Náttúrufræðingurinn - 2021, Page 35

Tímarit Hins íslenska náttúrufræðifélags
127
Ritrýnd grein / Peer reviewed
ENGLISH SUMMARY
Sprat, Sprattus sprattus
(Linnaeus, 1758), a new species
of fish in Icelandic waters
Sprat (Figure 1) was caught for the
first time in Icelandic waters in
August 2017 at 20 m depth off the
south coast (Figure 2A, Appendix).
The fish was 14.6 cm long and prob-
ably a sexually mature individual. In
autumn 2019, two more sprat were
caught in the Westfjords. In autumn
of 2020, sprat was caught during
three research cruises. Three fishes,
11–12 cm long, were caught at 14–29
m depth off the south coast in early
September, and four more, 8–12 cm
long, were caught in Ísafjarðardjúp
at 66–83 m depth about a month later.
During a fish survey in late October
2020, a total of 29 sprat were caught
at three stations off the south coast
and one in Breiðafjörður. These fishes
were 12−15 cm long and were caught
at 71–135 m depth.
In March 2021, a total of 375 sprat
were caught at several stations off
the west and south coast during a fish
survey. In most cases only one or two
fish were caught in each haul with a
few exceptions; in a single haul within
Faxaflói 68 specimens were caught
and in two further hauls off the south
coast 52 and 225 fishes were caught. Of
these, 118 fishes were frozen aboard the
research vessel and brought ashore for
further investigation.
In the three hauls in the March fish
survey of 2021 where most of the sprat
were caught, there was a difference in
the length distribution between hauls.
Particularly, sprat caught within Faxa-
flói differed from those caught off the
south coast (Figure 4A). In Faxaflói
most sprat were 14.5–16 cm long, how-
ever, off the south coast they were
11−12.5 cm. Sex ratio in the samples
was uneven, with females represent-
ing 79% of sexed fishes, but that differ-
ence seems unrelated to length groups
(Figure 4B).
All sprat brought ashore from the
March fish survey of 2021 were sexually
mature fish except for one 7.6 cm long
specimen (Figure 4B). Most females
were at maturity stage 3 and 4, but
males on stage 4 and 5, which indicates
that the fish were preparing for spawn-
ing. Otoliths were collected from 23 fish,
21 female and 2 males (Figure 4C). All
sprat 15 cm long or larger were four
years of age except one that was five
years. Fish in the smaller group were
almost all two years old.
In research surveys in October 2021,
about 300 sprat were caught south,
southwest, and northwest of Iceland.
The size of these fish was similar to that
already observed in Icelandic waters,
and sexual maturity staging showed
that most the fish had spawned in the
preceding summer. Samples collected
in Ísafjarðardjúp in March-August 2021
confirm that sprat spawned in the area
in the summer of 2021.
It is unknown how sprat arrived
in Icelandic waters. It is possible
they drifted as eggs/larvae with cur-
rents from Faroe Islands or the North
Sea. Time will tell whether sprat will
remain in Icelandic waters over the
coming years but that highly depends
on temperature remaining similar
or increasing.