Ægir - 15.05.1968, Qupperneq 16

174
ÆGIR
grafnar niður i leirbotninn. Þegar svo „með-
göngutímanum“ er lokið í maí, fara hrygn-
urnar aftur á stjá, sem veldur aukningu á
hlutfalli þeirra í veiðinni næstu mánuði á
eftir, eða þar til hrygning verður að nýju.
Unnið er nú að rannsóknum á hrygningu
letm-humars hér við land á vegum Hafrann-
sóknastofnunarinnar og henda líkur til þess,
að klaktími sé hér á vorin. Gæti þetta þvi
skýrt, að einhverju leyti, þá aukningu, sem
verður á hlutfalli kvendýra í aflanum þegar
líður á sumarið. Enn sem komið er er þó
aðeins hægt að álíta, að þetta séu aðallega
áhríf veiða eins og hreytingar þær, sem orðið
hafa ár frá ári.
Sést á þessu yfiriiti, að minnkun á afla á
togtima á tímahilinu maí—ágúst er afleiðing
sóknar, sem einkum er mikil í júní og júli.
Aukning á hlutfalli kvendýra í veiðinni yfir
sama tíma er afleiðing sóknar og e. t. v. einn-
ig árstíðasveiflna, sem eiga sér stað af nátt-
úrunnar hendi. Athuganir, sem verið er að
gera á hrygningu og klaki leturhumarsins,
eiga væntanlega eftir að varpa nákvæmara
Ijósi á þær greinilegu breytingar, sem sjást
á hlutfalli kynja milli mánaða og árstima.
SUMMARY
The article deals with monthly and yearly varia-
tions that have occurred in size and composition of
Norway lohster stocks in Icelandic waters, over the
years 1962 to 1967.
The effect of fishing, as reflected in average mean
size of males, catch per hour of trawling, and propor-
tion of females in the catch, is shown on the main
fishing areas at Southwest, South an Southeast Ice-
land (see Fig. 1).
Average carapace langth of males has decreased
considerably over the period 1962 to 1967 in all areas
investigated. This is especially noticeable in the last
two years 1966 and 1967. Similarly there has been a
marked decrease in maximum carapace lengths recor-
ded (see Tables 1, 2 and 3).
A decrease in catch (kgs) per trawling hour is seen
over the period 1962 to 1967 accompanied by an
appreciable increase in the proportion of females in
the catch. This is particularly evident at Southwest
Iceland (areas 106—148), where the fishery has been
intensive since before 1960 (see Fig. 2). The increase
in catch per effort seen in 1963 and to a lesser extent
in 1965 is due to the discovery of new important Nor-
way lobster grounds in those years. The decrease in
the proportion of females in the catch in 1963 and
1965 is associated with the exploitation of these virgin
grounds. The data from South Iceland (area 169),
although rather limited, are indicative of a propor-
tionally similar decrease in catch per effort and in-
crease in female percentage as seen Southwest Ice-
land. The exploitation of this area dates back to 1958
when Norway lobster fishery in Iceland first became
commercially important. In Southeast Icelandic waters
(areas 152—154), the decrease in catch per hour of
trawling and increase in proportion of females, is
less prominent as the fishery here was relatively light
until 1963. However the data for 1967, especially far
catch/effort, show signs of the increasing exploitation
of these areas as well (see Fig. 3).
The year to year decrease in mean size of males,
accompanied by a lesser catch per unit effort and an
increase in the proportion of females, is thus attributed
to the intensive fishery in recent years.
Monthly variations in catch per trawling hour and
sex ratio are seen in all areas. The catch/effort being
largest at the beginning of the Norway lobster season
in May and decreasing progressively towards the end
of the season in August-September (see Fig. 4 and 5).
Similarly a considerable increase in the proportion of
females to males occurs over the same period, parti-
cularly on the heavily exploited areas off the South-
west coast.
The monthly variations observed in catch per traw-
ling hour can be attributed to the high fishing inten-
sity, mainly in June and July, resulting in the lowly
catch towards the end of the season (see Fig. 6).
Monthly variations seen in sex ratio are probably the
result of intensive fishing, but possibly also affected
by seasonal variations in availability, owing to the
burrowing habit of berried females. As there are
indications of a hatching season in May or early
summer, the possibility of an increasing amount of
females coming into the catch after hatching has
occurred cannot be ruled out.
Apart from the continuation of these investigations,
work on various aspects of the biology of the Norway
lobster is either being carried out or planned at the
Marine Research Institute. Of paramount importance
at present are investigations into maturity size,
spawning and hatching seasons, and fecundity of Nor-
way lobsters in Icelandic waters.
HEIMILDARRIT
(References)
Aðalsteinn Sigurðsson: Leturhumarinn við ísland,
Ægir 56. árg. 9. tbl. 1963.
Aðalsteinn Sigurðsson: A preliminary report on
the Norway lobster (Nephrops norwegicus) in