order to produce growth models, which can ultimately contribute for stock assessment studies on this species. For conservation purposes, a precautionary approach to managing sharks stocks are now in more needed than ever; therefore this study aims to gather more information to accomplish a wiser and more sustainable utilization of this species as a natural resource. The study will be based in vertebrae analysis of samples being obtained by IPMA, I.P. observers on board Portuguese commercial longline vessels targeting swordfish in the North Atlantic Ocean, in which the most commonly captured species as by-catch is the blue shark (Prionace glauca).

ISCED Categories

The highlighted icons, represent the fields of education (in compliance with ISCED Classification) engaged during this course/programme.

0511 - Biology", "0521 - Ecology", "0831 - Fisheries