Global patterns for upper ceilings on migration distance in sea turtles and comparisons with fish, birds and mammals

1. Some animals migrate huge distances in search of resources with locomotory mode (flying/swimming/walking) thought to drive the upper ceilings on migration distance. Yet in cross-taxa comparisons, upper ceilings on migration distance have been ignored for one important group, sea turtles. 2. Using migration distances recorded for 407 adult and 4715 juvenile sea turtles across five species, we show that for adult cheloniid turtles, the upper ceiling on species migration distances between breeding and foraging habitats (1050–2850 km across species) is similar to that predicted for equivalent-sized marine mammals and fish. 3. In contrast, by feeding in the open ocean, adult leatherback turtles (Dermochelys coriacea) and juveniles of all turtle species can travel around 12 000 km from their natal regions, travelling across the widest ocean basins. For juvenile turtles, this puts their maximum migration distances well beyond those expected for equivalent-sized marine mammals and fish, but not those found in some similar sized birds. 4. Post-hatchling turtles perform these long-distance migrations to juvenile foraging sites only once in their lifetime, while adult turtles return to their breeding sites every few (generally ?2) years. Our results highlight the important roles migration periodicity and foraging mode can play in driving the longest migrations, and the implications for Marine Protected Area planning are considered in terms of sea turtle conservation.

Downstream spawning migration by the amphidromous Australian grayling (Prototroctes maraena) in a coastal river in south-eastern Australia

Understanding the reasons and cues for migration is crucial for developing effective conservation and management strategies of diadromous fishes. Spawning and movement patterns of the threatened diadromous Australian grayling (Prototroctes maraena) were investigated in the Bunyip River, Victoria, using drift sampling (2008–2011) and acoustic telemetry (2009–2010) during the autumn–winter spawning period of each year. Fifty-five adult fish (2009: n = 21; 2010: n = 34) were tagged and released in February ~15–30 km upstream of the Bunyip River estuary. Thirteen fish (2009: n = 7; 2010: n = 6) undertook rapid downstream migrations from March to April to reaches immediately upstream of the estuary. Drifting eggs were detected at multiple sites between April and July; however, the majority (78.8%) were collected in the lower reaches within ~0.5 km of the estuary in early–mid-May. Tagged adult fish arrived in this area 1–4 weeks before eggs were detected and usually moved back upstream within 2 weeks following the peak egg abundance. Downstream migration and peak egg abundance were associated with increased river flows. Although the proportion of fish that undertook migrations was low, low rates of tag retention in this species likely account for the failure to detect migration by many of the tagged individuals.

International vocational education and training - the migration and learning mix

International VET students have divergent, shifting and in some cases multiple purposes for undertaking their VET courses. Students' motives may be instrumental and/or intrinsic and can include obtaining permanent residency, accumulating skills that can secure good employment, gaining a foothold that leads to higher education, and/or personal transformation. Moreover, students' study purposes and imagining of acquired values are neither fixed nor unitary. They can be shaped and reshaped by their families and personal aspirations and by the social world and the learning environment with which they interact. We argue that, whatever a student's study purpose, s/he needs to engage in a learning practice and should be provided with a high quality education. Indeed, we insist this remains the case even if students enroll only in order to gain the qualifications needed to migrate. The paper details the association between migration and learning, and argues that the four variations emerging from the empirical data of this study that centre on migration and skills' accumulation better explain this association than does the 'international VET students simply want to migrate' perspective. We conclude with a discussion of why the stereotype that holds VET international students are mere 'PR hunters' is unjust and constitutes a threat to the international VET sector.

Individual variability in Diel Vertical migration of a marine copepod : why some individuals remain at depth when others migrate

The diel vertical migration (DVM) of the copepod Metridia pacifica was examined in Dabob Bay (47°45.05′N, 122°49.71′W), a fjord in Washington state. Although the population showed deep daytime residence (75-175 m), a proportion of the population was found in the surface waters at night. For individuals that migrated to the surface, the mean size of the oil sac was much smaller than those that remained at depth (mean lengths of oil sac 0.25 mm for individuals collected between 0 and 25 m at night, compared with 0.43 mm for individuals from between 125 and 175 m). Similarly, the C : N ratio was lower for animals collected from near the surface, indicative of their lower lipid reserves. These results suggest that individual variability in DVM was influenced by body condition, with those animals with larger lipid stores not needing to risk coming to the surface to feed at night.

The diving behaviour of green turtles undertaking oceanic migration to and from Ascension Island: dive durations, dive profiles and depth distribution

Satellite telemetry was used to record the submergence duration of green turtles (Chelonia mydas) as they migrated from Ascension Island to Brazil (N=12 individuals) while time/depth recorders (TDRs) were used to examine the depth distribution and dive profiles of individuals returning to Ascension Island to nest after experimental displacement (N=5 individuals). Satellite telemetry revealed that most submergences were short (<5 min) but that some submergences were longer (>20 min), particularly at night. TDRs revealed that much of the time was spent conducting short (2–4 min), shallow (approximately 0.9–1.5 m) dives, consistent with predictions for optimisation of near-surface travelling, while long (typically 20–30 min), deep (typically 10–20 m) dives had a distinctive profile found in other marine reptiles. These results suggest that green turtles crossing the Atlantic do not behave invariantly, but instead alternate between periods of travelling just beneath the surface and diving deeper. These deep dives may have evolved to reduce silhouetting against the surface, which would make turtles more susceptible to visual predators such as large sharks.

Changes in behaviour during the inter-nesting period and post-nesting migration for Ascension Island green turtles

Satellite transmitters were attached to green turtles Chelonia mydas while they were nesting on Ascension Island in the South Atlantic (7°57'S, 14°22'W) and individuals were subsequently monitored during the inter-nesting period and the post-nesting migration to Brazil. During the inter-nesting period, data from the transmitters suggested that turtles generally stayed within 5 km of the nesting beach on which they had originally been observed. During both the inter-nesting period and migration, turtles were submerged the vast majority (>95%) of the time, suggesting that they neither basked at the surface nor drifted passively during migration to any great extent. There was a clear dichotomy in submergence behaviour, with submergences tending to be of short duration during post-nesting migration (mean = 7.3 min, 3318 h of data from 5 individuals) and of longer duration during the inter-nesting period (mean = 22.1 min, 714 h of data from 5 different individuals). As submergence duration is generally linked to activity levels in sea turtles, this pattern suggests that turtles were comparatively inactive during the inter-nesting period and comparatively active during migration. During both the inter-nesting period and the post-nesting migration, diel submergence patterns were detected with dive duration tending to be longer at night. As the turtles migrated WSW from Ascension Island, there was a reduction in their speed of travel. A numerical model of the near-surface currents suggested that this reduction was associated with the weakening of the WSW flow of the prevailing South Atlantic Equatorial Current.