Total marine fisheries extractions by country in the Baltic Sea

10 Total marine fisheries extractions by country in the Baltic Sea: 1950-present, Rossing, Booth and Zeller
METHODS
ICES maintains two different publicly accessible databases that provide time series data of fisheries
statistics. The ‗ICES catch statistics database’ describes countries‘ reported landings by species (or higher
taxonomic grouping), ICES statistical reporting area and year (in two parts: 1950-1972 and 1973-present).
Throughout the present report, data from this database are referred to as ‗ICES landings statistics’. The
second ICES database, officially called ‗ICES stock assessment results database’, describes countries‘
catches by stock and year, and presents data used by the ICES stock assessment working groups for their
annual stock assessments. Hence, this database only presents data on cod, herring, sprat, brill
(Scophthalmus rhombus), dab (Limanda limanda), turbot (Psetta maxima), plaice (Pleuronectes
platessa) and flounder (Platichthys flesus) and no data on the remaining 145 taxa being caught. As we
utilize some of these data, generally in conjunction with information taken directly from the ICES stock
assessment working group reports (e.g., ICES Working Group on Baltic salmon and trout 2008 [ICES,
2008a]), we refer to the combined data source (i.e., ‗ICES stock assessment results database’ and ICES
stock assessment working group reports) as ‗ICES stock assessment working group data’. In addition to
the reported landings by stock, the ‗ICES stock assessment reports’ also contain some data on unallocated
(unreported) catches of cod, salmon and Riga herring. Both databases are available electronically from
ICES (ICES, 2009a) as are recent ICES stock assessment reports (ICES, 2009b).
As the aim of this study is to estimate total catches (as opposed to reported landings) taken in the Baltic
Sea for the time period considered here, all fisheries components were estimated for the nine Baltic
countries. The ‗reported data‘ baseline is represented by ‗ICES landings statistics‘. To this, we added four
IUU components: ‗adjustments‘ to ICES landings statistics (i.e., data source adjustments to reported
landings), unreported landings‘, ‗discards‘, and ‗recreational catches‘. ‗ICES landings statistics‘ formed the
baseline for estimating total catches, and estimates of IUU catches were added to these. Discard estimates
were applied to the sum of ICES landings, adjustments, and estimates of unreported catches. Recreational
catch estimates were also made for each country, allowing estimates of total catches taken from the Baltic
Sea from 1950-2007 to be derived. Catches reported by ICES on behalf of non-Baltic countries were
presented here, but excluded from this catch reconstruction as they amounted to only 60,000 t over the
entire time period considered. The basic methodological approach used here consisted of utilizing as wide
a range of information and data sources as possible. Information and data for each catch component that
were considered usable were transformed to create so-called ‗anchor points‘, and, when time series were
lacking, expansion methods, including linear interpolations between anchor points in time, were done to
create full time-series coverage for each catch component (Zeller et al., 2006; Zeller et al., 2007).
ICES landings statistics (ICES, 2009a) 2 are available as two data sets covering the time periods 1950-1972
and 1973-2007, and describe the annual commercial landings data by each country for each taxon and
statistical reporting area (Figure 1). ICES landings data were adjusted with information provided by our
Baltic collaborators, from national sources, or from other ICES documents (e.g., ICES working group
reports), and the adjustments plus ICES landings statistics represent what we consider to be the best
estimate of reported landings. Unreported catches were generally transformed into anchor points by
considering the available data as a proportion of corresponding reported landings per year (e.g.,
unreported landings data for cod for Denmark was related to the reported landings of cod by Denmark) in
order to expand unreported catch estimates to time periods when data were lacking. The same method
was used for discards; however, discard rates were applied to the sum of ICES landings statistics,
adjustments, and unreported landings. In order to expand to time periods when there was no neighboring
anchor point to interpolate to, an assumption-based approach was used. These methods allowed for a
complete time series of catch data to be estimated for each catch component for each country that
participates in Baltic Sea fisheries.
The general methods presented here represent the default approach for each component for each country.
However, whenever country specific data on any of the components were available, such specific data were
utilized in preference to the default approach. Each individual country report (this volume) describes such
details. To account for some political and economic differences between countries, we accounted for catch
components by considering groupings of countries. Western countries were considered to include
Denmark, Finland, West Germany (1950-1990) and Germany (after re-unification, 1991-2007), and
Sweden; former eastern bloc countries included East Germany (1950-1990), Poland, Russia Federation,
2
ICES refers to these data as ‗catch statistics‘.