What are possible explenations for absence of diel vertical migration (DVM)

We expect the blue circle: Dark – knight light – day. The orange cases are different – just spread out. Especially the ones in august and september are weird. DVM – diel vertical migration Can be explaned by other factors food avalability - is there any point in mooving up if theres no food there Predetor occurance – you don’t want to migrate to the top if theres a lot of predators there. Some copopods can see fish shadows above them 5 – 10 meters. And can also to some extend smell them. Mabey its also different water masses Seasonal effect. Some seasons it makes more sense to migrate down.