Diel movement patterns of ocean sunfish Mola mola off southern California

Shifts in the movement, activity or behaviour of individual animals in relation to changing environmental landscapes play an important role in determining re-distribution patterns of populations. Such spatial dynamics are poorly understood for pelagic sharks despite the decline of many species due to overfishing. Satellite-linked archival transmitters were used to record the movements of blue sharks Prionace glauca for the first time in the northeast Atlantic. A total of 256 tracking days were recorded, with sharks covering an estimated minimum distance of 11 432 km. Generally, blue sharks displayed wide-ranging southward movements away from the tagging areas (English Channel, southern Portugal and the Azores Islands), with juvenile sharks displaying less site fidelity than previously suggested from other methods. Vertical movements ranged from the surface to a maximum depth of 696 m, and water temperatures varied from 10.6 to 24.6°C. Shifts in both thermal and depth-use patterns were detected, with tracked sharks displaying behavioural variability correlated with the environment, both within and between individuals. Patterns of behaviour in coastal areas were generally linked to the thermal structure of the water column; sharks displayed some preference for surface layers in thermally stratified waters, but displayed less regular behaviour in wellmixed or weakly stratified waters. In offshore locations, sharks usually adopted either a surfaceoriented or a depth-oriented diving pattern, often switching between both in response to probable changes in prey distribution or prey type when in deeper water. Fishing-induced mortality of tracked sharks was approximately 10% during the period of 13 to 70 d post-tagging. Our results indicate a variety of short and longer range movements of juvenile and sub-adult blue sharks with respect to time and environment in the northeast Atlantic, which suggests complex spatial dynamics and population structuring in this exploited species.

Section: Vertical Movements and Behaviourmentioning

confidence: 75%

Short-term movements and diving behaviour of satellite-tracked blue sharks Prionace glauca in the northeastern Atlantic Ocean

Queiroz¹,

Humphries²,

Noble³

et al. 2010

“…1) to the similarity in rate of ascent and descent within yo-yo dives (Table 2). It is uncertain why the rate of descent was significantly greater than the rate of ascent in the other sharks, particularly given the variability of this relationship across pelagic planktivores (Cartamil & Lowe 2004, Graham et al 2006. However, the consistency of this relationship in C. maximus may indicate some functionality.…”

Section: Discussionmentioning

confidence: 93%

“…In this way the effect of diel, tidal and lunar cycles can propa-gate up the food chain, leaving stereotyped signatures in patterns of predator movement (e.g. Wilson et al 1993, Cartamil & Lowe 2004.…”

Section: Introductionmentioning

confidence: 99%

Diel and tidal rhythms in diving behaviour of pelagic sharks identified by signal processing of archival tagging data

Shepard¹,

Ahmed²,

Southall³

et al. 2006

Patterns of vertical movement in pelagic predators can be highly complex, reflecting behaviours such as foraging, thermoregulatory excursions and spawning. Here we used fast Fourier analysis to identify periodicity in the vertical movements of 6 basking sharks Cetorhinus maximus from archival tagging data that totalled 595 d. We analysed quantitatively fine-scale vertical movements of basking sharks over seasonal scales (May to February) and detected predominant periodicities related to the vertical movements of the sharks' zooplankton prey. Normal and reverse diel vertical migration (DVM) represented the main periodic dive behaviour, occurring for 11 to 72% of individual track times. A tidal pattern of vertical movement, previously unreported for sharks, was also identified. A possible mechanism for this behaviour appears related to the shark exploiting tidally-induced aggregations of zooplankton prey at depth. The youngest shark tagged showed a markedly different pattern of vertical behaviour. Long-term data sets of swimming depth are becoming increasingly available for pelagic predators from pressure-sensitive data loggers. This study demonstrates the utility of signal processing techniques in objectively identifying both expected and unexpected periodicity in these continuous, high-resolution tracks.

“…Dagorn et al 2000, Kitagawa et al 2000, Musyl et al 2003 and ocean sunfish (Cartamil & Lowe 2004). Tuna also use such dives to regulate body temperature (e.g.…”

Section: Discussionmentioning

confidence: 99%

Vertical migrations may control maturation in migrating female Anguilla dieffenbachii

Jellyman¹,

Tsukamoto²

2010

The marine spawning area of the New Zealand longfin eel Anguilla dieffenbachii is unknown. The present study used 3 popup tags to obtain information on the offshore swimming behaviour and possible swimming directions and destination of migrating eels. All 3 eels showed very consistent behaviour and underwent daytime dives to depths of 600 to 900 m, where they experienced temperatures of 6 to 7°C. These dives were followed by nighttime ascents to depths of 200 to 300 m. From the consistency of these dives, we propose that eels are using regular exposure to cool temperatures to regulate the rate of maturity. While swimming at depth could also reduce predation, the increased pressure would stimulate development of the ovaries, something mediated by ascent to shallower water. Comparisons of ascent locations and swimming speeds are consistent with spawning in the tropics, possibly in the South Fiji basin. KEY WORDS: Anguilla dieffenbachii · Freshwater eel · Diving · ThermoregulationResale or republication not permitted without written consent of the publisher