Impact of 21st century climate change on the Baltic Sea fish community and fisheries

Abstract

The Baltic Sea is a large brackish semienclosed sea whose species-poor fish community supports important commercial and recreational fisheries. Both the fish species and the fisheries are strongly affected by climate variations. These climatic effects and the underlying mechanisms are briefly reviewed. We then use recent regional -scale climate -ocean modelling results to consider how climate change during this century will affect the fish community of the Baltic and fisheries management. Expected climate changes in northern Europe will likely affect both the temperature and salinity of the Baltic, causing it to become warmer and fresher. As an estuarine ecosystem with large horizontal and vertical salinity gradients, biodiversity will be particularly sensitive to changes in salinity which can be expected as a consequence of altered precipitation patterns. Marine-tolerant species will be disadvantaged and their distributions will partially contract from the Baltic Sea; habitats of freshwater species will likely expand. Although some new species can be expected to immigrate because of an expected increase in sea temperature, only a few of these species will be able to successfully colonize the Baltic because of its low salinity. Fishing fleets which presently target marine species (e.g. cod, herring, sprat, plaice, sole) in the Baltic will likely have to relocate to more marine areas or switch to other species which tolerate decreasing salinities. Fishery management thresholds that trigger reductions in fishing quotas or fishery closures to conserve local populations (e.g. cod, salmon) will have to be reassessed as the ecological basis on which existing thresholds have been established changes, and new thresholds will have to be developed for immigrant species. The Baltic situation illustrates some of the uncertainties and complexities associated with forecasting how fish populations, communities and industries dependent on an estuarine ecosystem might respond to future climate change.

The Future of Baltic Sea Populations: Local Extinction or Evolutionary Rescue?

“…An additional species with large population size is herring (10 10 -10 11 ) that also has increased genetic variation generated by population differentiation also inside the Baltic Sea . Although cod has a relatively large population size, it only spawns in one site in the Baltic (Bleil et al 2009), and the recruitment is challenged by stochastic inflow of salt-water required for successful spawning (MacKenzie et al 2007), hence there is an increased risk of local extinction of this species unless fishery management allow for large enough population size and earlier spawning sites can be re-established.…”

The influence of temperature on the development of Baltic Sea sprat (Sprattus sprattus) eggs and yolk sac larvae

“…the water layer where sprat eggs occur (Nissling et al 2003) may be affected further due to the inflow of warm summer surface waters from the Kattegatt (Mohrholz et al 2006). This may be advantageous (MacKenzie et al 2007) as present average ambient conditions in the water layer where sprat eggs occur (45-65 m; *4°C) range well below the optimal survival temperature (8.4°C) found in this study and (5-13°C) as described by Nissling (2004). Additionally, low temperatures do not only directly influence survival but, as shown in the present study, also prolong the development time thus increasing the susceptibility to predation or malformation of the embryos (Nissling 2004).…”

Detecting range shifts among Australian fishes in response to climate change

“…Newton 1996), the buoyancy of eggs and early stages (e.g. Mackenzie et al 2007), shifts in the amount and location of suitable spawning grounds (Nicholson et al 2008) and the movement patterns of fish (e.g. Childs et al 2008).…”