"Great sea monsters" (Heb. tauninim, Genesis 1:21) were large fish, whales, squid, and all large creatures living in the water. The pagans worshipped these, but they are under God"s authority. The Old Testament writers adopted pagan imagery, but not pagan theology. [source][source][source]
Note that Moses wrote that God created both marine animals and birds on the same "day". Evolution claims that birds evolved from reptiles and that this process took millions of years. [source][source][source]
"The blessing of God is one of the great unifying themes of Genesis. God blesses animals ( Genesis 1:22), mankind ( Genesis 1:28), the Sabbath ( Deuteronomy 28:1-143), Adam ( Genesis 5:2), Noah ( Genesis 9:1), and frequently the patriarchs ( Genesis 12:3; Genesis 17:16; Genesis 17:20, etc.). God"s blessing is most obviously visible in the gift of children, as this is often coupled with "being fruitful and multiplying." But all aspects of life can express this blessing: crops, family, and nation ( 1714039885_72). Where modern man talks of success, OT man talked of blessing." [1][source]
Birds and fish rule their respective realms by multiplying. [2][source]