Changes in the past
For the fishing industry the greatest challenges are overfishing and climate change. The species richness of the Portuguese coast is generally higher than that found in northern Europe and similar to that of the Mediterranean, since many species have their southern or northern distribution limits along the Portuguese coast. For the period 1927–2011, Portuguese data on landings of species with affinity for temperate waters generally presented a decreasing trend, whereas species with affinity for subtropical/tropical waters showed an increasing trend. This variation was associated with variation in temperature, as warm years had lower landings of temperate species and higher landings of subtropical/tropical species. Sea surface temperature along the Portuguese coast has increased between 1927 and 2011 (5).
Landings from commercial fishery can provide indications of changes in population composition and abundance, and of the impact of climate change. These data, however, are also influenced by environmental factors, fishing techniques, fishing equipment, fishermen behaviour, changing markets, discarding, management and economic factors (6). Also, data on landings may differ from actual catches because fish with a high commercial value may be sold directly on the market and may not be present in landings data, and low-value species may be discarded (5).
Changes in the distribution of fish species associated with European tidal estuaries along the northeast Atlantic seaboard were studied by comparing the mean latitude of distributions according to fish survey data from the 1970s with data from 2004–2007. 55 tidal estuaries from Portugal to Scotland were studied. Among the 15 most common species, 11 displayed a positive difference between current and past mean latitudes suggesting a northward shift of the populations. These results indicate that a number of fish species associated to estuaries seem to have migrated northwards over the last 30 years, possibly due to water warming (2).
Fish species richness of the Portuguese coastal waters has been estimated to increase for 1 and 2°C sea-surface warming until the year 2100. A commercial opportunity for fisheries may arise from climate warming, since most of the new species were commercial species and not many commercial species were lost (3,7).
The comparison of the present species composition and future scenarios in terms of biogeographic type of species revealed the beginning of a shift from a subtropical–temperate fish assemblage toward a more subtropical–tropical fish assemblage (3).
The economic impact of climate change on the sardine fishery in Portugal and Spain has been estimated for 2030 based on the predicted increase in the temperature of the Iberian-Atlantic waters (1).
The results show that as the sea surface temperature of the Iberian-Atlantic fishing-grounds rises, lower biomass and catch levels are obtained, and as a result, the economic yield also decreases. If the current trend in rising sea surface temperature remains the same (0.27°C per decade), the annual profits will decrease by 1.27% between now and 2030. For scenarios of 10% faster or 10% slower rise of the fishing ground temperature, the profits will fall by about 1.40% and 1.14%, respectively, on average for each year of the period analysed (1).
In absolute terms, the economic losses from the sea surface warming will be higher in the Portuguese regions than in the Spanish regions involved in the fishery, because the Portuguese catches represent over 70% of total landings in this fishery (1).
There are three main fleet components in the Portuguese fisheries: trawl fisheries, seine fisheries and multi-gear fisheries. The fish species targeted by trawl fisheries are the Atlantic horse mackerel and the European hake, whereas the purse seine fishery targets small pelagic species (particularly sardines). Multi-gear fishery, which is the largest fleet component in Portugal, comprises a wide variety of fishing gears, such as gill nets, trammel nets or long lines. From the three main fleet components, Portuguese multi-gear fisheries seem to adapt relatively easy to the effects of climate change (being an increase of the relative importance of subtropical species in Portuguese fisheries). Especially trammel net fishers can adapt to changes in abundance of the main target species more readily than those using more species- and size-specific gears. Therefore, trammel net fisheries could more easily adapt to the effects of climate change on fish distribution than gill net or long line fisheries (4). Climate change may greatly affect small-scale fisheries, as their limited mobility makes the task of following target species almost impossible (5).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Portugal.
- Garza-Gil et al. (2011)
- Nicolas et al. (2011)
- Vinagre et al. (2011)
- Gamito et al. (2013)
- Teixeira et al. (2014)
- Anderson (1994); Daan (1997); Horwood and Millner (1998); Marchal et al. (2002), all in: Teixeira et al. (2014)
- Vinagre et al. (2011), in: Teixeira et al. (2014)