A Climate for Change

Human Development Report - Croatia 2008 The Fishing and Mariculture Industries^155

9.5. Assessment of the

vulnerability of the fishing sector

to climate change

The impact of climate change on the Croatian fishery
sector is complex, as the impacts are both positive and
negative. They include changes in the marine environ-
ment, changes in the migration patterns of fish in the
open sea (including pressure to migrate in cold-water
species), potential changes in the growing season and
rearing time for farmed fish, and the potential increase
of invasive species, which has increased catches of
certain new species but threatened the production of
others.

9.5.1. Existing impacts from climate change

Marine fish populations already show evidence of sig-
nificant long-term fluctuations in abundance, which
has implications for the medium and long-term pre-
dictions of fish catches. The relationship between
these fluctuations and large-scale climate change is
an important concern.

Research^11 in the Adriatic Sea has shown that the in-
flow of Mediterranean water into the Adriatic increas-
es productivity in the Adriatic waters, that otherwise
have relatively low nutrient levels. Different biological
phenomenaIX have been observed and linked to the
stronger inflow of water from the Mediterranean into
the Adriatic. In addition, the temperature and salinity
properties of the water (thermohaline properties) have
had proven impacts on phytoplankton and fisheries.^12

The level of fish biodiversity in the Adriatic Sea gen-
erally increases from north to south. While there is
a range of factors which may affect this pattern, the
main factor seems to be temperature. Research has
already shown a large northward expansive move-
ment of fish species that are more suited to warmer

waters (thermophilic).^13 This indicates a change in

marine biodiversity, as numerous fish species previ-

ously found in more southern areas are moving north-

wards. Numerous new species in the northern parts

of the Adriatic Sea have been recorded over the last

thirty years. During 1973-2003, there was a strong cor-

relation between average annual air and sea surface

temperatures and the number of species.^14 There was

also a strong correlation between annual sea surface

temperature and the yearly total number of fish.^15 The

variations in Adriatic temperature conditions correlate

to the North Atlantic Oscillation (NAO) index – indi-

cating that local temperature changes at least partly

result from hemispheric temperature changes. As the

NAO will be affected by climate change, so too will the

temperature changes in the Adriatic.

Year-to-year fluctuations of small pelagic fish landings

• the number of fish that are actually taken ashore –
  on the eastern Adriatic coast were compared with cli-
  matic fluctuations over the Northern Hemisphere and
  to salinity fluctuations in the Adriatic.^16 Basic climatic
  oscillations were determined over a period of approxi-
  mately 80 years, and researchers found a relation-
  ship between climatic fluctuations over the Northern
  Hemisphere and small pelagic fish landings.^17
  Such long-term variation was observed worldwide
  and was considered part of the normal life cycle of pe-
  lagic fish.^18 However, the latest observed changes on
  sardines in the Adriatic Sea include prolonged spawn-
  ing seasons and spawning on spawning grounds that
  were historically unknown.^19 This change in behav-
  iour should be attributed to global climate change. In
  other words, climate change is already changing the
  behaviour and migration patterns of pelagic fish in
  the Adriatic.

IX Such as production fluctuations, changes in phytoplankton spe-

cies composition, higher biomass and a changed zooplankton com-

munity composition

Climate change

is already

changing the

behaviour

and migration

patterns of

pelagic fish in the

Adriatic