Sillaginodes Research Articles

Citizen science aids the quantification of the distribution and prediction of present and future temporal variation in habitat suitability at species’ range edges

Citizen science programs are effective methods to collect large volumes of data to assist researchers in monitoring ecological environments. As species shift their distributions globally due to climate change, the use of citizen science data to detect these shifts is increasing. Using targeted citizen science programs to collect data on these species could provide information on range edges to inform species distribution modelling. Currently, species distribution models (SDMs) often rely on large data repositories that may lack observations, and hence ability, to detect changes at the range edge. Here, we developed a SDM to compare traditional data repository observations with targeted citizen science data at the southern distribution limit of two recreationally important marine fish in Tasmania, Australia to investigate the potential change in spatial predictions at their range edge. The SDM using the targeted citizen science data in addition to traditional observation data improved the representation of species by 2.3 and 52.7% and increased the southern distribution of the species by 277 and 438 km, for snapper and King George whiting, respectively. Future (centred around 2050 under IPCC RCP 8.5) habitat suitability was predicted to increase more over the winter season, with implications for species overwintering and persistence of populations. The use of citizen science data allowed for the modelling of historical and future change for two range-extending species, an outcome possible due to the collaboration of two citizen science programs that collected observational data on the target species. Species range shifts will require ongoing monitoring and we have demonstrated that complimentary citizen science initiatives are effective in capturing occurrences of species at their range edge. Increasing collaboration between programs may further increase data collection efforts and provide the knowledge to create a hub for these data to be used more efficiently in the future.

Seagrass valuation from fish abundance, biomass and recreational catch

The value of critical habitats, such as seagrass, to act as a nursery varies spatially and temporally; however, such information is essential for the public and stakeholders to appropriately value and manage these habitats. We use an existing systematic long-term fisheries dataset in Port Phillip Bay to examine variability in nursery habitat value for an important commercial and recreational species, King George Whiting (Sillaginodes punctatus). Port Phillip Bay represents one of the most important marine assets in the southern hemisphere and is surrounded by the second-largest city in Australia, Melbourne, home to 4.5 million people. We modelled the abundance of King George whiting as a function of environmental variables, using Boosted Regression Trees (BRT). Fish densities ranged from 1,000 to 30,000 individuals ha−1y−1, equalling an adult biomass of 110–3,300 kg ha−1y−1. This production supports between 69 and 2,062 recreational fishing trips a year, with an estimated value of seagrass of AUD 687–20,625 ha−1y−1. Based on biomass production of King George Whiting and recreational fisheries data, the 6662 ha of seagrass in Port Phillip Bay are valued at around AUD 36 million annually.

Spawning sources of a coastal fishery species inferred from otolith chemistry and microstructure: implications for management

Spawning sources of King George whiting Sillaginodes punctatus populations in the states of South Australia and Victoria (south-eastern Australia) were analysed using otolith chemistry and microstructure from post-larvae sampled from 3 nursery areas in each state in the spring of 2011 and 2012. Univariate and multivariate analysis of the chemistry of the core region of otoliths showed differences between states, particularly for the 2011 cohort, primarily related to higher Mg in South Australian samples, while differences in Sr and Zn also made a contribution. Even though spawning times overlapped, early larval growth rates were higher for post-larvae from South Australia than Victoria. Differences in microchemistry were most evident for elements influenced by physiological processes and were potentially influenced by the different larval growth rates. Overall, otolith chemical and microstructure analyses for post-larvae in Victoria and South Australia indicated that spawning sources for the 2 states were different, qualified by results from otolith microchemistry that were less clear for the 2012 cohort. Even though genetic analyses do not indicate genetic differentiation across the 2 states, and therefore would support cross-jurisdictional management, the results of this study give qualified support to the current arrangement wherein the S. punctatus fishery is managed separately by the individual jurisdictions, subject to further information on stock structure coming to light in the future.

Using a biophysical model to investigate connectivity between spawning grounds and nursery areas of King George whiting (Sillaginodes punctatus: Perciformes) in South Australia’s gulfs

AbstractMany demersal marine fish species depend on a dispersive larval stage that connects geographically discrete sub‐populations. Understanding connectivity between these sub‐populations is necessary to determine stock structure, which identifies the appropriate spatial scale for fishery management. Such connectivity is poorly understood for King George whiting (Sillaginodes punctatus; Perciformes) in South Australia's gulf system, even though spawning grounds and nursery areas are adequately defined. In response to declines in commercial catches and estimated biomass, this study aimed to determine the most important spawning grounds and nursery areas to recruitment, and the connectivity between them. A biophysical model was seeded with particles according to the distribution and density of eggs throughout the spawning area in 2017 and 2018. Despite inter‐annual differences in the origins of particles, dispersal pathways and predicted settlement areas remained consistent between years. Predicted settlement was generally highest to nursery areas only short distances from regional spawning grounds, consistent with previous hydrodynamic models. However, the model also predicted that spawning in one region could contribute to recruitment in an adjacent region later in the spawning season, which aligned with the breakdown of thermohaline fronts at the entrance of each gulf. The connectivity between spawning grounds and nursery areas predicted by the model is supported by spatio‐temporal patterns in the otolith chemistry of pre‐flexion larvae and settled juveniles. Consequently, the most parsimonious explanation is that the populations of King George whiting in South Australia's gulf system constitute a single, panmictic stock, which has implications for fishery management.

The application of recreational fishing survey data for ecological research, a case study from Western Port, Australia

AbstractThere is a world‐wide need for information on the ecology and habitat dependencies of important fish species. Recreational fishing surveys represent a potential source of data to increase our knowledge of fish distribution and habitat relationships. Here, a case study is provided on two key recreational species, King George Whiting Sillaginodes punctatus (Cuvier) and Snapper Chrysophrys auratus (Forster). The data came from a recreational fishing survey where 10,978 interviews were conducted from 1998 to 2013 in Western Port, Victoria, Australia. Spatial mapping of catch rate in relation to depth and habitat showed that S. punctatus distribution was related to seagrass cover while C. auratus distribution was related to deeper reef habitat. Juveniles of both species were more abundant in the south‐eastern section of the bay, where water quality is affected by catchment inputs. Overall, the study showed that the inclusion of spatial and habitat information in the design of recreational fishing surveys can significantly increase understanding of the ecology of key species.

Discriminating Natal Source Populations of a Temperate Marine Fish Using Larval Otolith Chemistry

The life cycles of many marine species depend on a dispersive larval stage that connects spatially segregated populations. However, quantifying larval movement among populations remains one of the greatest challenges in marine ecology. Such movement determines whether a population is essentially a self-recruiting stock, or if it forms part of a larger meta-population where recruits originate from multiple sources. Previous research has struggled to differentiate between such stock structure models for King George whiting (Sillaginodes punctatus; Perciformes) in southern Australia, largely due to difficulties in identifying the source populations of dispersing larvae. In this study, pelagic larvae were collected throughout the only recognized spawning area in South Australia in 2017 and 2018. First, we identified that the distribution of larvae was broadly divisible into two groups – those in southern Spencer Gulf and those in Investigator Strait. Then, the incremental structure and elemental composition of otoliths of larvae from the two regions were compared to determine if they had originated from a common source population. There were no spatial differences in the sizes (3.0-5.0 mm SL), ages (5-21 d), hatch dates (7-24 April) or average growth rates (0.09-0.21 mm d-1) of larvae. However, multi-elemental (Li, Mg, Mn, Sr and Ba) otolith signatures differed significantly between the two regions, primarily driven by differences in concentrations of Li and Ba. Although otolith signatures were year-specific, larvae were assigned to their region of capture with 70-82% accuracy. Larvae in each region hatched at the same time yet had significantly different otolith chemistry, providing strong evidence that those in southern Spencer Gulf and Investigator Strait originated from spatially segregated water masses. This study has demonstrated the ability of otolith chemistry to discriminate source populations of pelagic larvae in a fully marine environment, which provides a basis to quantify larval movement between fish populations.

Predicting catch per unit effort from a multispecies commercial fishery in Port Phillip Bay, Australia

Quantitative models that predict stock abundance can inform stock assessments and adaptive management that allows for less stringent controls when abundance is high and environmental conditions are suitable, or tightening controls when abundance is low and environmental conditions are least suitable. Absolute estimates of stock abundance are difficult and expensive to obtain, but data from routine reporting in commercial fisheries logbooks can provide an indicator of stock status. Autoregressive integrated moving average (ARIMA) models were constructed using catch per unit effort (CPUE) from commercial fishing in Port Phillip Bay from 1978–79 to 2009–10. Univariate and multivariate models were compared for short-lived species (Sepioteuthis australis), and species represented by 1–2 year-classes (Sillaginodes punctatus) and 5–6 year-classes (Chrysophrys auratus). Simple transfer models incorporating environmental variables produced the best predictive models for all species. Multivariate ARIMA models are dependent on the availability of an appropriate time series of explanatory variables. This study demonstrates an application of time series methods to predict monthly CPUE that is relevant to fisheries for species that are short lived or vulnerable to fishing during short phases in their life history or where high intra-annual variation in stock abundance occurs through environmental variability.

Evaluation of food competition and resource partitioning of recruiting fish with permanent residents in a seagrass habitat

ABSTRACT Recruiting King George whiting Sillaginodes punctatus were studied to assess the potential for food competition with permanent resident fish species in a nursery habitat. Marine migrant post larval S. punctatus (<60 mm TL) consumed primarily harpacticoid copepods and had high (>0.6) diet overlap with permanent resident fish species Favonigobius leteralis and Stigmatopora nigra. Food electivity index indicated that S. punctatus juveniles preferred harpacticoid copepods and amphipods, while juvenile Heteroclinus adelaide and Gymnapistes marmoratus migrating to the nursery habitat targeted larger prey such as amphipods. Preference for larger prey by H. adelaide and G. marmoratus species coupled with differences in prey composition in the stomach was due to mouth size and feeding habits, resulting in different food preferences to S. punctatus. The whiting showed an ontogenetic shift in diet with early settlers (>60 mm TL) consuming less copepods and more amphipods, while previous year recruits (>120 mm TL) consumed polychaete worms. This study indicates that competition for food resources between the new recruiting S. punctatus juveniles and permanent resident juveniles is reduced through differences in temporal and spatial feeding behaviours, mouth morphology, and ontogenetic shift in prey consumption.

Spatial connectivity during the early life history of a temperate marine fish inferred from otolith microstructure and geochemistry

Connectivity during the ontogenetic development of fishes identifies the spatial scale over which populations function, which is the appropriate scale for conservation and management. For many marine species, spawning grounds and nursery areas are spatially segregated and larval dispersal is an obligate process that connects life history stages. This study investigated the spatial scale of early life history for one such species, the King George whiting (Sillaginodes punctatus; Perciformes), through the retrospective analysis of otolith microstructure and elemental chemistry of recently-settled larvae. The aim was to determine whether the South Australian population constitutes a single panmictic stock, or if it comprises multiple sub-populations. Sizes (15.1–25.1 mm SL), ages (85–183 d) and hatch dates (24-Apr to 1-Aug) of larvae varied considerably between nursery areas at different spatial scales. Regional differences in multi-elemental otolith signatures indicated that multiple spawning grounds contribute to recruitment, and larvae that settled in each region dispersed through different water masses. Within each region, there were differences in hatch dates and otolith chemistry indicative of finer-scale relationships between particular spawning grounds and nursery areas, consistent with local oceanographic circulation patterns. Although multi-elemental signatures were year-specific, concentrations of Ba and Mn were largely responsible for spatial differences and assigned larvae to regional groups with 52–66% accuracy. The results suggest the State-wide stock is replenished by three putative source populations, and provide an example of how otolith chemistry can discriminate among geographically-close, yet-ecologically separated groups of fish in coastal marine ecosystems.

Comparing indicators of recreational fishing in Port Phillip Bay, Australia, from 2008 to 2011 with variability from a background period (2003–07)

Understanding the effects of anthropogenic disturbances on marine environments that support recreational fisheries requires suitable monitoring data. Although catch rates are frequently considered to inform resource status for commercial fisheries, similar time series data are generally unavailable for recreational fisheries. This study is based on 9 years of data from boat-based recreational fishing surveys in Port Phillip Bay, Australia. Harvest rates and length distributions of the retained catches for three target species were statistically compared over 4 years following commencement of shipping channel dredging (2008–11) with variability from a background period (2003–07). Mean harvest rates were generally within historical ranges, with increases for snapper (Chrysophrys auratus) and King George whiting (Sillaginodes punctatus) and decreases for sand flathead (Platycephalus bassensis). Length–frequency distributions were not significantly different to the background period, except for increased mean length of snapper and King George whiting in 2011. This study demonstrates that data obtained from sampling recreational fishers can provide valuable information to monitor harvested resources and maintain social amenity for recreational fisheries during periods of anthropogenic disturbance. Trends in harvest rates from recreational fishing surveys may also complement catch rates from commercial fisheries for assessments of multisector fisheries or stand-alone assessments for recreational-only fisheries.

Resolving the early life history of King George whiting (Sillaginodes punctatus: Perciformes) using otolith microstructure and trace element chemistry

Understanding the early life history processes of fish that lead to recruitment is critical for understanding population dynamics. This study explored the early life history of King George whiting (Sillaginodes punctatus) that recruited to an important nursery area in South Australia in 2016 and 2017. The early life history was reconstructed based on the retrospective analysis of otolith microstructure and chemistry for settlement-stage larvae collected fortnightly from July to November. These fish hatched between March and July, but a 3-week period in May led to 52–71% of recruitment. Recruits from successive sampling occasions differed in age, size and growth rate, potentially related to seasonal changes in water temperature and larval food availability. During both years, there were significant changes in otolith elemental chemistry among the groups of recruits that primarily related to changes in Sr:Ca. There are two hypotheses to account for the differences in otolith chemistry: either (1) a single, primary spawning source and within-season environmental change; or (2) multiple spawning sources. Further investigation with oceanographic models of larval dispersal will help differentiate between these. The retrospective analysis of otoliths has improved the understanding of early life history for this important species, with implications for fishery management.

Low levels of genetic structuring in King George whiting Sillaginodes punctatus across two geographic regions.

Postlarvae of King George whiting Sillaginodes punctatus, a commercially important fish species in southern Australia, were collected from multiple locations across south and south-eastern Australia. Genetic analyses using seven microsatellite markers found little evidence of genetic structure suggesting high levels of connectivity between the regions. The results found no evidence of a distinct source spawning population within the south-eastern range sampled in this study.

The effects of temperature and salinity on otolith chemistry of King George whiting

Otolith chemistry is used widely to reconstruct the environmental histories of fish. Examining the relationships between environmental conditions and otolith chemistry is an essential first step towards accurately reconstructing environmental histories, with lack of information potentially resulting in the erroneous interpretation of fish movement and the environments they have inhabited. We evaluated the influence of seawater temperature and salinity on the otolith chemistry of juvenile King George whiting (Sillaginodes punctatus) (Cuvier 1829), a commercially and recreationally important fish species in southern Australia. Juveniles were reared under controlled laboratory conditions at four temperatures (16, 19, 22 and 25°C) and two levels of salinity (30 and 40) for 90days. Otoliths were analysed for barium (138Ba), strontium (88Sr), magnesium (24Mg) and manganese (55Mn) using laser ablation inductively coupled plasma-mass spectrometry (LA ICP-MS), and ratioed to calcium (43Ca). Otolith chemistry data were analysed using generalized linear mixed models (GLMM). Analyses showed that Mg:Ca and Mn:Ca in the otolith of the fish increased with increasing salinity, whereas Sr:Ca and Ba:Ca decreased with increasing salinity. Temperature only had a minor influence on elemental concentration. The influence of salinity on otolith chemistry suggests that otolith chemistry could be used as a potential tool for reconstructing the salinity and movement history of King George whiting from estuaries to open coast regions.

Efficacy evaluation of a new water sanitizer for increasing the shelf life of Southern Australian King George Whiting and Tasmanian Atlantic Salmon fillets

The bacterial species and specific spoilage organisms associated with the Southern Australian King George Whiting (KGW) and Tasmanian Atlantic Salmon (TAS), and the efficacy of a HOCl-containing water-based sanitization product (Electro-Chemically Activated Solution, by ECAS4) in extending the shelf life of KGW and TAS fillets were evaluated. Fillets were washed with an ECAS4 solution containing either 45 ppm or 150 ppm of free chlorine and bacterial species enumerated on selective and non-selective media, followed by identification of pure isolates by 16 S rRNA gene sequencing. The dominant spoilage microbiota in KGW and TAS fillets stored at 4 ± 1 °C were Pseudomonas spp. and Shewanella spp. At either concentration, ECAS4 significantly reduced total bacterial load and specific spoilage organisms on KGW and TAS fillets (approx. 1–2 log colony-forming units) during storage and significantly extended the shelf life of the fillets by 2 and 4 days, respectively. The significant increase in shelf life and quality of fillets was corroborated by raw and cooked sensory evaluation. ECAS4 sanitization could have a significant impact on the overall food industry, translating into health and economic benefits through reduction of food spoilage bacteria and potentially, foodborne pathogens without many of the disadvantages of currently approved biocides.

Q10 measures of metabolic performance and critical swimming speed in King George whiting Sillaginodes punctatus.

This study examined thermally driven changes in swimming performance and aerobic metabolism (Q10 and aerobic scope of activity) of adult King George whiting Sillaginodes punctatus to the coldest (16° C) and the warmest (26° C) temperature encountered by this species. Compensation of aerobic scope, higher maximal swimming speeds and a maintained capacity to repay oxygen debt indicate that this species is capable of thermal acclimation to conditions expected under global warming.

Determining climate-growth relationships in a temperate fish: A sclerochronological approach

Otoliths of fish can provide long-term chronologies of growth. Differences in the width of the annual growth increments can reflect the effects of environmental variability on somatic growth rate. We used generalized linear mixed models (GLMM) to evaluate the influence of region, sea surface temperature (SST), El Niño–Southern Oscillation events, and recruitment on the otolith growth of King George whiting (Sillaginodes punctatus), a commercially and recreationally important fish species in southern Australia. Growth increment data spanned 25 years (1985–2010). The optimal model demonstrated that mean winter SST was negatively correlated to growth, and as the winter SST increased the average width of the growth increments declined. However, the temperature effect was very weak (r2: 0.0006). There were no regional growth differences and recruitment was not correlated with growth. Understanding long-term temperature-growth relationships is crucial for disentangling the effects of climate change and other parameters on fish growth, and thus predicting how populations will change in the future.

Thermal tolerance in juvenile King George whiting (Sillaginodes punctata) reduces as fish age and this reduction coincides with migration to deeper colder water

Heat shock proteins (HSPs) are sensitive and readily produced under thermal stress in many fish species and thus serve as a useful stress bio-indicator. Two experiments were conducted to test the hypothesis that King George whiting (KGW) Sillaginodes punctata approaching sexual maturity exhibits a decrease in HSP production and that exposure to high temperatures provokes HSP production in juvenile whiting. Both adult and juvenile whiting expressed significant increases in HSP69 in response to temperature shocks of 24, 26, 28 and 30°C. Juvenile whiting had significantly higher HSP69 than adults and expressed more HSP69 at 24 and 26°C. No mortalities were observed in juvenile fish at 30°C while 50% of adults suffered mortality at 30°C. Following exposure of juveniles to 24, 26 and 28°C, HSP69 was measured at 24, 96 and 168h. HSP69 peaked at 96h and returned to the 24h level after 168h exposure. This study indicates that juveniles can cope with high temperatures better than adults, which offers a partial explanation to fish movement patterns in nature where younger fish inhabit near shore waters and then migrate to deep water towards maturation. Further, this work implies that KGW growth and recruitment can be affected by increasing temperatures due to global warming.

A new species of Grillotia Guiart, 1927 (Cestoda: Trypanorhyncha) with redescriptions of congeners and new synonyms

A new species of Grillotia, G. gastrica n. sp., is described from the stomach musculature of the teleosts Upeneichthys lineatus (Bloch & Schneider) and Sillaginodes punctatus (Cuvier) from off Perth, Western Australia. The new species most closely resembles G. pristiophori Beveridge & Campbell, 2001 in having six hooks in each principal row of the metabasal tentacular armature but differs in having a smooth scolex tegument and in having a band of hooklets running the entire length of the external surface of the tentacle rather than diminishing in width to a single hooklet as occurs in G. pristiophori. Grillotia heptanchi (Vaullegeard, 1899) is redescribed and the details of the mature segment are described for the first time. Grillotia adenoplusius (Pintner, 1903) is redescribed from the type-specimens and is considered to be the larval stage of G. acanthoscolex Rees, 1944 (syns G. spinosissima Dollfus, 1969 and G. microthrix Dollfus, 1969). The adult of G. adenoplusius is also redescribed based on the types of G. spinosissima. The type-specimens of G. dolichocephala Guiart, 1935 and G. minor Guiart, 1935 were re-examined and G. minor is considered to be a synonym of G. dolichocephala as is G. meteori Palm & Schröder, 2001. Based on an examination of the type-specimens, G. scolecina (Rudolphi, 1819) is treated as a species inquirenda. A list is provided of the species currently placed in Grillotia.

Seagrass edge effects on fish assemblages in deep and shallow habitats

Shallow seagrass is an important habitat for many fish species, but little is known about fish distribution in deep seagrass or if depth affects fish distribution within patches. Using stereo video, fish distribution patterns in Port Phillip Bay, Australia, were examined in deep (3.5–6 m) and shallow (<1.5 m) areas over four months (December–March). Three positions were sampled in relation to seagrass patches; the interior of seagrass patches, at the edge of seagrass patches and over sand distant (>100 m) from seagrass. Recorded video was subsequently analysed using time in view (TiV) and MaxN, with fish showing strong responses to both depth and habitat type. Fish assemblages were different between deep and shallow seagrass, and many species were found only in shallow (e.g. Australian salmon, King George whiting, southern garfish) or deep (e.g. bridled leatherjackets, goatfish) seagrass. King George whiting spent more time at the edge than the middle of shallow patches, while TiV and MaxN indicated that garfish and odacids were more common in the middle than the edge of patches. Few species were observed over sand. Overall fish lengths were greater in shallow than deep seagrass and at the edge than middle of patches. Edge effects were found to occur in both deep and shallow seagrass and should be considered when designing sampling regimes and determining conservation strategies.

Growth, behaviour and colour changes of juvenile King George whiting (Sillaginodes punctata) mediated by light intensities

Light is an important environmental factor regulating physiological processes and ecological activities in fishes. This research aimed to examine the effect of light on the growth, distribution and body colour of juvenile King George whiting (Sillaginodes punctata) when fish were exposed to different light levels under laboratory conditions. In this study, the fish were exposed to three light levels (25, 500, and 1000 lux) in triplicate for two months. Comparisons were made for growth, body colour and behavioural changes between treatments. During the experimental period, there were no statistical differences in specific growth rate, survival, growth efficiency and condition factor between the light levels. Although light did not affect swimming speed or encounter rates, it did influence group flight activity and fish distribution in the tanks. Whiting in low light preferred to spend more time grouped at the bottom of the tank than at medium (500 lux) or high light (1000 lux). Likewise, after having been exposed to low light, whiting exhibited a brighter colour and had fewer body markings and counter-shading than fish in medium and high light intensities. Differences in fish distribution and body colour between medium and high light intensities were not detected. This study offers a new insight into understanding the impact of light on behaviour and body colour of fish, which may contribute to the spatial distribution, predator avoidance and recruitment of fish in inshore coastal waters.