Health and
Sustainable
Agriculture
Editors: Leif Norrgren and Jeffrey M. Levengood
Ecology and
Animal Health
Fish Communities
Magnus Appelberg
Swedish University of Agricultural Sciences, Öregrund, Sweden
The Baltic Sea has a species-poor fish community in comparison to other comparable marine areas, in average ca 100 fish species (EEA, 2002), with fewest species in NE, and highest species richness in SW. The fish species composition is the result of a fairly recent colonisation process. During the last 10,000 years, the salinity have changed from being fully marine to freshwater, ending up being brackish during the last 4,000 years. Today, the fish fauna comprise a mixture of marine and freshwater species, with most marine species found in the south-western and central part of the Baltic Proper, and the freshwater and migratory species dominating in the Gulf of Bothnia, Gulf of Finland and in the lagoons in the SE Baltic Proper.
Cod (Gadus morhua), sprat (Sprattus sprattus) and herring (Clupea harengus) constitute the most impor-tant species in the open sea. Other imporimpor-tant marine species are e.g. flatfishes, gobides and sculpins. Along the coasts freshwater species such as Eurasian perch (Perca fluviatilis), ruffe Gymnocephalus cernuus, zander (Stizostedion lucioperca), northern pike (Esox lucius) and cyprinids species such as roach (Rutilus rutilus), bream (Abramis brama), white bream (Blicca bjoerkna), rudd (Scardinius erythropthalmus) are dominating (Ådjers et al., 2006; HELCOM, 2006). Among cold water adapted
species whitefish (Coregonus lavaretus) and vendace (Coregonus albula), as well as migratory species Atlantic salmon (Salmo salar), sea trout (Salmo trutta), grayling (Thymallus thymallus). The European eel (Anguilla
an-guilla) has also been common in most coastal areas,
how-ever, it has become less abundant during recent years
Historical Development and Recent
Regime Shifts
Among factors structuring the Baltic fish fauna eutrophi-cation, including oxygen deficit in deeper areas, fishery, climate change, invasion of alien species and habitat degradation are considered to be of special importance. Decades of large-scale eutrophication and depletion of top-predators has resulted in dramatic changes in the Baltic Sea ecosystem (Österblom et al., 2007). Primary production has more than doubled since the 1920-40s (Elmgren, 1989, 2001), and the production of phytoplank-ton and macroalgae has become a serious environmen-tal problem for large parts of the Baltic Sea (Bonsdorff et al.,1997; Jansson and Dahlberg, 1999; SEPA, 2006). Intensive fishing of large fish predators has affected most
parts of the food web (Carpenter et al., 198�, 199�; Pace(Carpenter et al., 198�, 199�; Paceet al., 198�, 199�; Pace., 198�, 199�; Pace et al., 1999; Österblom et al., 1999; Österblom et alet al., 2007; Casini et al., 2008).et al., 2008).., 2008).
The fish community in the open Baltic Proper has undergone severe changes the past 100 years, includ-ing drastic reduction of the cod population, and changes in both sprat and herring abundances. Österblom et al. (2007) showed that reduced top-down control from seals and increased bottom-up forcing due to eutrophication largely could explain the historical dynamics of the main fish stocks (cod, herring and sprat) in the Baltic Sea be-tween 1900 and 1980. During the last three decades in-tegrated ecosystem analyses show that there have been two relatively stable periods in central Baltic Proper, 1974-1987 and 1994-2006 (ICES, 2008b). The former period was characterized by high abundance and recruit-ment of cod and herring, and also high abundance of the zooplankton species Pseudocalanus acuspes. During the latter period sprat have been the main planktivorous fish, and the zooplankton species Acartia spp. and Temora
longicornis have been abundant. The intermediate period
between the two periods was characterized by variable climate with no large saltwater inflows. Similar ecosys-tem shifts was also observed in other parts of the Baltic Sea within the same time period. It is suggested that the primary drivers to these shifts is decreasing salinity and increased temperature, i.e. possibly the effects of a cli-mate change.
The shift from a cod dominated to a clupeid dominat-ed system has resultdominat-ed in substantial trophic cascades in both the open sea and in coastal areas. The increase of sprat has negatively affected growth of zooplanktivores (sprat and herring; Casini et al., 2006) and the breeding success of the fish-eating common guillemot (Österblom et al., 2006). It also is suggested to have had cascading effects down the food web on zooplankton and phyto-plankton (Casini et al., 2008). Analogous to the shift in the offshore ecosystem, shifts in the coastal ecosystem have been observed. Despite a temperature increase since the end of the 1980s (Alheit et al., 200�), abundances of the major coastal predators (perch and pike) seem to have declined in open coastal areas of the Baltic Proper since the early 1990s (Ljunggren et al., 200�; Ask and Westerberg, 2008). Simultaneously, low or variable re-cruitment of both species has been documented in the same areas (Andersson et al., 2000; Nilsson et al., 2004;
Ljunggren et al., 200�). The reason to this situation is presently unclear, although factors such as increased pre-dation (Nilsson, 2006) or other interaction with stickle-back may contribute.
The development of the fish communities in Gulf of Finland and Gulf of Bothnia differs to some extent from that of Baltic Proper. In Gulf of Finland most open sea species, except for sprat, show a negative trend since ear-ly 1990s. These negative trends of fish stocks have been attributed to salinity decrease and frequently occurrence of anoxic conditions. In Gulf of Bothnia the pelagic fish species comprise herring, sprat and vendace. Sticklebacks have also become common in the open sea ecosystem (Swedish Board of Fisheries, unpublished data). Since late 1980s salmon and sea trout are together with grey seals the main predators on fish. Until the late 1980s, cod was found in quite high numbers in the gulf, but has since then more or less disappeared, possibly due to a combina-tion of high fishing pressure and climatic change. Due to the low salinity, there are no suitable spawning sites for cod in the Bothnian Sea.
Baltic Sea Fish Species
Baltic cod is usually divided in two different stocks,
one western and one eastern population, although there is some migration of fish between areas. Recruitment is variable and is dependent upon the strength of incoming year classes. Successful spawning of Baltic cod is related to the volume of water with appropriate salinity and oxy-gen levels (Köster et al., 2001), which in turn depends on climate driven salt water inflow and river run-off (Hinrichsen et al., 2002). Also ecological processes, such as the abundance and competition for zooplankton with zooplanktivores (herring and sprat, Casini et al., 2006) affect the recruitment success. Spawning of the eastern population is limited to the deep basins where fertilized eggs are neutrally buoyant. The total and spawning-stock biomass increased by the end of the 1970s due to favour-able reproduction conditions in the southern and central Baltic Sea, where after it fell to a historical low level the most recent years (ICES, 2008a). The decline of the cod stock in the Baltic Sea in mid-1980s possibly was the
re-sult of a combination of high fishing pressure negatively affecting spawning stock, and decreased salinity and oxygen levels restricting the recruitment volume in the Bornholm Basin (Figure 7.1).
Baltic Sea herring comprises a number of spawning components. This population complex experienced a high biomass level in the early 1970s, but has then declined until 2001 (Figure 7.1). The southern Baltic Proper her-ring have declined, and the more northerly and somewhat smaller herring now dominate the catches (ICES, 2008a). Since 1990, mean weight-at-age has decreased by 1�-4�% across all age groups to the early 2000’s, where after mean weights have stabilized, and now remain at a low level. As in the Baltic Proper, herring in Gulf of Finland has decreased since late 1980s and sprat has increased since mid-1990s. The herring population in Bothnian Sea was assessed to be at a relatively low level of until the mid-1980s, after which the spawning stock biomass more than tripled by 1994 (ICES, 2008a). Favourable environ-mental conditions (warm summers and mild winters) have possibly contributed to good recruitment. The most northerly herring population in Bothnian Bay is the small-est herring stock in the Baltic Sea, and largely influenced by environmental factors. Like in Bothnian Sea, the her-ring stock of the Gulf of Riga increased in the late 1980s. The year-class strength of this population is significantly influenced by climatic variation and mild winters in the second half of the 1990s is suggested to have governed several rich year-classes and an increase of the biomass.
Spawning stock of sprat, which was low during the first half of the 1980s have been at a high level during the last decade in Baltic Proper. In the beginning of the 1990s, the stock increased rapidly, possibly due to both strong re-cruitment and a declining natural mortality (effects of low cod biomass), and in mid-1990s it reached the maximum observed spawning-stock biomass (ICES, 2008a). During the same period, sprat abundance has also increased in Gulf of Finland and possibly also in Gulf of Bothnia.
Flatfishes of the Baltic Sea consists of turbot (Psetta
maxima), brill (Scopthalmus rhombus), European
floun-der (Platichthys flesus), plaice (Pleuronectes platessa), sole (Solea solea) and dab (Pleuronectes limanda). Among those, flounder, turbot and dab are the most wide-ly distributed, whereas the other species are restricted to the south-western part of the sea.
Flounder is distributed over the whole Baltic Sea,
ex-cept the most part of Bothnian Bay. It appears to be sepa-rated in several distinct populations; earlier studies by Aro (1989) and Bagge and Steffensen (1989) suggested that there are eight rather northern distinct flounder popula-tions. However, in a more recent study Florin et al. (200�) could separate three major flounder populations, one in Skagerrak/Kattegat, one in southwestern Baltic Sea, and one in eastern Baltic Sea. These three populations
corre-Figure 7.1. Trends of (a) cod biomass (squares) and sprat biomass (cir-cles); (b) sprat abundance (diamonds) and zooplankton biomass (tri-angles) (ind., individuals); and (c) zooplankton biomass (tri(tri-angles) and chlorophyll a (squares). The horizontal lines indicate periods of different average levels in the biological time series as detected by the cumula-tive z -scores. After Casini et al., 2008.
spond with differences in spawning behaviour (Nissling
et al., 2002), with demersal eggs in the eastern Baltic, and
with buoyant pelagic eggs in the south-western Baltic.
Turbot is a coastal species distributed over the Baltic
Proper (Molander, 1964; Neuman and Píriz, 2000; Voigt, 2002). It displays a size and age dependent depth distri-bution where young fish are found in shallow water while old and large fish is found in deeper waters (Molander, 1964; Pihl, 1989; Støttrup et al., 2002). Spawning takes place on sandy bottoms for feeding and reproduction, but migrates to deeper areas during winter. Despite a station-ary behaviour, small genetic differences among popula-tions indicate exchange between separate sub-popula-tions. Females are generally growing faster than the males, which seldom reach lengths above �0 cm TL. An intense fishery in the mid 1990’s resulted in a decrease in relative abundance, but the population has recovered since then. A continuous decrease of large individuals in-dicates that fishing pressure from both commercial and recreational fishery is high.
Plaice and dab are mainly occurring in the southern
and western Baltic Proper. Both species are living close to the coast at sandy bottoms. The plaice population in the southern Baltic Sea is regarded to be weak, possi-bly dependent on migration from the Kattegat area. The population status of dab is uncertain, however, there are indications of an increasing trend (Ask and Westerberg, 2008). Dab from the Bornholm basin differs from those of the Belt Sea area (Temming, 1989), suggesting that the species comprise several separate stocks.
Atlantic Salmon populations in the main Basin and the
Gulf of Bothnia was severely impaired by the damming of rivers along the coasts of the Baltic Sea. The development of hydro-electrical power resulted in extensive stocking programmes, strongly affecting the survival of wild salmon. A Baltic wide Salmon Action Plan was launched in 1997, and according to ICES (2008a) the total wild smolt pro-duction has increased about fourfold in the North-eastern Bothnian Bay and Bothnian Sea stocks since the plan was adopted. Wild smolt production is estimated to be about two thirds of the potential total smolt production, although smolt production is still low in rivers where salmon were extirpated and are now being reintroduced. In the Gulf of Finland salmon consists of only a few small wild popula-tions together with a number of mixed/reared stocks. The
wild salmon populations are genetically distinct from each other, indicating that these are still original salmon stocks. Surveys show that rivers where the stock mainly depends on enhancement releases still support fractions of the orig-inal wild salmon populations.
Survival through the post-smolt phase has decreased from about 20-�0% during the 1990s to 10-1�% for wild, and lower for reared, salmon during the years 2004-2006 (ICES, 2008a). The resasons to the decrease in post-smolt survival is unclear, however, an increased abundance of seals (both grey and ringed seals) during the same pe-riod is suggested to be one important factor. Despite a low survival at-sea the estimated smolt production has increased and rivers in the northern Baltic Sea is expected to reach �0% of their natural production capacity within some years. The status of less productive wild stocks, especially in southern Baltic Sea, is still poor. The pro-portion of wild salmon has increased relative to reared in catches, reflecting an increased wild smolt production. Commercial fishery has decreased recent years, whereas the recreational catches has increased and are likely to increase further.
High mortality rates in yolk-sac fry is caused by the reproduction disorder, the so called M74 syndrome. It was first detected in 1974 in Swedish Atlantic salmon hatcheries, where it caused increased mortality among alevins. Although the cause of the syndrome is still un-known, a linkage between the syndrome and a deficiency of thiamine has been established (Börjeson and Norrgren, 1997; Romakkaniemi et al., 200�). Norrgren et al. 199� suggested that one factor involved in the etiology of M74 was organochlorine substances. This has later been sup-ported by Michielsen et al. (2006) suggesting that oxida-tive stress may play a key role in the disease.
Sea trout in the Baltic consists of approximately 1,000
stocks, whereof about half are wild. Populations in Gulf of Bothnia are relatively stationary in the coastal areas, whereas most populations in Baltic Proper are migratory and spend there growth at sea. In the Bay of Bothnia, the populations are weak, possibly as the effects of fishery, migratory obstacles, and habitat degradation in spawn-ing areas (Ask and Westerberg, 2008). In the Bothnian Sea, the situation is slightly better and the populations are showing a positive trend in abundance in some rivers. The development of sea trout in the Baltic Proper is
nega-tive, with the exception for the most southerly streams. Most of the stocks in the Baltic Sea migrate in the coastal area within about 1�0 km of the home river, but particu-larly those from Poland and some from southern Sweden and Denmark migrate further into offshore areas. The fish that migrate only short distances are mainly exploited in coastal and river fisheries. A recent ban of driftnets is ex-pected to benefit the sea trout populations.
The immigration of European eel to the Baltic Sea has declined considerably; indices of young yellow eel recruitment show a reduction since about 19�0 and is now just a few percent as compared to the mid 1900 (ICES, 2008c). The decline is more pronounced in the more northern and southern parts of the species distri-bution. The species is now regarded as one of the most endangered species in the Baltic Sea (HELCOM, 2006). Under natural conditions eel migrates to most freshwaters along the Baltic coasts, however, due to the extensive ex-ploitation of rivers for hydro-electricity production, many of the migration routes are closed. In addition, eel is sub-jected to a high fishing pressure increasing the mortality of both growing yellow eels and mature silver eels return-ing to the Sargasso Sea. Recently, the European commis-sion decided that national management plans have to be in force, with the goal to let at least �0% of the silver eel to return to there spawning habitats in the Sargasso Sea. If this management measure will be effective is not known.
Vendace is a pelagic freshwater species common in
the coastal areas of Bothnian Bay. It is mainly fished for the roe, and the distribution is now mainly restricted to western part of the bay (Ask and Westerberg, 2008). As for herring, population size seems to be strongly related to climatic variation, although high fishing pressure also is a restricting factor. In 1990s the species was subjected to overfishing, but the situation has changed due to a number of strong year classes in the early 2000th
Whitefish display several different traits, and exists
in two major forms in the Baltic Sea, one anadromous form spawning in streams and rivers, and one stationary form spawning in coastal areas on sandy bottoms. As for salmon and sea trout, the anadromous whitefish has over the years been negatively affected by the damming of riv-ers, especially in the northern part of the Baltic Sea. Due to stocking, the genetic variation among populations has become less pronounced, and river specific strains are
uncommon (Florin and Aho, 2004). Fishery independ-ent data suggest that the population abundance decreased in the late 1980s, and has been low since then (Ask and Westerberg, 2008). Additional reasons to this decline could be a climatic shift as well as a population increase of grey and ringed seals in the Bothnian Sea and Bothnian Bay. Seals are suggested to be one of the most important predators on whitefish presently. Like whitefish,
gray-ling appear in one anadromous and one sea spawning
form in the Gulf of Bothnia. The latter form is classified as endangered, but the reasons to the low population size are not clear. Attempts to restore the sea spawning form are ongoing.
Coastal Fish
The coastal fish communities comprise a variety of fresh-water, marine and migratory species, and also glacial rel-icts. Species composition varies among Baltic Sea regions in relation to their different habitat characteristics, with salinity, temperature, and nutrient availability being the most important factors. Both the number of species and the abundance of marine species decline with decreasing salinity. Salinity also determines the distribution of most freshwater species.
On the west coast of the Baltic Proper, freshwater species such as perch, pikeperch and pike constitute the main predatory fishes. Frequently marine species such as young cod, flounder and turbot are present part of the year. Freshwater cyprinid species (e.g. roach, bream, white bream, silver bream, tench and rudd) are abundant, especially in more eutrophied areas. Among coldwater adapted species burbot and eelpout are common. In the eastern and southern coastal areas, salinity is higher and the marine species more common. The Curonian and Vistula lagoons in SE Baltic, being more or less freshwa-ter habitats, are dominated by a variety of cyprinid and percid species, typical for eutrophied waters.
Eutrophication affects species composition and long-term development of the coastal fish communities, also resulting in increased production of fish biomass and changes in fish community structure and function. In general, eutrophication increases the abundance of
cyprinids (Anttila, 197�; Hansson, 2007; Bonsdorff et al., 1997; Lappalainen, 2002). Water transparency, a proxy for high nutrient load, has decreased in the entire Baltic Sea during the past century (Laamanen et al., 2004). A relationship between trophic state, expressed as Secchi disc depth, and cyprinid fish is suggested by the negative relationship between water transparency and catch per unit effort of roach and other cyprinids in coastal areas (Figure 7.2). The smallest Secchi depth (i.e., least water transparency) and largest catches per unit effort of roach and other cyprinid species appeare in the Curonian la-goon, whereas the largest Secchi depth and small catches per unit effort of roach and other cyprinid species appeare in the Archipelago Sea, between Baltic Proper and Gulf of Bothnia.
Also climatic variation has had a substantial impact on the development of the coastal fish communities. Several coastal freshwater fish taxa living in the Baltic Sea (e.g., percids and cyprinids) prefer warm-water conditions. Temperature has been proved to be an important factor governing the recruitment success, growth, and year-class strength of, for example, perch in the Baltic Sea (Böhling et al., 1991; Karås and Thoresson, 1992; Karås, 1996, Appelberg et al., 2007). High water temperature gain population and invidual growth rate of species with high temperature optima (e.g. Figure 7.�), but restrain growth
Figure 7.2 Relationship between Secchi depth and CPUE in terms of numbers of roach and other cyprinids. Significant relationships between CPUE and Secchi disc depth were found forboth roach (linear regression, p=0.032) and cyprinids (linear regression, p=0.006, After HELCOM, 2006).
Figure 7.3. Growth of Y-O-Y perch in the coastal area of Baltic Proper. Change in growth rate reflects a temperature increase during the same period. Data from Institute of Coastal Research, Swedish Board of Fisheries
rate of species with low temperature optima. However, as climate change also affects e.g. primary production and land run-off, secondary effects may counteract the direct temperature effects.
The increase in sea surface temperature in the Baltic Sea the last decades is suggested to strongly affect the fish communities (MacKenzie, et al., 2007) and marine species will possibly be displaced by freshwater spe-cies due to increased precipitaiton and decreased salin-ity. In Gulf of Bothnia increased water temperature has resulted in a substantial increase in biomass of roach and bleak, and a reduction of whitefish (Appelberg et al., 2007). Significant increasing trends in relative abun-dance of European perch and roach have been observed in the Archipelago region between the southern Gulf of Bothnia and the northern Baltic Proper. Possible reason for these trends is an ongoing coastal eutrophication as well as increased temperatures during the past decade. In southern Gulf of Bothnia the two cold water adapted species, burbot and eelpout, display negative population development, despite an increase in relative biomass of coastal fish species the last 2� years. In some areas bream and pikeperch, both warm water adapted species have in-creased, possibly as an effect of a change in climate. In sheltered coastal areas in western Baltic Proper, number of species with high temperature optima increased dur-ing the same period. A strong indication of the effects of temperature change is an increased growth rate of perch starting in mid-1980s (Sandström et al., 200�)
Although the spread of non-indigenous species has been suggested to be among the most severe threats to global biodiversity (Leppäkoski et al., 2002), the sig-nificance of most non-indigenous fish species introduced into the Baltic Sea remain of less importance since they have failed to form self-sustaining populations. However, two species, the accidentally introduced round goby (Neogobius melanostomus) and the intentionally intro-duced Prussian carp (Carassius gibelio), are exceptions in this respect. In particular, the round goby is spreading from the Gulf of Gdansk region and new records of its occurrence are reported every year (Almqvist, 2008). The most recent report is from the southern coast of Sweden, where it was reported for the first time in mid 2008.
Vetema et al. (200�) reported that the invasive species gibel carp Carassius gibelio has increased significantly
along parts of the east coast of Baltic Proper. The spe-cies, which was first observed in Estonian brackish water in 198�, has spread along the entire Estonian coastline, now being one of the most frequently occurring coastal species. They suggest that warm summers and low abun-dance of predatory fish are two major reasons to this change.
Conclusions
Baltic Sea fish communities are presently experiencing dramatic changes. Ongoing eutrophication, high fishing pressure, climate change, habitat degradation and spread-ing of invasive species, together with indirect effects from food web feed back loops, provides the basis for continous, and maybe irreservible, changes in the fish community structure and function. A drastic example is the recent reduction of piscivorous fish species (e.g. cod in the open sea area, which strongly have influenced lower trophic levels and possibly also affected primary production. Even if the nutrient load will be substantially reduced, it is probable that the retention from sediments and global warming will continue to affect the Baltic Sea, thereby governing community changes also affecting the Baltic Sea fish.
Chapter 3
Andren, H. 1994. Effects of habitat fragmentation on birds and mam-mals in landscapes with different proportions of suitable habitat – a review. In: Oikos 71:355-366.
Aquilar, R., Ashworth, L. and Galletto, L. et al. 2006. Plant reproduc-tive susceptibility to habitat fragmentation: review and synthesis through a meta-analysis. In: Ecology Letters 9, 968-980.
Baguette, M. and Van Dyck, H. 2007. Landscape connectivity and ani-mal behavior: functional grain as a key determinant for dispersal. In:
Landscape Ecology 22, 1117-1129.
Baillie, S.R., Sutherland, W.J. and Freeman, S.N. et al. 2000. Consequences of large-scale processes for the conservation of bird populations. In: Journal of Applied Ecology 37, 88-102.
Best, L.B., Bergin, T.M. and Freemark, K.E. 2001. Influence of land-scape composition on bird use of rowcrop fields. In: Journal of
Wildlife Management 65, 442-449.
Brawn, J.D. and Robinson, S.K. 1996. Source-sink dynamics may com-plicate the interpretation of long-term census data. In: Ecology 77, 3-12.
Brawn, J.D., Robinson, S.K. and Thompson III, F.R. 2001. The role of disturbance in the ecology and conservation of birds. In: Annual
Review of Ecology and Systematics 32, 251-276.
Brawn, J.D. 2006. Effects of restoring oak savannas on bird communi-ties and populations. In: Conservation Biology 20, 460-469. Chetkiewicz, C.L.B., Clair, C.C.S. and Boyce, M.S. 2006. Corridors for
conservation: integrating attern and process. In: Annual Review of
Ecology and Systematics 37, 317-342.
Cushman, S.A. 2006. Effects of habitat loss and fragmentation on am-phibians: a review and prospectus. In: Biological Conservation 128, 231-240.
Davros, N.M., Debinski, D.M. and Reeder, K.F. et al. 2006. Butterflies and continuous conservation reserve program filter strips: Landscape considerations. In: Wildlife Society Bulletin 34, 936-943.
Donovan, T.M., Jones, P.W., Annand, E.M. and Thompson III, F.R. 1997. Variation in local-scale edge effects: mechanisms and land-scape context. In: Ecology 78, 2064-75.
Fletcher, R.J. and Koford, R.R. 2001. Habitat and landscape associa-tions of breeding birds in native and restored grasslands. In: Journal
of Wildlife Management 66, 1011-1022.
Henningsen, J.C. and Best, L.B. 2005. Grassland bird use of riparian filter strips in southeast Iowa. In: Journal of Wildlife Management 69, 198-210.
Herkert, J.R. 1994. The effects of habitat fragmentation on midwestern grassland bird communities. In: Ecological Applications 4, 461-471.
Kleijn, D. and Sutherland, W.J. 2003. How effective are European agri-environmental schemes in conserving and promoting biodiversity? In: Journal of Applied Ecology 40, 947-969.
Kleijn, D., Baquero, R.A., Clough, Y. and Diaz, M. et al. 2006. Mixed biodiversity benefits of agri-environmental schemes in five European countries. In: Ecology Letters 9, 243-254.
Robertson, G.P. and Swinton, S.M. 2005. Reconciling agricultural pro-ductivity and environmental integrity: a grand challenge for agricul-ture. In: Frontiers in Ecology 3,38-46.
Robinson, S.K., Thompson III, F.R., Donovan, T.M. Whitehead, D.R. and Faaborg, J. 1995. Regional forest fragmentation and the nesting success of migratory birds. In: Science 267, 1987-1990.
Van Bael, S.A., Philpott, S.M. and Greenberg, R. et al. 2008. Birds as predators in agroforestry systems. In: Ecology 89, 928-934. Wade, M.R., Gurr, G.M. and Wratten, S.D. 2007. Ecological restoration
of farmland: progress and prospects. In: Philosophical Transactions
of the Royal Society, Series B. 363, 831-847.
Chapter 4
Great Lakes Commission. 1999a. “Counterattack: Great Lakes Panel
Targets Aquatic Nuisance Species.” Accessed November 29, 2008.
http://www.glc.org/ans/counterattack.html.
Hallman, G.J. and Schwalbe, C.P. 2002. Invasive Arthropods in
Agriculture: Problems and Solutions. Science Publishers, Inc.
Enfield, NH, USA.
Kaufman, S.R. and Kaufman, W. 2007. Invasive Plants: Guide to
Identification and the Impacts and Control of Common North American Species. Stackpole Books, Mechanicsburg, PA.
Mack et al. 2002. Predicting Invasions of Nonindigenous Plants and
Plant Pests. National Academy of Sciences, Washington, D.C.
McCullough, D.G. and Katovich, S.A. Pest Alert: Emerald Ash Borer. United States Department of Agriculture, NA-PR-02-04.
National Invasive Species Council. 2001. Meeting the Invasive Species
Challenge: National Invasive Species Management Plan. 80 pp.
Nixon, P. 2008. Emerald Ash Borer Insecticidal Management. University of Illinois Extension Fact Sheet, NHE-163.
Nuzzo, V. 1993. Distribution and spread of the invasive biennial
Alliaria petiolata (garlic mustard) in North America. Pp
137-145, In: McNight, B. (Ed.) Biological Pollution: The Control and
Impact of Invasive Exotic Species. Indiana Academy of Sciences,
Indianapolis, IN.
Pimentel, D., Zuniga, R. and Morrison, D. 2005. “Update on the Environmental and Economic Costs of Alien-invasive Species in the United States.” In: Ecological Economics 52(3):273-288. Stein, B.A. and Flack, S.R. (eds.) 1996. America’s Lease Wanted: Alien
Species Invasions of the U.S. Ecosystems. The Nature Conservancy,
Arlington, VA.
Chapter 5
Alien Species in Swedish seas and coastal areas. http://www.framman-dearter.se/0/2english/species_Sv.html?reload_coolmenus
Chapter 7
Alheit, J., Möllmann, C., Dutz, J., Kornilovs, G., Loewe, P., Mohrholz, V. and Wasmund, N. 2005. Synchronous ecological regime shifts in the central Baltic and the North Sea in the late 1960s. In: ICES J.
Almqvist, G. 2008. Round goby, Neogobius melanostomus in the Baltic
Sea – Invasion biology in practice. PhD thesis in Brackish Water
Ecology, Stockholm University, 2008. 46 p.
Andersson, J., Dahl, J., Johansson, A., Karås, P., Nilsson, J., Sandström, O. and Svensson, A. 2000. Utslagen fiskrekrytering och sviktande
fiskbestånd i Kalmar läns kustvatten. Fiskeriverkets rapport, 5. 42
pp. (in Swedish with English summary).
Anttila, R. 1973. Effect of sewage on the fish fauna in the Helsinki area. In: Oikos Suppl., 15: 226–229.
Appelberg, M., Andersson, J., Ljunghager, F. and Söderberg, K. 2007. Kustfisk – speglar miljön. In: Havet 2007. SEPA. 2007. (In Swedish: Coastal fish – reflecting the environment)
Aro, E. 1989 A review of fish migration patterns in the Baltic. In: Rapp.
P.-v. Re´un. Cons. int. Explor. Mer 190, 72–96.
Ask, L. and Westerberg, H. 2008. Fiskbestånd och miljö i hav och
sötvatten. Resurs- och miljööversikt. Swedish Board of Fisheries,
Sweden. (In Swedish)
Bagge, O. and Steffensen, E. 1989. Stock identification of demersal fish in the Baltic. In: Rapp. P.-v. Réun. Cons. int. Explor. Mer.190:3–16. Bonsdorff, E., Blomqvist, E.M., Mattila, J. and Norkko, A. 1997. Long-term changes and coastal eutrophication. examples from the Åland Islands and the Archipelago Sea, northern Baltic Sea. In: Oceanol.
Acta, 20: 319–329.
Böhling, P., Hudd, R., Lehtonen, H., Karås, P., Neuman, E. and Thoresson, G. 1991. Variations in year-class strength of different perch (Perca fluviatilis) populations in the Baltic Sea with special reference to temperature and pollution. In: Can. J. Fish. Aquatic
Sci., 48(7): 1181–1187.
Börjeson, H. and Norrgren, L. 1997. M74 syndrome: a review of po-tential etiological factors. In: Rolland, R.M., Gilbertson, M. and Peterson, R.E. (Eds.) Chemically Induced Alterations in Functional
Development and Reproduction of Fishes. Proceedings from a Session at the 1995 Wingspread Conference. SETAC, Pensacola,
FL, 153–166.
Carpenter, S.R., Kitchell, J.F. and Hodgson, J.R. 1985. Cascading Trophic Interactions and Lake productivity. In: Bioscience 35:634-639.
Carpenter, S.R. and Kitchell, J.F. 1993.The Trophic Cascade in Lake
Ecosystems. Cambridge University Press.
Casini, M., Cardinale, M. and Hjelm, J. 2006 Inter-annual variation in herring (Clupea harengus) and sprat (Sprattus sprattus) condi-tion in the central Baltic Sea: what gives the tune? In: Oikos 112, 638–650.
Casini, M., Lövgren, J., Hjelm, J., Cardinale, M., Juan-Carlos Molinero, J-C., and Kornilovs, G. 2008. Multi-level trophic cascades in a heavily exploited open marine ecosystem. In: Proc. R. Soc. B. 2007.1752
EEA [European Environment Agency] 2002. Europe’s biodiversity
– biogeographical regions and seas. Baltic Sea. EEA 2002. http://
reports.eea.europa.eu/report_2002_0524_154909/en/BalticSea.pdf Elmgren, R. 1989. Man’s impact on the ecosystem of the Baltic Sea:
Energy flows today and at the turn of the century. In: Ambio 18, 326–332.
Elmgren, R. 2001. Understanding Human Impact on the Baltic Ecosystem: Changing Views in Recent Decades. In: Ambio 30( 4–5):222-231
Florin, A-B. and Aho, T. 2004. Stock identification and genetic varia-tion in fishes in the Baltic Sea. In: ICES CM 2004/EE:07. Florin, A-.B., Höglund, J. and Aho, T. 2005. Genetic variation and
stock identification of flatfishes in the Baltic Sea. In: ICES CM 2005/T:19.
Hansson, S., Hjerne, O., Harvey, C., Kitchell, J.F., Cox, S.P. and Essington, T.E. 2007. Managing Baltic Sea Fisheries under Contrasting Production and Predation Regimes: Ecosystem Model Analyses. In: Ambio 36(2–3):265-271
HELCOM 2006. Assessment of coastal fish in the Baltic Sea. In: Baltic
Sea Environment Proceedings No 103A, 28 p.
Hinrichsen, H.-H., St. John, M.A., Lehmann, A., MacKenzie, B.R. and Köster, F.W. 2002. The impact of physical forcing variations on eastern Baltic cod spawning conditions. In: Journal of Marine
Systems 32:281–294.
ICES [International Council for the Exploration of the Sea], 2008a. Report of the Baltic Fisheries Assessment Working Group. CM 2008/ACOM:06.
ICES [International Council for the Exploration of the Sea], 2008b. Report of the Working Group on Integrated Assessment of the Baltic Sea (WGIAB) CM 2008/BCC:04.145 pp.
ICES [International Council for the Exploration of the Sea], 2008c. Report of the joint EIFAC/ICES working group on Eels (WGEEL), CM 2008/ACOM:15
Jansson B.O. and Dahlberg, K. 1999. The environmental status of the Baltic Sea in the 1940’s, today, and in the future. In: Ambio 28:312-319.
Karås, P. and Thoresson, G. 1992. An application of a bioenergetic model to Eurasian perch (Perca fl uviatilis L.). In: J. Fish. Biol., 2: 53–70.
Karås, P. 1996. Recruitment of perch (Perca fl uviatilis L.) from Baltic coastal waters. In: Arch. Hydrobiol., 138(1): 99–121.
Köster, F.W., Hinrichsen, H-H., St. John, M.A., Schnack, D., MacKenzie, B.R., Tomkiewicz, J. and Plikshs, M. 2001. Developing Baltic cod recruitment models. II. Incorporation of environmental variabil-ity and species interaction. In: Canadian Journal of Fisheries and
Aquatic Sciences, 58: 1534-1556.
Laamanen, M., Fleming, V. and Olsonen, R. 2004. Water transparency
in the Baltic Sea between 1903 and 2004. http://www.helcom.fi
/en-vironment/ indicators2004/secchi.
Lappalainen, A. 2002. The effects of recent eutrophication on
freshwa-ter fish communities and fishery on the northern coast of the Gulf of Finland, Baltic Sea. Ph.D. thesis. Finnish Game and Fisheries
Institute, Helsinki. 24 pp.
Leppäkoski, E., Gollasch, S., Gruszka, P., Ojaveer, H., Olenin, S. and Panov, V. 2002. The Baltic—a sea of invaders. In: Can. J. Fish.
Aquat. Sci., 59: 1175–1188.
Ljunggren, L., Sandström, A., Johansson, G., Sundblad, G. and Karås, P. 2005. Rekryteringsproblem hos Östersjöns kustfiskbestånd. Finfo, 2005:5. (in Swedish with English summary).
MacKenzie, B. Gislason, H., Möllmann, C. and Köster, F.W. 2007. Impact of 21st century climate change on the Baltic Sea fish com-munity and fisheries. In: Global Change Biology, 13(7):1348-1367 Michielsens, C.G.J., Mäntyniemi, S. and Vuorinen, P.J. 2006. Estimation
(EMS) and their impact on salmonid stock–recruit relationships. In:
Can. J. Fish. Aquat. Sci. 63: 1968–1981
Molander, A.R. 1964. Underordning plattfiskar. In: Andersson, K.A. (Ed.) Fiskar och fiske i norden, pp. 90–113. Natur och kultur, Stockholm. (In Swedish)
Neuman, E. and Píriz, L. 2000. Svenskt småskaligt kustfiske – problem och möjligheter. In: Fiskeriverket Rapport 2: 3–40. (In Swedish with English summary).
Nilsson, J., Andersson, J., Karås, P. and Sandström, O. 2004. Recruitment failure and decreasing catches of perch (Perca
fluvia-tilis L.) and pike (Esox lucius L.) in the coastal waters of southeast
Sweden. In: Boreal Environmental Research 9: 295-306.
Nilsson, J. 2006. Predation of Northern Pike (Esox lucius L.) Eggs: A Possible Cause of Regionally Poor Recruitment in the Baltic Sea. In: Hydrobiologia 553(1):161-169.
Nissling, A., Westin, L. and Hjerne, O. 2002. Reproductive success in relation to salinity for three flatfish species, dab (Limanda limanda), plaice (Pleuronectes platessa) and flounder (Pleuronectes flesus), in the brackish water Baltic Sea. In: ICES J. Mar. Sci. 59(1):1054– 3139.
Norrgren, L., Andersson, T., Bergqvist, P-A. and Björklund, I. 1993. Chemical, physiological and morphological studies of feral Baltic salmon (Salmo salar) suffering from abnormal fry mortality. In: Env.
Tox. Chemistry. 12; 2065-2075
Pace, M.L., Cole, J.J., Carpenter, S.R. and Kitchell, J.F. 1999. Trophic cascades revealed in diverse ecosystems. In: Trends Ecol. Evol. 14, 483–488.
Pihl, L. 1989. Abundance, biomass and production of juvenile flatfish in southeastern Kattegat. In: Neth. J. Sea Res. 24: (1) 69–81. Romakkaniemi, A., Perä, I., Karlsson, L., Jutila, E., Carlsson, U. and
Pakarinen, T. 2003. Development of wild Atlantic salmon stocks in the rivers of the northern Baltic Sea in response to management ac-tions. In: ICES J. Mar. Sci. 60: 329–342.
Sandström, O, Larsson, Å., Andersson, J., Appelberg, M., Bignert, A., Ek, H., Förlin, L. and Olsson, M. 2005. Three Decades of Swedish Experience Demonstrates the Need for Integrated Long-Term Monitoring of Fish in Marine Coastal Areas Water. In: Qual. Res. J.
Canada, V 40, No. 3, 233–250.
SEPA 2006. Sweden environmental objectives – buying into a better
future. 91-620-1251-7 Swedish Environmental Protection Agency,
Stockholm, Sweden.
Støttrup, J.G., Sparrevohn, C.R., Modin, J. and Lehmann, K. 2002. The use of releases of reared fish to enhance natural populations. A case study on turbot Psetta maxima (Linné, 1758). In: Fish. Res. 59:161–180.
Temming, A. 1989. Long-term changes in stock abundance of the com-mon dab (Limanda limanda L.) in the Baltic Proper. In: Rapp. P.-v.
Réun. Cons. int. Explor. Mer. 190: 39–50.
Vetemaa, M., Eschbaum, R., Albert, A. and Saat, T. 2005. Distribution, sex ratio and growth of Carassius gibelio (Bloch) in coastal and inland waters of Estonia (north-eastern Baltic Sea). In: Journal of
Applied Ichthyology 21: 287–291
Voigt, H.-R. 2002. Piggvaren i våra kustvatten. In: Fiskeritidskrift för
Finland 1: 25–27. (In Swedish)
Ådjers, K., Appelberg, M., Eschbaum, R., Lappalinen, A., Minde, A., Repecka, R. and Thoresson, G. 2006. Trends in coastal fish stocks of the Baltic Sea. In: Boreal Environment Research 11:13-25. Österblom, H., Casini, M., Olsson, O. and Bignert, A. 2006. Fish,
sea-birds and trophic cascades in the Baltic Sea. In: Mar. Ecol. Prog.
Ser. 323, 233–238.
Österblom, H., Hansson, S., Larsson, U., Hjerne, O., Wulff, F., Elmgren, R. and Folke, C. 2007 Human-induced trophic cascades and ecolog-ical regime shifts in the Baltic Sea. In: Ecosystems 10, 877–889.
Chapter 8
Bucke, D., Feist, S., Norton, M. and Rolfe, M. 1983. A histopatho-logical report of some epidermal anomalies of Dover sole, Solea solea L., and other flatfish species in coastal waters off south-east England. In: J. Fish Biol. V. 23, 564-578.
Ekman, E., Börjeson, H. and Joaphansson, N. 1999. Flavobacterium
psychrophilum in Baltic salmon Salmo salar brood fish and their
offspring. In: Diseases of Aquatic Organisms, 37, 159-163. Gercken, J. and Sordyl, H. 2002. Intersex in feral marine and
fresh-water fish from northeastern Germany. In: Marine Environmental
Research. Vol. 54, Issues 3-5, 651-655.
Holt, R.A., Rohovec, J.S. and Fryer, J.L. 1993. Bacterial cold-water dis-ease. In: V. Inglis, R.J. Roberts & N.R. Bromage (Eds.). Bacterial
diseases of fish. Blackwell Scientific Publications, Oxford, UK, 3-23
Jobling S. and Tyler C. 2003. Endocrine disruption, parasites and pol-lutants in wild freshwater fish. In: Parasitology. Vol. 126, N 7, 103-107.
Kinne, O. 1984. Diseases of Marine Animals. Vol. IY, Part 1. Biologische Anstalt Helgoland, Hamburg, FRG, 541 pp.
Lang, T. and Rodjuk, G. 2006. Guidelines for fish disease monitoring in the Baltic Sea. In: Report of the ICES/BSRP Sea-going Workshop
on Fish Disease Monitoring in the Baltic Sea (WKFDM). ICES
Council Meeting Paper. BCC: 02 (Annex 6), 68-84.
Maccubbin, A.E. and Ersing, N. 1991. Tumors in fish from the Detroit River. In: Hydrobiol. 219, 301-306.
Matthiessen P. 2003. Endocrine disruption in marine fish. In: Pure
Appl. Chem. Vol. 75. Nos. 11–12, 2249–2261.
Möller, H. and Anders, K. 1986. Diseases and Parasites of Marine
Fishes. Kiel: Möller, 365 p.
Pulkkinen, K., Suomalainen, L.-R., Read, A.F., Ebert, D., Rintamäki, P. and Valtonen, E.T. 2010. Intensive fish farming and the evolution of pathogen virulence: the case of columnaris disease in Finland. In:
Proceedings of the Royal Society B, 293-600
Rodjuk, G.N. 2007. Results of Studies on Herring (Clupea haren-gus membras L.) Infestation with Anisakis simplex (Nematoda: Anisakidae) Larvae in the Russian Waters of the South Baltic in 1997-2005. In: Fisheries and Biological Research by AtlantNIRO
in 2004-2005. Vol. 2. Bioproductivity of Waters and Commercial
Populations Ecology. Kaliningrad, 2007. Trudy AtlantNIRO, 139-154 (in Russian).
Sindermann, C. 1979. Pollution-associated disease and abnormalities of fish and shellfish: a review. In: Fishery Bulletin, vol. 76, N 4, 717-749.
