Interpreting vertical movement behavior with holistic examination of depth distribution: a novel method reveals cryptic diel activity patterns of Chinook salmon in the Salish Sea

Abstract

Aquatic organisms exhibit a variety of diel changes in vertical movement that are investigable through the use of biotelemetry. While certain species do not change their movements between day and night, others exhibit diel vertical migration (DVM) or a diverse range of diel activity patterns (DAPs). Consequently, day-night differences in depth distribution may be stark and easily detectable, or more subtle and difficult to identify. To augment the discovery and classification of cryptic diel vertical movement behavior, we developed and utilized a novel method that analyzed entire depth distributions while comparing diel period, season, and season/diel period models. This analysis revealed a seasonally variable DAP previously unreported in Chinook salmon (Oncorhynchus tshawytscha). In summer and fall, Chinook salmon in the Salish Sea juxtaposed shallow and confined daytime movements with nighttime bounce diving. This DAP was reversed in winter, when they occupied deeper sections of the water column during the day, resulting in a substantially overlapping, but more even depth distribution than at night. These results demonstrate the analytical utility of accompanying other metrics with holistic examination and visualization of the entire distribution of depth data. Additionally, we highlight the need to use a framework that answers all of the following questions: (1) does the target species exhibit seasonal variation in depth, (2) does it undergo DVM, (3) if it does not undergo DVM, does it follow a DAP, and (4) if it follows a DAP, what is the difference in vertical movement behavior between diel periods?

Warm oceans exacerbate Chinook salmon bycatch in the Pacific hake fishery driven by thermal and diel depth‐use behaviours

“…Salmon may be using daylight in surface waters for foraging or navigation and/or retreating deeper at night to avoid noc- SST qC Tanaka et al, 2000;Todd et al, 2022;Wilson et al, 2014). Two tagging studies also found that the deepest Chinook salmon dives occurred at night; however, other studies have observed opposite and variable patterns (Arostegui et al, 2017;Courtney et al, 2019;Hinke, Foley et al, 2005). We add broader spatial and temporal evidence for Chinook salmon diel depth-use behaviours of moving deeper at night, which increased overlap with deeper-dwelling hake at the most common fishing depths of the hake fishery.…”

Vertical ambush corridors: Intriguing multi‐mechanism ecological structures embedded in the kinetic fluid architectures of ocean living resource production systems

“…In any case, these extreme bounce‐diving behaviours may seem remarkable to terrestrially adapted humans who may naturally expect to see mostly horizontally oriented prey‐hunting activities such as predominate in the terrestrial world. But even chinook salmon ( Onchoryncus tshawytscha , Salmonidae) operating inside the confines of Puget Sound (in Washington State, USA) appear to employ a form of bounce diving (Arostegui et al, 2017). Apparently, something we are not expecting seems to be going on in an important manner in the submerged ‘other world’ of the ocean.…”

Behavior and thermal environment of Chinook salmon Oncorhynchus tshawytscha in the North Pacific Ocean, elucidated from pop-up satellite archival tags

“…The variable and discontinuous occurrence of diel diving behaviors are similar to that of the only other electronic tagged Chinook salmon (n = 3) in the central Bering Sea (Walker and Myers 2009;Walker unpublished data) and Southeast Alaska (Murphy and Heard 2001;Murphy and Heard 2002). Further south, studies on Chinook salmon off the coast of Oregon, California, and the Salish Sea have all suggested that the presence/absence of diel vertical behaviors is correlated to multiple factors, including season and geographic location (Arostegui et al 2017;Hinke et al 2005b), which may be driven by foraging, thermoregulation, and/or predator avoidance.…”