The shallow water gobiid assemblage of the Venice Lagoon: abundance, seasonal variation and habitat partitioning

The gobiid assemblage of the Venice Lagoon shallow waters was investigated by means of a semi-quantitative standardized sampling (using a small beach seine), stratified into five main types of shallow subtidal habitats and conducted on a seasonal basis during 1 year. The degree of overlap in resource utilization among six coexisting goby species was assessed, along both the time axis, by analysing the seasonal variation in abundance and reproductive status (as revealed by the gonado-somatic index) and the habitat axis, by comparing species abundance across different habitat types and controlling for the effects of some abiotic factors. Smaller species, and especially the marbled goby Pomatoschistus marmoratus, dominated the local assemblage. Although the cycle of shallow water colonization and seasonal variation in total abundance were basically similar, species showed differences in timing of reproduction and recruitment, as well as in habitat preference. The larger species belonging to the genera Gobius and Zosterisessor tended to overlap their habitat use, being more abundant in seagrass habitats than in the unvegetated habitats, whereas the smaller species belonging to the genera Knipowitschia and Pomatoschistus avoided seagrasses, preferring in most cases mud flats and salt marsh creeks. Within these two groups of species some further slight differences in species habitat preference, relationship with abiotic factors and reproductive ecology could be detected. Results are discussed in the light of both ecological mechanisms underlying coexistence of closely related species and the current knowledge of the phylogeny of Mediterranean gobies. (c) 2005 The Fisheries Society of the British Isles

Comparative habitat use by large riverine fishes

The present radio-tracking study compared adult daytime microhabitat use by three large Australian native freshwater fishes (Murray cod, Maccullochella peelii, trout cod, M. macquariensis, golden perch, Maquaria ambigua) and introduced carp, Cyprinus carpio, in the Murray River, south-eastern Australia. The paper describes habitat patches used by all species and quantifies differences among species. All species were strongly associated with structural woody habitat (&gt;68% cover), deeper (&gt;2.4m), slower water (&lt;0.2ms-1) closer to the river bank, with variations in substrate. Murray cod and trout cod used deeper habitats (2.8m and 2.9m, respectively), with higher surface water velocities (0.37ms-1 and 0.49ms-1, respectively) and further from the bank than the habitats of golden perch (2.6m; 0.31ms-1) or carp (2.4 m; 0.20ms-1), the latter species using wood higher in the water column than did cod species. Trout cod used habitats furthest from the bank and carp those closest. These data provide support and direction for reintroduction of structural woody habitat patches for rehabilitation which, in general, should have &gt;70% cover, be &gt;1.5m high, located &lt;15% of the river channel (width) closest to the bank, with surface water velocities of 0.3-0.6ms-1.</p