Convergence of marine megafauna movement patterns in coastal and open oceans.

The extent of increasing anthropogenic impacts on large marine vertebrates partly depends on the animals' movement patterns. Effective conservation requires identification of the key drivers of movement including intrinsic properties and extrinsic constraints associated with the dynamic nature of the environments the animals inhabit. However, the relative importance of intrinsic versus extrinsic factors remains elusive. We analyze a global dataset of ∼2.8 million locations from >2,600 tracked individuals across 50 marine vertebrates evolutionarily separated by millions of years and using different locomotion modes (fly, swim, walk/paddle). Strikingly, movement patterns show a remarkable convergence, being strongly conserved across species and independent of body length and mass, despite these traits ranging over 10 orders of magnitude among the species studied. This represents a fundamental difference between marine and terrestrial vertebrates not previously identified, likely linked to the reduced costs of locomotion in water. Movement patterns were primarily explained by the interaction between species-specific traits and the habitat(s) they move through, resulting in complex movement patterns when moving close to coasts compared with more predictable patterns when moving in open oceans. This distinct difference may be associated with greater complexity within coastal microhabitats, highlighting a critical role of preferred habitat in shaping marine vertebrate global movements. Efforts to develop understanding of the characteristics of vertebrate movement should consider the habitat(s) through which they move to identify how movement patterns will alter with forecasted severe ocean changes, such as reduced Arctic sea ice cover, sea level rise, and declining oxygen content.

Population differentiation in the context of Holocene climate change for a migratory marine species, the southern elephant seal.

Understanding observed patterns of connectivity requires an understanding of the evolutionary processes that determine genetic structure among populations, with the most common models being associated with isolation by distance, allopatry or vicariance. Pinnipeds are annual breeders with the capacity for extensive range overlap during seasonal migrations, establishing the potential for the evolution of isolation by distance. Here, we assess the pattern of differentiation among six breeding colonies of the southern elephant seal, Mirounga leonina, based on mtDNA and 15 neutral microsatellite DNA markers, and consider measures of their demography and connectivity. We show that all breeding colonies are genetically divergent and that connectivity in this highly mobile pinniped is not strongly associated with geographic distance, but more likely linked to Holocene climate change and demographic processes. Estimates of divergence times between populations were all after the last glacial maximum, and there was evidence for directional migration in a clockwise pattern (with the prevailing current) around the Antarctic. We discuss the mechanisms by which climate change may have contributed to the contemporary genetic structure of southern elephant seal populations and the broader implications.

Weaning mass affects changes in body composition and food intake in harbour seal pups during the first month of independence.

In phocid seals, the transition to nutritional independence is abrupt, with females abandoning their offspring after weaning and returning to sea. We hypothesized that body size at weaning may play an important role in the nature of this transition. We studied the changes in body composition and water flux of newly weaning harbour seals over the first 4-6 wk postweaning. Thirty-three pups were dosed with deuterium oxide to estimate total body water (TBW) and a subset of 24 was dosed twice to estimate changes in body composition and water flux. All pups lost body mass over the study period, but TBW increased during the period of mass loss, indicating continued lean tissue growth. Combined data from this and our early study indicated that heavy (>median mass) pups were relatively fatter (41.0% vs. 37.1%) and had significantly greater total body energy at weaning than did light (< or = median mass) pups. Percentage TBW declined linearly over time in light pups but was constant in heavy pups for the first 19 d postweaning and then declined linearly. Both the temporal pattern and composition of mass loss differed between light and heavy pups. Estimated food intake increased in the second 2 wk of study compared to the first 2 wk, in both light and heavy pups, reflecting increased foraging success but at levels still insufficient to meet daily expenditures of most individuals.