Long-Term (1976-2002) Changes in Freshwater And

International Council ICES CM 2003/R:07 for the Exploration of the Sea Theme Session: Freshwater and Diadromous Fishes in the Baltic Sea

Long-term (1976-2002) changes in freshwater and diadromous fishes occurrence in the bottom layer of the southern Baltic Sea (on the basis of the Polish Young Fish Surveys)

:áRG]LPLHU]*U\JLHODQG.RUGLDQ7UHOOD

Sea Fisheries Institute, ul. Kollataja 1, 81-332 Gdynia, POLAND fax: +48 58 6202831, e-mail: [email protected]

ABSTRACT. The main purpose of the Polish Young Fish Surveys programme was to estimate both the spatial distribution and year-classes abundance of cod, flounder, herring and sprat in the southern Baltic Sea. Freshwater and diadromous fishes occur as by-catch in these research catches. The basic aim of this paper is to assess the long-term changes in the occurrence of freshwater and diadromous fishes in hauls and in their CPUE, in the relation to nine trawling profiles at 10-m strata between depths of 10-110 m and time periods. The results of 2953 bottom research catches carried out from 1976 to 2002 were analysed. Nine freshwater fish taxa (pikeperch, perch, ruffe, bream, roach, pike, sabrefish, rainbow trout, three-spined stickleback) were recorded in the catch composition. Moreover, nine diadromous fish species (eel, whitefish, shad, allis shad, vimba, sea trout, salmon, smelt, river lamprey) were also noted. Pikeperch was the dominant species occurring in 8.4% of the hauls followed by shad and eel at 4.3 and 3.0%, respectively.

Keywords: by-catch, freshwater and diadromous fishes, geographical and bathymetrical distribution, southern Baltic.

INTRODUCTION According to various classifications, the freshwater and diadromous fishes of the Baltic are considered either as commercial species with an unlimited, annual catch (except salmon for which there is a quota) or as coastal fishes, some of which are migratory or euryhaline. Some species are permanent inhabitants in particular areas, while others appear periodically within a certain time period during their life or annual cycles. Some species have also been observed sporadically in given regions. Although Baltic cod, sprat, herring and flounder contribute to the bulk of the total annual catch in majority of the Baltic countries, such species as eel, trout, salmon, pikeperch, perch, bream, are the most valuable and have the highest impact on the profitability of fishing operations in the coastal zone (Draganik 1996). Coastal fishing is the main source of income for most people living near the sea. In some the Baltic Sea regions, coastal fishes like perch, pikeperch, vimba, pike, roach, ide, eel and whitefish constitute a significant part of annual catches (Draganik 1996, Erm et al. 1991, Skóra 1996, Birzaks 1997, Thoresson 1997, Nylander 1998). For example, in Estonia until the 1990s these species constituted 2-19% of the total national catch and were caught mainly in the Pärnu Bay (Erm et al. 1991, Erm 1996). The share of freshwater and diadromous fishes in Finnish commercial sea fisheries in the Baltic Sea in 1996 was 4.7% (after Nylander 1998). However, in the Szczecin Lagoon, pikeperch, perch, roach and common bream are the basic commercial species and constitute 92% of total Polish catches in this region, and this figure rises to 96% when eel is included (:\VRNLVNL The share of the species mentioned above, for example in Estonian and Latvian catches, temporarily increased during the 1980-1990 period in connection with the introduction of fishing limits for Baltic herring and the sudden decrease in the smelt stock abundance (Erm et al. 1991, Birzaks 1997, Plikshs and Aleksejevs 1998). In contrast, the abundance of pike, whitefish and smelt have decreased in the Pärnu Bay as a result of deteriorating spawning conditions. A similar situation was also observed with several freshwater species in Polish coastal waters, namely in the Puck Bay (Skóra 1993, 1996, Jackowski 2002). The primary cause of declining freshwater fish stocks in this basin was the temporary disappearance of spawning grounds, which resulted from changes in the species structure of the phytobenthos. The deterioration of the southern Baltic environment, including Polish coastal waters and the damming of rivers, caused decreased numbers of spawners in the spawning grounds of anadromous fishes (Bartel 1991, 1993). The first information on several commercial marine Baltic fish species, and to a lesser degree on freshwater and diadromous fishes, inhabiting Polish waters can be found in the SXEOLFDWLRQVRI6LHGOHFNL 'HPHO 3 F]DOVND DQG*VRZVND 0RUH recently, complex data have been made available concerning the settlement, biology and biomass of the majority of freshwater and diadromous fishes inhabiting coastal waters of south-eastern and north-HDVWHUQ %DOWLF %U\OLVND 3OLNVKV DQG $OHNVHMHYV %RURZVNL Jackowski 2002). Scientific publications on Baltic ichthyofauna present some detailed information on fish species composition and yield in particular lagoons, bays, experimental areas and in very shallow waters. Of the 57 fish species recorded in the Puck Bay over the last 80 years, only a dozen have been the subject published ichthyological papers (Jackowski 2002). Approximately 64 species of freshwater and sea fishes and three species of lamprey occur in the coastal area of the southern Baltic Sea (within the Polish EEZ), including lagoons and bays (Skóra 1996, Hesse 1998). This figure represents almost 70% of the domestic ichthyofauna. According to Draganik (1996), a greater variety of fish species is recorded in the western part of the Polish coastal zone. The Szczecin Lagoon has the highest species abundance - Skóra (1996) reported about 52 species, Garbacik-:HVRáRZVND XQSXEOLVKHGGDWD DQG'UDJDQLN DERXW DQG:\VRNLVNL DERXWIUHVKZDWHUDQGEUDFNLVKZDWHUVSHFLHV PLJUDWRU\ species and approximately 13 sea species which occur sporadically. In the materials collected by Psuty-Lipska and Garbacik-:HVRáRZVND LQ-1995, 35 fish taxa were recorded in the Szczecin Lagoon and 27 species in the Pomeranian Bay. Moreover, the frequency of occurrence of fish species in experimental hauls in the Pomeranian Bay was year dependent. Freshwater fish species such as common bream, pikeperch and perch were fished sporadically. ,QWKHFHQWUDOSDUWRIWKH3ROLVK%DOWLFFRDVWEHWZHHQWKHKDUERXUVLQ.RáREU]HJDQGàHED Heese (1998) registered a total 14 freshwater and diadromous fishes in catches. Investigations conducted by Trella (1998) in nearly the same region show that the freshwater fishes contribution in control catches was strongly connected with the location of the research profiles and was greatest at stations located near river mouths or canals which connect lakes with the sea. In the western as well as in the eastern parts of the Polish coastal zone, 60% of all the fish species are typical freshwater fish (Skóra 1996). Approximately 40 species of fish – 24 freshwater, 7 diadromous, and 9 marine – occur in the Polish part of the Vistula Lagoon; common bream, pikeperch, eel, roach, perch, smelt, sabrefish and herring are of commercial significance (Borowski 2000). Three-spined stickleback was the absolute dominant among 14 ILVK WD[D IRXQG E\ 6DSRWD DQG 6NyUD LQ WKH VKDOORZHVW ZDWHU RI WKH *XOI RI *GDVN (within the Polish EEZ). This species comprises almost 70% of the number and more than 80% of the biomass of all the fishes in this area. Anadromous fish like salmon and sea trout are widely distributed throughout the Polish EEZ. They also occur in neighbouring areas of the Baltic. However, in the Polish EEZ whitefish LQKDELWWKH*XOIRI*GDVNZKHUHWKH\DUHFDXJKWRQO\RFFDVLRQDOO\DQGWKH3RPHUDQLDQ%D\ Vimba inhabit some Polish rivers. Lamprey catches are made only in the Vistula River and did not exceed 2 tons per year (Bartel 1991, 1993). Freshwater fishes occur most frequently in relatively shallow waters e.g. in the central coast of the southern Baltic up to one km from the shore (Heese 1995). Pikeperch is the species, which migrates the farthest into the open sea and has been caught 15 km from the shore. Bream is one of the species which is most often caught in the strip of water up to 4 km from the shoreline, mainly at a distance of 200-300 m from the shore at depths of 3 m. Roach and perch 2 mainly occurred from 50 to 300 m from the shore in the vicinity of river outlets and the canals of lakes located near the sea. The description of the quantitative relationships among the Baltic freshwater and diadromous species in deeper, offshore waters and their geographical distribution according to depth and seasons is lacking in the scientific literature. The goal of this paper is to present the long-term (1976-2002) and geographic (within the Polish EEZ) variation in freshwater and diadromous fishes frequency of occurrence in the southern Baltic as well as the variations in their catch per unit effort (CPUE, in kg/h) in relation to nine trawling profiles, each 10-m strata between depths of 10-110 m and time periods. Possible relationships between the frequency of occurrence, share in catches and CPUE of the above mentioned fishes and year, quarter, depth strata and location were also analysed.

MATERIALS AND METHODS The research materials were collected by the authors within the framework of the Polish Young Fish Surveys program realised by the Sea Fisheries Institute in Gdynia in the close co-operation with the ICES Working Group on Baltic International Fish Surveys. The main purpose of this programme, also known as the BITS-surveys (bottom international trawl surveys), was to estimate both the spatial distribution and year-classes abundance of cod, flounder, herring and sprat in the Baltic Sea. Freshwater and diadromous fishes also occur in these research catches as by-catch. The material originated from 2953 bottom catches sampled from November 1976 to November 2002 during the same type of research cruises conducted on vessels of similar size. One type of fishing gear was used - a P20/25 herring bottom trawl with 6-mm bar length in the codend. In the majority of hauls the effective catch time was 30 minutes. The vessel speed was usually three knots. The hauls were made only during the day (from sunrise to sunset) in 10- meter isobath intervals in a depth range of 10 to 110 m. Shallower areas were inaccessible due to the relatively deep draught of the research vessels, on average 4.5-m, and the widespread use of set nets (gill-nets) in coastal areas. The number of hauls at a depth of 10 m was also limited for the same reasons. The list of bottom control hauls performed by research vessels in the southern Baltic (within the Polish EEZ) from 1976 to 2002 is presented in Table 1. The geographical location of the ninH SHUPDQHQWO\ LQYHVWLJDWHG UHVHDUFK SURILOHV .U\QLFD 0RUVND :LVáRXMFLH 3XFN %D\ :áDG\VáDZRZR *GDVN 'HHS 8VWND-àHED 6áXSVN )XUURZ .RáREU]HJ-'DUáRZR Pomeranian Bay) is presented in Figure 1. Each whole catch <500 kg was sorted according to species; if the haul was larger then samples were taken. Particular fish species in the catch was weighed separately, and then the total weight of the catch was determined per hour of trawling. The CPUE (in kg/h) of freshwater and diadromous fishes, which is used in this work as a dependent variable, represents their geographical and temporal distribution. According to Thoresson et al. (1996, 1997), the mean CPUE can serve as an index for “true” stock size variations, thus enabling spatial and temporal comparisons, and, following the example of Baltic perch, it is possible to using this index in resource assessment. It's necessary to emphasise that, in addition to the freshwater and diadromous fish species discussed in this work (Table 2), three-spined stickleback (Gasterosteus aculeatus) and smelt (Osmerus eperlanus) were also observed in control catches. However, due to a temporary lack of access to these data, these two species were not included in the final analyses. Rainbow trout was included in the freshwater fish group since in Polish waters it does not originate from natural spawning and does not migrate like typical diadromous species. According to the evaluations of .*RU\F]NR FLWHGLQ%U\OLVND WKHFXUUHQWGDWDGRQRWLQGLFDWHWKDWDQDWXUDOSopulation of a diadromous form of a rainbow trout is maintained in the Polish coastal area. Brook (river) lamprey was arbitrarily added to the group of diadromous fish, although, according to animal systematics, this species belongs to Petromyzoniformes and not to Pisces. The geographic, bathymetric and seasonal distribution of freshwater and diadromous fishes (based on CPUE) and the frequency of occurrence of selected fish (pikeperch, eel, shad) in

3 control hauls (expressed as the numerical percentage of the haul) and their relative contribution to the catch weight, were analysed in relation to: • years from 1976 to 2002; • quarters of the year (1976-2002 period); • nine research profiles of the southern Baltic; • selected areas (where particular species were most frequently recorded in hauls) and all areas; • 11 depth stratums in the range of 10-110 m at 10-m intervals. This work also presents the results of the analyses of statistical dependencies between three different, dependent variables – CPUE, frequency of occurrence in hauls and the relative share of the catch weight - and factors which potentially determine the distribution of these variables, i.e. years, quarters, depths and study areas. Therefore, trend analysis, linear regression analysis (with different models) and ANOVA were applied.

RESULTS Frequency of occurrence of fishes in control hauls The nine following freshwater fish species were observed in bottom hauls made from 1976 to 2002 in the southern Baltic Sea (Fig. 1): pikeperch; perch; ruffe; bream; roach; pike; sabrefish; rainbow trout; three-spined stickleback (the latter not analysed in this work). Nine species of diadromous fish were also recorded in these control hauls: vimba; whitefish; eel; salmon; sea trout; shad; allis shad; river lamprey; smelt (the latter not analysed in this work). The average frequencies of occurrence of the 18 freshwater and diadromous species in the hauls according to study area are presented in Table 2; the areas, which are especially preferred by particular species, are denoted in bold blue. The table also includes the information about the deepest places of occurrence of the species. Variations in the average frequency of occurrence of freshwater and diadromous fishes, including pikeperch, eel and shad, in control hauls versus years, quarters and depths are illustrated in Figures 2, 5 and 7. In 1976-2002, the frequency of occurrence of pikeperch in hauls made near the bottom layer of the southern Baltic Sea was the highest in comparison with other species at an average of 8.4%. This species was most commonly caught in the Puck Bay (22.1% of the hauls), :LVáRXMFLH DQG.U\QLFD0RUVND WKHDYHUDJHIUHTXHQF\RIRFFXUUHQFHLQWKHVH three areas was 17.1% (Table 2). The deepest place where pikeperch were caught was 70 m near :LVáRXMFLH The second and third most common species in the hauls were shad and eel. The average frequency of occurrence of shad in all the investigated areas was 4.3% and in selected areas – 6.5%, while for eel these figures were 3.0 and 5.1%, respectively. The areas preferred by shad ZHUH WKH *GDVN 'HHS :áDG\VáDZRZR WKH 3XFN %D\ :LVáRXMFLH DQG .U\QLFD 0RUVND 7KH GHHSHVW SODFH ZKHUH WKLV VSHFLHV ZDV FDXJKW ZDV P QHDU :áDG\VáDZRZR (HO ZHUH PRVW commonly caught in the Puck Bay, Ustka-àHEDDQG:LVáRXMFLHDQGWKHGHHSHVWSODFHZKHUHLW ZDV FDXJKW ZDV P QHDU :áDG\VáDZRZR 7DEOH 7KH UHPDLQLQJ VSHFLHV VXFK DV SHUFK bream and brook lamprey, were much less frequent in the hauls, and their appearance in hauls made in selected regions oscillated around 3%. The majority of these fish species was observed also at significant depths (up to 70-100 m), and only whitefish, rainbow trout, bream, sabrefish and vimba were present in shallow waters at 10-20(30) m. Freshwater fishes ZHUH PRVW FRPPRQO\ FDXJKW QHDU :LVáRXMFLH DYHUDJH IUHTXHQF\ RI occurrence of 25.7%), the Puck Bay (19.5%) and Krynica Morska (8.5%), i.e. in the southern and south-HDVWHUQSDUWVRIWKH*XOIRI*GDVN7KHIUHVKZDWHUVIORZLQJLQWRWKH%DOWLF6HDIURP the Vistula River influence the freshwater fish appearance in this region. In these three research profiles, the average, long-term (1976-2002) frequency of occurrence of this fish group was 18%, and throughout the southern Baltic Sea it was 9%. The highest average frequencies of occurrence of the freshwater fishes in hauls, including pikeperch, were registered: • in 1984, 1988-1999 and 2002, from 15 to 30%, throughout the southern Baltic Sea and from 20 to 55% in the selected, preferred area (Fig. 2); • in the fourth quarter, 14.5 and 30%, respectively, according to groups of compared regions (Figures 5 and 6); 4

• at a depth of 10 m, 36 and 33%, respectively, throughout the study area and in selected regions (Fig. 7). In 1976-1977 and 2000-2001 and in the second quarter and at depths 80-110 m, the frequency of occurrence of freshwater fish in hauls was close to zero. Diadromous fishes occurred most often in the following areas: Ustka-àHED RQDYHUDJHLQ RIKDXOV :LVáRXMFLH .U\QLFD0RUVND WKH3XFN%D\ ,QWKHVH regions the average, long-term frequency of occurrence of diadromous fishes was 10.1%, and in the entire study area it was 7.9%. The highest frequency of occurrence of diadromous fishes in hauls was observed in 1981-1985, 1992-1994, and especially in 1998-2002, from 5 to 35% throughout the study area and from 10 to 40% in the selected, preferred areas (Fig. 2). It must be noted that the increase of the frequency of occurrence of diadromous fishes in 1998-2002 was influenced by the increased presence of shad in the control hauls. Diadromous fishes were most commonly caught in the third quarter at 11 and 22% and at a depth of 10 m, where the value of the variable was 35 and 38%, respectively, throughout the study area and in selected areas. In 1977, 1986, 1987, 1989 and 1995 and in the second quarter as well as at depths of 100-110 m, the frequency of occurrence of diadromous fishes in the hauls was negligible or equal to zero (Figures 5 and 7). Figure 2 and Tables 4 and 5 present the results of the analyses of the dependence between the average frequency of occurrence of freshwater and diadromous fishes in control hauls and years and depths. The results of the applied trends analysis for the frequency-year dependence, best fitted according to the 5th order of the multinomial model applied, indicate that the frequency of occurrence of freshwater fishes, including pikeperch, and diadromous fishes, including shad, in the hauls was significantly determined by the "year" factor (Table 4). The correlation coefficient (r) varied from 0.716 to 0.827 and the determination coefficient (R2), which explains the variance of the changes in the frequency of occurrence of fish in the hauls with the applied model, varied from 51 to 69%. In the aim to fully confirmation of the statistically significant relationship described above deeper investigations are needed. The values of the basic parameters of the regression analysis, from the best fitted linear model, for the dependence of the average frequency of occurrence of freshwater fishes in hauls on depth, and with the exponential model for the same dependence but with diadromous fishes, indicate that there was a statistically significant and inversely proportional dependence between these variables. The values of the correlation coefficient from –0.642 to –0.955 and of the determination coefficient from 41 to 91% confirm the foregoing (Table 5).

Changes in the share of freshwater and diadromous fishes in survey bottom catches Variations of the average share of freshwater and diadromous fishes in survey catches by years from 1976 to 2002, quarters and depth are presented in Figures 3, 5 and 7. Changes in this variable for particular fish species with regard to study profiles are presented in Table 3. The relatively high frequency of occurrence of freshwater fishes in the areas of :LVáRXMFLHWKH3XFNBay and Krynica Morska (Table 2) did not correspond with a high share of this fish group in the weight of the control hauls. In 1976-2002 the highest, average share of mentioned fish group in the catches were observed in the Pomeranian Bay (10.3‰), near Krynica Morska (3.0‰), Ustka-àHED Å :LVáRXMFLH Å DQGWKH3XFN%D\ Å Table 3). The highest, average freshwater fishes share of the catch weight was observed: • in 1984-1985 and 1993 - from 4 to 14‰ throughout the study area of the southern Baltic Sea and from 9 to 38‰ in the selected, preferred area; • in the fourth quarter - 12 and 26‰, respectively, for groups of compared regions; • at a depth of 10 m - 40 and 44‰, respectively, throughout the study area and in selected regions (Figures 3, 5 and 7). The average, long-term share of freshwater and diadromous fishes in survey catches throughout the study area was 1.26 and 0.63‰, respectively. The relatively high average contribution of diadromous fishes in the catches, as well as their frequency of occurrence, were observed in the following areas: Ustka-àHED Å .U\QLFD 0RUVND Å WKH 3XFN %D\

Å DQG :LVáRXMFLH Å 7KH KLJKHVW DYHUDJH GLDGURPRXV ILVK VKDUH RI WKH FDWFK weight was observed: • in 1981-1982, 1992 and 2000-2002 - from 2 to 8‰ throughout the study area of the southern Baltic Sea and from 3 to 11‰ in the selected, preferred area; • in the third quarter - 7 and 15‰, respectively, for groups of compared regions; • at a depth of 10 m - 36 and 54‰, respectively, throughout the study area and in selected regions. Similar to the highest pikeperch, comparing with others freshwater and diadromous fishes, frequency of occurrence in control hauls its average, long-term (1976-2002) share in the survey catches conducted throughout the study areas was the highest at 1.14‰, with maximum value recorded near Krynica Morska (2.92‰; Table 3). The relatively high contributions of pikeperch in survey catches in 1984 of about 38‰ in selected regions (Fig. 3) are noteworthy. The second and the third species for which the average, long-term share in the catches was significant were eel (0.34‰) and vimba (0.11‰). The high share ÅRIHHOLQWKHFDWFKHVLQ 1980-1984 and 1992 in selected regions (Fig. 3) is also noteworthy. The significant share of perch (especially in 1984-1985) in catches conducted in the Pomeranian Bay (9.16‰) and the same for whitefish from Ustka-àHED Å) are worth mentioning. The average, long-term contribution of other fish species to the catch weight was negligible at Å In order to compare the data regarding the contribution of freshwater and a diadromous fishes in survey catches (Table 3), comparable data collected from Polish commercial catches in 2001-2002 is presented in Table 6. The average, annual contribution of freshwater fishes in Polish commercial catches in the Baltic Sea (including lagoons and the coastal zone) was in the range of 22.1-25.3‰ and for diadromous fishes – 5.8-8.6‰. These figures are 18- and 12-times more, respectively, than those of the survey catches conducted in 1976-2002. Of the 12 freshwater fish species registered in the commercial catches, roach dominated at a share of 8.6- 9.9‰, and of the eight diadromous fish species, sea trout dominated with a contribution of 3.4- 5.2‰ (Table 6). The results of trends analysis (with the 5th order multinomial model) applied to study the dependence of average share of freshwater and diadromous fishes in survey catches vs. years not indicated a statistically significant relationship between variables with except for shad (Table 4). The values of the basic parameters of regression analysis, with the best fitted exponential model for the dependence of the average share of freshwater and diadromous fishes in the catches and depth, indicate that the dependence between these variables was statistically significant and inversely proportional. The correlation coefficient ranged from –0.846 to –0.985 and the determination coefficient ranged from 72 to 97%, which confirm the foregoing (Table 5).

Analysis of the temporal-spatial sources of catches (CPUE) variations Changes in the average catch (CPUE) of freshwater and diadromous fishes in the control hauls made in subsequent years from 1976-2002, quarters, depths and study profiles are presented in Figures 4-9 and in Table 3. The table includes data concerning the minimum and maximum values of individual hauls and some data regarding the location and time of the largest catches of given fish species. In the 1976-2002 period the highest average CPUE of freshwater fishes was noted in Krynica Morska (0.83 kg/h), the Pomeranian Bay (0.70 kg/h), the Puck Bay (0.32 kg/h) and :LVáRXMFLH NJK7DEOH 1RIUHVKZDWHUILVKHVZHUHQRWHGLQFDWFKHVPDGHLQWKH*GDVN 'HHS DQG WKH 6áXSVN )XUURZ 3LNHSHUFK DQG SHUFK GRPLQDWHG WKH &38( RI IUHVKZDWHU ILVKHV with average, long-term values of 0.19 and 0.16 kg/h, respectively. Over the last 27 years relatively high average CPUE values were noted for pikeperch in the III-IV quarters and near Krynica Morska (1.9 kg/h). The largest, single catch of this species (132.0 kg/h) was noted in mentioned region at a depth of 30 m in October 1980 (Table 3, Fig. 6). High average, long-term CPUE values of perch (1.43 kg/h) were noted in the Pomeranian Bay, where the largest single catch of this species (25.7 kg/h) was made at a depth of 10 m in October 1985. The highest average CPUE values for freshwater fishes were obtained:

• in 1980, 1984-1985 and particularly in 2002 (mainly pikeperch), from 0.9 to 2.0 kg/h – throughout the southern Baltic Sea and from 2.1 to 4.0 kg/h in selected, preferred regions; • in the 4th quarter, 1.3 and 3.0 kg/h, respectively, according to groups of the compared regions; especially high CPUE values were recorded, mainly for perch, pikeperch, bream and roach, in the Pomeranian Bay at 9.3 kg/h (Fig. 6); • at a depth of 10 m, 2.9 and 4.4 kg/h, respectively, throughout the studied area and in selected regions (Figures 4, 5 and 7). During the research cruises, the highest average, long-term CPUE values for diadromous fishes were noted in Ustka-àHED NJK .U\QLFD0RUVND NJK DQGthe Puck Bay (0.16 kg/h). Representatives of this fish group were caught in all nine of the research profiles. The maximum, single catches of vimba and eel (40.0 and 17.0 kg/h, respectively) were made near Krynica Morska at a depth of 10-20 m (Table 3). Of the diadromous fishes group, shad and eel dominated in terms of CPUE with average, long-term values of 0.054 and 0.053 kg/h, respectively. The highest average CPUE values for diadromous fishes were obtained: • in 1980-1983, 1992 and 1999-2002, from 0.16 to 1.27 kg/h throughout the southern Baltic and from 0.35 to 0.86 kg/h in selected regions; due to the relatively high CPUE of shad (average 1.14-3.34 kg/h), obtained in 2001 in regions which are not considered in the long-term for the selected groups, the upper limit of the CPUE average for all studied regions was higher, in this exceptional case, than for the selected regions; • in the 3rd quarter, 0.5 and 1.0 kg/h, respectively, according to groups of compared regions; • at a depth of 10 m, 2.6 and 3.7 kg/h, respectively, throughout the studied area and in selected regions (Figures 4, 5 and 7). In the 1976-2002 period the highest average CPUE values of freshwater fishes were achieved subsequently in somewhat different research regions than those in which were noted the highest relative average share or the highest frequency of occurrence (Table 3). However, with diadromous fishes there was relatively high consistency with regard to the research region and the occurrence of the highest values of the three investigated dependent variables. The average, long-term CPUE of freshwater and diadromous fishes throughout the studied region was 0.25 and 0.13 kg/h, respectively. The results of trends analysis used to study the dependence between the average CPUE- year, best fitted according to the 5th order of the multinomial model applied, indicate that the CPUE of freshwater fishes, including pikeperch, and diadromous fishes, including eel and shad, was statistically significantly determined by the time factor “year” (Fig. 4, Table 4). The value of the correlation coefficient was from 0.544 to 0.721. The applied model explained 30-52% of the variance of change of this variable. Further, the basic parameters of the regression analysis, with the best fitted exponential model, of the dependence between the average CPUE of freshwater and diadromous fishes and depth indicated that there was a statistically significant, inversely proportional dependence between these variables. The value of the correlation coefficient ranged from –0.838 to –0.975 and the determination coefficient, which oscillated around 70-95%, confirmed the foregoing (Table 5). In the final phase of the analysis an attempt was made to statistically model the dependent variable of the CPUE of freshwater and diadromous fishes obtained in each successive haul with four sources of variation – year, quarter, study profile and depth (Figures 8 and 9). In order to stabilise the variance of these dependent variables, all of the values were transformed logarithmically. ANOVA one-way analysis of variance was used in the calculations, which, due to the large dataset and the available computer programming, was the only type of calculation possible. In the last figures mentioned above, the average value calculated according to the model and its range of standard deviation (95% confidence intervals for factor means) is marked. The graphic analysis (multiple range analysis - which is not discussed in detail in the paper) of the applied 95% LSD test allowed groups of homogeneous levels to be defined in each of the factors with regard to the modified dependent variable - LOG(CPUEtotal freshwater or diadromous fishes + 0.0001 kg/h).

Four of the sources of variation in the model discussed had a statistically significant, although not uniformly strong, impact on the shaping of the CPUE values of freshwater and diadromous fishes in the southern Baltic. The calculated significance level for each of the analysed pair of variables was lower than 0.001, and the value of the statistics F-ratio (ranged from 7.2 to 33.8 for freshwater fishes and from 9.9 to 35.8 for diadromous fishes) was above the critical value. The calculations indirectly indicate that the effect of the location and depth of research catches most significantly shaped change in the CPUE values of freshwater fishes, while that of season (quarter) and depth did so with regard to diadromous fishes. Statistically significant differences were assessed with regard to the modified CPUE of freshwater fishes (Fig. 8): – between depths of 10 - 20 m and 10 - 30 m; the remaining depth pairs did not vary statistically with regard to the CPUE variable; – between research profiles 1 - 2, 1 - 3, 1 - 4 and 1 - 5, the remaining pairs of regions were homogeneous; – between quarters 1 - 2, 1 - 4, 2 - 3 and 2 - 4, the remaining pairs of quarters were homogeneous; – between 1976-1987 and 1989-1996 and with each group of a.m. years and 2002; year groups 1976-1988 and 1995-2000 (except 1996) were similar. Statistically significant differences were assessed with regard to the modified CPUE of diadromous fishes (Fig. 9): – between depths of 10 - 20 m and 10 - 30 m; the remaining depth pairs did not vary statistically with regard to the CPUE variable; – between research profiles 1 - 4, the remaining pairs of regions were homogeneous; – between quarters 1 - 2, 1 - 3, 1 - 4, 2 - 3, 2 - 4 and 3 - 4 (all possible pairs); – between 1976-1980 and 1981-1982 and with each group of a.m. years and 1992 and 2001.

CONCLUSIONS 1) In 1976-2002 nine freshwater fishes (pikeperch, perch, ruffe, bream, roach, pike, sabrefish, rainbow trout and three-spined stickleback) were registered in bottom research catches FRQGXFWHGSDUWLFXODUO\QHDU:LVáRXMFLHLQWKH3XFN%D\DQG.U\QLFD0RUVND- the long-term mean frequency of occurrence in these areas was 18%. Nine diadromous species (vimba, whitefish, eel, salmon, sea trout, shad, allis shad, smelt and river lamprey), recognised in samples, preferred following areas - Ustka-àHED:LVáRXMFLH.U\QLFD0RUVNDDQGWKH3XFN Bay, their mean frequency of occurrence in selected areas was 10%. 2) In comparison with other species, the frequency of occurrence of pikeperch in the bottom layer of the southern Baltic was the highest at an average of 8.4%. The share of this species in the catches also was the highest at an average of 1.14‰. The second and third most common species, which occurred in the hauls, were shad and eel with an average frequency of occurrence of 4.3 and 3.0%, respectively. 3) The average, long-term (1976-2002) frequency of occurrence of freshwater and diadromous fishes in hauls conducted in the all studied areas was 9 and 8%, respectively, the average share in catches was 1.3 and 0.6‰, respectively, and the mean CPUE of these fish groups was 0.25 and 0.13 kg/h, respectively. High frequencies of occurrence of freshwater fishes in a given region did not correspond with a high share in catches and high CPUE. The divergence between these variables with diadromous fishes was negligible. 4) The average frequency of occurrence of freshwater and diadromous fishes in the hauls was year and depth dependent, e.g. the results of regression analysis indicate that was a statistically significant, inversely proportional dependence between the frequency of occurrence and factor "depth". 5) Highest long-term mean of the CPUE of freshwater and diadromous fishes was obtained on depths 10 m, in the 4th and the 3rd quarter, respectively. 6) Four of the sources of variation (year, quarter, depth, region) in the mathematical model (ANOVA) applied had a statistically significant, although not steadily strong, impact on the shaping of the CPUE values of investigated groups of fishes in the southern Baltic. The 8

calculations indicate that the effect of the location and depth of research catches most significantly shaped changes in the CPUE values of freshwater fishes, while that of season (quarter) and depth did so with regard to diadromous fishes.

REFERENCES Bartel, R. 1991. Anadromous fishes in the Polish coastal waters. [in:] Symposium on the Baltic environment and fisheries, Gdynia 24-25 June 1991. Paper, abstracts. Bartel, R. 1993. Anadromous fishes in Poland. Bull. Sea Fish. Inst., Gdynia, 1(128): 3-15. Birzaks, J. 1997. Piekrastes zveja (Coastal fishery). [in:] Latvijas Zivsaimniecibas. Gadagramata 1996/97, Riga, Zivju Founds: 110-131 [in Latvian]. Borowski, W. 2000. 6WDQ ]DVREyZ U\E =DOHZX :LODQHJR L ZDUXQNL LFK HNVSORDWDFML >)LVK UHVRXUFHV LQ the Vistula Lagoon and conditions for their exploitation]. [in:] Oszacowanie stanu zasobów ryb SROVNLHM VWUHI\ SU]\EU]H*QHM L QDWXUDOQH ZDUXQNL LFK HNVSORDWDFML 6WXGLD L 0DWHULDá\ VHU % monograph, edited by Sea Fish. Inst., Gdynia: 9-33 [in Polish]. %U\OLVND 0 5\E\ VáRGNRZRGQH 3ROVNL >)UHVKZDWHU ILVK RI 3RODQG@ 3UDFD ]ELRURZD 3:1 Warszawa [in Polish]. 'HPHO . %LRORJLD U\E %DáW\NX >%LRORJ\ RI WKH %DOWic fishes]. Edited by Sea Fish. Inst., Gdynia [in Polish]. Draganik, B. 1996. Polish inshore waters, their properties and role in the coastal area economy. [in:] Proceedings of Polish-Swedish Symposium on Baltic coastal fisheries resources and management. Gdynia, 2-3 April 1996: 51-70. Erm, V., I. Sormus and T. Pritsik. 1991. The state of coastal fish stock in the northern and north-eastern Gulf of Riga. [in:] Symposium on the Baltic environment and fisheries. Gdynia 24-25 June 1991; Paper, abstracts. Erm, V. 1996. On the state of pikeperch Schizostedion lucioperca (L.) stock in Pärnu Bay. [in:] Proceedings of Polish-Swedish Symposium on Baltic coastal fisheries resources and management. Gdynia, 2-3 April 1996: 71-76. *VRZVND 0 .OXF]H GR R]QDF]DQLD NU JRZFyZ 3ROVNL >.H\V IRU WKH LGHQWLILFDWLRQ RI 3ROLVK 9HUWHEUDWHV@ 3DUW , .UJáRXVWH - Cyclostomi, ryby - Pisces (Praca zbiorowa). Edited by PAS in Kraków, PWN, Warszawa, Kraków [in Polish]. +HHVH 7 :\VW SRZDQLH L SRáRZ\ U\E VáRGNRZRGQ\FK Z VWUHILH SU]\EU]H*QHM SRPL G]\ XMFLDPL 3DUV W\ L :LHSU]\ >2FFXUUHQFH DQG FDWFKHV RI IUHVKZDWHU ILVK LQ WKH FRDVWDO DUHD EHWZHHQ WKH PRXWKV RI WKH 3DUV WD DQG Wieprza Rivers]. Bull. Sea Fish. Inst. Gdynia, 2 (135): 59-64 [in Polish]. Heese, T. 1998. Populations of non-commercial fish species of the coastal area of the southern Baltic Sea. Bull. Sea Fish. Inst. Gdynia, 3 (145): 21-39. Jackowski, E. 2002. Ryby Zatoki Puckiej [The Puck Bay fishes]. Monograph edited by Sea Fish. Inst. Gdynia [in Polish]. Nylander, E. 1998. Finnish Fisheries. Facts and statistics. Publisher - Finnish Game and Fisheries Research Institute, Helsinki. Editor - Eija Nylander: 33 pp. 3 F]DOVND $ 5\E\ X*\WNRZH %DáW\NX >&RPPHUFLDO ILVK RI WKH %DOWLF@ (GLWHG E\ 3DVWZ =DNá Wyd. Szkol., Warszawa [in Polish]. Plikshs, M., E. Aleksejevs 1998. Zivis [Fishes]. Latvijas Daba. Riga, edited by Gandrs: 304 pp. [in Latvian]. Psuty-Lipska, I., A. Garbacik-:HVRáRZVND 6SHFLHV FRPSRVLWLRQ DQG ILVK GLVWULEXWLRQ LQ WKH Pomeranian Bay and Szczecin Lagoon. Bull. Sea Fish. Inst. Gdynia, 3(145): 3-20. 6DSRWD 0 . 6NyUD )LVK DEXQGDQFH LQ VKDOORZ LQVKRUH ZDWHUV RI WKH *XOI RI *GDVN. [in:] Proceedings of Polish-Swedish Symposium on Baltic coastal fisheries resources and management. Gdynia, 2-3 April 1996: 215-223. 6LHGOHFNL 0 5\E\ PRUVNLH F] FLHM SRáDZLDQH QD %DáW\NX L ]DFKRGQLP $WODQW\NX >6HD ILVK RIWHQ caught in the Baltic and western Atlantic]. Edited by Sea Fish. Inst. Gdynia [in Polish]. Skóra, K. 1993. Ichtiofauna [Ichthyofauna]. [in:] Zatoka Pucka [The Puck Bay]; monograph, praca zbior. SRG UHGDNFM K. Korzeniowskiego ,QVW\WXW 2FHDQRJUDILL 8QLZHUV\WHWX *GDVNLHJR *GDVN - 467 [in Polish]. Skóra, K. 1996. A comparison of changes in the composition of fish catches in the Polish lagoons in 1960-1989. [in:] Proceedings of Polish-Swedish Symposium on Baltic coastal fisheries resources and management. Gdynia, 2-3 April 1996: 225-241. Thoresson, G., M. Kangur, R. Repecka, T. Saat, M. Vitinsh. 1996. Development of a resource assessment system for Baltic coastal fish stocks. [in:] Proceedings of Polish-Swedish Symposium on Baltic coastal fisheries resources and management. Gdynia, 2-3 April 1996: 283-292. 9

Thoresson G., M. Kangur, R. Repecka, T. Saat, M. Vitinsh. 1997. Development of a resource assessment system for Baltic coastal fish stocks with perch (Perca fluviatilis L.) as a model species. Bull. Sea Fish. Inst. Gdynia, 3(142): 27-36. Thoresson, G. 1997. The Swedish coastal fishery in the Baltic Sea. Bull. Sea Fish. Inst. Gdynia, 2(141): 67-78. Trella, K. 1998. The results of ichthyofauna research at investigation areas near the central coast. Bull. Sea Fish. Inst. Gdynia, 3(145): 57-64. :\VRNLVNL $ )LVKHU\ PDQDJHPHQW LQ WKH 6]F]HFLQ /DJRRQ %XOO 6HD )LVK ,QVW *G\QLD 65-81.

Table 1. List of bottom control hauls performed by the Polish research vessels during the BITS surveys (within the Polish EEZ) on particular research profiles of the southern Baltic in 1976- 2002 and at depth stratums from 10 m to 110 m; the numerical code of research profiles used in the study are in brackets. Year Research profiles and Krynica :LVáR- Puck :áDG\- Gdansk Ustka- Slupsk .RáREU]HJ- Pomeranian Total depth Morska XMFLH Bay VáDZRZR Deep àHED Furrow 'DUáRZR Bay [m] (1) (2) (3) (4) (5) (6) (7) (8) (9) 1976 8 – 7 16 4 – – – – 35 1977 35 – 14 68 – – – 23 – 140 1978 57 – 30 69 – 2 17 11 – 186 1979 32 3 15 45 4 – 8 15 – 122 1980 39 – 18 46 3 – 9 – – 115 1981 37 7 16 37 – 15 12 – – 124 1982 52 4 22 79 3 15 37 29 5 246 1983 39 1 15 41 – 4 15 20 7 142 1984 35 2 20 58 13 22 5 6 – 161 1985 18 6 9 45 – 2 – 8 2 90 1986 13 3 7 25 3 – 5 13 1 70 1987 25 18 18 55 1 3 1 – – 121 1988 24 19 20 58 12 17 9 1 2 162 1989 18 11 8 36 2 – – – – 75 1990 26 19 11 52 – – – – – 108 1991 38 22 16 68 – – – – – 144 1992 15 10 7 29 – 10 – – 71 1993 21 11 15 42 – 2 7 5 – 103 1994 22 12 10 51 – – 16 – – 111 1995 7 7 3 21 1 5 8 12 2 66 1996 17 11 5 39 1 1 18 3 – 95 1997 21 13 7 45 4 6 23 26 8 153 1998 18 12 5 39 – 3 23 16 8 124 1999 11 7 2 23 2 3 9 13 3 73 2000 7 6 2 12 – 3 5 16 3 54 2001 6 6 3 1 2 – 1 2 – 21 2002 10 8 3 5 – 8 – 7 – 41 Total 651 218 308 1103 57 111 238 226 41 2953 10 6 1 – 11 – 17 – – 6 41 20 80 37 8 125 – 51 – 12 14 327 30 83 38 60 117 – 32 – 24 8 362 40 80 37 81 132 – 7 36 35 9 417 50 80 39 81 129 – 3 41 38 4 415 60 77 35 78 139 – 1 41 51 – 422 70 75 31 – 129 1 – 55 40 – 331 80 66 – – 126 14 – 41 21 – 268 90 60 – – 104 26 – 24 5 – 219 100 44 – – 91 7 – – – – 142 110 – – – – 9 – – – – 9 Total 651 218 308 1103 57 111 238 226 41 2953

Table 2. Average (1976-2002) frequency of occurrence (in % of hauls) of particular freshwater and diadromous fishes in the survey bottom hauls, conducted on research profiles of the southern Baltic; the selected areas where a particular group of species or separate species were most frequently recorded are marked in bold-blue; the numerical code of research profiles used are in brackets. Long-term Research profiles mean for Deepest places of Krynica :LVáRXM Puck :áDG\VáD *GDVN Ustka- 6áXSVN .RáREU]HJ- Pomera- occurrence of all selected Species Morska -FLH Bay -wowo Deep àHED Furrow 'DUáRZR nian Bay species areas areas (1) (2) (3) (4) (5) (6) (7) (8) (9) pikeperch (Stizostedion lucioperca L.) 9,18 19,98 22,11 0,51 0,00 0,00 0,00 1,49 5,00 8,43 17,09 70 m - (2) perch (Perca fluviatilis L.) 0,33 0,40 2,08 1,45 0,00 0,83 0,00 0,00 5,00 0,99 2,84 70 m - (1) ruffe [=bullrout] (Gymnocephalus cernua L.) 0,37 2,72 0,53 0,06 0,00 0,00 0,00 0,00 0,00 0,52 1,21 80 m - (4) bream (Abramis brama L.) 0,07 0,00 0,00 0,00 0,00 1,67 0,00 0,00 5,00 0,41 3,33 20 m - (6) roach (Rutilus rutilus L.) 0,30 0,00 1,23 0,19 0,00 0,42 0,00 0,00 1,25 0,36 1,24 60 m - (3) pike (Esox lucius L.) 0,18 0,23 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,07 0,20 40 m – (1 and 2) rainbow trout (Salmo gairdneri Rich.) 0,00 0,00 0,00 0,00 0,00 2,08 0,00 0,00 0,00 0,21 2,08 10 m - (6) sabrefish [=rasorfish] (Pelecus cultratus L.) 0,25 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,05 0,25 20 m - (1) total freshwater 8,45 25,69 19,48 2,09 0,00 7,21 0,00 0,88 7,32 9,86 17,87 - vimba (Vimba vimba vimba L.) 0,94 2,17 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,36 1,56 30 m - (1) whitefish (Coregonus lavaretus L.) 0,00 0,00 0,00 0,15 0,00 3,33 0,00 0,00 0,00 0,34 1,74 10 m - (6) eel (Anguilla anguilla L.) 1,93 3,71 6,22 2,16 0,00 5,36 0,00 2,78 5,00 2,99 5,10 90 m - (4) sea trout (Salmo trutta m. trutta L.) 0,56 0,00 0,00 0,14 0,00 1,20 0,00 0,00 0,00 0,20 0,88 90 m - (1) salmon (Salmo salar L.) 0,00 0,36 0,00 0,00 0,00 0,00 0,22 2,78 0,00 0,33 1,57 80 m - (7) shad (Alosa fallax Lacepede 1803) 5,37 5,33 6,05 5,41 11,67 0,00 5,00 0,69 0,00 4,33 6,47 100 m - (4) allis shad (Alosa alosa (L.) 0,34 0,54 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,11 0,44 60 m - (2) brook [=river] lamprey (Lampetra fluviatilis L.) 3,53 2,40 3,50 0,32 0,00 0,00 0,00 0,00 0,00 1,39 3,15 70 m – (1, 2 and 4) total diadromous 8,29 10,55 6,17 2,81 7,02 15,32 0,42 1,77 2,44 7,91 10,08 - total freshwater and diadromous 19,19 30,13 32,45 9,52 11,67 7,81 5,22 7,74 11,25 16,76 27,26 -

Table 3. Average CPUE and average share of the particular freshwater and diadromous fish species in the survey bottom catches conducted in 1976-2002 by research profiles of the southern Baltic.

5HVHDUFK SURILOHV 6RPH SHFXODULWLHV RI LQGLYLGXDO FDWFKHV FLH FLH 0HDQ 0HDQ &38( >NJK@ 'HWDLOV DERXW PD[LPXP FDWFK 3XFN %D\ 3XFN %D\ 8VWNDàHED 8VWNDàHED :LVáRXM :LVáRXM *GDQVN 'HHS *GDQVN 'HHS 6OXSVN )XUURZ 6OXSVN )XUURZ :áDG\VáDZRZR :áDG\VáDZRZR .U\QLFD 0RUVND .U\QLFD 0RUVND 3RPHUDQLDQ %D\ 3RPHUDQLDQ %D\ .RáREU]HJ'DUáRZR .RáREU]HJ'DUáRZR GHSWK 6SHFLHV 6KDUH >R @ &38( >NJK@ PLQ PD[ GDWH RR UHJLRQ >P@

SLNHSHUFK .U\QLFD 0RUVND

SHUFK 3RPHUDQLDQ %D\

UXIIH :LVáRXMFLH

EUHDP .U\QLFD 0RUVND

URDFK .U\QLFD 0RUVND

SLNH :LVáRXMFLH

UDLQERZ WURXW 8VWNDàHED

VDEUHILVK .U\QLFD 0RUVND

WRWDO IUHVKZDWHU

YLPED .U\QLFD 0RUVND

ZKLWHILVK 8VWNDàHED

HHO .U\QLFD 0RUVND

VHD WURXW .U\QLFD 0RUVND

VDOPRQ .RáREU]HJ'DUá

VKDG :LVáRXMFLH

DOOLV VKDG .U\QLFD 0RUVND

ULYHU ODPSUH\ .U\QLFD 0RUVND

WRWDO GLDGURPRXV

Table 4. Equations of the 5th order multinomial model applied for trends analysis of the average frequency of occurrence, average CPUE and average share of freshwater and diadromous fish changes by years in the survey bottom catches by all investigated areas of the southern Baltic (1) and by selected areas (2) where a particular group of species or separate species was most frequently recorded in the 1976-2002 period.

)UHTXHQF\ RFFXUUHQFH RI KDXOV QXPEHU YV \HDUV R &38( LQ NJK YV \HDUV 6KDUH LQ RR RI FDWFK ZHLJKW YV \HDUV IUHVKZDWHU ILVKHV 1) y = 0.0002x5 – 0.012x4 + 0.2625x3 – 2.411x2 1) y = -3E-05x5 + 0.0021x4 - 0.0498x3 + 0.426x2 \ ([5 ± [4 [3 ± [2 [ + 9.636x – 10.055; r = 0.730; R2 = 53.3% - 0.5743x - 0.2285; r = 0.474; R2 = 22.47% ± U 52 2) y = 0.0003x5 – 0.0204x4 + 0.469x3 – 4.44x2 2) y = -7E-05x5 + 0.0052x4 - 0.1256x3 + 1.1275x2 \ ([5 ± [4 [3 ± [2 [ + 17.585x – 18.226; r = 0.728; R2 = 53.1% - 2.2939x + 0.9067; r = 0.432; R2 = 18.68% ± U 52 GLDGURPRXV ILVKHV \ ± [5 [4 ± [3 [2 1) y = 8E-06x5 - 0.0007x4 + 0.0239x3 - 0.3681x2 \ ±([5 ([4 ± [3 [2 ± [ U 52 + 2.2899x - 2.8592; r = 0.476; R2 = 22.64% [ ± U 52 \ ±[5 [4 ± [3 [2 2) y = 1E-05x5 - 0.0011x4 + 0.0374x3 - 0.5838x2 \ ±([5 [4 ± [3 ± [2 [ ± U 52 + 3.6511x - 4.6053; r = 0.486; R2 = 23.63% [ ± U 52 SLNHSHUFK \ [5 ± [4 [3 ± [2 [ \ ([5 [4 [3 [2 \ ([5 ± [4 [3 ± [2 ± U 52 [ U 52 [ ± U 52 \ [5 ± [4 [3 ± [2 \ ([5 [4 [3 [2 \ ([5± [4 [3 ± [2 [ ± U 52 [ U 52 [ ± U 52 HHO \ ([ ± [ [ ± [ [ \ ([5 [4 [3 [2 \ ([5 ± ([4 [3 ± [2 ± U 5 [ U 52 [ ± U 52 \ ([ ± [ [ ± [ [ \ ([5 [4 [3 [2 \ ±([5 ± ([4 [3 ± [2 ± U 5 [ U 52 [ ± U 52 VKDG \ ± [5 [4 ± [3 [2 \ ([ [ [ [ \ ([5 [4 [3 [2 ± [ U 52 [ U 52 [ U 52 \ ± [5 [4 ± [3 [2 \ ([ [ [ [ \ ([5 [4 [3 [2 ± [ U 52 [ U 52 [ U 52

Table 5. Simple regression analysis results between the average frequency of occurrence, average CPUE and the average share of freshwater and diadromous fishes in the survey bottom catches and depth stratums; 1 - all investigated areas of the southern Baltic, 2 - selected areas where a particular group of species or separate species were most frequently recorded in the 1976-2002 period.

R )UHTXHQF\ RFFXUUHQFH RI KDXOV QXPEHU YV GHSWK 6KDUH LQ RR RI FDWFK ZHLJKW YV GHSWK &38( LQ NJK YV GHSWK IUHVKZDWHU ILVKHV OLQHDU PRGHO H[SRQHQWLDO PRGHO H[SRQHQWLDO PRGHO \ ± [ U ± \ H[S ± [ U ± \ H ±[ 5 U ± SUREDELOLW\ OHYHO )UDWLR 5 SUREDELOLW\ OHYHO )UDWLR 5 \ ± [ U ± \ H[S ± [ U ± \ H ±[ 5 U ± SUREDELOLW\ OHYHO )UDWLR 5 SUREDELOLW\ OHYHO )UDWLR 5 GLDGURPRXV ILVKHV H[SRQHQWLDO PRGHO \ H±[ U ± \ H[S ± [ U ± \ H ±[ 5 U ± SUREDELOLW\ OHYHO 5 SUREDELOLW\ OHYHO )UDWLR 5 \ H±[ U ± \ H[S ± [ U ± \ H ±[ 5 U ± SUREDELOLW\ OHYHO 5 SUREDELOLW\ OHYHO )UDWLR 5 SLNHSHUFK OLQHDU PRGHO H[SRQHQWLDO PRGHO H[SRQHQWLDO PRGHO \ ± [ U ± \ H[S ± [ U ± \ H ±[ 5 U ± SUREDELOLW\ OHYHO )UDWLR 5 SUREDELOLW\ OHYHO )UDWLR 5 \ ± [ U ± \ H[S ± [ U ± \ H ±[ 5 U ± SUREDELOLW\ OHYHO )UDWLR 5 SUREDELOLW\ OHYHO )UDWLR 5 HHO H[SRQHQWLDO PRGHO \ H[S ± [ U ± \ H[S ± [ U ± \ H ±[ 5 U ± SUREDELOLW\ OHYHO )UDWLR 5 SUREDELOLW\ OHYHO )UDWLR 5 \ H[S ± [ U ± \ H[S ± [ U ± \ H ±[ 5 U ± SUREDELOLW\ OHYHO )UDWLR 5 SUREDELOLW\ OHYHO )UDWLR 5

Table 6. Average annual share of the freshwater and diadromous fishes in total Polish catches of all species in the Baltic, 2001-2002; the input data was provided by courtesy of the Department of Fishery Economics, Sea Fisheries Institute in Gdynia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

Figure 1. Geographical distribution of the research profiles (solid coloured line) and bottom trawling stations (small rings) in the Polish EEZ; the numerical code of the research profiles used in the study: 1 – Krynica Morska, 2 – :LVáRXMFLH– the Puck Bay, 4 –:áDG\VáDZRZR–WKH*GDVN'HHS– Ustka-àHED–6áXSVN)XUURZ–.RáREU]HJ-'DUáRZR– the Pomeranian Bay.

55.5 °

55.0 °

54.5 °

54.0 °

13.0 ° 14.0 ° 15.0 ° 16.0 ° 17.0 ° 18.0 ° 19.0 ° E 20.0 °

Figure 2. Average, annual frequency of occurrence of freshwater and diadromous fishes in the survey bottom hauls, according to all investigated areas and selected areas, where a particular group of species or separate species was most frequently recorded in the southern Baltic.

)UHVKZDWHU ILVKHV 'LDGURPRXV ILVKHV

2FFXUUHQFH > RI KDXOV QXPEHU@ 2FFXUUHQFH > RI KDXOV QXPEHU@ PHDQ IRU DOO DUHDV PHDQ IRU VHOHFWHG DUHDV

3LNHSHUFK 6WL]RVWHGLRQ OXFLRSHUFD / 6KDG $ORVD IDOOD[ /DFHSHGH

2FFXUUHQFH > RI KDXOV QXPEHU@ 2FFXUUHQFH > RI KDXOV QXPEHU@ PHDQ IRU DOO DUHDV PHDQ IRU VHOHFWHG DUHDV

Figure 3. Average yearly (1976-2002) share of freshwater and diadromous fishes in survey bottom catches, separately for all investigated areas of the southern Baltic and for selected areas where a particular group of species or separate species was most frequently recorded.

)UHVKZDWHU ILVKHV 'LDGURPRXV ILVKHV RI FDWFK ZHLJKW@ RI FDWFK ZHLJKW@ RR RR R R 6KDUH > 6KDUH > PHDQ LQ DOO DUHDV PHDQ LQ VHOHFWHG DUHDV

3LNHSHUFK 6WL]RVWHGLRQ OXFLRSHUFD / (HO $QJXLOOD DQJXLOOD / RI FDWFK ZHLJKW@ RI FDWFK ZHLJKW@ RR RR R R 6KDUH > 6KDUH > PHDQ LQ DOO DUHDV PHDQ LQ VHOHFWHG DUHDV

Figure 4. Average catch (CPUE) of freshwater and diadromous fishes by years (1976-2002), according to all investigated areas of the southern Baltic and selected areas where a particular group of species or separate species was most frequently recorded.

)UHVKZDWHU ILVKHV 'LDGURPRXV ILVKHV 6 1,6

5 1,4 1,2 4 1,0 3 0,8 0,6

&38( > NJK @ 2 &38( >NJK@ 0,4 1 0,2 0 0,0 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002

3LNHSHUFK 6WL]RVWHGLRQ OXFLRSHUFD / (HO $QJXLOOD DQJXLOOD / 4,5 0,6 4,0 0,5 3,5 3,0 0,4 2,5 0,3 2,0 &38( >NJK@ 1,5 &38( >NJK@ 0,2 1,0 0,1 0,5 0,0 0,0 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002

o Figure 5. Average CPUE, the average share (in /oo of catch weight) and the average frequency of occurrence (in % of hauls) of freshwater and diadromous fishes in the survey bottom catches by quarters - in the all investigated areas of the southern Baltic and in selected areas where a particular group of species or separate species was most frequently recorded in the 1976-2002 period.

)UHVKZDWHU ILVKHV 'LDGURPRXV ILVKHV &38( LQ DOO DUHDV &38( LQ VHOHFWHG DUHDV VKDUH LQ DOO DUHDV VKDUH LQ VHOHFWHG DUHDV RFFXUUHQFH LQ DOO DUHDV RFFXUUHQFH LQ VHOHFWHG DUHDV 6KDUH DQG RFFXUUHQFH 6KDUH DQG RFFXUUHQFH &DWFK &38( LQ NJK &DWFK &38( LQ NJK , ,, ,,, ,9 TXDUWHU , ,, ,,, ,9 TXDUWHU

3LNHSHUFK 6WL]RVWHGLRQ OXFLRSHUFD / (HO $QJXLOOD DQJXLOOD /

6KDUH DQG RFFXUUHQFH 6KDUH DQG RFFXUUHQFH &DWFK &38( LQ NJK &DWFK &38( LQ NJK , ,, ,,, ,9 TXDUWHU , ,, ,,, ,9 TXDUWHU

Figure 6. Average (1976-2002) quarterly catch (CPUE) of freshwater and diadromous fishes by research profiles of the southern Baltic.

)UHVKZDWHU ILVKHV 'LDGURP RXV ILVKHV &38( >NJK@ &38( >NJK@ 012345678910 0,0 0,5 1,0 1,5 2,0 2,5 3,0

.U\QLFD 0RUVND .U\QLFD 0RUVND

:LVáRXM FLH :LVáRXM FLH

WKH 3XFN % D\ WKH 3XFN % D\

:áDG\VáDZRZR :áDG\VáDZRZR

WKH * GD VN ' HHS WKH * GD VN ' HHS

8VWNDàHED 8VWNDàHED

6áXSVN )XUURZ 6áXSVN )XUURZ

.RáREU]HJ' DUáRZ R .RáREU]HJ' DUáRZR

WKH 3RP HUDQLDQ %D\ WKH 3RP HUDQLDQ % D\

I II III IV quarter I II III IV quarter

3LNHSHUFK 6WL]RVWHGLRQ OXFLRSHUFD / (HO $ QJXLOOD DQJXLOOD / &38( >NJK@ &38( >NJK@ 0,00 0,25 0,50 0,75 1,00 1,25 1,50 1,75 2,00 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4

.U\QLFD 0RUVND .U\QLFD 0RUVND

:LVáRXM FLH :LVáRXM FLH

WKH 3XFN % D\ WKH 3XFN % D\

:áDG\VáDZRZR :áDG\VáDZRZR

WKH * GD VN ' HHS WKH * GD VN ' HHS

8VWNDàHED 8VWNDàHED

6áXSVN )XUURZ 6áXSVN )XUURZ

.RáREU]HJ' DUáRZ R .RáREU]HJ' DUáRZR

WKH 3RP HUDQLDQ %D\ WKH 3RP HUDQLDQ % D\

I II III IV quarter I II III IV quarter

o Figure 7. Average CPUE, the average share (in /oo of catch weight) and the average frequency of occurrence (in % of hauls) of freshwater and diadromous fishes in the survey bottom catches versus depth stratums, according to all the investigated areas of the southern Baltic and to selected areas where a particular group of species or separate species was most frequently recorded in the 1976-2002 period.

)UHVKZDWHU ILVKHV 'LDGURPRXV ILVKHV &38( LQ DOO DUHDV &38( LQ VHOHFWHG DUHDV VKDUH LQ DOO DUHDV VKDUH LQ VHOHFWHG DUHDV RFFXUUHQFH LQ DOO DUHDV RFFXUUHQFH LQ VHOHFWHG DUHDV 6KDUH DQG RFFXUUHQFH &DWFK &38( LQ NJK 6KDUH DQG RFFXUUHQFH &DWFK &38( LQ NJK 'HSWK >P@ 'HSWK >P@

3LNHSHUFK 6WL]RVWHGLRQ OXFLRSHUFD / (HO $QJXLOOD DQJXLOOD / 6KDUH DQG RFFXUUHQFH 6KDUH DQG RFFXUUHQFH &DWFK &38( LQ NJK &DWFK &38( LQ NJK 'HSWK >P@ 'HSWK >P@ 22

Figure 8. Average catches (CPUE) of freshwater fishes in the southern Baltic (1976-2002), according to the model [LOG(y+0.0001kg/h)] with 95% confidence intervals for factor means and graphic analysis of group homogeneity of this variable versus temporal-spatial sources of variation.

&38( DFFRUGLQJ WR WKH PRGHO &38( DFFRUGLQJ WR WKH PRGHO

5HVHDUFK SURILOH 7UDZOLQJ GHSWK>P@

Figure 9. Average catches (CPUE) of diadromous fishes in the southern Baltic (1976-2002), according to the model [LOG(y+0.0001kg/h)] with 95% confidence intervals for factor means and graphic analysis of group homogeneity of this variable versus temporal-spatial sources of variation.

&38( DFFRUGLQJ WR WKH PRGHO &38( DFFRUGLQJ WR WKH PRGHO

5HVHDUFK SURILOH 7UDZOLQJ GHSWK > P @