Pelagic marine predators face unprecedented challenges and uncertain futures. Overexploitation and climate variability impact the abundance and distribution of top predators in ocean ecosystems. Improved understanding of ecological patterns, evolutionary constraints and ecosystem function is critical for preventing extinctions, loss of biodiversity and disruption of ecosystem services. Recent advances in electronic tagging techniques have provided the capacity to observe the movements and long-distance migrations of animals in relation to ocean processes across a range of ecological scales. Tagging of Pacific Predators, a field programme of the Census of Marine Life, deployed 4,306 tags on 23 species in the North Pacific Ocean, resulting in a tracking data set of unprecedented scale and species diversity that covers 265,386 tracking days from 2000 to 2009. Here we report migration pathways, link ocean features to multispecies hotspots and illustrate niche partitioning within and among congener guilds. Our results indicate that the California Current large marine ecosystem and the North Pacific transition zone attract and retain a diverse assemblage of marine vertebrates. Within the California Current large marine ecosystem, several predator guilds seasonally undertake north-south migrations that may be driven by oceanic processes, species-specific thermal tolerances and shifts in prey distributions. We identify critical habitats across multinational boundaries and show that top predators exploit their environment in predictable ways, providing the foundation for spatial management of large marine ecosystems.
Knowledge of how animals move through heterogeneous environments is essential to understanding the ecological functions they fulfill in each habitat and their responses to environmental change. Upper trophic level organisms exert structural influences through the food web, so information on their range, migration and foraging strategy is necessary to understanding ecosystem function. Recent technological advances have enabled researchers to follow individual animals over seasonal and multi-year timescales, revealing long-distance migrations in a variety of taxa. We used satellite telemetry to monitor female salmon sharks Lamna ditropis and remote sensing to characterize their environment. Salmon sharks ranged throughout the entire eastern North Pacific Ocean during a seasonal migration cycle. During long-distance migrations, quantitative movement analyses of speed, path straightness and first passage time (FPT) revealed area-restricted search (ARS) behaviors in northern and southern regions, with transiting behaviors at mid-latitudes. Individuals migrating to a highly productive southern region displayed more ARS behaviors than those moving to a low productivity region. The combination of multi-year time-series of animal behavior with synoptic environmental data reveals factors influencing migration and indicates that different life history functions are fulfilled in each habitat.KEY WORDS: Migration · Behavior · Habitat selection · Landscape ecology · Oceanography · Foraging behavior · Reproduction · Elasmobranch · Lamna ditropis Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 372: [253][254][255][256][257][258][259][260][261][262][263][264] 2008 has been used as a feeding proxy for a variety of marine vertebrates (Robinson et al. 2007), and studies combining both movement and feeding data have validated ARS in fish and bird species (Hill et al. 2000, Nolet & Mooij 2002.Like all proxies, the use of ARS behavior to indicate foraging is not perfect. Animals may move for reasons other than foraging (Dingle 1996), so ARS behavior could be foraging, mating, parturition or selection of environment. By combining measurements of both behavior and the environment we may gain clues to the ecology of organisms that cannot be directly observed (Pinaud & Weimerskirch 2005). ARS can be measured with analyses of speed, turning and straightness, or with more complex analyses (Robinson et al. 2007). First passage time (FPT) is a useful indicator of ARS behavior (Fauchald & Tveraa 2003) and is defined as the time an organism takes to cross a circle of a given radius. It is more robust to gaps in track records than speed or straightness.Top-down processes can have structural impacts on ecosystems (Hunter & Price 1992), so knowledge of upper trophic levels is essential to understanding ecosystem function. The salmon shark Lamna ditropis Hubbs et Follet, 1947 is an important component of the ecosystem due to its upper trophic level, abundance and high forage requirement...
The blue marlin (Makaira nigricans) is a highly migratory pelagic predator of tropical and subtropical seas. Information on the habitat use of marine species is fundamental to understanding their ecology and population dynamics and is needed to inform responsible management strategies. Using a long‐term satellite tagging data set from The International Game Fish Association Great Marlin Race, we examined habitat use and how oxygen and temperature influence the horizontal and vertical distributions of blue marlin in the Central Pacific. Blue marlin primarily occurred in warm waters (26–30°C) and exhibited a diel bimodal depth distribution across the 5‐year data record (2009–2013), with fish spending the majority of their time near the surface at night and at deeper depths during the day (25–100 m). The depth distribution of blue marlin was limited in areas where low oxygen and/or temperature conditions occur closer to the surface, with the extent of habitat compression being greatest when both oxygen and temperature were limiting. The migrations of blue marlin appeared restricted during the 2010 La Niña, when increased equatorial upwelling resulted in an extension of the cold, low oxygen waters of the cold tongue into the Central Pacific, creating a barrier to the trans‐equatorial migrations that occurred during all other tagging years. If the frequency and intensity of La Niña events increases and the oxygen minimum layer continues to expand as has been predicted under certain climate change scenarios, the migratory behavior and habitat availability of blue marlin may be impacted.
The objective of this study was to advance the use of pop-up satellite archival tags to track the migrations of Atlantic bluefin tuna (Thunnus thynnus) to their spawning grounds. Deployment of tags occurred in the Gulf of St. Lawrence, Canada, during fall months from 2007 to 2013. Pop-up satellite archival tags (n = 135) were attached to 125 Atlantic bluefin tuna (curved fork length (CFL) = 268 ± 20 cm (mean ± SD)) with the objective of keeping tags on until visitation to a spawning area or longer. A dataset of 18 800 days was acquired, which included 5800 days of time-series data from 19 recovered satellite tags. Many Atlantic bluefin tuna visited the Gulf of Mexico spawning grounds (74%), the mean size of which was 275 ± 14 cm (CFL ± SD, n = 49), with a measured CFL of 243 to 302 cm. These fish had a mean entry date into the Gulf of Mexico of 14 January ± 42 days (SD). The mean residency period for fish that had tracks with entrance and exit from the Gulf of Mexico was 123 ± 49 days (SD) (n = 22). Atlantic bluefin tuna that moved into the Gulf of Mexico during the spawning season remained west of the 45°W meridian for the duration of the track. Electronic tagging datasets from two fish were obtained before, during, and after the Deepwater Horizon oil spill. Both fish utilized habitat in the vicinity of the Macondo Well on 20 April 2010 when the Deepwater Horizon oil drilling rig accident occurred. Spawning hotspots are identified in the Gulf of Mexico using kernel density analyses and compared with the newly established closed areas.
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