Hg Pederson

The influence of environmental parameters on the performance and detection range of acoustic receivers

Acoustic telemetry is being increasingly used to study the ecology of many aquatic organisms. This widespread use has been advanced by national and international tracking programs that coordinate deployment of passive acoustic telemetry networks on a regional and continental scale to detect tagged animals. While it is well-known that environmental conditions can affect the performance of acoustic receivers, these effects are rarely quantified despite the profound implications for tag detection and hence the ecological inferences. Here, we deployed eight receivers at different depths within the water column and at different orientations (hydrophone up or down) and 12 tags 200-800m from the receivers for 234 days to investigate how the tag detection range of acoustic receivers varied through time and under different meteorologic and oceanographic conditions. The study showed that receiver depth and orientation, and time since deployment had the largest effect on the detection range. Thermocline gradient and depth, and wind speed were the environmental factors most affecting detection range, while wind direction, precipitation and atmospheric pressure had negligible or no effect. Comparison of results to a proposed general acoustic theory model and previous studies showed that findings from specific habitat types cannot be generalised and applied across other habitats or environments. A good understanding of the acoustic coverage and temporal variations in relation to environmental conditions are crucial to accurate interpretation of results, and ensuing management recommendations. We recommend that each study include stationary reference tags to measure changes in detection probability with time, help refine detection range, and be used to improve confidence in the reporting and interpretation of the data.

The usefulness of fatty acid analysis in differentiating species of Pythium, Rhizoctonia and Gaeumannomyces and as a tool for their detection in infected wheat roots

Principal component analysis (PCA) of cellular fatty acids extracted from cultures of Gaeumannomyces spp., Rhizoctonia solani (anastamosis groups AG4 and AG8) and Pythium spp. showed strong clustering of cultures within genera and good discrimination between genera. PCA of the fatty acid profiles was successful in distinguishing between seven different Pythium spp. tested (P. arrhenomannes, P. australe, P. echinulatum, P. irregulare, P. ostracodes, P. spinosum and P. ultimum) but did not distinguish between the Gaeumannomyces spp. (G. graminis var. avenae, G. graminis var. graminis, G. graminis var. tritici, G. cylindrosporus and G. incrustans) nor the isolates of the two AG groups of Rhizoctonia examined. Significant differences between species were detected in the relative amounts of individual fatty acids. The presence of two fatty acids (20:4ω6c and 20:5ω3c), found only in the Pythium species examined, was used to detect the presence of P. echinulatum and P. irregulare in wheat roots infected with these two fungi.

Overlap of Home Ranges of Resident and Introduced Southern Rock Lobster after Translocation

Translocation, sea ranching, and assisted migration are under scrutiny as methods to augment populations so that harvests can be increased or populations can better adapt to changing environmental conditions. Understanding the ecological effects of any such environmental manipulation is critical to its successful application. One potential ecological effect of any type of stock enhancement is the displacement of either resident or released groups such that finding shelter or foraging habitat is adversely affected. This study examined behavioral interactions of resident and translocated Jasus edwardsii rock lobster after an introduction of 1,961 “small pale” phenotypic morphs to an area populated by the resident “large red” phenotypic morph. This translocation was an experimental stock enhancement conducted as part of a larger study to increase the yield and value of the fishery. Most translocated individuals established a home range within a couple of days of release (generally <2), and these ranges were generally less than 1.0 ha in size. Home-range kernels and foraging ranges overlapped between the two morphs, and there was no evidence of avoidance (Jacobs cohesion index 0.01, Z = 1.06, p = 0.28). This case of translocation for stock enhancement between ecotypes had no detectable adverse effect on either the resident or the translocated population, and in this species, stock enhancement could become part of an integrated conservation and harvest optimization strategy.