56 research outputs found
Differences in vertical and horizontal distribution of fish larvae and zooplankton, related to hydrography
Spatial linkages in the early life history of north eastern Atlantic herring populations across the north of the British Isles
Coupling otolith microstructure analysis and hydrographic backtracking suggests a mechanism for the 2000s North Sea herring recruitment failure
Seasonal Dynamics of Atlantic Herring (Clupea harengus L.) Populations Spawning in the Vicinity of Marginal Habitats
Gillnet sampling and analyses of otolith shape, vertebral count and growth indicated the presence of three putative Atlantic herring (Clupea harengus L.) populations mixing together over the spawning season FebruaryâJune inside and outside an inland brackish water lake (Landvikvannet) in southern Norway. Peak spawning of oceanic Norwegian spring spawners and coastal Skagerrak spring spawners occurred in MarchâApril with small proportions of spawners entering the lake. In comparison, spawning of Landvik herring peaked in MayâJune with high proportions found inside the lake, which could be explained by local adaptations to the environmental conditions and seasonal changes of this marginal habitat. The 1.85 km2 lake was characterized by oxygen depletion occurring between 2.5 and 5 m depth between March and June. This was followed by changes in salinity from 1â7â° in the 0â1 m surface layer to levels of 20â25â° deeper than 10 m. In comparison, outside the 3 km long narrow channel connecting the lake with the neighboring fjord, no anoxic conditions were found. Here salinity in the surface layer increased over the season from 10 to 25â°, whereas deeper than 5 m it was stable at around 35â°. Temperature at 0â5 m depth increased significantly over the season in both habitats, from 7 to 14°C outside and 5 to 17°C inside the lake. Despite differences in peak spawning and utilization of the lake habitat between the three putative populations, there was an apparent temporal and spatial overlap in spawning stages suggesting potential interbreeding in accordance with the metapopulation concept
A conceptual framework for understanding the implications of and potential solutions for mismatches in scale of biological population structure and stock units
The First Data Release of the Sloan Digital Sky Survey
The Sloan Digital Sky Survey has validated and made publicly available its
First Data Release. This consists of 2099 square degrees of five-band (u, g, r,
i, z) imaging data, 186,240 spectra of galaxies, quasars, stars and calibrating
blank sky patches selected over 1360 square degrees of this area, and tables of
measured parameters from these data. The imaging data go to a depth of r ~ 22.6
and are photometrically and astrometrically calibrated to 2% rms and 100
milli-arcsec rms per coordinate, respectively. The spectra cover the range
3800--9200 A, with a resolution of 1800--2100. Further characteristics of the
data are described, as are the data products themselves.Comment: Submitted to The Astronomical Journal. 16 pages. For associated
documentation, see http://www.sdss.org/dr
Lessons learned from practical approaches to reconcile mismatches between biological population structure and stock units of marine fish
Recent advances in the application of stock identification methods have revealed inconsistencies between the spatial structure of biological populations and the definition of stock units used in assessment and management. From a fisheries management perspective, stocks are typically assumed to be discrete units with homogeneous vital rates that can be exploited independently of each other. However, the unit stock assumption is often violated leading to spatial mismatches that can bias stock assessment and impede sustainable fisheries management. The primary ecological concern is the potential for overexploitation of unique spawning components, which can lead to loss of productivity and reduced biodiversity along with destabilization of local and regional stock dynamics. Furthermore, ignoring complex population structure and stock connectivity can lead to misperception of the magnitude of fish productivity, which can translate to suboptimal utilization of the resource. We describe approaches that are currently being applied to improve the assessment and management process for marine fish in situations where complex spatial structure has led to an observed mismatch between the scale of biological populations and spatially-defined stock units. The approaches include: (i) status quo management, (ii) "weakest link" management, (iii) spatial and temporal closures, (iv) stock composition analysis, and (v) alteration of stock boundaries. We highlight case studies in the North Atlantic that illustrate each approach and synthesize the lessons learned from these real-world applications. Alignment of biological and management units requires continual monitoring through the application of stock identification methods in conjunction with responsive management to preserve biocomplexity and the natural stability and resilience of fish species.</p
Distribution and abundance of Norwegian spring spawning herring larvae on the Norwegian shelf in April 2008
- âŠ