Population dynamics of fisheries resources
The population dynamics of resources is one of the most important topics in fisheries science. In particular, stock assessments provide information about the abundance at sea of resources over time and space, which are of primary importance for management purposes. These assessments also provide information on the mortality due to fishing activity. Some relatively complex assessment methods and classic ecology approach can allow to evaluate also the role, in the dynamic of a specific stock, exerted by interactions with other species and environmental factors.
The methods employed in stock assessments are indirect or direct. Population dynamics methods belong to the former group and require, as input data, the amount caught by the fishing fleet. The latter group includes all surveys carried out directly at sea; these can be based, for example, on acoustics technology or experimental fishing activity. For both indirect and direct methods, a demographic perspective is also possible as the estimates of abundance can be structured by length or age of animals.
In particular, for small pelagic fish, ISMAR has carried out assessments of the Adriatic stocks of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) by means of population dynamics methods like Virtual Population Analysis, using time series starting in 1975. On the basis of acoustics surveys, the Adriatic stocks of anchovy, sardine and sprat (Sprattus sprattus) have been assessed since 1976. Acoustics surveys were also carried out to estimate the krill biomass in the Ross Sea, in the ambit of Italian Antarctic Research Programme. As regards the demersal species, stock assessments based on population dynamics methods were conducted by ISMAR for Norway lobster (Nephrops norvegicus), clam (Chamelea gallina), red mullet (Mullus barbatus), hake (Merluccius merluccius) and common sole (Solea solea) in the Adriatic Sea. At the present time, the assessment of sole stock is also based on beam trawl surveys, while underwater television, another type of indirect method, is used for Norway lobster.
