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ICES Marine Science Symposia, 215: 361-370. 2002 migration studies in the - a historical review

Eero Aro

Aro, E. 2002. studies in the Baltic Sea: a historical review. - ICES Marine Science Symposia, 215: 361-370.

The distribution of Baltic Sea fish throughout their life history may be random or patterned, and these changes have been estimated by tagging programmes since the early years of ICES. The adaptive value of fish migration is strongly coupled with the optimization of the surrounding environment. The hydrographic conditions in the Baltic form an uneven continuity from southwest to northeast, and the physiological selection of fish species, their distribution, and their capability to migrate has taken place in varying environmental temperatures and salinities. In the life history of fish species in the Baltic Sea, the eurythermie and species have had more adap­ tive value than those species which prefer constant salinities and temperatures. The euryhaline and eurythermie species are usually able to migrate more intensively than stenothermic and stenohaline species. Marine species have both rather local and more migratory stocks. Freshwater species are, in general, more stationary than marine species. The advantage of migrations in a patchy environment is that the impact of environmental variability on reproduction, survival, foraging, and growth decreases. ICES, as a coordinating organization, has played an important role in migration stud­ ies during the last 100 years and has been significant as a forum for developing new ideas and hypotheses on fish migration in the Baltic Sea.

Keywords: Baltic , Baltic , . , freshwater species, ICES, migration, , sea , tagging.

Eero Aro: Finnish Game and Research Institute, Pukinmäenaukio 4, PO Box 6, FIN-00721 Helsinki, Finland; tel: +358 205 751 253; fax: +358 205 751 201; e-mail: [email protected].

Introduction Historical background of ICES and fish migration research in the Baltic Sea If the environmental needs of fish species were constant through time, there would be no reason for them to move from place to place. The distribution of fish Early years at the beginning of the 20th century throughout their life history may be random or pat­ terned, and the environmental needs of individuals may Since the early years of ICES, fish migration, distribu­ vary from day to night, summer to winter, and from the tion, and interaction studies have formed an important time of hatching to their adulthood. The spatial and tem­ part of ICES research activities (Hoek and Hjort, 1903; poral distributions of many fish species change in more Garstang, 1903; Hoek and Garstang, 1903). These activ­ or less regular and cyclical patterns. The adaptive value ities led to the development of Petersen's famous princi­ of fish migration is strongly coupled with the optimiza­ ple (Petersen button), attaching a tag button by a silver tion of the surrounding environment. The Baltic Sea is wire near the middle of the dorsal edge of the body. the product of the last glacial period and has many Finnish Fisheries Inspector Oscar Nordqvist, who was unusual characteristics. It hosts an aquatic biota where Convener of ICES Committee C (Committee for the both marine and freshwater organisms live side by side Baltic) at the very beginning was the first to propose with a number of living relict species. The hydrograph­ migration studies and large-scale tagging research in the ic conditions in the Baltic Sea form an uneven continu­ Baltic Sea. He drafted a research proposal in 1902 for ity from southwest to northeast, so the physiological the Baltic (Nordqvist, 1903) which included basic work selection of fish species, their distribution, and their on salmon, , , , cod, and flounder and capability to migrate has taken place in varying envi­ the effect of seals on . His first draft also ronmental temperatures and salinities. included migration studies, but his work had to be com­ 362 E. Aro

FIN

NOR Salmon Eel

SWE EST RUS

LAT

LIT RUSI GER POL

Figure 1. The first recaptures of Baltic salmon and eel in early 1900 as reported to ICES in 1907. pleted by Filip Trybom (Sweden) and C. G. J. Petersen catch by the erection of hatcheries where the greatest () after Nordqvist’s unfortunate departure possible quantities of salmon might be bred". This pro­ caused by the political situation in Finland. The Czar of posal, considered a predecessor of the present Inter­ Russia issued an edict on 26 September 1902 to the national Baltic Sea Commission’s (IBSFC) Sal­ Finnish Senate to discharge Oscar Nordqvist for politi­ mon Action Plan (Anon., 1995), was not supported by cal reasons, effective 1 October 1902. the Baltic countries, and the ICES Bureau was not yet However, the outcome of Nordqvist’s initiative was a prepared to bring forward a definite proposal on the draft report, produced in 1907 by P. P. C. Hoek and F. matter in June 1907. Trybom and assisted by Nordqvist’s successor J. A. The special report by Trybom (1907b) gave detailed Sandman, to the governments of Denmark, Finland, results of Baltic salmon and sea trout tagging and mi­ Russia, and Sweden regarding the Baltic salmon fish­ gration studies conducted by various Member Countries eries (Hoek and Trybom, 1907). The report included a in the Baltic area during 1902-1906. Among the recap­ discussion about the reasons for the declining stock, the tures was one salmon originally tagged off Bornholm in nature of the fishery and its distribution between coastal April 1906 and recaptured four months later in Bothnian and open-sea areas, , and mini­ Bay. This is believed to be the first documented Baltic mum mesh size (Nordqvist, 1907), all in relation to the salmon record in the scientific literature. timing and pattern of salmon migrations. Trybom Another salmon tagged in September 1905 in the east­ (1907a) also drafted a special "proposal regarding an ern part of the Gulf of Finland outside the mouth of the international Treaty between the Baltic countries" which Kymijoki was recaptured in May 1907 in the contained a number of actions to be taken to "prevent neighbourhood of Memel (Klaipeda) showing, as a first any further diminution of the stock of salmon, maintain record, the possible extent of the feeding migration of the salmon stock in the Baltic and possible increase of Baltic salmon ( Figure 1 ). These early taggings of Baltic Fish migration studies in the Baltic Sea - a historical review 363

A. Coastal zone B. Small restricted "shells" C. Rocky areas D. Steep slopes E. Open/deep sea area F. Larger reefs in open sea G. Special areas (wrecks etc).

Figure 2. Typical ground categories in the Baltic Sea.

salmon and sea trout were aimed mainly at estimating special attention from ICES, although many laboratories the distribution area and proportion removed by open- tagged in coastal areas (Ekman, 1916; sea fisheries and coastal fisheries (Trybom, 1907b), and Henking, 1923). although the number of tagged fish each year was rather The main aims of all tagging studies during this peri­ low, tagging provided new information on migration pat­ od were to estimate the spatial and temporal distribution terns of Baltic salmon and sea trout. patterns and their annual changes. In the 1920s and The state of the eel stock in the Baltic also received 1930s, scientists began the practice of categorizing the attention (Trybom and Schneider, 1907) in Committee recapture information according to distance travelled C at the beginning of 1900. O. Nordqvist and J. A. Pal- and to the typical fishing grounds in the Baltic Sea mén started tagging in 1903 at the Tvärminne Zoo­ (Figure 2). logical Station founded by Palmén in 1902 on Hanko In the 1920s, special attention was paid to the most Peninsula, Finland, the westernmost part of the Gulf of abundant species in the pelagic system, Baltic herring Finland (Nordqvist, 1903). Eel taggings were expanded and sprat, and to their predator, Baltic cod (Heidrich, further in 1904-1907. These first silver eel taggings 1925; Hessle, 1923, 1925, 1927). Hessle (1925) showed and the subsequent recaptures in the that the slow-growing, long-lived, open-sea herring (Figure 1) contributed to the development of Johannes mainly along the Swedish east coast from Hanö Schmidt’s famous hypothesis on Bay to the Åland Sea in deeper water than the coastal (Schmidt, 1906). spring-spawning herring in other locations. Hessle (1925) also showed that Baltic herring along the Swe­ dish coast undertook long migrations extending from Priorities during the 1920s-1940s the Åland Sea to the southern part of the Baltic. In the 1920s, sprat were shown to inhabit the Baltic Fish migration studies in the Baltic in the 1920s-1940s from the Belt Seas and Western Baltic (ICES Subdivi­ concentrated mainly on commercially important marine, sions 22 and 24), to the Quark area in the north (Sub­ anadromous, and catadromous species such as Baltic division 30), and to the northeastern part of the Gulf herring, sprat, cod, plaice, flounder, eel, and salmon. of Finland (Subdivision 32) (Hessle, 1927). Three dif­ The freshwater species in the Baltic did not receive any ferent sprat stock components were considered at that 364 E. Aro time, with a low rate of mixing with the Kattegat and Main results from tagging and migra­ Skagerrak stocks due to the salinity gradient and differ­ tion studies during 1950-1980 ences in many abiotic factors between the Western Bal­ tic and the Kattegat (Hessle, 1927). Herring Hessle ( 1923) and his colleagues reported on the dis­ tribution, spawning, growth, and periodicity of Baltic Tagging and migration studies have shown that in some cod year classes along the Swedish coast. Although areas Baltic herring can be divided into two or three these studies included only areas in the vicinity of the components by their different migration patterns, such Swedish coast, they indicated great fluctuation caused as spring-spawning coastal herring, spring-spawning by changes in the distribution patterns of cod year class­ open-sea herring, and autumn-spawning herring. Baltic es. Kändler ( 1944), in his classical work in which small herring in the southwestern Baltic, Kattegat, and Skag­ numbers of cod were tagged, showed differences be­ errak have both spring-spawning and autumn-spawning tween cod stocks in the Baltic in the Transition Area components (Anwand, 1963a, 1963b), with spring- around Bornholm (14°E). spawning stocks having a very clear migration pattern. In the case of Baltic salmon, Järvi (1938) reported The majority of the fish migrate from the feeding and that they nearly all fed in the Baltic Main Basin (Sub­ wintering areas in the Skagerrak and Kattegat through divisions 24-29) and that the most important feeding the Öresund and the Belts into the Baltic in autumn and grounds were the Gotland Deep, the waters around early winter, with a minority coming from other feeding Bornholm, and the Gdansk Basin. This important work areas around Bornholm, off the Polish coast, and Hanö summarized 15 years of information (1921-1935) on Bay to the spawning grounds (Biester, 1979; Otterlind, the basic biology, the fisheries, and obvious reasons for 1985). The migration pattern of adult herring from the fluctuations in the Baltic salmon. Baltic to the Kattegat and Skagerrak has also been con­ firmed by the occurrence of Anisakis larvae in the adult herring from the Southwestern Baltic Decades of tagging and migration studies (Strzyzewska and Popiel, 1974; Friess, 1977; Kiihlmor- during 1950-1980 gen-Hille, 1983). Herring in the Southwestern Baltic seem to have a clear homing ability (Jönsson and Fish migration studies using tagging were intensified Biester, 1979) despite some controversy. In the Central considerably in ICES circles in the 1950s. An initial Baltic, there are assumed to be three different stocks: stimulus came when a Danish cutter accidentally dis­ spring-spawning coastal herring, spring-spawning open- covered dense concentrations of young herring on the sea herring, and autumn-spawning herring (Popiel, Bløden Grounds in July 1950 about 60-100 miles west 1984). These stock components have different migration of Esbjerg, Denmark, in the North Sea. This discovery patterns in the Southeastern and Central Baltic. In the and the fishery which subsequently developed stimulat­ Bothnian Sea, there are two spring-spawning coastal ed discussion about the role and effect of the Bløden herring components (Hannerz, 1955, 1956; Otterlind, fishery on the North Sea herring fishery and led to an 1957; Parmanne and Sjöblom, 1982, 1986), one along extensive tagging programme for herring in the North the west coast and one on the east coast, both of which Sea and the Baltic Sea. The establishment of the Inter­ show high spawning-site fidelity. national Baltic Sea Fishery Commission (IBSFC), and two ICES working groups necessary for IBSFC activities served to elevate the need for tag­ Sprat ging studies in the early 1970s. Thus, the present knowledge of fish migration in the Sprat inhabit the Baltic Sea from the Belt Seas and west­ Baltic is based mainly on taggings made from the early ern Baltic (Subdivisions 22 and 24), to the Quark area in 1950s to the 1980s, except in the case of Baltic salmon the north (Subdivision 30), and to the northeastern part and sea trout, large numbers of which have been tagged of the Gulf of Finland (Subdivision 32) (Hessle, 1927; each year up to the present. Between 1950 and 1980, Veldre, 1986; Rechlin, 1986). There are three different several hundred thousand fish were tagged throughout sprat stocks in the Baltic, and mixing with the Kattegat the entire Baltic area (Aro, 1989) including Baltic her­ and Skagerrak stocks is considered to be very low, ring, sprat, cod, plaice, flounder, Baltic salmon, sea although there is no significant difference in morpho- trout, and freshwater species such as whitefish, pike, metric characters and vertebrae counts (Lindquist, pikeperch, perch, bream, and burbot. 1968). Mixing is probably prevented by the salinity gra­ A common feature of all the tagging work has been to dient and differences in many abiotic factors between estimate annual migration patterns and their changes, the Western Baltic and the Kattegat (Hessle, 1927; Aps the home range of various species, site fidelity for et al„ 1987). Boundaries between neighbouring stocks spawning, distribution of stock components and their are unclear, and stock mixing during feeding and win­ mixing, and the effects of fishing at stock level, and also tering is apparent (Rechlin, 1986). During the feeding to evaluate the timing of annual migration patterns. period in July-November in the south and central parts Fish migration studies in the Baltic Sea - a historical review 365 of the Baltic (van Khan et al., 1972) and in August- and Auvinen, 1984a, 1985). On these feeding grounds, December in the north, sprat migrate from the more the stocks mix thoroughly, and there is no clear evidence coastal areas to the offshore parts of the Baltic basins on the preferred feeding areas of individual stocks, al­ forming feeding shoals which contain mainly older age though there are some aggregations on the main fishing groups (Lindquist, 1971). The range and amplitude of grounds (Carlin, 1959; Halme, 1964). Feeding salmon the migration patterns of sprat stocks and their mixing are more or less clustered, and changes in density on the in the Baltic is not yet very clear. Some observations feeding grounds reflect their active movement in search indicate more locality (Aps and Lotman, 1984; Aps et of food (Thurow, 1973). at., 1987), but some, on the contrary, indicate more All Baltic salmon stocks exhibit homing behaviour, migratory behaviour and stock mixing (Grauman, 1976; but in some releases, homing has not developed because Khoziosky et al., 1983). of environmental factors (Christensen, 1982).

Salmon Sea trout

Salmon in the Baltic are distributed from the Belt Seas Sea trout in the Baltic are distributed from the south­ and Western Baltic to the northern parts of the Gulf of western part to the northern parts of the Gulf of Bothnia Bothnia and the Gulf of Finland and very seldom and eastern parts of the Gulf of Finland. Their migration migrate outside the Baltic (ICES, 1980; Lindroth et al., may be divided into two patterns: the long-distance 1982). There are naturally spawning stocks and artifi­ migrating stocks and the more stationary stocks cially reared stocks of various origin. During the marine (Zarnecki and Duszynski, 1961; Ikonen and Auvinen, phase, the Baltic salmon have very clear migration pat­ 1984b). In the Baltic, sea trout occupy an intermediate terns in the coastal and pelagic area. In general, both the position between the pelagic and communi­ wild and hatchery-reared stocks have the same migra­ ties, and their migration pattern is dependent on stock tion patterns, with some exceptions. The migrations are origin and the dimensions of the archipelago. divided into post-smolt, feeding, and spawning phases. During their feeding migration, the stocks in the Salmon smolts enter the Baltic usually in April-June, Bothnian Sea and Bothnian Bay intermix when migrat­ with those from the southern Baltic running a few weeks ing from the east coast to the west coast and vice versa. earlier than those from the north. The wild and hatch­ The migration southwards from Bothnian Bay to the ery-reared smolts start their post-smolt migration at Bothnian Sea and to the Main Basin has also been about the same time. During the first few weeks, post- observed even if the northern stocks are considered to smolts are relatively stationary, adapting to the new be more local and less migratory in nature (Carlin, environment, and they remain close to the river mouth 1965; Ikonen and Auvinen, 1984b). In the Gulf of or releasing place (Bartel, 1976; Ikonen and Auvinen, Finland, the feeding migration encompasses the whole 1985). From releases on the Finnish side of Bothnian area from west to east, and there appears to be some Bay (Subdivision 31), post-smolts migrate southwards migration to the Archipelago Sea, the Bothnian Sea, and along the Finnish coast to the Quark area where they the Main Basin (Ikonen and Auvinen, 1984b). In the shift to the Swedish coast. From the Swedish releases, northeastern Baltic near the island of Saaremaa, the the post-smolts migrate south along the Swedish coast stock seems to be quite local, but in some cases it of Bothnian Bay to the Quark where some shift to the extends into the Bothnian Sea, the Åland Sea, near Finnish side following the main current northwards Gotland Island, and southwards to the Bornholm region along the Finnish coast, and do not leave Bothnian Bay (Rannak et al., 1983). In the Southern Baltic, the feed­ (Larsson and Atheskar, 1979). In the Bothnian Sea ing migrations are more intensive and extend to quite (Subdivision 30) stock, the post-smolts behave like the large areas. From the Pomeranian coast and the Vistula northern stocks, except for the River Neva stock (from region, sea trout migrate mainly eastwards, but parts of Russian origin in the eastern Gulf of Finland, Sub­ the stock also move westward along the Polish coast. division 32) releases in the Bothnian Sea (Ikonen and The feeding migration of these stocks may reach the Auvinen, 1982), which seem to have more localized ten­ Gulf of Riga, the Gulf of Finland, and the Bothnian Sea dencies. (Backiel and Bartel, 1963; Chrzan, 1963). The stocks Nearly all Baltic salmon stocks feed in the Baltic along the Swedish south and east coasts migrate north­ Main Basin (Subdivisions 24-29), except those of River wards and to the Bothnian Sea, and the Gulf of Finland, Neva origin. From the releases in the Gulf of Finland, the Gulf of Riga, as well as southeasterly to the Gulf of about 31% of the Neva-origin fish feed in the Main Gdansk (Svärdson and Fagerström, 1982). Basin, while the percentage from the Bothnian Sea releases is less. The most important feeding grounds are the Gotland Deep, the waters around Bornholm, and the Gdansk Basin (Järvi, 1938; Halme, 1964; Carlin, 1959; Thurow, 1973; Christensen and Larsson, 1979; Ikonen 366 E. Aro

Cod 1978). There are at least three stocks in the Southwest­ ern and Southeastern Baltic (Subdivisions 22-26), three There are two cod stocks in the Baltic which have been in the Central and Northeastern Baltic (Subdivisions shown to differ in many ways. The Western Baltic stock 27-28), one each in the Åland Sea, Archipelago Sea, (Gadus morhua morhua L.; the or Tran­ and southern Bothnian Sea, and two in the Gulf of sition Area cod) is distributed west of Bornholm, in Finland (Anon., 1978). Migrations between the mature the Western Baltic, the Belt Seas, and the Sound (Sub­ flounder stocks in the southern and central Baltic are divisions 22-24) and has regular connections to the quite rare, extending from the southern part of Öland Kattegat (Division Ilia) and to the southeastern Baltic Island to the Rosewie on the Polish coast (Otterlind, (Bagge et a i , 1994). The Eastern Baltic stock (Gadus 1965, 1967; Vitinsh, 1976, 1977). Migrations are effec­ morhua callarias L.; the Baltic Sea cod) is distributed tively blocked in the Southeastern and Central Baltic by east of Bornholm to the northern parts of the Bothnian the Gdansk and Gotland Deeps and in the Northern Sea and to the eastern parts of the Gulf of Finland Baltic by the Gotland Deep and the deep southwest of (Bagge et al., 1994). The border between these two the Åland Islands (Otterltnd, 1965; Vitinsh 1972, 1976, stocks is diffuse, and mixing is evident in the Arkona 1977; Aro and Sjöblom, 1983b). The annual migration and Bornholm Basins. patterns of flounder stocks are quite well known and, Western Baltic cod migrate in all directions after because of their general locality, the homing behaviour spawning (Berner, 1981) from the deep waters to more of flounder is obvious. shallow coastal areas to feed. The young, immature age groups usually remain in the coastal areas before joining the mature stock. From the Arkona region, feeding Plaice migrations of adults may reach the Belt Seas in the west and extend eastwards to the Slupsk Furrow, the Plaice are distributed in the Baltic Sea from the Belt Bornholm region, the Gdansk Deep, and even to the eastwards to the Gdansk Bay area and northwards to the southern Gotland Deep (Lamp andTiews, 1974; Berner, southern Gotland Deep (Bagge, 1981). Plaice are very 1981 ). Cod in the Arkona Basin are always a mixture of rare in the Northern Baltic. Feeding migrations from the the two main stocks, and the spawning migration occurs deeper spawning grounds to shallower waters are pri­ in two directions. According to transplantation experi­ marily west and to a lesser extent east from the Arkona ments, the homing of cod is not well developed (Bagge, Basin. The westward feeding migration may reach the 1983). Belt Sea, the Sound, the southern Kattegat, and even the Eastern cod migrate to the Bornholm Basin spawning Skagerrak (Otterlind, 1967). Those emigrating out of grounds in December-February from the feeding the Baltic Sea are assumed not to return (Otterlind, grounds in Slupsk Furrow, Gdansk Bay, Hanö Bay, and 1967). The eastward migration is most intensive from the Gotland Deep (Netzel, 1968, 1974). The spawners in the Arkona Region to the east and southeast of Born­ the Gdansk Deep originate from areas south of the holm during November-February. Plaice feeding in the Bornholm Basin and from southern parts of the Gotland Gdansk Deep have been shown to migrate to the Born­ Deep (Netzel, 1974; Otterlind, 1976). There is also a holm Basin to spawn (Cieglewicz, 1961). spawning migration from the Swedish east coast, the Åland Sea, the southern Bothnian Sea, and the Gulf of Finland to the Bornholm Basin, the Gdansk Basin, and Freshwater species the southern parts of the Gotland Basin in December- March (Otterlind, 1976; Sjöblom et al., 1980; Aro and In the Southern Baltic where the freshwater species are Sjöblom, 1983a). The homing behaviour of cod in the almost totally absent, shallow coastal bottoms and Southeastern and Northern Baltic is also unclear, and pelagic areas serve as habitat for the young stages of cod may use different spawning grounds in successive several marine pelagic and demersal species of econom­ years (Bagge, 1983; Otterlind, 1984, 1985). During the ic importance. These areas also serve as habitat for a feeding period, cod are distributed over large areas and number of other littoral and coastal species of substan­ may undertake extensive migrations (Otterlind, 1985; tial ecological but minimal economic importance. In the Aro 1989) that exhibit no pattern. Central and Northern Baltic Sea, there is a clear domi­ nance of freshwater species in the littoral and coastal areas (Neuman, 1982), but their abundance decreases Flounder towards the seaward limit of their distribution (Lehtonen and Toivonen, 1981). The number of freshwater species There are several rather distinct flounder stocks or pop­ is greatest in the archipelagoes, bays, inlets, and river ulations in the Baltic (ICES, 1978). Flounder are regu­ mouths. The migrations of freshwater species are gener­ larly distributed in all parts of the Baltic, except Both­ ally local, although some species long distances. Some nian Bay, the easternmost part of the Gulf of Finland, of the freshwater species lack a migration pattern or and the deepest areas of the Gotland Deep (Anon., their migrations are too short to identify. Two whitefish Fish migration studies in the Baltic Sea - a historical review 367

species, river-spawning whitefish (Coregonus lavaretus community, a benthic community, and a littoral and L.) and sea-spawning whitefish (Coregonus widegreni coastal community. The borders between them are not Malmgren), have different migration patterns. They are sharp, and individuals from neighbouring communities distributed along the coastal areas in the Baltic and are cross them frequently, particularly the littoral and rare in the Belt Seas and along the south coast of coastal regions which serve the pelagic community as Sweden (Svärdson, 1979), but are more abundant in the spawning and nursery areas. In the Gulf of Bothnia, the Gotland Island area, along the west coast of Estonia, and littoral and coastal community is dominated by fresh­ in the Gulf of Finland, and the Gulf of Bothnia water species, which very seldom migrate outside this (Lehtonen, 1981). The feeding migration patterns vary environment, and the Baltic herring is actually the only between species and populations. Sea-spawning white- native pelagic species using that environment as a fish do not migrate very much and feed near the spawn­ spawning and nursery area (Andreasson and Petersson, ing grounds (Lehtonen, 1981). 1982). The migration and movements of the Baltic fish Pike exhibit a local distribution pattern and territorial species occur at micro- and macroscales inside and be­ behaviour (Ekman, 1916; Segerstråle, 1951; Halme, tween these communities in annual, diurnal, horizontal, 1957; Halme and Korhonen, 1960; Strandman, 1964; and vertical patterns. Lehtonen, 1973). Local migrations or movements dur­ The migration, spatial, and temporal distribution pat­ ing feeding are very limited since the pike is an ambush tern of Baltic fish exhibits an annual cycle between hunter or stalker (Neill and Cullen, 1974). The home spawning, feeding, and nursery habitats. Homing in range of an individual pike is usually several square spawning migrations and site fidelity has been ob­ kilometres and when displaced it attempts to return to served, but results suggest that this link is weak in the its original home range (Halme and Korhonen, 1960). case of cod, and the ratio of emigration to other spawn­ Pike-perch spawn in inlets and shallow bays in ing grounds seems to be dependent on the conditions of April-May (Lehtonen and Toivonen, 1981). After the spawning grounds. This also applies to spring- spawning, they remain on the spawning grounds and spawning Baltic herring and freshwater species. Baltic feed (Lehtonen and Toivonen, 1987) or migrate inside fish may use different spawning grounds in successive the archipelagoes, to the open sea, or along the coasts years, and evidence indicates that spawning migrations (Henking, 1923). Annual migrations take place between are more strongly linked to prevailing hydrographical spawning inlets or bays, feeding areas in the archipela­ conditions than to homing. goes, and wintering areas in deeper waters (Toivonen, The feeding migration of Baltic fish seems to have 1968). The average dispersal area is smaller when the different patterns for Baltic herring, sprat, salmon, and coast is open and larger when the archipelago is rich sea trout, but not in the case of cod. The movements of (Toivonen, 1968; Lehtonen and Toivonen, 1987). The Baltic fish from one place to another during the feeding mixing of local neighbouring stocks occurs in the win­ period seem to be once-a-year events. However, they tering areas, but pike-perch exhibit a clear homing may be just local seasonal movements, dispersals, or behaviour to their former spawning grounds (Lehtonen, "true" migrations. The advantage of movements and 1985). In the Southern Baltic, the feeding migration is migration in a patchy environment is, in general, that the directed to the open sea, and pike-perch overwinter in impact of environmental variability on reproduction, shallow inlets (Henking, 1923; Filuk, 1962). survival, foraging, and growth decreases. The migratory The perch is one of the most common freshwater behaviour promotes more flexibility in the face of un­ species in the Baltic archipelagoes. Perch form more or certainty. With migration, the risk from predation and less separate local but non-discrete stocks along the cannibalism is balanced against the advantage of re­ Baltic coasts (Böhling and Lehtonen, 1985). Spawning maining in one place to exploit resources. occurs all along the coast, and the mixing of neighbour­ The freshwater species in the Baltic have unfortunate­ ing stocks during spawning is unlikely (Ekman, 1916). ly been more or less neglected in ICES activities even After spawning, feeding migrations, usually short though they are an important component of the ecosys­ (Johnson, 1978), but sometimes long (Henking 1923), tem. The number of original freshwater species in the take place to deeper areas along the coasts and inside the Baltic is 23 (Lehtonen and Toivonen, 1981). The fresh­ archipelagoes. The range of feeding migrations is affect­ water species are practically absent in the southwestern ed by the distribution of food resources, optimum tem­ part of the Baltic except in some , fjords, and perature, and the abundance of neighbouring stocks, as bays (Henking, 1923; Hempel and Nellen, 1974). There well as the morphology of the archipelago (Böhling and are 18 species in the Central Baltic, and freshwater Lehtonen, 1985). species dominate in the north and northeastern parts of the Baltic (Lehtonen and Toivonen, 1981). The general problem in quantifying movements and Conclusions migrations (feeding or spawning) on a robust and usable spatial and temporal scale is that the tagging data rely The fish fauna in the Baltic Sea may be classified into totally on commercial fishermen’s catch and effort and three different and intermediate communities: a pelagic their willingness to return tags. Tagging of Baltic fish 368 E. Aro was very popular from the 1950s to the early 1980s. Aro, E., and Sjöblom, V 1983b. The migration of flounder in Most of these tagging studies and experiments were the northern Baltic Sea. ICES CM 1983/J:26. 12 pp. planned to estimate movements and fishing mortality. Backiel. T., and Bartel, R. 1963. Preliminary results of sea- and lake-trout tagging. ICES CM 1963/120. 6 pp. The results of these studies have only been partly pub­ Bagge, O. 1981. Demersal . In The Baltic Sea. Elsevier lished in the scientific literature. Oceanography Series, 30: 311-333. Ed. by A. Voipio. Else­ The analytical tools for mark-release experiments vier Scientific Publishing Company, Amsterdam. 418 pp. were developed decades ago and are well described Bagge, O. 1983. Migration of transplanted cod. ICES CM (Seber, 1973; Burnham et a l., 1987). However, data 1983/J : 16. 12 pp. analysis is hampered by a lack of essential information Bagge, O., Thurow, F., Steffensen, E., and Bay, J. 1994: The Baltic cod. Dana, 10: 1-28. on fishing effort, spatial and temporal distribution of Bartel, R. 1976. The Drava river salmon in the light of some fishing activities, systematic determination of tag return recent tagging experiments. ICES CM 1976/M:6. 8 pp. rates from the commercial fishery, and so on. Many Berner, M. 1981. Dislocation parameters of tagging experi­ tagging experiments have neglected these issues by al­ ments on cod in the Baltic (Subdivision 22-25) from 1959— locating resources mainly to catching and tagging of 1975. ICES CM 1981 /J: 15. 26 pp. fish instead of to the recovery and reporting rates Biester, E. 1979. The distribution of the Rügen spring herring. ICES CM 1979/J:31. 6 pp. of tags. Burnham, K. P., Anderson, D. R., White, G. C., Brownie, C., Before the establishment of the IBSFC in the early and , K. H. 1987. Design and analysis methods for 1970s, there were national fishing zones and a huge fish survival experiments based on release-recapture. Amer­ international fishing zone in the Baltic Sea where fish­ ican Fisheries Society Monograph, 5., Bethesda, Maryland, ing activities were largely unregulated. Consequently, USA. 437 pp. detailed information on fishing and fisheries was very Böhling, P., and Lehtonen, H. 1985. Effect of environmental factors on migrations of perch (Perea fluviatilis L.) tagged scarce, and the systematic collection of fisheries data in the coastal waters of Finland. Finnish Fisheries Research, did not exist on a large scale. The situation has changed 5: 31-40. considerably since the beginning of the 1970s, and the Carlin. B. 1959. Results of salmon smolt tagging in the Baltic parameters necessary for the design and analysis of tag­ area. Rapports et Procès-Verbaux des Réunions du Conseil ging experiments are now accessible. However, Baltic International pour l’Exploration de la Mer, 147: 89-96. fish tagging experiments are not very appealing because Carlin. B. 1965. Märkning av odlade havsöringsungar i utvan- dringsfardig storlek (Tagging of reared sea trout at the size conducting an experiment takes at least 6-8 years before ready to migrate). Svensk Fiskeri Tidskrift (Journal of Swe­ final results are available. Despite these shortcomings, dish Fisheries), 74(7/8): 97-101. (In Swedish). new tagging experiments on Baltic cod and herring Christensen, O. 1982. Danish experiments with salmon smolt should be encouraged. released into the Baltic Sea from the Island of Bornholm. ICES CM 1982/M:9. 7 pp. Christensen, O., and Larsson, P. O. 1979. Review of Baltic salmon research. Cooperative Research Report, 89. 124 pp. References Chrzan, E 1963. Preliminary report on tagging experiment of sea trout in the region of Vistula Firth. ICES CM 1963/95. 7 Andreasson, S., and Petersson, B. 1982. The fish fauna of the pp. Gulf of Bothnia. In Coastal Research in the Gulf of Bothnia, Cieglewicz, W. 1961. Tagging experiments with in the pp. 301-315. Ed. by K. Müller. Dr W. Junk Publishers, The southern Baltic. ICES CM 1961/95. 2 pp. Hague. 462 pp. Ekman, T. 1916. Meddelanden rörande utförda märkningar af Anonymous. 1995. Proceedings of the twenty first session. gädda m. fl. fiskar i Södermanslands och Östergötlands International Baltic Sea Fishery Commission. Warsaw, 4-8 skärgärd (Communications on tagging of pike in the archi­ September 1995. IBSFC, Warsaw. pelago of Södermansland and Östergötland). Svensk Fiskeri Anwand, K. 1963a. Markierungen am Riigenschen Frühjahrs­ Tidskrift (Journal of Swedish Fisheries), 1914-1916: 62-68. hering im Jahrel961 (Tagging of spring-spawning Rügen (In Swedish). herring in 1961). Internationale Revue der Gesamte Hydro­ Filuk, J. 1962. Nachkriegsstudium über Biologie und Fang des biologie (International Review of General Hydrobiology), Zanders des Frischen Haffs (Studies after the war on the 48: 2-8. (In German). biology and catches of pike-perch in Frischen Haff). Zeit­ Anwand, K. 1963b. Vergleichende Untersuchungen an Früh­ schrift für Fischerei (Journal of Fisheries), 10: 705-709. (In jahrs- und Herbst-heringe aus den Gewässern um Rügen German). (Comparative studies on spring- and autumn-spawning her­ Friess, C. 1977. Investigations on the spring spawning Rügen ring off Rügen). Zeitschrift für Fischerei (Journal of Fish­ herring infested by Anisakis in 1975-1977. ICES CM 1977/ eries), 11:211-249. (In German). P: 16. 6 pp. Aps. R.. and Lotman, K. 1984. Natural tags of sprat in the Gulf Garstang, W. 1903. Report of the Convener of Committee B. of Finland. ICES CM 1984/J:12. 11 pp. Rapports et Procès-Verbaux des Réunions du Conseil Inter­ Aps, R., Benenson, I., Kaleis, M., Korytin, N., and Kryazhim- national pour l’Exploration de la Mer, 1, Annex C: 47-49. sky, F. 1987. Spatial model of the Baltic sprat population Grauman, G. 1976. On the distribution and passive migrations dynamics. ICES CM 1987/J: 16. 18 pp. of Baltic sprat eggs and larvae in Bornholm-Slupsk spawn­ Aro, E. 1989. A review of fish migration patterns in the Baltic. ing ground. ICES CM 1976/P:8. 11 pp. Rapports et Procès-Verbaux des Réunions du Conseil Inter­ Halme. E. 1957. Gäddmärkningar utförda av Timmer Spinn- national pour l’Exploration de la Mer. 190: 72-96. fiskeklubb r.f. 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Halme, E. 1964. Report on salmon tagged in Finland in 1959— Ikonen, E., and Auvinen. H. 1985. Migration of salmon post- 1964. ICES CM 1964/Salmon and Trout Committee, 61. 7 pp. smolts (Salmo salar L.) in the Baltic Sea. ICES CM 1985/ Halme, E., and Korhonen, M. 1960. Haukien vaelluksista ran- M:19. 11 pp. nikoillamme (On migration of pike off our coast). Kalamies Johnson, T. 1978. Dispersal area of perch, Perea fluviatilis, (Fisherman), 4: 1-12. (In Finnish). tagged in a stream flowing into the Bothnian Sea. Aquilo Hannerz, L. 1955. Strömmingsmärkningen i Bottenhavet 1954 Serie Zoologica, 18: 62-64. (Tagging of herring in the Bothnian Sea in 1954). Ostkusten Järvi, T. H. 1938. Fluctuations in the Baltic stock of sal­ (East Coast), 1: 14-15. (In Swedish). mon 1921-1935. Rapports et Procès-Verbaux des Réunions Hannerz, L. 1956. Preliminary results of the herring investiga­ du Conseil International pour l’Exploration de la Mer, 106: tions in the Bothnian Sea 1954. Annales Biologiques du 1-114. Conseil International pour l’Exploration de la Mer, 11: Jönsson, N., and Biester, E. 1979. Results of tagging experi­ 156-158. ments on the Rügen spring herring 1977/78. ICES CM Heidrich, H. 1925. Über die Fortpflanzung von sprattus 1979/J:29. 13 pp. in der Kieler Bucht ( Reproduction of sprat, Clupea sprattus, Khan. N. van, Drzycimski, I., and Chojnacki, J. 1972. A con­ in the Kiel Bay). Wissenschaftliche Meeresunter-suchungen tribution to the biology of sprat (Sprattus sprattus balticus (Scientific Marine Research), 20: 1-47. (In German). Schneider) from the Bornholm Basin. ICES CM 1972/H:23. Hempel, G., and Nellen, W. 1974. Fische der Ostsee (Fishes in 9 pp. the Baltic Sea), ln Meereskunde der Ostsee (Baltic Sea Khoziosky, S., Shvetsov, F.. and Uzars, D. 1983. The dynamics Marine Research), pp. 215-232. Ed. by L. Magaard and G. of mortality components in Baltic sprat in Sub-divisions 26 Rheinheimer. Springer-Verlag, Berlin. 269 pp. (In German). and 28. 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Fiskeritidskrift for Finland (Journal of Finnish Re­ Hoek, P. P. C., and Hjort, J. 1903. Réunions d’Édinbourg des search), 23( 1): 8-9. (In Swedish). Commissions A et B. (4-9 Septembre 1902). Commission Lehtonen, H. 1973. Gäddans vandringar i våra kustvatten A: Pour les problèmes de la migration des poissons. Rap­ (Migration of pike in our coastal waters ). Fiskeritidskrift for ports et Procès-Verbaux des Réunions du Conseil Inter­ Finland (Journal of Finnish Fisheries), 17(3): 53-57. (In national pour l'Exploration de la Mer, 1, Commissions Spé­ Swedish). ciales: 88-96. Lehtonen, H. 1981. Biology and stock assessments of corego- Hoek, P. P. C., and Garstang, W. 1903. Réunions d’Édinbourg nids by the Baltic coast of Finland. Finnish Fisheries Re­ des Commissions A et B. (4-9 Septembre 1902). Commis­ search, 3: 31-83. sion B: Pour les questions de la diminution du rendement de Lehtonen, H. 1985. Stocks of pike-perch (Stizostedion luciop- la pêche. 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Netzel, J. 1968. Polish cod tagging experiments in the region Segerstråle, C. 1951. Återfångade märkta Ingä-gäddor ( Recap­ of Slupsk Furrow in the years 1957/1963. ICES CM 1968/ tures of pike tagged in Ingå). Finlands Jakt och Fisketid- F:7. 13 pp. skrifter (Journal of Finnish Game and Fisheries), 26: Netzel, J. 1974. Polish cod tagging experiments in the Baltic in 284-285. (In Swedish). 1969 and 1970. Rapports et Procès-Verbaux des Réunions Sjöblom, V, Aro, E., and Suuronen, P. 1980. Migrations, mor­ du Conseil International pour l’Exploration de la Mer, 166: tality and growth of cod in the northern Baltic Sea. ICES 40-46. CM 1980/J:8. 15 pp. Neuman, E. 1982. Species composition and seasonal migra­ Strandman, M. 1964. Monika SF 1517 (Tagged pike named tions of the coastal fish fauna in the southern Bothnian Sea. Monika, tag number SF 1517). Fiskeritidskrift for Finland, In Coastal Research in the Gulf of Bothnia, pp. 317-351. Ed. Ny Serie (Journal of Finnish Fisheries, New Series), 8: 84- by K. Müller. Dr W. Junk Publishers, The Hague. 462 pp. 86. (In Swedish). Nordqvist, O. 1903. Ein Vorschlag zum Programm der Strzyzewska. K.. and Popiel, J. 1974. Characteristic of herring Fischereiuntersuchungen in der Ostsee. Annexe A: Rapports infested by Anisakis larvae caught in the Gulf of Gdansk. et Procès-Verbaux des Réunions du Conseil International ICES CM'l974/H:15. 4 pp. pour l’Exploration de la Mer, 1: 143-146. (In German). Svärdson, G. 1979. Spéciation of Scandinavian Coregonus. Nordqvist, O. 1907. Die Längenmasse von in der südlichen Reports of the Institute of Freshwater Research, Drottning- Ostsee gefangenen Lachsen und Meerforellen als Vorberei­ holm, 57: 1-95. tung einer eventuellen Einführung von vereinbarten Min­ Svärdson, G., and Fagerström, A. 1982. Adaptive differences destmassen dieser Fische. Rapports et Procès-Verbaux des in the long distance migration of some trout, Salmo trutta. 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