The Septuagint LXX is the oldest known translation of the Old Testament into ancient Greek. It is generally believed that the formation of the Septuagint began in the 280s BC and in general ended in the I century BC The Masoretic text MT is the authoritative Jewish and Aramaic text of the 24 books of the Hebrew Bible (Tanakh) in Rabbinic Judaism and Christianity.
When researching the book of the Prophet Jonah, I compared the Masoretic text with the ancient Greek translation by the Septuagint. And I saw an interesting and at the same time incomprehensible moment for me.
In Jonah 1:17, the Hebrew word [דָּ֣ג] FISH is translated in the Septuagint as [κήτει] WHALE
MT Jonah 1:17 And the LORD had prepared a great FISH to swallow up Jonah.
LXX Jonah 1:17 And the LORD assigned a great WHALE to swallow Jonah
MT Jonah 1:17 וַיְמַ֤ן יְהוָה֙ דָּ֣ג גָּדֹ֔ול לִבְלֹ֖עַ אֶת־יֹונָ֑ה
LXX Jonah 1:17 Καὶ προσέταξεν Κύριος κήτει μεγάλῳ καταπιεῖν τὸν Ἰωνᾶν·
In Jonah 4:6 the Hebrew word [קִיקָיֹ֞ון] PLANT in the Septuagint translated as [κολοκύνθῃ] GOURD
MT Jonah 4:6 So the LORD God appointed a PLANT and it grew up over Jonah
LXX Jonah 4:6 And assigned the lord God a GOURD, and it ascended above the head of Jonah
MT Jonah 4:6 וַיְמַ֣ן יְהוָֽה־אֱ֠לֹהִים קִיקָיֹ֞ון וַיַּ֣עַל ׀ מֵעַ֣ל לְיֹונָ֗ה
LXX Jonah 4:6 καὶ προσέταξεν Κύριος ὁ θεὸς κολοκύνθῃ, καὶ ἀνέβη ὑπὲρ κεφαλῆς τοῦ Ἰωνᾶ
I don't understand why the Septuagint translators translated it this way?
Undoubtedly, they translated into ancient Greek from the Hebrew text. Perhaps, at that time, there was a Hebrew source that was different from the Masoretic text?
Can anyone cite these passages from the Qumran DSS scrolls?