Deep-diving of Atlantic salmon ($\textit{Salmo salar}$) during their marine feeding migrations

TL;DR

This study analyzed depth movement data from tagged Atlantic salmon during their marine migration, revealing patterns of deep diving, especially in late winter, likely related to feeding behavior.

Contribution

It provides new insights into the timing, depth, and duration of deep dives in Atlantic salmon during marine migration, highlighting seasonal and nocturnal patterns.

Findings

Deep dives increased in frequency and depth in late winter.

Most dives were nocturnal and lasted up to 33 hours.

Dives correlated with potential feeding periods in winter.

Abstract

Data from seven data storage tags recovered from Atlantic salmon marked as smolts were analyzed for depth movements and patterns of deep diving during the marine migration. The salmon mostly stayed at the surface and showed diurnal activity especially from autumn until spring. During the first months at sea the salmon stayed at shallower depths (< 100 m). The salmon took short deep dives (> 100 m), that were rare or absent during the first summer at sea but increased in frequency and duration especially in late winter. The maximum depth of the dives varied from 419 to 1187 m. Most of dives were short, (< 5 hours) but could last up to 33 hours. The duration of dives increased in late winter until spring and the overall depth and maximum depth per dive increased exponentially over time. The initiation of the dives was more common in evenings and at night, suggesting nocturnal diving. We hypothesized that deep diving is related to feeding of salmon as mesopelagic fish can be important food for salmon during winter.