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Batemans Bay, Australia

Gray C.A.,Cronulla Fisheries Research Center | Gray C.A.,WildFish Research | Gray C.A.,University of New South Wales | Barnes L.M.,Cronulla Fisheries Research Center | And 6 more authors.
Aquatic Biology | Year: 2014

This study examined whether differences existed in the depth distributions and reproductive strategies of the co-occurring Sillago robusta and S. flindersi in coastal waters off eastern Australia. Marked spatial and temporal dis similarities in demography and reproduction were observed between the 2 species, with S. robusta being more abundant in the shallow (15-30 m) strata and S. flindersi in the mid (31-60 m) strata, with neither species being consistently abundant in the deep (61-90 m) strata. The size composition of S. robusta was similar across depths, but smaller and immature S. flindersi predominantly occurred in the shallow strata, with larger and mature individuals occurring deeper. These data indicate partitioning of habitat resources, which may aid species coexistence. Both species potentially spawned year-round, which is probably an adaptation to the region's dynamic coastal environment. However, a greater proportion of S. robustawas in spawning condition between September and March, whereas S. flindersi displayed no such temporal pattern. Maturity ogives differed significantly between sexes and locations for both species. Both species displayed similar ovarian development, with females having multiple concurrent oocyte stages, indicating potential multiple spawning events as evidenced in other Sillaginidae. For both species, estimated batch fecundity increased with fish length, but S. robustahad a greater fecundity at any given length than S. flindersi. In contrast, S. flindersi potentially produced larger-sized eggs and invested greater energy into gonad development than S. robusta, indicating the 2 species have evolved slightly different reproductive strategies. Despite this, both species are subjected to substantial trawl fisheries, which may have already impacted their reproductive ecologies. © The authors 2014.

Gray C.A.,WildFish Research | Gray C.A.,University of New South Wales | Gray C.A.,Sydney Institute of Marine Science | Barnes L.M.,Cardno | And 6 more authors.
Fisheries Science | Year: 2014

This study investigated variability in the growth, length, and age compositions and the rates of mortality of Flinders’ sillago Sillago flindersi exploited in a demersal trawl fishery in eastern Australia. Sampling was done over 2 years across three depth strata at two locations approximately 400 km apart. Ageing of sectioned sagittal otoliths indicated that the observed maximum age of females was 6 years and that of males 5 years, that growth was variable and that the von Bertalanffy growth parameters significantly differed according to gender and location. Females attained a greater L than males, but males displayed greater k values. The L values of both sexes and the mean length-at-age for fish aged 3–5 years were greater at the location of highest latitude. Length and age compositions differed according to depth, with smaller (<15 cm FL) and younger (<2 years) fish generally more predominant in the shallow (<30 m) strata than in the deeper (>31 m) strata. S. flindersi appear to use the shallow strata as a juvenile habitat, moving to deeper waters as they grow. This depth stratification between cohorts may reduce intraspecific competition and could potentially be used as a spatial management tool to reduce any fishing-associated impacts on juveniles. Fish between 1 and 3 years old dominated the age compositions of populations combined across all depths, with estimated total mortality ranging between 2.24 and 2.40. Fishing mortality ranged between 1.54 and 1.70 and was more than twice the derived natural mortality. Exploitation rates were approximately 0.70, indicating that the species was heavily fished. © 2014, Japanese Society of Fisheries Science.

Stocks J.R.,University of New South Wales | Stocks J.R.,Batemans Bay Fisheries Center | Gray C.A.,University of New South Wales | Gray C.A.,WildFish Research | And 2 more authors.
Journal of Fish Biology | Year: 2015

Latitudinal variation in the reproductive characteristics of a temperate marine herbivore, rock blackfish Girella elevata, was examined from three regions of the south-eastern Australian coast. Biological sampling covered 780 km of coastline, including the majority of the species distribution. The sampling range incorporated three distinct oceanographic regions of the East Australian Current, a poleward-flowing western boundary current of the Southern Pacific Gyre and climate-change hotspot. Girella elevata are a highly fecund, group synchronous (multiple batch)-spawner. Mean fork length (LF) and age at maturity were greater for females than males within all regions, with both male and female G. elevata of the southern region maturing at a greater size and age than those from the central region. Estimates of batch fecundity (FB) were greatest in the northern and southern regions, relative to the central region where growth rates were greatest. Significant positive relationships were observed between FB and LF, and FB and total fish mass. Gonado-somatic indices indicated latitudinal synchrony in spawning seasonality between G. elevata at higher latitudes, spawning in the late austral spring and summer. A late or prolonged spawning period is evident for G. elevata from the northern region. Juvenile recruitment to intertidal rock pools within the central and southern regions was synchronous with the spawning season, however, no juveniles were found within the northern region. The implications of latitudinal variation in reproductive characteristics are discussed in the context of climate and oceanographic conditions of south-east Australia. © 2015 The Fisheries Society of the British Isles.

Gannon R.,University of New South Wales | Gannon R.,Sydney Institute of Marine Science | Taylor M.D.,University of New South Wales | Taylor M.D.,Port Stephens Fisheries Institute | And 9 more authors.
Journal of Experimental Biology | Year: 2014

Theoretical and laboratory studies generally show that ectotherm performance increases with temperature to an optimum, and subsequently declines. Several physiological mechanisms probably shape thermal performance curves, but responses of free-ranging animals to temperature variation will represent a compromise between these mechanisms and ecological constraints. Thermal performance data from wild animals balancing physiology and ecology are rare, and this represents a hindrance for predicting population impacts of future temperature change. We used internally implanted accelerometers near the middle of a species' geographical distribution and gill-net catch data near the species' latitudinal extremes to quantify temperature-related activity levels of a wild predatory fish (Platycephalus fuscus). We examined our data in the context of established models of thermal performance, and the relationship between thermal performance thresholds and biogeography. Acceleration data approximated a thermal performance curve, with activity peaking at 23° C but declining rapidly at higher temperatures. Gill-net catch data displayed a similar trend, with a temperature-associated increase and decrease in catch rates in temperate and tropical regions, respectively. Extrapolated estimates of zero activity (CTmin and CTmax) from the accelerometers were similar to the minimum and maximum mean monthly water temperatures experienced at the southern and northern (respectively) limits of the species distribution, consistent with performance-limited biogeography in this species. These data highlight the fundamental influence of temperature on ectotherm performance, and how thermal performance limits may shape biogeography. Biologging approaches are rarely used to examine thermal performance curves in freeranging animals, but these may be central to understanding the tradeoffs between physiology and ecology that constrain species' biogeographies and determine the susceptibility of ectotherms to future increases in temperature. © 2014. Published by The Company of Biologists Ltd.

Stocks J.R.,University of New South Wales | Stocks J.R.,Batemans Bay Fisheries Center | Gray C.A.,University of New South Wales | Gray C.A.,WildFish Research | And 2 more authors.
Journal of Sea Research | Year: 2014

Spatial and temporal variation in the growth of a widely distributed temperate marine herbivore, Girella elevata, was examined using length-at-age data and multi-decadal otolith increment growth chronologies. In total 927 G. elevata were collected from three regions of the Australian south-east coast, extending 780. km and covering the majority of the East Australian Current, a poleward-flowing western boundary current of the Southern Pacific Gyre and climate change hotspot. A validated ageing method using sectioned sagittal otoliths was developed to enumerate both daily (juvenile fish) and annual otolith increments. G. elevata exhibited great longevity with a maximum recorded age of 45. +. yrs. Spatial variation in growth from length-at-age data was observed with the highest growth rates within the centre of the species distribution. Analysis of otolith growth chronologies of 33. yrs showed a positive relationship with the Southern Oscillation Index. Identifying links between life-history characteristics and variation in oceanographic conditions across latitudinal gradients may shed light on potential impacts of expected climate shifts on fish productivity. © 2014 Elsevier B.V.

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