Trachurus Declivis Research Articles

Hydrophobic natural deep eutectic solvents for marine lipid extraction

Abstract‘Type V' natural deep eutectic solvents (TV NADES) are a novel class of solvent media with many potential ‘green chemistry’ applications. Here, we assess the potential of two TV NADES: menthol:carvacrol (M:C) and menthol:thymol (M:T), and a single terpenoid extraction media carvacrol (C), as media from total lipid extraction of three compositionally diverse, freeze‐dried marine tissues: hoki (Macruronus novaezelandaiae), jack mackerel (Trachurus declivis) and green‐lipped mussel (kuku, Perna canaliculus). Room temperature extraction yields into these media were benchmarked relative to lipid yields from chloroform‐methanol‐water extractions. Relative extraction yields using the M:C and M:T media were (both) 87% for jack mackerel, 85%–87% for hoki, and 43%–47% for green‐lipped mussels. Comprehensive chemical analyses of TV NADES lipid extracts suggested that neutral lipids were extracted in greater yield than phospholipids, and that phosphatidylinositol, lysophospholipids and (in the case of mussels) ceramideaminoethylphosphonates were particularly resistant to extraction into C, M:C and M:T. C—a thymol isomer that, unlike menthol and thymol is a liquid at room temperature—appeared to perform (marginally) better than M:C and M:T systems, implying there may be no advantage to using the TV NADES over a single terpenoid with similar chemistry for total lipid extraction.

Environmental correlates of temporal variation in the prey species of Australian fur seals inferred from scat analysis.

Marine ecosystems in southeastern Australia are responding rapidly to climate change. We monitored the diet of the Australian fur seal (Arctocephalus pusillus doriferus), a key marine predator, over 17 years (1998–2014) to examine temporal changes. Frequency of occurrence (FO) of prey was used as a proxy for ecosystem change. Hard part analysis identified 71 prey taxa, with eight dominant taxa in greater than 70% of samples and predominantly included benthic and small pelagic fish. FO changed over time, e.g. redbait (Emmelichthys nitidus) reduced after 2005 when jack mackerel (Trachurus declivis) increased, and pilchard (Sardinops sajax) increased after 2009. Using generalized additive models, correlations between FO and environmental variables were evident at both the local (e.g. wind, sea surface temperature (SST)) and regional (e.g. El Niño–Southern Oscillation Index (SOI), Southern Annular Mode (SAM)) scales, with redbait and pilchard showing the best model fits (greater than 75% deviance explained). Positive SAM was correlated to FO for both species, and wind and season were important for redbait, while SOI and SST were important for pilchard. Both large-scale and regional processes influenced prey taxa in variable ways. We predict that the diverse and adaptable diet of the Australian fur seal will be advantageous in a rapidly changing ecosystem.

Using otolith chronologies to identify extrinsic drivers of growth of 2 commercially targeted small pelagic fish species

Climate variability is a major cause of changes in marine ecosystems, including changes in both the environment and in many fish species. Understanding the factors influencing key biological characteristics, such as growth, is important for commercially targeted species because these characteristics are used in stock assessments that inform fisheries management. In this study, otoliths were used to examine the growth rates and growth chronologies of 2 commercially targeted small pelagic fish species, the common jack mackerel (Trachurus declivis) and redbait (Emmelichthys nitidus), from 2 regions of southeastern Australia. Both species grew larger off Kangaroo Island (common jack mackerel: asymptotic length [L∞]=299.40; redbait: L∞=259.79) than off southern New South Wales (common jack mackerel: L∞=249.52; redbait: L∞=238.89). Temporal growth synchrony in both species and regions (0.17–3.50%) was low compared with that of more-site-attached benthic species. Interannual variations in growth rates of common jack mackerel off Kangaroo Island were positively correlated with sea-surface temperature (SST), with growth rates 18% higher at 18.0°C than at 16.4°C. However, growth was not correlated with SST or chlorophyll-a concentration for the other species and locations. Developing a more complete understanding of the environmental drivers of growth in these small pelagic fish species may require chronologies to be extended and extrinsic variables in the models to be increased.

Ingestion of microplastics and mesoplastics by Trachurus declivis (Jenyns, 1841) retrieved from the food of the Australasian gannet Morus serrator: First documented report from New Zealand

During the process of studying some morphological characters of fish found in the food of the Australasian gannet Morus serrator breeding at Horuhoru Rock and Mahuki islands in the Hauraki Gulf, New Zealand, one carangid specimen of fish species Trachurus declivis out of the 25 fish specimens examined revealed seven small plastic particles in its stomach of different colours: black, red, blue, green, and transparent. Fourier transform infrared (FTIR) spectroscopy was used to identify the compositions of the particles as low and high density polyethylene, poly (methyl methacrylate), polypropylene, and a copolymer of butadiene, acrylonitrile, and methacrylamide. The plastic particles comprised several different shapes and sizes, ranging between 4.5 and 10 mm, and are therefore categorized as micro-and mesoplastic fragments.

Current status (as of end of 2020) of marine alien species in Turkey

The 2020’s update of marine alien species list from Turkey yielded a total of 539 species belonging to 18 taxonomic groups, 404 of which have become established in the region and 135 species are casual. A total of 185 new alien species have been added to the list since the previous update of 2011. The present compilation includes reports of an ascidian species (Rhodosoma turcicum) new to the marine fauna of Turkey and range extensions of six species. Among the established species, 105 species have invasive characters at least in one zoogeographic region, comprising 19% of all alien species. Mollusca ranked first in terms of the number of species (123 species), followed by Foraminifera (91 species), Pisces (80 species) and Arthropoda (79 species). The number of alien species found in seas surrounding Turkey ranged from 28 (Black Sea) to 413 (Levantine Sea). The vectoral importance of the Suez Canal diminishes when moving from south to north, accounting for 72% of species introductions in the Levantine Sea vs. only 11% of species introductions in the Black Sea. Most alien species on the coasts of Turkey were originated from the Red Sea (58%), due to the proximity of the country to the Suez Canal. Shipping activities transported 39% of alien species, mainly from the Indo-Pacific area (20%) and the Atlantic Ocean (10%). Misidentified species (such as Pterois volitans, Trachurus declivis, etc.) and species those classified as questionable or cryptogenic were omitted from the list based on new data gathered in the last decade and expert judgements. The documented impacts of invasive species on socio-economy, biodiversity and human health in the last decade as well as the legislation and management backgrounds against alien species in Turkey are presented.

The growth and age structure of Chilean jack mackerel (Trachurus murphyi) following its influx to New Zealand waters

The Chilean jack mackerel (Trachurus murphyi) is a predominantly Southeast Pacific Ocean species. It is relatively difficult to determine its age, and multiple studies of its growth off South America have produced markedly different sets of von Bertalanffy parameters. T. murphyi was first identified from New Zealand waters in the mid-1980s and has comprised part of the commercial landings of Trachurus species (along with Trachurus declivis and Trachurus novaezelandiae) since then. Results from 13 years of age determination of New Zealand samples using sectioned otoliths indicate that a partially validated age determination method has been developed, with a precision level (average percentage error) of 4.6%. The best available von Bertalanffy growth parameters for the New Zealand population (sexes combined) are as follows: L∞ , 51.9 cm fork length; K, 0.223 per year; t0 , -0.5 year. Analyses by sex showed that males have a significantly larger L∞ than females. Estimated annual catch-at-length and catch-at-age distributions from the fishery are presented for 2007-2019. There have been at least two episodes of immigration of T. murphyi from international waters, but little evidence of spawning success to maintain the New Zealand population.

Colony relocation of Greater Crested Terns Thalasseus bergii in Bass Strait, south-eastern Australia

A newly established Greater Crested Tern Thalasseus bergii colony was observed on Kanowna Island, northern Bass Strait, in December 2019 and was monitored through January 2020. A maximum of 532 ± 28 nests was counted,representing ~15–20% of the known northern Bass Strait breeding population. Resightings of 69 leg-banded individuals (from 3 to 24 years of age) demonstrated that founding individuals originated from colonies in Victoria [The Nobbies on Phillip Island (54%), Corner Inlet Barrier Islands (39%), Mud Islands in Port Phillip Bay (6%)] and one individual from South Australia. Breeding began 2 months later than usual for northern Bass Strait, perhaps because the birds only moved to Kanowna Island after failed nesting attempts elsewhere (Corner Inlet and Phillip Island). Individuals were observed to mainly feed their chicks with Barracouta Thyrsites atun and Jack Mackerel Trachurus declivis, contrasting with the usual predominance of Australian Anchovy Engraulis australis in the diet of this species in the Bass Strait region. This relocation may result from local changes in prey availability and/or a combination of potential human disturbance, predation and storm events. The recent 50% decrease in the number of breeding Greater Crested Terns in Victoria suggests substantial changes in the regional environmental conditions, highlighting the importance of understanding the impact of environmental variations on seabird species.

Biometric relationships between body and otolith measurements in nine demersal fishes from north-eastern Tasmanian waters, Australia

Relationships between fish and otolith measurements were analyzed in nine demersal fishes from the north-eastern Tasmanian waters: Foetorepus calauropomus, Trachurus declivis, Parequula melbournensis, Neosebastes scorpaenoides, Platycephalus aurimaculatus, Platycephalus bassensis, Platycephalus conatus, Lepidotrigla mulhalli and Lepidotrigla vanessa. The values of exponent b from the relationships between fish weight and fish total length, total length and otolith length, total length and otolith width, and fish weight and otolith length were estimated. All above relationships were statistically significant. The analysis of covariance (ANCOVA) was used to test the effect of the categorical factor of species in the fish length and otolith length relationship. Significant differences in fish length and otolith length relationship between species were highlighted in both gurnards and flatheads. Results from this study will provide novel information on quantitative biometric relationships between body and otolith measurements of fish species in Australian waters.

Characterising the spawning patterns of Jack Mackerel (Trachurus declivis) off eastern Australia to optimise future survey design

Estimates of spawning biomass obtained using the daily egg production method (DEPM) are used to establish catch limits for Jack Mackerel (Trachurus declivis) off eastern Australia. Information from concurrent ichthyoplankton and adult surveys conducted between Port Stephens, New South Wales and South East Cape, Tasmania during January 2014 was used to assess the environmental factors that determine the spawning patterns of Jack Mackerel. Adults were collected using a modified demersal trawl net deployed during daylight hours. Samples were unbiased with respect to sex, spawning activity and size. Large fish were collected from both the inner shelf and shelf break; spawning fractions and egg densities were high inshore and low offshore. These findings suggest complex spatio-temporal patterns of spawning, different to previous studies suggesting that most spawning occurred at the shelf break (∼200m). Eggs were most abundant in sea surface temperatures (SSTs) of 15–20°C and at depths of <130m. Future ichthyoplankton surveys should target waters with SSTs of 14–23°C and depths of 30–250m. Future adult surveys should sample the same range of depths and latitudes as the ichthyoplankton surveys and be structured as systematically as permitted by the availability of habitats suitable for demersal trawling. The DEPM does not provide information about the abundance of non-spawning adults outside the main spawning area. Extending future adult surveys beyond the spawning area would address this limitation by providing estimates of the distribution and relative abundance of adults across the entire range of the population. Findings of this study will help to improve the design of future DEPM surveys.

First record of greenback horse mackerel, Trachurus declivis (Jenyns, 1841) in the Mediterranean Sea

Journal of Applied IchthyologyVolume 32, Issue 5 p. 976-977 Short Communication First record of greenback horse mackerel, Trachurus declivis (Jenyns, 1841) in the Mediterranean Sea M. Gurlek, Corresponding Author M. Gurlek mevlutgurlek@hotmail.com mevlut.gurlek@iste.edu.tr Molecular Ecology and Fisheries Genetic Laboratory, Department of Marine Sciences, Marine Science and Technology Faculty, Iskenderun Technical University, Iskenderun, Hatay, Turkey Correspondence M. Gurlek, Molecular Ecology and Fisheries Genetic Laboratory, Department of Marine Sciences, Marine Science and Technology Faculty, Iskenderun Technical University, Iskenderun, Hatay, Turkey. Email: mevlutgurlek@hotmail.com; mevlut.gurlek@iste.edu.trSearch for more papers by this authorD. Erguden, D. Erguden Molecular Ecology and Fisheries Genetic Laboratory, Department of Marine Sciences, Marine Science and Technology Faculty, Iskenderun Technical University, Iskenderun, Hatay, TurkeySearch for more papers by this authorS. A. Dogdu, S. A. Dogdu Molecular Ecology and Fisheries Genetic Laboratory, Department of Marine Sciences, Marine Science and Technology Faculty, Iskenderun Technical University, Iskenderun, Hatay, TurkeySearch for more papers by this authorC. Turan, C. Turan Molecular Ecology and Fisheries Genetic Laboratory, Department of Marine Sciences, Marine Science and Technology Faculty, Iskenderun Technical University, Iskenderun, Hatay, TurkeySearch for more papers by this author M. Gurlek, Corresponding Author M. Gurlek mevlutgurlek@hotmail.com mevlut.gurlek@iste.edu.tr Molecular Ecology and Fisheries Genetic Laboratory, Department of Marine Sciences, Marine Science and Technology Faculty, Iskenderun Technical University, Iskenderun, Hatay, Turkey Correspondence M. Gurlek, Molecular Ecology and Fisheries Genetic Laboratory, Department of Marine Sciences, Marine Science and Technology Faculty, Iskenderun Technical University, Iskenderun, Hatay, Turkey. Email: mevlutgurlek@hotmail.com; mevlut.gurlek@iste.edu.trSearch for more papers by this authorD. Erguden, D. Erguden Molecular Ecology and Fisheries Genetic Laboratory, Department of Marine Sciences, Marine Science and Technology Faculty, Iskenderun Technical University, Iskenderun, Hatay, TurkeySearch for more papers by this authorS. A. Dogdu, S. A. Dogdu Molecular Ecology and Fisheries Genetic Laboratory, Department of Marine Sciences, Marine Science and Technology Faculty, Iskenderun Technical University, Iskenderun, Hatay, TurkeySearch for more papers by this authorC. Turan, C. Turan Molecular Ecology and Fisheries Genetic Laboratory, Department of Marine Sciences, Marine Science and Technology Faculty, Iskenderun Technical University, Iskenderun, Hatay, TurkeySearch for more papers by this author First published: 27 August 2016 https://doi.org/10.1111/jai.13159Citations: 11Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume32, Issue5October 2016Pages 976-977 RelatedInformation

Spawning biomass of jack mackerel (Trachurus declivis) off eastern Australia: Critical knowledge for managing a controversial fishery

Jack mackerel (Trachurus declivis) is a key target species of the Australian Small Pelagic Fishery. The fishery was subject to extensive public scrutiny following an attempt to introduce a large factory-trawler in 2012. One of the concerns raised related to the reliability and age of estimates of the spawning biomass of jack mackerel. This study reports on the first dedicated application of the Daily Egg Production Method (DEPM) to jack mackerel. Large numbers of samples of eggs and adults were collected concurrently from the key spawning area off eastern Australia during what has been previously identified as the main spawning period. This study established an effective adult sampling method and provides the first estimates for this species of adult reproductive parameters required for application of the DEPM. Estimates of all DEPM parameters, except batch fecundity, were based on relatively large sample sizes. The spawning biomass of jack mackerel off eastern Australia during January 2014 was estimated to be approximately 157,805 t (95% CI=59,570–358,731 t). Sensitivity analyses indicate this estimate is robust to likely uncertainty in estimates of key parameters. Future research should focus on elucidating the size-fecundity relationship and spatial, temporal and size-related variations in spawning fraction.

Investigating photoreceptor densities, potential visual acuity, and cone mosaics of shallow water, temperate fish species

The eye is an important sense organ for teleost species but can vary greatly depending on the adaption to the habitat, environment during ontogeny and developmental stage of the fish. The eye and retinal morphology of eight commonly caught trawl bycatch species were described: Lepidotrigla mulhalli; Lophonectes gallus; Platycephalus bassensis; Sillago flindersi; Neoplatycephalus richardsoni; Thamnaconus degeni; Parequula melbournensis; and Trachurus declivis. The cone densities ranged from 38 cones per 0.01mm2 for S. flindersi to 235 cones per 0.01mm2 for P. melbournensis. The rod densities ranged from 22800 cells per 0.01mm2 for L. mulhalli to 76634 cells per 0.01mm2 for T. declivis and potential visual acuity (based on anatomical measures) ranged from 0.08 in L. gallus to 0.31 in P. melbournensis. Higher rod densities were correlated with maximum habitat depths. Six species had the regular pattern of four double cones arranged around a single cone in the photoreceptor mosaic, while T. declivis had only rows of double cones. P. melbournensis had the greatest potential ability for detecting fine detail based on eye anatomy. The potential visual acuity estimates and rod densities can be applied to suggest the relative detection ability of different species in a commercial fishing context, since vision is a critical sense in an illuminated environment for perceiving an oncoming trawl.

The genus Rhadinorhynchus (Acanthocephala: Rhadinorhynchidae) from marine fish in Australia with the description of four new species.

Species of Rhadinorhynchus, collected from Australian waters were examined. Specimens of Rhadinorhynchus from Scorpis aequipinnis, Girella tricuspidata, Johnius australis and Grammatobothus polyophthalmus could not be identified further. New host and locality records are reported for R. bicircumspinus found in Trachurus declivis and Rexea solandri from the east coast of Tasmania; R. carangis found in Trachinotus bailonii and T. copperingi from Queensland and Western Australian coasts; R. polynemi from Queensland; R. seriolae found in Seriola lalandi from the east coast of Australia. An immature female specimen of R. johnstoni provided no additional data on the species. Rhadinorhynchus biformis sp. nov., described from Pelates quadrilineatus and a trumpeter from Moreton Bay, Queensland differs from all its congeners in the pattern of the trunk spines, a single field of numerous small spines ventro-laterally, overlapping with irregular rows and circles of larger spines extending posteriorly. Rhadinorhynchus pichelinae sp. nov. described from Upeneichthys vlamingi from Point Peron, Western Australia differs from all its congeners in having proboscis armature of 10 longitudinal rows of 24-28, usually 26-27 hooks up to 87 long and a single field of 21-24 irregular circles of spines on the anterior trunk, with the posterior circles incomplete dorsally. Rhadinorhynchus polydactyli sp. nov. described from Polydactylus sp. from Moreton Bay is differentiated from all congenerics by the elongated neck of the females and having a proboscis armature of up to 34 hooks in 10 longitudinal rows. Rhadinorhynchus pomatomi sp. nov. found in Pomotomus saltrix differs from its most similar congeners, those without dorsal trunk spines, in having a proboscis armature of 12-15 rows of 20-22 hooks up to 73.5-80.5 long. Rhadinorhynchus bicircumspinus, R. biformis, R. pichelinae, R. polydactyli and R. pomatomi are known only from Australian waters while R. carangis and R. seriolae are also known from Japanese waters, R. johnstoni from the western Pacific and R. polynemi from the Indian coast.

A prey-related shift in the abundance of small pelagic fish in eastern Tasmania?

Abstract McLeod, D. J., Hobday, A. J., Lyle, J. M., and Welsford, D. C. 2012. A prey-related shift in abundance of small pelagic fish in eastern Tasmania? – ICES Journal of Marine Science, 69: 953–960. Shifts in the relative abundance of small pelagic fish species have signalled a change in the ocean environment in a number of locations. Here we show that the replacement of jack mackerel, Trachurus declivis, with redbait, Emmelichthys nitidus, as the dominant small pelagic species from eastern Tasmania, following a period of high fishing pressure on jack mackerel, is consistent with altered zooplankton communities and long-term climate change. Stomach contents analysis and morphology measurements were conducted on both species to determine if they were functionally equivalent with regard to zooplankton prey. Diet varied between species and with fish size. Krill (Nyctiphanes australis) was consumed by both species, with redbait feeding more heavily on small copepods. The diet overlap and morphometric characteristics indicated that these species are not equivalent with regard to prey and therefore changes in prey availability may have contributed to the observed shifts in relative abundance. The continued poleward extension of the East Australian Current is expected to favour small warm-water copepods; thus, redbait may have an advantage over jack mackerel due to prey preferences. An increase in relative abundance of redbait has decreased effort in surface fisheries and may impact on surface-feeding higher predators in this region.

Diet of young southern bluefin tuna Thunnus maccoyii in the southwestern coastal waters of Australia in summer

The diet of juvenile (predominantly age 1) southern bluefin tuna Thunnus maccoyii (SBT, N = 720), caught over 11 years of the recruitment monitoring survey off southern Western Australia during summer, consisted overwhelmingly of teleosts (97.4% by volume). Pilchard Sardinops sagax (27.4%V), blue mackerel Scomber australasicus (16.7%V), and jack mackerel Trachurus declivis (14.2%V) were the major taxa, with pilchard more abundant in coastal waters and jack mackerel more frequently encountered in fish caught closer to the shelf-edge. Prey size varied from 5 to 240 mm, with 67% of ingested items measuring between 30 and 50 mm. Pilchard dominated the prey size category 130–190 mm (84% by number), but the overall contribution of this species to the diet of juvenile SBT was much lower than previously reported. Future research in relation to the feeding ecology of juvenile SBT should focus on the biology and ecology of the young lifestages of the main prey species in this area and on prey distribution and dynamics as a key factor linking environmental change and SBT distribution.

Analysis of Australian fur seal diet by pyrosequencing prey DNA in faeces

DNA-based techniques have proven useful for defining trophic links in a variety of ecosystems and recently developed sequencing technologies provide new opportunities for dietary studies. We investigated the diet of Australian fur seals (Arctocephalus pusillus doriferus) by pyrosequencing prey DNA from faeces collected at three breeding colonies across the seals' range. DNA from 270 faecal samples was amplified with four polymerase chain reaction primer sets and a blocking primer was used to limit amplification of fur seal DNA. Pooled amplicons from each colony were sequenced using the Roche GS-FLX platform, generating > 20,000 sequences. Software was developed to sort and group similar sequences. A total of 54 bony fish, 4 cartilaginous fish and 4 cephalopods were identified based on the most taxonomically informative amplicons sequenced (mitochondrial 16S). The prevalence of sequences from redbait (Emmelichthys nitidus) and jack mackerel (Trachurus declivis) confirm the importance of these species in the seals' diet. A third fish species, blue mackerel (Scomber australasicus), may be a more important prey species than previously recognised. There were major differences in the proportions of prey DNA recovered in faeces from different colonies, probably reflecting differences in prey availability. Parallel hard-part analysis identified largely the same main prey species as did the DNA-based technique, but with lower species diversity and no remains from cartilaginous prey. The pyrosequencing approach presented significantly expands the capabilities of DNA-based methods of dietary analysis and is suitable for large-scale diet investigations on a broad range of animals.

The influence of age on reproductive success and diet in Australasian gannets (Morus serrator) breeding at Pope's Eye, Port Phillip Bay, Victoria

The influence of age on reproductive success and diet was examined in ‘old’ (experienced; 12 years and older) and ‘young’ (5–8 years of age) Australasian gannets (Morus serrator) breeding at Pope’s Eye, Port Phillip Bay, Victoria during the 2002–2003 breeding period. Although food availability, as indicated by commercial fish catches, throughout this breeding period was low, there were no significant differences in breeding success or chick growth between groups. Nevertheless, old birds tended to have higher reproductive success, replacing more lost eggs and fledging chicks of a greater mass. However, old birds also laid more eggs that failed to hatch. Five fish species, including jack mackerel (Trachurus declivis), barracouta (Thyrsites atun), redbait (Emmelichthys nitidus), anchovy (Engraulis australis) and red mullet (Upeneichthys vlamingii), were important in the gannet diet during this breeding period. There were no significant differences in dietary parameters, including range of species and size of prey, between old and young gannets, nor were there any differences between those of the chicks and their parents, suggesting that adults do not forage selectively for their chicks. This study showed that even during a period of presumed low food availability, when experienced (older) birds might be expected to have enhanced success, the differences between these and less experienced (younger) birds may not be apparent.

Summer and winter plankton fish assemblages around offshore oil and gas platforms in south-eastern Australia

Opportunistic plankton surveys were conducted within a 5-nmi radius of nine offshore oil and gas platforms in Bass Strait, south-eastern Australia, in February 1998 and 1999 (summer) and August 1998 (winter). The 108 day-night samples collected alongside (vertical tows) and nearby (surface and oblique tows) platforms yielded 1526 larval and early juvenile fishes representing 55 taxa from 45 families. Epipelagic/mesopelagic taxa dominated the catches, whereas hard/soft habitat-associated taxa were uncommon. Carangidae (36.2%) and Myctophidae (31.5%) dominated in summer and winter, respectively. The most abundant taxon was Trachurus declivis (Carangidae, 35.1%), followed by Bovichtus angustifrons (Bovichtidae, 8.7%), Scomberesox saurus (Scomberesocidae, 3.7%), Centroberyx affinis (Berycidae, 3.0%) and Arripis trutta (Arripidae, 1.7%). Fish concentrations (nos. per 100 m 3) alongside platforms did not differ significantly between day and night across all surveys. Likewise, concentrations nearby platforms in February 1999, including those of T. declivis, did not vary significantly by tow type (surface vs. oblique) or day vs. night. The far greater diversity and abundance recorded in February 1999 are likely the result of upwelling conditions over the eastern Bass Strait shelf during the sampling period, and which were not detected in February 1998. In the absence of data on adult fishes associated with the Bass Strait platforms, and given the limited availability of reefs directly around the area, it could be argued that some of the taxa caught may originate from spawning around neighboring natural reefs, particularly those off the Gippsland coastline and the south-east corner of mainland Australia. However, the prime position of the platforms almost right in the center of a productivity “hotspot” would have a confounding effect on the potential source(s) of larval fishes in that region of south-eastern Australia. The role of platforms as potential de-facto reefs for juvenile fishes in Bass Strait, as well as spawning areas, is discussed based on the findings of this study, the first on early stages of fishes around oil and gas platforms in Australia.

Spatial and temporal variation in the diet of a high trophic level predator, the Australian fur seal ( Arctocephalus pusillus doriferus )

This study quantifies the manner in which Australian fur seals, Arctocephalus pusillus doriferus, use their prey in a spatial and temporal context. We analysed 977 scat and 66 regurgitate samples collected from Tasmanian breeding colonies and haul-outs between 1994 and 2000. Diagnostic prey remains identified in the scats represented 35 fish taxa and 8 cephalopod taxa. The main taxa identified in scats, where frequency of occurrence was ≥10%, were leatherjacket species (family Monocanthidae), redbait (Emmelichthys nitidus), barracouta (Thyrsites atun), jack mackerel (Trachurus declivis) and red cod (Pseudophysis bachus). Regurgitates were dominated by cephalopods, primarily Gould’s squid (Nototodarus gouldi), Octopus maorum, O. berrima/pallidus and Sepia apama. Discriminant function analyses indicated that there were generally no significant differences in the composition of the diet between colonies within a year, suggesting that prey distribution is fairly uniform throughout Bass Strait at those time scales. The diet at breeding colonies, however, exhibited significant inter- and intra-annual variation, determined by the presence of several key taxa, such as barracouta and a species of scorpionfish (family Scorpaenidae). The diet composition also varied regionally, between Bass Strait and southern Tasmania in spring 1999 and autumn 2000, with redbait, barracouta and a species of scorpionfish identified as the main taxa contributing to this difference. Redbait occurred in the diet only in southern Tasmania, whereas barracouta and scorpionfish occurred only in Bass Strait.

The diet of Crested Tern (Sterna bergii) chicks on Phillip Island, Victoria, Australia

The diet of juvenile Crested Terns (Sterna bergii) at Phillip Island, Victoria was examined throughout two breeding periods, 1999–2000 and 2000–01. Nine species of fish and two species of squid were identified in the chick regurgitations, with significant differences among sampling days and between seasons. Anchovy (Engraulis australis) and Jack Mackerel (Trachurus declivis) were the two most abundant prey in both seasons, making up 63% and 21% of the diet, respectively, followed by Barracouta (Thyrsites atun, 4%) and other fish (12%). Anchovy was also the main prey for Little Penguins (Eudyptula minor) in 2000–01. In addition, years of low numbers of breeding Crested Terns coincided with years of low breeding success of Little Penguins over seven breeding seasons at Phillip Island. It seems that the breeding performance of both terns and penguins may be affected by the same variation of food supply. We also estimated roughly that this tern population consumes 28.7 tonnes of fish per breeding period based on the daily energy expenditure of seabirds. This consumption is about 10% of the commercial catches of Anchovy and Jack Mackerel in 2000–01, highlighting the importance of terns as natural consumers in the local ecosystem during the breeding period.