Marine and 2006. In the tropical regions, the

Marine
fisheries provide a very large contribution to the economy for many countries,
and are important for the food security in a number of coastal communities.

Different species of marine fish and invertebrates each have a unique temperature
range at which their growth and reproduction is optimal. This determines the
global distribution of all marine fish and invertebrates. Climate change has
been increasing the sea surface temperature of the ocean over the past few
decades, which may be creating a distributional shift for species of marine
fish and invertebrates as they move in order to live in their optimal
temperature. The impact of climate change on fisheries needs to be understood
since many communities depend on fisheries for their economy and food security.

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This paper studies the potential effect of increasing sea surface temperature on
the distribution of marine fish. It was hypothesized that increasing sea
surface temperature generally forces marine fish to higher latitudes.

 

            In order to study the effect in
question, an index called the mean temperature of the catch (MTC) was created.

For a given region and year, the MTC was the weighted average temperature
preference of all fish caught in that region that year. The changing
distribution of marine fish could then be studied by observing the change of
the MTC in a given region. Several observational data sets were used to calculate
this MTC index. First, the temperature preference of 990 fish species were obtained
by using an algorithm from the Sea Around Us project, which models the
distribution of fish species globally. Next, a data set of mapped fisheries
landings from the Sea Around Us project was used to determine the total weight
of each species caught in each region each year. The MTC for each region
(called large marine ecosystems, LME’s) could then be calculated. However,
large-scale oceanographic factors and fishing effort are different between
regions, which affected the fisheries for each region. The fishing effort was
obtained from a data set in the Sea Around Us project. Finally, the MTC of each
region was calculated using a generalized additive mixed model (GAMM), which
considered the large-scale oceanographic factors and fishing effort. The rate
of change of the MTC in each of the 52 regions was calculated between 1970 and
2006 to determine how climate change has been affecting marine fisheries.

 

            In the non-tropical regions, the
rate of increase of MTC was 0.23°C per decade between 1970 and 2006. In the
tropical regions, the rate of increase of MTC was 0.6°C from 1970 to 1980. The
MTC maintained a value of about 26°C from then on, even as the average sea surface
temperature in tropical regions increased by 0.14°C per decade. As well, it was
shown that there was a significant positive relationship between the MTC
increase and the sea surface temperature increase in the 52 regions between
1970 and 2006.

 

            The results of this study show that
non-tropical regions are going through a 
“tropicalization” effect as the presence of warm-water species of fish
increases in non-tropical areas. In tropical regions, there was initially a
large increase in the MTC from 1970 to 1980, as any subtropical fish species
present were forced to leave the warming tropical waters. Following that, the
MTC in the tropical regions stabilized, but the sea surface temperature
continued to increase. There is reason for major concern in the tropical
regions, as a continued increase in the sea surface temperature will likely
force many tropical fish species to move to higher latitudes in order to remain
in their optimal temperature of water. This would greatly decrease the amount
of fish present in the tropical regions, and therefore would be a major issue
for tropical communities that depend on fisheries for their economy and for
food security.

 

            The MTC index was an appropriate
measure to study the effect of increasing sea surface temperature on the
distribution of species of marine fish. However, there were a few limitations
from the data that was required to calculate the MTC index. First,
over-reporting in China on the fish caught in fisheries is a significant
problem. This decreases the reliability of the MTC index in marine regions
around China. Another issue is a potential evolutionary adaptation from some
species of fish in response to the warming waters. This could allow species of
fish to live in higher water temperatures than their preference temperatures
from this study, slowing down the MTC increase rate. 

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