DCF (Data Collection Framework): Assessing the stock development for cod, herring, flounder and sprat in the Baltic within the frame of ICES assessment working groups
What is the status of a commercially used fish stock in the Baltic Sea – and how does it develop? Given that most stocks are “shared stocks”, this question is raised annually and can only be answered in cooperation with other Baltic Sea countries. The answer is highly important for both fishing industry and anglers, and conservationist.
The recruitment of fish stocks is subject to strong natural variation. An extremely strong year class allows the fisheries to prosper for years, whereas, if recruitment fails, the fisheries can be severely hit. Therefore, the status of commercially used fish stocks is usually assessed on a yearly basis. Thus, changes – both upwards and downwards – can be anticipated and taken into account by the fisheries management.
In the Baltic Sea, each spring the fisheries-dependent and fisheries-independent data are compiled. This takes place within the scope of “assessment” working groups of the International Council for the Exploration of the Sea (ICES). The ICES headquarter is in Copenhagen. There German experts participate in an international effort to calculate and estimate the stock status of the different commercially used fish stocks of the Baltic Sea.
The commercially used fish stocks in the Baltic Sea with importance for the German fisheries are cod, herring, sprat and the flatfishes flounder, plaice, dab, turbot and brill.
Important for us is the participation in the „Herring Assessment Working Group for Herring South of 62°N“ (HAWG) and „Baltic Fisheries Assessments Working Group“ (WGBFAS). These tasks are conducted within the EU-cofinanced project „Data Collection Framework“ (DCF).
The stock assessment uses fisheries-dependent and fisheries-independent data. Fisheries-dependent data are logbook information and landing slips of the commercial fisheries. These are provided by responsible control authority, the Federal Office for Agriculture and Food (BLE). These data are merged with our own samplings of the commercial fisheries. At-sea observer of the OF measure the catch and length compositions on board of German commercial fishing vessels. In addition, we purchase unsorted catch samples from fishing vessels. The samples are analysed in our laboratory using standard procedure of fishery biology. We determine important parameters such as sex, maturity and age. These biological data are then used to raise the mere landing figures from the fisheries into data that can be used in stock assessment, e.g. the number age 1, age 2, age 3 etc year old fish, discard rates etc.
Parallel to these activities, we carry out elaborate, internationally coordinated fisheries-independent monitoring programmes, such as the Baltic International Trawl Survey (BITS) tailored for demersal fishes like cod and flatfishes, or the Baltic International Acoustic Survey (BIAS) for herring and sprat. They provide a measure to collect standardized information independent from the fisheries on age and frequency distribution of fish covering the whole range of entire stocks.
The large data sets are used in stock assessment models. The data are stored in national and international data bases.
Results of the annual fisheries assessment working groups are available as freely downloadable documents (see www.ices.dk).
Permanent task 1.2001 - 12.2020
Project status: ongoing