Marine and Freshwater Fisheries Research Institute

Queenscliff, Australia

Marine and Freshwater Fisheries Research Institute

Queenscliff, Australia
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Jung C.A.,University of Melbourne | Swearer S.E.,University of Melbourne | Jenkins G.P.,Marine and Freshwater Fisheries Research Institute
Marine and Freshwater Research | Year: 2010

Comprehensive assessment of spatiotemporal variation in assemblages, particularly relating to management and conservation efforts, should include examination of variation across scales. The present study investigated spatiotemporal variation at various scales in the fish fauna of Port Phillip, Australia, over 17 years. There were significant increases in diversity and changes in faunal composition in the most recent study, compared with 17 (+38%) and 7 (+151%) years ago. No significant year-to-year differences and no fortnightly differences within a season were found, supporting the notion of long-term changes. However, inter-seasonal variation was significant, with diversity highest in summer and lowest in winter (42.3% of summer diversity), illustrating substantial variation only at particular scales. The spatial structuring of assemblages was consistent at all temporal scales over 17 years. Fish assemblages and diversity varied significantly among sites and regions, but diversity was always highest on reefs in the eastern region of Port Phillip. However, the majority of spatial variation occurred among replicate transects (up to 75% of overall variation). Despite the high degree of small-scale spatiotemporal variability, the results provide evidence of long-term changes in faunal composition and diversity within the bay. Moreover, the results underline the necessity for multi-scalar approaches in ecological studies like abundance assessments. © 2010 CSIRO.

Smith T.M.,Victorian Marine Science Consortium | Smith T.M.,University of Melbourne | Hindell J.S.,University of Melbourne | Hindell J.S.,Arthur Rylah Institute for Environmental Research | And 4 more authors.
Journal of Experimental Marine Biology and Ecology | Year: 2011

Predation is often described as an underlying mechanism to explain edge effects. We assessed the importance of predation in determining edge effects in seagrass using two approaches: a video survey to sample predators at small scales across seagrass edges, and a tethering experiment to determine if predation was an underlying mechanism causing edge effects. Underwater videos were placed at four positions: middle of seagrass patches; edge of seagrass; sand immediately adjacent to seagrass and sand distant from seagrass. Fish abundances and the time fish spent in view were measured. The main predatory fish (Australian salmon, Arripis spp.) spent more time over adjacent sand than other positions, while potential prey species (King George whiting, Sillaginodes punctata (Cuvier), recruits) were more common in the middle of seagrass patches. Other species, including the smooth toadfish, Tetractenos glaber (Freminville), and King George whiting adults, spent more time over sand adjacent to seagrass than distant sand, which may be related to feeding opportunities. King George whiting recruits and pipefish (Stigmatopora spp.) were tethered at each of the four positions. More whiting recruits were preyed upon at outer than inner seagrass patches, and survival time was greater in the middle of shallow seagrass patches than other positions. Relatively few pipefish were preyed upon, but of those that were, survival time was lower over sand adjacent to seagrass than at the seagrass edge or middle. Video footage revealed that salmon were the dominant predators of both tethered King George whiting recruits and pipefish. The distribution of predators and associated rate of predation can explain edge effects for some species (King George whiting) but other mechanisms, or combinations of mechanisms, are determining edge effects for other species (pipefish). © 2011 Elsevier B.V.

Grixti D.,Marine and Freshwater Fisheries Research Institute | Grixti D.,Deakin University | Morison A.,Marine and Freshwater Fisheries Research Institute | Bell J.D.,Marine and Freshwater Fisheries Research Institute
North American Journal of Fisheries Management | Year: 2010

A substantial decline in the commercial catches and catch rates of black bream Acanthopagrus butcheri in the Gippsland Lakes, Australia, signified a depletion of the stock and prompted management to increase the legal minimum length (LML) from 26 cm to 28 cm (total length) in December 2003. The effectiveness of this increase depends on the postrelease survival rate of undersized fish. The present study estimates the rates of release and initial survival (1 h after capture) of undersized A. butcheri during commercial fishing by gill nets in the Gippsland Lakes. Field capture and holding trials were also used to estimate initial and delayed survival (72 h after capture). Almost 6,000 A. butcheri from 347 gill net shots were caught during 2005-2006. The average total length increased by 1 cm from 2005 to 2006, increasing the proportion of the catch that was retained in 2006 (75%) compared with 2005 (50%). The best estimates of initial and delayed survival were 97.2% (SE, 0.3%) and 94.4% (SE, 3.8%), respectively. The total survival rate, which combines the initial survival rate from observer work with the delayed survival rates from the trials, was estimated as 90.8% (SE, 3.8%). The increase in the LML from 26 to 28 cm afforded significant protection to fish between these size limits, but the level of protection will be short term (1 or at most 2 years) for each year-class because of the growth rate of the species. Released, retained, and postrelease survival rates are discussed for various LMLs and with regard to their implications for fishery management. © American Fisheries Society 2010.

Guest M.A.,University of Tasmania | Hirst A.J.,University of Tasmania | Hirst A.J.,Marine and Freshwater Fisheries Research Institute | Nichols P.D.,CSIRO | And 2 more authors.
Marine Ecology Progress Series | Year: 2010

Stable isotopes of carbon and nitrogen and fatty acid analyses are increasingly being used in combination to determine the trophic structure of marine systems. For stable isotopes, the variability in carbon and nitrogen isotopic signatures has long been recognised and has been characterised for some taxa. Whilst it is known that metabolic processes may influence fatty acid profiles, the spatial variability of fatty acid profiles has not been documented. Understanding at what scale these 2 biochemical tracers vary, and if the scale of variability corresponds between tracers, is crucial for the correct design and interpretation of combined tracers in trophic studies. This study is the first to examine spatial variability in fatty acid profiles per se, and in combination with stable isotope ratios in the same organisms at multiple spatial scales. We used a spatially hierarchical design which sampled across broad geographic regions, reefs within regions, and also between different parts of macroalgal plants common on temperate reefs. For stable isotopes of carbon and nitrogen, variability was greatest at intermediate spatial scales (between locations within regions, and sites within locations). In contrast, fatty acid profiles showed the greatest variation amongst individual replicates of lobster, abalone and macroalgae. This study demonstrates that for the increasing number of trophic studies using combined biochemical tracers, sampling design should cater to the differences in the variability of each tracer technique and allocate sampling accordingly. Copyright © Inter-Research 2010.

Grixti D.,Marine and Freshwater Fisheries Research Institute | Grixti D.,Deakin University | Conron S.D.,Marine and Freshwater Fisheries Research Institute | Morison A.,Marine and Freshwater Fisheries Research Institute
Fisheries Management and Ecology | Year: 2010

Snapper, Pagrus auratus (Forester), is an important recreational species in marine waters of Victoria, Australia. This study estimated survival for compulsorily released undersized P. auratus by holding fish in cages and tanks for 3 days. In all, 620 P. auratus caught by angling were assessed for post-release survival and 200 additional fish were used as controls. The survival rate was greater for shallow-hooked (97%) than deep-hooked (48%) P. auratus. Post-mortems showed that hooking injuries to the throat and/or gill area caused most deaths, while piercing of the heart also caused mortalities. Removing deeply ingested hooks decreased survival. To estimate survival of P. auratus across the Victorian fishery, this study's results should be combined with estimates of shallow-hooking rates in the fishery. Shallow-hooking rate estimates would quantify the impact of the low survival rate found for deep-hooked fish. © 2010 Blackwell Publishing Ltd.

Smith T.M.,Victorian Marine Science Consortium | Smith T.M.,University of Melbourne | Hindell J.S.,University of Melbourne | Hindell J.S.,Arthur Rylah Institute for Environmental Research | And 4 more authors.
Journal of Fish Biology | Year: 2011

Diets of the pipefish Stigmatopora nigra were analysed to determine if food availability was causing S. nigra to distribute according to habitat edge effects. Gut analysis found little difference in the diets of S. nigra at the edge and interior of seagrass patches, regardless of time of day or season. Fish diets did, however, vary with seagrass density: S. nigra in denser seagrass consumed more harpacticoid copepods and fewer planktonic copepods. The lack of difference in prey eaten by S. nigra at the edge and interior of patches suggests either that food was not determining S. nigra distribution patterns within patches or that differences in fish densities across patches meant that relative fish-prey densities were similar at edge and interior positions. Alternatively, any edge effects in diet might be masked by gradients in seagrass structure. © 2011 The Authors. Journal of Fish Biology © 2011 The Fisheries Society of the British Isles.

Macreadie P.I.,University of Melbourne | Macreadie P.I.,University of Technology, Sydney | Hindell J.S.,Arthur Rylah Institute for Environmental Research | Keough M.J.,University of Melbourne | And 3 more authors.
Ecology | Year: 2010

According to conceptual models, the distribution of resources plays a critical role in determining how organisms distribute themselves near habitat edges. These models are frequently used to achieve a mechanistic understanding of edge effects, but because they are based predominantly on correlative studies, there is need for a demonstration of causality, which is best done through experimentation, Using artificial seagrass habitat as an experimental system, we determined a likely mechanism underpinning edge effects in a seagrass fish. To test for edge effects, we measured fish abundance at edges (0-0.5 m) and interiors (0.5-1 m) of two patch configurations: continuous (single, continuous 9-m2 patches) and patchy (four discrete 1-m2 patches within a 9-m2 area). In continuous configurations, pipefish (Stigmatopora argus) were three times more abundant at edges than interiors (positive edge effect), but in patchy configurations there was no difference. The lack of edge effect in patchy configurations might be because patchy seagrass consisted entirely of edge habitat. We then used two approaches to test whether observed edge effects in continuous configurations were caused by increased availability of food at edges. First, we estimated the abundance of the major prey of pipefish, small crustaceans, across continuous seagrass configurations. Crustacean abundances were highest at seagrass edges, where they were 16% greater than in patch interiors. Second, we supplemented interiors of continuous treatment patches with live crustaceans, while control patches were supplemented with seawater. After five hours of supplementation, numbers of pipefish were similar between edges and interiors of treatment patches, while the strong edge effects were maintained in controls. This indicated that fish were moving from patch edges to interiors in response to food supplementation. These approaches strongly suggest that a numerically dominant fish species is more abundant at seagrass edges due to greater food availability, and provide experimental support for the resource distribution model as an explanation for edge effects. © 2010 by the Ecological Society of America.

Johnson P.,CSIRO | Fulton E.,CSIRO | Smith D.C.,CSIRO | Jenkins G.P.,Marine and Freshwater Fisheries Research Institute | Barrett N.,Tasmanian Aquaculture and Fisheries Institute
Natural Resource Modeling | Year: 2011

Ecosystem processes function at many scales, and capturing these processes is a challenge for ecosystem models. Nevertheless, it is a necessary step for considering many management issues pertaining to shelf and coastal systems. In this paper, we explore one method of modeling large areas with a focus at a range of scales. We develop an ecosystem model that can be used for strategic management decision support by modeling the waters off southeastern Australia using a polygon telescoping approach, which incorporates fine-scale detail at the coastal zone, increasing in scale to a very coarse scale in the offshore areas. This telescoping technique is a useful tool for incorporating a wide range of habitats at different scales into a single model. © 2011 Wiley Periodicals, Inc.

Hutchinson N.,Marine and Freshwater Fisheries Research Institute | Rhodes K.L.,University of Hawaii at Hilo
Coral Reefs | Year: 2010

The aim of the study was to estimate home range areas and distance of movement away from a squaretail coralgrouper (Plectropomus areolatus) spawning aggregation site located within a small-scale 1.5 km2 Marine Protected Area (MPA) in Pohnpei, Micronesia. Fifteen P. areolatus were acoustically tagged and re-located within a ca. 50 km2 search area over a 4-month period that included reproductive and non-reproductive months. All relocated fish were found in areas of moderate to high coral cover either on the fore reef or inside the lagoon in home ranges of 0.048 ± 0.018 km2 (μ ± S. E.). Variability in home range area (0.004-0.12 km2) and distance of movement from aggregation sites following spawning (0.02-23.0 km; 5.3 ± 3.6 km, μ ± S. E.) was observed, but did not appear to be sex specific. Five of the six relocated individuals were found within 0.02-6.1 km of the aggregation. This evidence and that from recent tag-recapture studies of epinephelids suggest that a substantial proportion of individual P. areolatus spawning populations reside within close proximity to their respective aggregation sites. Reproductive populations could be protected by MPAs of moderate scale (10 s of km2) that include aggregation sites, migratory corridors and adjacent home range habitats. © Springer-Verlag 2010.

Grixti D.,Marine and Freshwater Fisheries Research Institute | Grixti D.,Deakin University | Conron S.D.,Marine and Freshwater Fisheries Research Institute | Ryan K.,Marine and Freshwater Fisheries Research Institute | Versace V.L.,Deakin University
Fisheries Research | Year: 2010

Snapper (Pagrus auratus) and King George whiting (Sillaginodes punctata) are major recreational species in Victoria, with P. auratus having a high catchability among anglers targeting S. punctata. Hooking location is the most important survival factor for P. auratus caught incidentally in Victoria by anglers targeting S. punctata, with shallow-hooked fish having better survival rates than deep-hooked fish. Circle hooks have been proposed as an alternative to longshank hooks to reduce deep-hooking. During 39 fishing trips in Port Phillip Bay and Western Port, size 6 circle hooks were compared against conventional size 6 longshank hooks. The distance the hook was off the sea bed was also contrasted. Neither of these factors affected hooking location. Longshank hooks captured more legal-size P. auratus than circle hooks, while mean fish lengths were the same across hook types and hook positions for both species. As the total length of S. punctata increased, the shallow-hooking rates decreased. Using similar-sized circle hooks to conventional longshank hooks was not demonstrated as a technique for improving P. auratus survival under typical S. punctata angling practices. The ability of circle hooks to increase shallow-hooking appears to be a function of both fish species and angling technique interactions. The benefits of circle hooks may be limited for fish species that are captured by a tight line and vigorous hook-striking technique. © 2010 Elsevier B.V.

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