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Offshore Regions (offshore + regions)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

A spatial model of population dynamics of the early life stages of Japanese sardine, Sardinops melanostictus, off the Pacific coast of Japan

FISHERIES OCEANOGRAPHY, Issue 2 2003
Maki Suda
Abstract We constructed a numerical model reproducing the transport, survival and individual growth of the early life stages of Japanese sardine, Sardinops melanostictus, off the Pacific coast of Japan during 1978,93. The causes of early life stage mortality, including the influence of the effects of the spatial relationship between the spawning grounds and the Kuroshio on the mortality rate, were investigated. Survival and transport from egg stage to 60 days after spawning were modelled daily in a 1 × 1 degree mesh cell and individual growth in the period was modelled in each region (Kuroshio, Inshore, Offshore and Transition regions). Individual growth and survival from 60 to 180 days after spawning were modelled daily in the Transition region. Environmental data were taken from outside the model system. Our simulation indicates that survival variability in the larval stage (5,25 mm in standard length) is the key factor in determining the year-class strength. The simulation revealed that strong year classes occurred with good survival in the spawning ground and whilst entrained in the Kuroshio current being transported to the main feeding grounds in the Transition region. The simulation also indicated that survival rates in 1988,93 were low in the Inshore, Kuroshio and Offshore regions, which depressed the year-class strength during that period. [source]

Spatial utilisation of fast-ice by Weddell seals Leptonychotes weddelli during winter

ECOGRAPHY, Issue 3 2005
Samantha Lake
This study describes the distribution of Weddell seals Leptonychotes weddelli in winter (May,September 1999) at the Vestfold Hills, in Prydz Bay, East Antarctica. Specifically, we describe the spatial extent of haul-out sites in shore,fast sea-ice, commonly referred to as fast-ice. As winter progressed, and the fast-ice grew thick (ca 2 m), most of the inshore holes closed over, and the seals' distribution became restricted to ocean areas beyond land and islands. Using observations from the end of winter only, we fitted Generalised Additive Models (GAMs) to generate resource selection functions, which are models that yield values proportional to the probability of use. The models showed that seal distribution was defined mainly by distance to ice-edge and distance to land. Distance to ice-bergs was also selected for models of some regions. We present the results as maps of the fitted probability of seal presence, predicted by the binomial GAM for offshore regions, both with and without autocorrelation terms. The maps illustrate the expected distribution encompassing most of the observed distribution. On this basis, we hypothesise that propensity for the fast-ice to crack is the major determinant of Weddell seal distribution in winter. Proximity to open water and pack-ice habitats could also influence the distribution of haul-out sites in fast-ice areas. This is the first quantitative study of Weddell seal distribution in winter. Potential for regional variation is discussed. [source]

Mesoscale eddies and survival of late stage Pacific sardine (Sardinops sagax) larvae

FISHERIES OCEANOGRAPHY, Issue 1 2001
Elizabeth A. Logerwell
We examined the distribution of sardine larvae relative to environmental conditions with the purpose of identifying and characterizing habitat that encourages high larval growth and survival, based on the 1983,1998 surveys of the California Cooperative Oceanic Fisheries Investigations (CalCOFI). Long-term averages show that sardine ,survivors' (spatially aggregated larvae , 18 days old) were most abundant offshore, whereas sardine egg density, chlorophyll biomass and zooplankton volume were greatest inshore. In contrast, mesoscale eddies, observed in remotely sensed sea surface temperature imagery, were found only in offshore regions. To further examine the link between eddies , which often result in locally elevated chlorophyll and zooplankton , and sardine survival, we compared the distribution of larvae and eddies survey by survey. Sardine survivors were most abundant offshore in only one-quarter of the research surveys, and when they were most abundant offshore they were associated with eddies. This indicates that the offshore eddy habitat produced exceptionally large numbers of survivors, as evidenced by the disproportionate effect on the long-term average. [source]

Marine fish diversity on the Scotian Shelf, Canada

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2003
Nancy L. Shackell
Abstract 1.Marine life in offshore regions has not been fully censused, yet related conservation policy relies on our ability to identify areas of high biodiversity. 2.We assessed the census of marine finfish on the Scotian Shelf, Northwest Atlantic using data collected during annual research vessel surveys between 1970 and 2000. The species accumulation curve did not reach an asymptote reflecting that new species continued to be discovered throughout the survey period. Only 0.12% of the area of the Scotian Shelf has been sampled since 1970. 3.Since 1974, when over 50% of the species had been discovered, the community composition has been relatively constant. However, the dominance structure has changed dramatically as reflected in the geographic contraction of the formerly abundant, large-bodied piscivores concomitant with the geographic expansion of their prey species. 4.The region is under-sampled, and species' distribution and abundance are changing. A precise estimate of diversity is elusive. As an alternative, we searched for physical correlates of finfish diversity to identify its possible surrogates. Surrogates have potential both as a method for understanding process and as a tool for conservation management. We examined the effect of area and depth range on species richness. High species richness was associated with larger areas and greater depth range at large spatial scales. 5.Highly diverse areas include the Bay of Fundy, the Eastern Gully, the slopes, Western Bank and the northeastern shelf. Until now, the northeastern shelf has been under-appreciated as a highly diverse area. Such information will be important for environmental impact assessments as well as selection of ,sensitive' or protected areas. Copyright © 2003 John Wiley & Sons, Ltd. [source]