Large scale surveys suggest limited mercury availability in tropical north Queensland (Australia)

Little is known about the threat of mercury (Hg) to consumers in food webs of Australia's wet-dry tropics. This is despite high concentrations in similar biomes elsewhere and a recent history of gold mining that could lead to a high degree of exposure for biota. We analysed Hg in water, sediments, invertebrates and fishes in rivers and estuaries of north Queensland, Australia to determine its availability and biomagnification in food webs. Concentrations in water and sediments were low relative to other regions of Hg concern, with only four of 138 water samples and five of 60 sediment samples above detection limits of 0.1 mu g L-1 and 01 mu g g(-1), respectively. Concentrations of Hg in fishes and invertebrates from riverine and wetland food webs were well below international consumption guidelines, including those in piscivorous fishes, likely due to low baseline concentrations and limited rates of biomagnification (average slope of log Hg vs. delta N-15 = 0.08). A large fish species of recreational, commercial, and cultural importance (the barramundi, Lates calcarifer), had low concentrations that were below consumption guidelines. Observed variation in Hg concentrations in this species was primarily explained by age and foraging location (floodplain vs. coastal), with floodplain feeders having higher Hg concentrations than those foraging at sea. These analyses suggest that there is a limited threat of Hg exposure for fish-eating consumers in this region. (C) 2011 Published by Elsevier B.V.

Sensory Systems in Sawfishes. 2. The Lateral Line.

The lateral line system allows elasmobranchs to detect hydrodynamic movements in their close surroundings. We examined the distribution of pit organs and lateral line canals in 4 species of sawfish (Anoxypristis cuspidata, Pristis microdon, P. clavata and P. zijsron). Pit organs could only be located in A. cuspidata, which possesses elongated pits that are lined by dermal denticles. In all 4 pristid species, the lateral line canals are well developed and were separated into regions of pored and non-pored canals. In all species the tubules that extend from pored canals form extensive networks. In A. cuspidata, P. microdon and P. clavata, the lateral line canals on both the dorsal and ventral surfaces of the rostrum possess extensively branched and pored tubules. Based on this morphological observation, we hypothesized that these 3 species do not use their rostrum to search in the substrate for prey as previously assumed. Other batoids that possess lateral line canals adapted to perceive stimuli produced by infaunal prey possess non-pored lateral line canals, which also prevent the intrusion of substrate particles. However, this hypothesis remains to be tested behaviourally in pristids. Lateral line canals located between the mouth and the nostrils are non-pored in all 4 species of sawfish. Thus this region is hypothesized to perceive stimuli caused by direct contact with prey before ingestion. Lateral line canals that contain neuromasts are longest in P. microdon, but canals containing neuromasts along the rostrum are longest in A. cuspidata.