Migration and habitat of white sharks (<Emphasis Type="Italic">Carcharodon carcharias</Emphasis>) in the eastern Pacific Ocean

Satellite telemetry studies of 20 adult and sub-adult white sharks (360–530 cm estimated total length (TL)) in the eastern North Pacific during 1999–2005 revealed long distance seasonal migrations from the coast of California to an offshore focal area 2,500 km west of the Baja Peninsula, as well as the Hawaii Islands. Three tags were recovered allowing detailed behavioral analyses, including one shark’s migration cycle from the coast to the offshore focal area and back. While near pinniped rookeries in autumn and winter, sharks avoided the surface and used water to 50 m depth, consistent with a silhouette-based hunting strategy. Offshore migrations were initiated during November–March and followed periods of decreasing pinniped abundance. Migrations were highly directed, taking 23 ± 5 days to reach the offshore focal area along similar paths among sharks and years, defining a migration corridor. Sharks exhibited a broad depth distribution (0–644 m) in the offshore focal area, and remained there for up to 167 days during spring and summer, though primary productivity and fishery data suggest that forage resources are scarcer there than in other regions of the eastern North Pacific. Archival data from one shark revealed intensive oscillatory movements while in the offshore focal area, a behavior that may be related to foraging or mating. Sharks traveling to Hawaii remained near the islands up to 122 days, potentially feeding on pelagic fishes and marine mammals that concentrate around the islands. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structure and migration corridors in Pacific populations of the Swordfish Xiphius gladius, as inferred through analyses of mitochondrial DNA

 The swordfish Xiphias gladius is a migratory oceanic species distributed in sub-tropical and temperate waters worldwide. Studies utilizing mitochondrial DNA (mtDNA) have demonstrated genetic subdivision between ocean basins, as well as within the Atlantic basin. However, there has been no support of population subdivision within the Pacific. We sequenced 629 base pairs of the control region for 281 swordfish collected in the Pacific. A rate heterogeneity parameter, alpha, was found to be 0.201, indicating substantial variation in mutation rate within the control region of swordfish. Hierarchical analysis of molecular variance supported significant genetic structuring among Pacific populations. Northern and southern populations in the western Pacific were significantly divergent, while populations in the east appeared to be genetically continuous. Regression analysis supported a correlation of genetic differentiation with geographic distance along a U-shaped corridor of gene flow. These results reveal a pelagic biogeographic pattern heretofore unrecognized in the Pacific, and reject the null hypothesis that Pacific populations of swordfish are unstructured and comprise only a single homogeneous stock. Received: 10 November 1998 / Accepted: 4 February 2000     

Spanish agriculture from 1900 to 2008: a long-term perspective on agroecosystem energy from an agroecological approach

Regional Environmental Change - According to the agroecological approach, energy analyses applied to agriculture should provide information about the structure and functions of the agroecosystem;...     

Fish predation selects for reduced foraging activity

Despite the importance of foraging activity for the growth/predation risk trade-off, studies that demonstrated predator-induced survival selection on foraging activity under semi-natural conditions are relatively rare. Here, we tested for fish-induced selection for reduced foraging activity in two larval Enallagma damselflies using a field enclosure experiment. Fish imposed considerable mortality in both damselfly species and survival selection on foraging activity could be detected in Enallagma geminatum. We did not detect selection in Enallagma hageni, probably because this species already was not eating very much in the absence of fish compared to E. geminatum. Both species responded strongly to the presence of predators by reducing their foraging activity. The documented survival selection on foraging activity was detected despite the already low activity levels in fish lake prey species and despite strong predator-induced plasticity in this trait.     

Movements,behavior, and habitat utilization of yellowfin tuna (<Emphasis Type="Italic">Thunnus albacares</Emphasis>) in the northeastern Pacific Ocean,ascertained through archival tag data

Sixty-eight yellowfin tuna, Thunnus albacares, (60-135 cm fork length) were caught and released with implanted archival tags offshore off Baja California, Mexico, during October 2002 and October 2003. Thirty-six fish (53%) were recaptured and the data were downloaded from all 36 recovered tags. Time at liberty ranged from 9 to 1,161 days, and the data were analyzed for the 20 fish that were at liberty for 154 or more days. The accuracy in the position estimates, derived from light-level longitude data and sea-surface temperatures (SSTs) based latitude, is about 0.41° in longitude and 0.82° in latitude, in this region. The movement paths, derived from position estimates, for the 20 yellowfin indicated that 19 (95%) remained within 1,445 km of their release locations. The estimated mean velocity along movement paths was 77 km/day. The southern and northern seasonal movement paths observed for yellowfin off Baja California are influenced by the seasonal movements of the 18°C SST isotherm. Cyclical movements to and from suitable spawning habitat (≥24°C SST) was observed only for mature fish. For the 12 fish that demonstrated site fidelity, the mean 95 and 50% utilization distributions were 258,730 km² and 41,260 km², respectively. Evaluations of the timed depth records resulted in discrimination of four distinct behaviors. When exhibiting type-1 diving behavior (78.1% of all days at liberty) the fish remained at depths less than 50 m at night and did not dive to depths greater than about 100 m during the day. Type-2 diving behavior (21.2% of all days at liberty) was characterized by ten or more dives in excess of 150 m during the day. Type-2 diving behavior is apparently a foraging strategy for fish targeting prey organisms of the deep-scattering layer during the day, following nighttime foraging within the mixed layer on the same prey. Yellowfin tuna exhibited occasional deep-diving behavior, and some dives exceeded 1,000 m, where ambient temperatures were less than 5°C. Surface-oriented behavior, defined as the time fish remained at depths less than 10 m for more than 10 min, were evaluated. The mean number and duration of surface-oriented events per day for all fish was 14.3 and 28.5 min, respectively. Habitat utilization of yellowfin, presented as monthly composite horizontal and vertical distributions, indicates confined geographical distributions, apparently resulting from an affinity to an area of high prey availability. The vertical distributions indicate greater daytime depths in relation to a seasonally deeper mixed layer and a greater proportion of daytime at shallower depths in relation to a seasonally shallower mixed layer.     

Males are faster foragers than females: intersexual differences of foraging behaviour in the Apennine chamois

Availability of food resources and individual characteristics can influence foraging behaviour, which can differ between males and females, leading to different patterns of food/habitat selection. In dimorphic species, females are usually more selective in food choice, show greater bite rates and spend more time foraging than males. We evaluated sexual differences in foraging behaviour in Apennine chamois Rupicapra pyrenaica ornata, during the warm season, before the rut. Both sexes selected nutritious vegetation patches and spent a comparable amount of time feeding. However, males had a significantly greater feeding intensity (bite rate) and a lower search effort for feeding (step rate), as well as they spent more time lying down than females. Females selected foraging sites closer to refuge areas than males. In chamois, sexual size dimorphism is seasonal, being negligible in winter–spring, but increasing to 30–40 % in autumn. Our results suggest that males enhance their energy and mass gain by increasing their food intake rate during the warm season, to face the costs of the mating season (November). Conversely, females seem to prioritize a fine-scale selection of vegetation and the protection of offspring. A great food intake rate of males in the warm season could have developed as a behavioural adaptation leading herbivores to the evolutionary transition from year-round monomorphism to permanent dimorphism, through seasonal dimorphism.