The Functional and Ecological Significance of Deep Diving by Large Marine Predators

Abstract

Many large marine predators make excursions from surface waters to the deep ocean below 200 m. Moreover, the ability to access meso- and bathypelagic habitats has evolved independently across marine mammals, reptiles, birds, teleost fishes, and elasmobranchs. Theoretical and empirical evidence suggests a number of plausible functional hypotheses for deep-diving behavior. Developing ways to test among these hypotheses will, however, require new ways to quantify animal behavior and biophysical oceanographic processes at coherent spatiotemporal scales. Current knowledge gaps include quantifying ecological links between surface waters and mesopelagic habitats and the value of ecosystem services provided by biomass in the ocean twilight zone. Growing pressure for ocean twilight zone fisheries creates an urgent need to understand the importance of the deep pelagic ocean to large marine predators.

Diving into the vertical dimension of elasmobranch movement ecology

“…However, many of these species frequented deeper bathomes, with 31 recorded at mesopelagic depths (>200 m) and 13 at bathypelagic depths (>1000 m). The motivation for irregular movements into deep, dark, cold waters for epipelagic species is difficult to determine but could be related to some combination of foraging opportunities, thermoregulation, bioenergetics, reproduction, predator avoidance, and/or navigation through magnetic, chemical, topographic, electric, and light cues ( 20 ). Entering deep waters for sustained periods, however, requires a capacity to endure cooler temperatures and potentially more hypoxic conditions that are likely to be outside the “normal” environmental niche of many epipelagic species.…”

“…To date, studies on elasmobranch depth distributions have generally been conducted on a species-specific basis ( 14 , 16 , 17 ). Yet, an early study ( 18 ) and recent reviews have identified consistent vertical patterns among certain taxa, including diel vertical movement (DVM) and deep-diving behaviors ( 19 , 20 ). Furthermore, a recent synthesis of a regional predator assemblage in the South Atlantic revealed that dynamic species-specific space use was tied to water column structure ( 21 ).…”

Cool runnings: behavioural plasticity and the realised thermal niche of basking sharks

“…This suggestion does not negate other reasons for extensive forays into the water column. For example, oscillatory and or 'yo yo' deep-diving and surfacing events can serve several functions (reviewed by Braun et al 2022) Vol:. ( 1234567890) chemical cues, improving magnetic perception and thermoregulation (Nelson et al 1997;Klimley et al 2002;.…”

Movement Shapes the Structure of Fish Communities Along a Cross-Shore Section in the California Current

“…Note that the maximum size reached by migratory predators (L Mig cut = 1.5m) is below the maximum size allowed by the model (2 m), while observations show the occurrence of larger species (max(Lm Mig obs ) > 2 m), such as swordfish or white sharks. Many large deep-diving predators develop thermoregulation apparatuses (Legendre and Davesne, 2020;Braun et al, 2021) that might increase feeding efficiency and assimilation in deep waters (Fritsches et al, 2005). These adaptations may contribute to the increased asymptotic size of migratory species, but are absent in the model.…”

“…Moreover, in the model, large pelagic predators completing diel migrations spend half of the day at depth, half of the day at the surface. This pattern is applied to all migratory predators; however, some species adopt different behaviors, e.g., sub-daily vertical migrations with sporadic deep dives (Braun et al, 2021). Fine-tuning or new parameterizations could also help reduce this bias (see Figure 6).…”