Northward movement of marine species

Recordings of two tropical fish 1963-1996

Note: Recordings of the migration of the tropical species silvery john dory (Zenopsis conchifer) and rosy dory (Cyttopsis roseus) 1963-1996

Data source:

Quero, J.-C.; Du Buit, M.-H. and Vayne, J.-J., 1998. Les observations de poissons tropicaux et le rechauffement des eaux dans l'Atlantique européen. Oceanologica Acta 21: 345351.

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Northward movement of zooplankton between 1958-2005

Note: The northward movement of zoo-plankton spanning five decades

Data source:

Beaugrand, G.; Reid, P. C.; Ibañez, F.; Lindley, J. A. and Edwards, M., 2002. Reorganization of North Atlantic marine copepod biodiversity and climate. Science 296: 16921694.

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Relative abundance of warm-water to cold-water flatfish species

Note: Data are shown for four different seas and three sections of the North Sea, depending on mean annual SST

Data source:

Brander, K. M.; Blom, G.; Borges, M. F.; Erzini, K.; Henderson, G.; MacKenzie, B. R.; Mendes, H.; Ribeiro, J.; Santos, A. M. P. and Toresen, R., 2003. Changes in fish distribution in the eastern North Atlantic: Are we seeing a coherent response to changing temperature? ICES Marine Science Symposia 219: 261270.

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Past trends

The increase in regional sea temperatures has triggered a major re-organisation of zooplankton species composition and biodiversity over the entire North Atlantic basin (Beaugrand et al., 2003), shown in Figure 2. During the past 40 years there has been
a northerly movement of warmer-water plankton by 10^o latitude (1 100 km) in the north-east Atlantic and a similar retreat of colder-water plankton to the north. This northerly movement has continued over the past few years and appears to have accelerated since 2000.
Marine species generally have a large potential to spread. Ocean currents are able to spread plankton and larvae rapidly over large distances and many species of fish have migration patterns that exceed 100 km each year. Their movement is particularly pronounced along the European continental shelf edge and has been associated with the Shelf Edge Current running north. Consequently the rate of  northward movement is faster in the ocean than on land, partly because the marine environment has fewer barriers to dispersal than terrestrial systems; many terrestrial species, for example, are not able to cross water.
Some clear, well-documented examples of fish species shifts are shown in Figure 1. The silvery john dory (Zenopsis conchifer) was first recorded in European waters off the coast of Portugal at 38^oN in 1966 and has since been recorded progressively further north, to north of 55^oN by the early 1990s (Quero et al., 1998). It is probably transported northward in the continental slope current and the rate of northward shift in distribution of this species is more than 50 km per year. Other species which have become much more common further north, such as sea bass (Dicentrarchus labrax), red mullet (Mullus surmulletus) and European anchovy (Engraulis encrasicolus), are probably now able to overwinter and establish breeding populations there (Brander et al., 2003).
The ratio of catches of two common flatfish species - European plaice (Pleuronectes platessa) and Common sole (Solea solea) can be used as an index of the increase in the relative abundance of a warm-water vs. a cold-water species of flatfish (Figure 3). This change is linked to a steadily increasing temperature trend in the past 25 years, which has caused the sole to plaice ratio to change, particularly in the southern North Sea, the Irish Sea and the northern North Sea. This change is a change in their distribution, as sole and other warm-water species have become relatively more abundant in northerly areas, while plaice and other cold-water species have become rare in southerly areas (Brander et al., 2003). Recently it has been shown that a further temperature increase may lead sole to spawn earlier in the season and thus increase the duration of their growing season whereas plaice does not seem to be affected (Teal et al., 2008). Climate is only one of many factors which affect distribution and abundance, but the consistency of the response of this particular index to temperature, both within particular areas (i.e. time trend) and across all areas (i.e. geographic trend) suggest that the causal relationship is quite strong. In addition, an index based on ratios of catches minimises the influence of fishing when fishing acts on both species in a similar way, as is the case with these flatfish, which are caught in the same kinds of gear and often in the same fishing operations.
Other factors affecting abundance and distribution include fishing pressure, biological interactions, salinity, oxygen, the North Atlantic Oscillation, and pollution. In some cases changes in distribution are probably due to geographic patterns of fishing and not to climate effects.

Projections

Scenario projections of future movements of marine species have not yet been made. Uncertainty in making projections of fish distribution changes over the next 20-50 years arise from both the uncertainties in projections of ocean climate and uncertainties of fish community responses to those changes.