Reproductive biology of mangrove jack (Lutjanus argentimaculatus) in northeastern Queensland, Australia

Lutjanus argentimaculatus is an Indo-Pacific species that inhabits riverine, coastal and offshore reef habitats. An investigation of the reproductive biology of Lutjanus argentimaculatus in northeastern Queensland waters (Australia) was undertaken between 1999 and 2002. Individuals in inshore estuarine and freshwater riverine habitats were mostly immature whereas those captured in offshore reef waters were predominantly mature. Males matured at a smaller size than females, with the length-at-50%-maturity (Lm50) for males estimated to be 470.7 mm fork length (FL) and 531.4 mm FL for females. The spawning season in northeastern Queensland was mostly during the austral spring-summer and peaked in December. The presence of ripe female fish and occurrence of postovulatory follicles in histological sections provided evidence that spawning activity was more pronounced during the full and third quarter moon phases. Lutjanus argentimaculatus were highly fecund with estimates of up to 4 x 106 ova per spawning event. Immature fish concentrated in inshore areas where they were targeted by recreational fishers whereas, in offshore areas, commercial fishers caught predominantly larger, mature fish.

Genetic population structure of red snappers (Lutjanus malabaricus Bloch & Schneider, 1801 and Lutjanus erythropterus Bloch, 1790) in central and eastern Indonesia and northern Australia

The genetic population structure of red snapper Lutjanus malabaricus and Lutjanus erythropterus in eastern Indonesia and northern Australia was investigated by allozyme electrophoresis and sequence variation in the control region of mtDNA. Samples were collected from eight sites in Indonesia and four sites in northern Australia for both species. A total of 13 allozyme loci were scored. More variable loci were observed in L. malabaricus than in L. erythropterus. Sequence variation in the control region (left domain) of the mitochondrial genome was assessed by RFLP and direct sequencing. MtDNA haplotype diversity was high (L. erythropterus, 0.95 and L. malabaricus, 0.97), as was intraspecific sequence divergence, (L. erythropterus, 0.0-12.5% and L. malabaricus, 0.0-9.5%). The pattern of mtDNA haplotype frequencies grouped both species into two broad fisheries stocks with a genetic boundary either between Kupang and Sape (L. malabaricus) or between Kupang and Australian Timor Sea (L. erythropertus). The allozyme analyses revealed similar boundaries for L. erythropterus. Seven allozymes stocks compared to two mtDNA stocks of L. malabaricus including Ambon, which was not sampled with mtDNA, however, were reported. Possible reasons for differences in discrimination between the methods include: i) increased power of multiple allozyme loci over the single mtDNA locus, ii) insufficient gene sampling in the mtDNA control region and iii) relative evolutionary dynamics of nuclear (allozyme loci) and mitochondrial DNA in these taxa. Allozyme and haplotype data did not distinguish separate stocks among the four Australian locations nor the central Indonesian (Bali and Sape locations) for both L. malabaricus and L. erythropterus.

An improved technique for estimating short-term survival of released line-caught fish, and an application comparing barotrauma-relief methods in red emperor (Lutjanus sebae Cuvier 1816).

Promotion of better procedures for releasing undersize fish, advocacy of catch-and-release angling, and changing minimum legal sizes are increasingly being used as tools for sustainable management of fish stocks. However without knowing the proportion of released fish that survive, the conservation value of any of these measures is uncertain. We developed a floating vertical enclosure to estimate short-term survival of released line-caught tropical and subtropical reef-associated species, and used it to compare the effectiveness of two barotrauma-relief procedures (venting and shotline releasing) on red emperor (Lutjanus sebae). Barotrauma signs varied with capture depth, but not with the size of the fish. Fish from the greatest depths (40-52 m) exhibited extreme signs less frequently than did those from intermediate depths (30-40 m), possibly as a result of swim bladder gas being vented externally through a rupture in the body wall. All but two fish survived the experiment, and as neither release technique significantly improved short-term survival of the red emperor over non-treatment we see little benefit in promoting either venting or shotline releasing for this comparatively resilient species. Floating vertical enclosures can improve short-term post-release mortality estimates as they overcome many problems encountered when constraining fish in submerged cages.

Biology, Management and Genetic Stock Structure of Mangrove Jack, (Lutjanus argentimaculatus) in Australia.

This project has contributed to the ecologically sustainable management of mangrove jack in Australia by providing comprehensive information on its biology, habitat requirements, population parameters and stock structure. Specifically, the project has resulted in an enhanced understanding of the life history of Australian mangrove jack, the levels of exploitation in its local fishery and the likely existence of a single genetic stock throughout Queensland.

Physiological Factors Influencing Toughness in Cooked Saddletail Snapper (Lutjanus malabaricus)

Saddletail snapper (Lutjanus malabaricus) is a commercially significant tropical species in Australia and has been the subject of consumer complaints of extreme toughness in cooked fillets. Textural and biochemical analyses including collagen and hydroxylysyl pyridinoline (PYD) cross-links concentrations were conducted on 101 commercially harvested Saddletail snapper to identify causes of toughness. Fish age was found to account for 75.6% of observed variation in cooked muscle texture (work done) of Saddletail snapper. A significant linear relationship (P < 0.001) between PYD content and cooked muscle texture was also identified accounting for 50.3% of observed variation. The concentration ratio of PYD to total collagen (TC) ranged from 0.04 to 0.38 mol PYD per mol of TC. Fish size was also found to be a poor indicator of fish age and therefore a poor indicator of the potential risk of toughness of the cooked muscle.

A novel method for the age estimation of Saddletail snapper (Lutjanus malabaricus) using Fourier Transform-near infrared (FT-NIR) spectroscopy

Near infrared (NIR) spectroscopy was investigated as a potential rapid method of estimating fish age from whole otoliths of Saddletail snapper (Lutjanus malabaricus). Whole otoliths from 209 Saddletail snapper were extracted and the NIR spectral characteristics were acquired over a spectral range of 800–2780 nm. Partial least-squares models (PLS) were developed from the diffuse reflectance spectra and reference-validated age estimates (based on traditional sectioned otolith increments) to predict age for independent otolith samples. Predictive models developed for a specific season and geographical location performed poorly against a different season and geographical location. However, overall PLS regression statistics for predicting a combined population incorporating both geographic location and season variables were: coefficient of determination (R2) = 0.94, root mean square error of prediction (RMSEP) = 1.54 for age estimation, indicating that Saddletail age could be predicted within 1.5 increment counts. This level of accuracy suggests the method warrants further development for Saddletail snapper and may have potential for other fish species. A rapid method of fish age estimation could have the potential to reduce greatly both costs of time and materials in the assessment and management of commercial fisheries.

Improving Profitability to Industry Through the Identification and Management of 'tough' Fish Syndrome in Tropical Saddletail Snapper (Lutjanus Malabaricus)

OBJECTIVES: 1. To determine whether incomplete rigor mortis resolution and 'cold shock' play a role in development of tough fish syndrome (TFS) in tropical Saddletail snapper. 2. To identify links between TFS and specific physiological factors in tropical Saddletail snapper. 3. Communicate findings and recommendations to stakeholders and assist with implementation of any changes to fishing or handling practices required.

Investigation of movement and factors influencing post-release survival of line-caught coral reef fish using recreational tag-recapture data

Six species of line-caught coral reef fish (Plectropomus spp., Lethrinus miniatus, Lethrinus laticaudis, Lutjanus sebae, Lutjanus malabaricus and Lutjanus erythropterus) were tagged by members of the Australian National Sportsfishing Association (ANSA) in Queensland between 1986 and 2003. Of the 14,757 fish tagged, 1607 were recaptured and we analysed these data to describe movement and determine factors likely to impact release survival. All species were classified as residents since over 80% of recaptures for each species occurred within 1 km of the release site. Few individuals (range 0.8-5%) were recaptured more than 20 km from their release point. L. sebae had a higher recapture rate (19.9%) than the other species studied (range 2.1-11.7%). Venting swimbladder gases, regardless of whether or not fish appeared to be suffering from barotrauma, significantly enhanced (P < 0.05) the survival of L. sebae and L. malabaricus but had no significant effect (P > 0.05) on L. erythropterus. The condition of fish on release, subjectively assessed by anglers, was only a significant effect on recapture rate for L. sebae where fish in "fair" condition had less than half the recapture rate of those assessed as in "excellent" or "good" condition. The recapture rate of L. sebae and L. laticaudis was significantly (P < 0.05) affected by depth with recapture rate declining in depths exceeding 30 m. Overall, the results showed that depth of capture, release condition and treatment for barotrauma influenced recapture rate for some species but these effects were not consistent across all species studied. Recommendations were made to the ANSA tagging clubs to record additional information such as injury, hooking location and hook type to enable a more comprehensive future assessment of the factors influencing release survival.

Assessing the effects of line capture and barotrauma relief procedures on post-release survival of key tropical reef fish species in Australia using recreational tagging clubs.

Common coral trout, Plectropomus leopardus Lacepede, crimson snapper, Lutjanus erythropterus Bloch, saddletail snapper, Lutjanus malabaricus (Bloch & Schneider), red emperor, Lutjanus sebae (Cuvier), redthroat emperor, Lethrinus miniatus (Schneider) and grass emperor, Lethrinus laticaudis Alleyne & Macleay, were tagged to determine the effects of barotrauma relief procedures (weighted shot-line release and venting using a hollow needle) and other factors on survival. Release condition was the most significant factor affecting the subsequent recapture rate of all species. Capture depth was significant in all species apart from L. malabaricus and L. miniatus, the general trend being reduced recapture probability with increasing capture depth. Recapture rates of fish hooked in either the lip or mouth were generally significantly higher than for those hooked in the throat or gut. Statistically significant benefit from treating fish for barotrauma was found in only L. malabaricus, but the lack of any negative effects of treating fish indicated that the practices of venting and shot-lining should not be discouraged by fisheries managers for these species.

Fisheries resources of the Bohle River, Queensland.

The fisheries resources of the Bohle River and its small catchment area adjacent Townsville, north Queensland, were investigated through available literature, scientific research surveys and analysis of commercial and recreational catch and effort data. Research surveys produced a total of 4383 fish from the waters of the Bohle River during 1997-1998. These were classified into 104 fish species from 49 families. Gillnetting, cast netting, fish trapping and crab potting techniques were used in the estuarine waters of the Bohle River with freshwater reaches in the upper catchment surveyed by electrofishing. This range of survey techniques was used to estimate the relative abundance of ten commercially and recreationally important species: Barramundi (Lates calcarifer), king threadfin (Polydactylus macrochir), blue threadfin (Eleutheronema tetradactylum), mangrove jack (Lutjanus argentimaculatus), banded and spotted grunter (Pomadasys kaakan and Pomadasys argenteus), pikey and yellowfin bream (Acanthopagrus berda and Acanthopagrus australis), tilapia (Oreochromis spp.), jungle perch (Kuhlia rupestris) and mud crab (Scylla serrata). The results of each survey method are discussed with a focus on spatial and temporal patterns in diversity and catch rate.

Abundance indices for long-lived tropical snappers: estimating standardized catch rates from spatially and temporally coarse logbook data

The Northern Demersal Scalefish Fishery has historically comprised a small fleet (≤10 vessels year−1) operating over a relatively large area off the northwest coast of Australia. This multispecies fishery primarily harvests two species of snapper: goldband snapper, Pristipomoides multidens and red emperor, Lutjanus sebae. A key input to age-structured assessments of these stocks has been the annual time-series of the catch rate. We used an approach that combined Generalized Linear Models, spatio-temporal imputation, and computer-intensive methods to standardize the fishery catch rates and report uncertainty in the indices. These analyses, which represent one of the first attempts to standardize fish trap catch rates, were also augmented to gain additional insights into the effects of targeting, historical effort creep, and spatio-temporal resolution of catch and effort data on trap fishery dynamics. Results from monthly reported catches (i.e. 1993 on) were compared with those reported daily from more recently (i.e. 2008 on) enhanced catch and effort logbooks. Model effects of catches of one species on the catch rates of another became more conspicuous when the daily data were analysed and produced estimates with greater precision. The rate of putative effort creep estimated for standardized catch rates was much lower than estimated for nominal catch rates. These results therefore demonstrate how important additional insights into fishery and fish population dynamics can be elucidated from such “pre-assessment” analyses.

Characterization, development and multiplexing of microsatellite markers in three commercially exploited reef fish and their application for stock identification

Thirty-four microsatellite loci were isolated from three reef fish species; golden snapper Lutjanus johnii, blackspotted croaker Protonibea diacanthus and grass emperor Lethrinus laticaudis using a next generation sequencing approach. Both IonTorrent single reads and Illumina MiSeq paired-end reads were used, with the latter demonstrating a higher quality of reads than the IonTorrent. From the 1–1.5 million raw reads per species, we successfully obtained 10–13 polymorphic loci for each species, which satisfied stringent design criteria. We developed multiplex panels for the amplification of the golden snapper and the blackspotted croaker loci, as well as post-amplification pooling panels for the grass emperor loci. The microsatellites characterized in this work were tested across three locations of northern Australia. The microsatellites we developed can detect population differentiation across northern Australia and may be used for genetic structure studies and stock identification.