This study describes and maps demersal fish assemblages for the east coast of North America from Cape Hatteras, North Carolina, to Cape Chidley, Labrador, evaluates evidence for interannual shifts ...

Assemblages and biogeography of demersal fishes of the east coast of North America

Poleward declines in species diversity [latitudinal diversity gradients (LDG)] remain among the oldest and most widespread of macroecological patterns. However, their contemporary dynamics remain largely unexplored even though changing ecological conditions, including global change, may modify LDG and their respective ecosystems. Here, we examine temporal variation within a temperate Northwest Atlantic LDG using 31 years of annual fisheries-independent surveys and explore its dynamics in relation to a dominant climate signal [the wintertime North Atlantic Oscillation (NAO)] that varies interannually and alters the latitudinal gradient of Northwest Atlantic continental shelf bottom water temperatures. We found that the slopes of the annual LDG vary dramatically due to changes in geographic distributions of 100+ species, variations that are concealed within the cumulative, static LDG. These changes are strongly associated with changes in NAO sign and strength. This is the first illustration of temporal dynamics in a contemporary LDG and the first demonstration of the speed at which local environmental variations can alter an LDG. Our findings underscore the need to investigate factors that modify LDG separately from those that contribute to their origins.

Temporal dynamics within a contemporary latitudinal diversity gradient

A density prediction model for juvenile brown shrimp (Farfantepenaeus aztecus) was developed by using three bottom types, five salinity zones, and four seasons to quantify patterns of habitat use in Galveston Bay, Texas. Sixteen years of quantitative density data were used. Bottom types were vegetated marsh edge, submerged aquatic vegetation, and shallow nonvegetated bottom. Multiple regression was used to develop density estimates, and the resultant formula was then coupled with a geographical information system (GIS) to provide a spatial mosaic (map) of predicted habitat use. Results indicated that juvenile brown shrimp ( 0.50. These results indicate that this model may have a broader geographic application and is a plausible approach in refining current EFH designations for all Gulf of Mexico estuaries with similar geomorphological and hydrological characteristics.

A habitat-use model to determine essential fish habitat for juvenile brown shrimp (Farfantepenaeus aztecus) in Galveston Bay, Texas

The paper deals with the spatio-temporal organization patterns demersal assemblages along the east coast of Corsica. We analysed data collected by the first standardized experimental bottom trawl surveys performed in this region from 1994 to 1999 (MEDITS programme). The use of a multiway table method (STATIS-CoA) showed that the spatial organization pattern of the demersal assemblages of eastern Corsica was highly stable during the period studied. This pattern was structured around three bathymetric areas (i) the continental shelf (between 50 to 200 m depth), (ii) the upper slope (from 200 to 500 m) and (iii) the deeper slope (from 500 to 800 m), but it did not show any heterogeneity in relation with latitude. Along the cast coast of Corsica-characterized by one of the lowest fishing pressure rates within the whole northern Mediterranean Sea and by the scarcity of information on fishing patterns-our results contribute to the basic information required for multispecies fishery management. They suggest that all the trawlable areas along the cast coast of Corsica could be considered as a single biogeographical unit, possibly split up into three bathymetric strata. Furthermore, if compared with results from studies carried out in Mediterranean regions with more intensive fishing rates, our results might provide a quantitative basis for achieving a better understanding of the impact of fishing pressure on organization patterns of demersal assemblages.

Spatio-temporal organization patterns of demersal assemblages of the east coast of Corsica (Mediterranean Sea)

Spatial variation in benthopelagic fish assemblage structure along coastal East Africa from recent bottom trawl surveys

The species composition in a comparative trawl fishing experiment on the Scotian Shelf was analysed to determine if two ships using different gear resulted in different pictures of assemblage structure. A multiple regression technique was used with an index of biological dissimilarity as the dependent variable, and dummy variables to control day-n ig ht differences, sam pi ing stratu m and location. T he analysis showed that the dissi milarity index val ues between vessels were not significantly larger than those within vessels. Pairs of tows by the different vessels and gear at the same location, were significantly less dissimilar than pairs of tows by the same vessel in the same sampling stratum (i.e. nearby). The study shows that it is valid to compare assemblage structure on the basis of surveys by these two vessels. The results also suggest that there are spatial patterns in the demersal fish assemblages on the Scotian Shelf at a scale between the area covered by a trawl tow and the area of a stratum.

R Mahon

Papers

Comparison of Species Composition in a Bottom Trawl Calibration Experiment