This chapter explains some theoretical and technical aspects of stock assessments that may be familiar to those directly involved in fisheries science and analysis of fish populations. The information about stock and recruitment concepts, assessment of population growth, natural and fishing moralities, selectivity of fishing gears and relationship between catch and selectivity. It is written particularly for persons involved in scientific activity, for students and for stakeholders who have never been exposed to formal fisheries science training, but are interested in better understanding complicated fisheries concepts. An enhanced knowledge of assessment concepts and fisheries science will promote an increased understanding of fisheries management and give stakeholders greater confidence as they participate in fisheries management process. Understanding how all factors interact is a challenging task, even for experts in fisheries science.
TopIntroduction
Particularly for the coastal regions, the fish catching is an economic activity of a great importance. This fact is supported primarily on the contribution that the ichthyic stocks and their products give in the human nutrition and its commitment at work, in different sectors of the fishing industry. Another important aspect of the value of the ichthyic reserves is their renewable character. If the fishery reserves will be managed in a sustainable way, then their existence can actually be unlimited in time and space. The successful management and conservation of ichthyic stocks can be guaranteed due to the recognition of the biological features of the exploitable populations and real forecast of anthropogenic alterations of these characteristics. It is very important that the economic exploitation plans take into account the peculiarities of the structure of fishery populations (age structure, sex ratios, mortalities etc.) in order that the human interventions to guarantee their resiliency.
According to the data of the (MOE, 2010) in Albania 821 fishermen are engaged in sea fishing and 750 fishermen in the fishing of the interior waters that is carried out in three large lakes. The coastal artisanal fishing employs about 500-600 fishermen. However ichthyic products consumption is relatively low, about 3.3 kg / capita / year, compared with the average of the Mediterranean countries that is estimated at 15.1 kg / capita / year. Currently in Albania, the value of the fishing production by catching and aquaculture, it is estimated at about 40 million USD. Out of the total value, about 22 million USD comprises sea fishing, coastal and inland waters, about 8 million USD aquaculture and the rest bivalve mollusks. In the passing that this production makes along all the marketing chain, in retail sale, its value increases by 10-30% depending on the type of fish. The trade balance of import and export of fishery products is positive in value.
For what reasons the exploitable reserves (stock) should be evaluated? Fish catching is a human activity that involves live resources and therefore renewable. But unfortunately the reality of their exploitation is associated with certain practices that have generated overexploitation situations. It is known that in most frequent cases the fishery resources are common property and this situation hasn’t led to their abusive exploitation (Larkin,1972). On the other hand, there are not rare the cases when particular people, for various reasons (mostly economic) exploit the fish stocks without having a license. The abusive fishing and the illegal one may be accompanied with a spurring competition for the use of a similar reserve, a fact that promotes biological overfishing as well as the economic overfishing (Beverton & Holt, 1956).
The determination of the solutions for the rational exploitation of the fish resources includes diverse implications ranging from policy interventions and socio- economic problems to the taking into consideration of a number of biological aspects as those of the biodiversity conservation, recognizing of the ecosystems functional characteristics as a whole and the exploitable populations’ dynamics in particular (Beverton & Holt, 1956; Gulland, 1983). The information that shall be treated in this chapter shall primarily involve the analysis of some biological characteristics of fish populations and the use of information on these features for the analytical evaluation of the exploitable reserves. The methods of assessment (Anderson & Gutreuter. 1983Baranov, 1914; Baranov, 1918; Beverton, 1963Beverton & Holt 1956; Garrod, 1961; Gulland, 1983; Gayanilo & Pauly 1997; Hamley, 1975; Ihsen, et al. 1981; Kolding, 2006; Munro, 1984; Pauly, 1980.; Pauly, 1985; Ricker, 1975; Schaefer, 1954; Sparre, 1987. Sparre & Venema, 1998) will help in the first place to reduce the frequency of situations that jeopardize the ichthyic types that are subject to intensive fishing and to stimulate the rational fishing. We must add that when the results of the assessment of the stock are used for the purposes of its well-management it would be reasonable to include the economic and social components. In reality, the main purpose for which it is realized the stock assessment is to provide the technical information necessary for the preservation of the productive skills of the exploitable fish populations.