Total marine fisheries extractions by country in the Baltic Sea

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66 Total marine fisheries extractions by country in the Baltic Sea: 1950-present, Rossing, Booth and Zeller Adjustments to ICES landings statistics Adjustments were made to the ICES landings statistics using a range of available sources (Table 1). Commercial landings for Estonia from 1950-1989, obtained from LATFRA, were considered adjustments to landings as the ICES landings statistics did not report data separately for Estonia prior to 1990, nor were they retroactively adjusted. Landings data for herring from 1950-1990 from Ojaveer (1999) were considered more reliable than the LATFRA data and provided this taxa‘s source of adjustments (H. Ojaveer, pers. comm., EMU). From 1991-2007, adjustments were made to cod (ICES, 2007; 2008a) and flatfish (ICES, 2008a) landings using ICES stock assessment working group data. The ICES working group data provided better taxonomic accounting, as cod landings were broken into eastern and western stocks, and flatfish data were disaggregated by species. A linear interpolation was done to estimate landings between 1989 and 1991 to estimate landings for all species, excluding herring, for 1990. These interpolated values were also considered adjustments to landings. Table 1. Sources of adjustments to ICES landings statistics for Estonia from 1950- 2007. Common Year Source name Cod 1950-1989 LATFRA 1990 Interpolated 1991-2007 ICES 2007, 2008a Herring 1950-1990 Ojaveer (1999) Sprat 1950-1989 LATFRA 1990 Interpolated Salmon 1950-1989 LATFRA 1990 Interpolated Flatfishes 1950-1989 LATFRA 1990 Interpolated 1991-2007 ICES 2008a ‘Others’ 1950-1989 LATFRA 1990 Interpolated Unreported landings Unreported landings as a rate were applied to landings (i.e. ICES landings statistics + adjustments) to derive tonnage of unreported landings for Estonia from 1950-2007. We assumed that unreported landings for Estonia were zero from 1950-1990, following our conservative assumption-based methodology for all former eastern bloc countries (see ‗Methods‘ in Zeller et al., this volume). To estimate unreported landings for 1991 and 1992, the years which reflect the transition from a state-controlled economy to a market-based economy, rates were obtained through linear interpolation from 0% in 1990 to the first anchor point established for 1993 (Table 2). Unreported cod landings for the period 1993-2007 were estimated to range from 50-100% (Anon. pers. comm.), and we used the average of this range (75%) as the rate for unreported cod landings. Unreported landings of salmon were estimated using our default methodology. Baltic-wide unreported landings of salmon were reported for 1981-2007 (ICES, 2008b) as a minimum, mode and maximum amount, and here we used the mode, following our default approach for countries that did not report recreational catches (see ‗Methods‘ in Zeller et al., this volume). The amount of unreported landings was converted to a rate by considering the amount as a proportion of the total landings presented in the same working group report. The Baltic-wide default rate was applied since country specific contributions to unreported landings were lacking. All other taxa had unreported landings based on our default values using anchor points developed from the years 1993, 1994, 2004, and 2005 (see ‗Methods‘ in Zeller et al., this volume). Table 2. Anchor points for unreported landings (as a %) for cod (LATFRA, see text for detail), salmon (Table 2.1.1. in ICES, 2008b) and all other taxa (Tables 2.3.1 and 2.4.1 in ICES, 2007; Table 2.3.1. and 2.4.1 in ICES, 2008a; and Table 2.1.1 ICES, 2008a). Dashed lines (-) indicate years when the rates were derived through linear interpolation. Year Cod Salmon Other taxa 1950-1990 0.0 a 0.0 a 0.0 a 1991-1992 - - - 1993 75.0 19.4 24.6 1994 75.0 18.7 30.3 1995 75.0 19.5 - 1996 75.0 20.4 - 1997 75.0 20.8 - 1998 75.0 20.1 - 1999 75.0 20.4 - 2000 75.0 19.9 - 2001 75.0 20.4 - 2002 75.0 20.5 - 2003 75.0 20.1 - 2004 75.0 20.6 12.3 2005 75.0 20.7 11.2 2006 75.0 22.2 11.2 b 2007 75.0 21.4 11.2 b a default assumption based rate; b 2005 value carried forward. Discards Discards were considered as four separate categories, each estimated as a rate and applied to total landings (i.e. ICES landings statistics + adjustments + unreported landings) for each respective taxonomic entity. The sum of discards in all four categories gave us total discard amounts for Estonia from 1950- 2007. The four categories considered were: a) ‗underwater‘ discards accounting for the mortality of fish
Total marine fisheries extractions by country in the Baltic Sea: 1950-present, Rossing, Booth and Zeller 67 lost from gear prior to being brought on board; b) ‗ghostfishing‘ due to lost or abandoned fishing gear that continues to fish; c) ‗boat-based discards‘, usually resulting from fishers‘ catch retention behavior; and d) ‗seal-damaged discards‘ representing the fraction of catch lost because of seal damage. ‗Underwater discards‘: We only applied an underwater discard rate to herring and sprat as few studies have been conducted on this kind of discard in the Baltic (Kelleher, 2005). For herring caught with trawl-gear, Rahikainen (2004) related underwater discard amounts to observed catches of herring. We transformed this into a rate of approximately 9% for underwater discards of herring caught by trawl (see ‗Methods‘ in Zeller et al., this volume). Since herring and sprat are both caught in a mixed species fishery using similar gear-types, we applied the same underwater discard rate to both species. However, herring and sprat landings for Table 4. Boat-based salmon discard rates for Estonia (ICES, 2008b) used in all subdivisions except in subdivision 32 when sealdamaged discard rates based on sources (Königson et al., 2005; FGFRI) were greater (1981-2007). Values in italics indicate an interpolated rate. Year Boatbased Sealdamaged 1950-1980 2.0 0.0 1981 2.0 6.9 1982 2.0 13.8 1983 2.0 20.7 1984 2.0 27.6 1985 2.0 34.4 1986 2.0 41.3 1987 2.0 48.2 1988 2.0 55.1 1989 2.0 62.0 1990 2.0 68.9 1991 6.0 75.8 1992 10.1 82.7 1993 14.1 89.5 1994 12.9 96.4 1995 13.9 103.3 1996 15.1 110.2 1997 14.9 117.1 1998 14.2 124.0 1999 14.8 130.9 2000 10.3 137.8 2001 15.0 203.4 2002 15.8 255.8 2003 15.4 337.3 2004 15.6 380.5 2005 15.2 113.2 2006 17.4 149.3 2007 14.2 102.7 Estonia are not reported by gear type, so the underwater discard rate of 9 % for trawl fisheries was reduced to a more conservative estimate of 5% to account for the lack of catch data by gear-type. This rate was then applied to herring and sprat landings (i.e. ICES landings statistics+ adjustments + unreported landings) for all years between 1950 and 2007. Table 3. Boat-based discard rates (in %) for taxa included in our grouping ‗others‘ derived from Estonian study for the period 1993-2007 (Anon., 2006b, 2007a). Common name Anchor point Trout 25.72 Perch 7.67 Pikeperch 4.88 Roach 6.36 Garfish 4.74 Smelt 4.32 Burbot 3.00 ‗Ghostfishing‘: The estimated ghostfishing discard rate was based on Tschernij and Larsson (2003), who estimated the amount of cod caught by lost gear in Sweden and related it to commercial catches in Sweden. Using these data, Brown et al. (2005) estimated the range of ghostfishing rates by lost gear to be between 0.01% and 3.2%, and here we used the average of 1.65% applied to all taxa, except herring and sprat, for all years from 1950-2007. ‗Boat-based discards‘: Boat-based discard rates were compared to seadamaged discard rates from 1980-2007 in subdivisions where sealdamaged discard rates were reported. The higher rate between the two categories was the only rate used to avoid the possibility of double accounting as some seal-damaged discards may have already been accounted for in estimates of boat-based discards. From 1950-1990 a boat-based discard rate of 2% was applied to all taxa, except herring and sprat, according to our default assumption-based methodology for boat-based discards (see ‗Methods‘ in Zeller et al., this volume). Our assumption that boat-based discards for herring and sprat were zero over the entire study period was supported by an ICES report indicating that boat-based discards for herring and sprat were almost n0n-existent (ICES, 2005; 2007; 2008a). Rates for 1991 and 1992 were derived through linear interpolation between the default assumptionbased rate for 1990 of 2% and the first available anchor point in 1993. Boat-based discard rates for the period 1993-2007 were derived from three sources, the first being the Estonian government provided boatbased discard tonnage for various taxa for 2005. The rates were derived from the total landings presented in the same report, and were estimated for cod (3.7%), herring (3.9%), sprat (3.0%), European flounder - the only reported flatfish - (17.2%), and several other taxa (Table 3) that were included in our grouping ‗others‘ (Anon., 2006b, 2007a). The 2005 rate was used as the discard rate throughout the 1993-2007 time period. The second source estimated boat-based discard rates of salmon from ICES stock assessment working group data (ICES, 2008b), which presents Baltic-wide, boat-based salmon discards (in tonnes) as a minimum, mode and maximum for the 1993-2007 time period (Table 4). The mode was used for Estonia, following our default assumption-based approach for countries that do not report recreational catches (see ‗Methods‘ in Zeller et al., this volume). These values were converted to rates using the total landings presented in the same working group report. The third source for estimating discards for all remaining individual taxa, included here in our group ‗others‘, was a boat-based discard rate of 6.2% for
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Total marine fisheries extractions by country in the Baltic Sea

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