Status of inshore demersal scalefish stocks on the south coast of Western Australia. NRM Project 12034 Final Report

Inshore demersal scalefish in waters of 20-250 m depth in the South Coast Bioregion (SCB) are an important resource targeted by commercial, recreational and charter fishing sectors

Biology and stock status of inshore demersal scalefish indicator species in the Gascoyne Coast Bioregion

(114°50\u27E), includes the iconic Shark Bay and Ningaloo World Heritage areas plus the regional centre of Carnarvon and coastal towns of Denham, Coral Bay and Exmouth. The Gascoyne Bioregion is a transition zone between tropical and temperate waters and supports a diverse range of commercial invertebrate and scalefish fisheries and provides a large variety of recreational fishing opportunities. This report investigates the stock status of the inshore demersal scalefish “suite” of species for the Gascoyne region. These bottom dwelling fish are primarily taken by line fishing in waters of 20-250 m depth by both the commercial and recreational sectors

Longevity in Australian snapper Pagrus auratus (Sparidae)

In fisheries biology, longevity is one of the estimators of natural mortality, an essential parameter for age-based stock assessments. Increased fishing pressure progressively truncates older fish from the population, highlighting the importance of documenting observations of exceptionally old individuals. Snapper (Pagrus auratus) constitute important fisheries around the southern half of mainland Australia. A literature search and survey of government and semi government agencies responsible for managing snapper fisheries in 5 Australian states reveals the species is capable of living to at least 40 years throughout much of its range. The oldest recorded age, from near Bunbury, Western Australia, was recently estimated to be 40 years and 10 months

The status of the black bream Acanthopagrus butcheri (Pisces: Sparidae) population in Lake Clifton, south-western Australia

Lake Clifton hosts the largest living, non-marine thrombolite (microbialite) reef in the southern hemisphere. The thrombolite reef was recently listed as a critically endangered ecological community. The main threat to the ecology of the lake is increasing salinity, but other threats have also been identified, including the impact of the introduced fish Acanthopagrus butcheri (Munro, 1949). Samples opportunistically collected after a fish kill in 2007 indicated that A. butcheri in this lake experienced very low somatic growth and recruitment failure between 1995 and 2007, probably in response to hypersalinity. The evidence suggests that the A. butcheri population in Lake Clifton is effectively extinct. The proposed conservation strategy for Lake Clifton addresses a range of identified threats, including the eradication of A. butcheri. However, management action in response to this particular threat may no longer be required. The abundance of A. butcheri in the lake is probably very low and the population is likely to become extinct if current environmental trends continue. A dramatic reduction in growth rate after 1995 demonstrates the extraordinary growth plasticity of A. butcheri in response to environmental influences

Identifying the developmental stages of preserved eggs of snapper, Pagrus auratus, from Shark Bay, Western Australia

The characteristics used to identify 19 developmental stages of preserved eggs of snapper, Pagrus auratus, collected from Shark Bay, Western Australia, during annual plankton surveys, are described and illustrated. A key is provided to enable the age of each egg stage to be estimated based on sea surface temperature and salinity observed during sampling. This report is intended as a reference for inexperienced staff, to ensure that between-year comparisons of snapper spawning biomass, estimated using the daily egg production method, are based on consistent egg staging and ageing methods

A substantial recruitment year for the western yellowfin bream (Acanthopagrus latus, Sparidae) sustains years of high catch rates in the inner gulfs of Shark Bay, Western Australia

A large increase in the annual commercial catch and catch per unit effort of western yellowfin bream (Acanthopagrus latus) in the inner gulfs of Shark Bay, Western Australia, from 2002 to 2005 prompted an examination of the age structure of the 2005 catch. Sectioned otoliths from 108 fish were assessed to determine whether the cause was related to an increased abundance following a substantial recruitment. The 1999 age class was exceptionally strong, contributing 48.1% of the sample, and according to published growth rate estimates, this cohort would have recruited to the fishery at the same time catch rates began to increase. Year class strengths of older cohorts were consistent with catch sampling carried out in 1999 and 2000, together demonstrating highly variable interannual recruitment, a trait commonly reported for sparids. Neither Leeuwin Current strength nor rainfall was found to be associated with year class strength. Factors determining and possibly predicting year class strength in this species in Shark Bay remain unknown and require further research

Comparing fishery-independent measures of snapper (Pagrus auratus) abundance in inner Shark Bay; daily egg production method vs. mark-recapture

Snapper (Pagrus auratus) comprise about 50% of the catch landed by recreational boats in the inner gulfs of Shark Bay, Western Australia, and have been attracting large numbers of recreational fishers for many years, mostly during the winter tourist season when snapper are aggregated to spawn at predictable locations. Anecdotal information in the mid 1990s suggested recruitment overfishing in the Eastern Gulf, but no estimate of snapper abundance was available at that time. The daily egg production method (DEPM), where snapper eggs were collected in plankton surveys, has generated spawning biomass estimates annually since 1997. To confirm these estimates, a fishery-independent mark-recapture study was undertaken in 2004 (4,285 snapper tagged, 200+ recaptured), providing a biomass estimate (86 t, 95% ci 59 to 112) that was not significantly different to a comparable, concurrent DEPM estimate (38 t, 95% ci 22 to 73). The tagging study was assisted by about 70 volunteer fishers in 21 recreational vessels, who were trained in fish handling and tag application. Tagging generated an abundance estimate more quickly than the DEPM (one month v. six months, approx.), was relatively well received and understood by stakeholders, and helped foster a sense of custodianship of the resource and acceptance of management arrangements in the fishery. DEPM was less expensive, although tagging costs should decrease in future. The results help to develop a future research and management framework for inner Shark Bay snapper

Tagging studies reveal restricted movement of snapper (Pagrus auratus) within Shark Bay, supporting fine-scale fisheries management

The snapper (Pagrus auratus) fisheries of Shark Bay’s complex inner gulfs are managed on a fine spatial scale (tens of kilometres). Following the splitting of the Western Gulf into two management zones, results from an earlier 1980s tagging study were revisited to assess the suitability of management arrangements. Recaptures up to 15 years at liberty showed highly restricted movement, with 300 of 491 occurring within 5 nautical miles of the tagging site and only 3.3% crossing the new zone boundary. A simple stock-trajectory model simulating the two Western Gulf populations demonstrated a negligible impact from a 1% per annum level of mixing. The 1980s study was repeated between 1998 and 2003 by tagging 2558 snapper, mainly in areas previously under-represented. Recaptures up to 2 years at liberty again showed highly restricted movement, with 181 of 197 recaptures occurring at the tagging site. Juveniles were more sedentary than adults, the latter showing limited evidence of inter-annual spawning-site fidelity. Together, both studies support the use of three small management zones. Community acceptance of these complex arrangements was aided by collaborating with volunteers on research programs, which improved their understanding of the population structure

Population growth and mass mortality of an estuarine fish, Acanthopagrus butcheri, unlawfully introduced into an inland lake

1. In 2006, two periods of hypoxia resulted in the death of approximately 35 tonnes of black bream (Acanthopagrus butcheri) in Lake Indoon, a small inland lake in Western Australia. 2. Acanthopagrus butcheri was the first fish species to be recorded in this lake, along with the mosquitofish (Gambusia holbrooki) which was also observed during sampling in 2006. Acanthopagrus butcheri appears to have been introduced to Lake Indoon between 1998 and 2003 and formed a self-sustaining population. It is believed to have been deliberately introduced for the purpose of creating a recreational fishery, despite the existence of substantial penalties for illegal translocation of fish in Western Australia. 3. Recent human-induced environmental changes, including rising groundwater and salinization, have probably aided the establishment of both species in Lake Indoon. The importance of salinity to recruitment success by A. butcheri was indicated by the presence of only two age classes in 2006, with estimated recruitment dates coinciding with the years of highest recorded salinity in the lake. 4. The ‘fish kills’ provided an opportunity to examine aspects of A. butcheri biology in a relatively low salinity environment which is atypical for this estuarine species. In particular, the recruitment period in Lake Indoon was delayed until autumn/winter, rather than spring/summer as seen in other populations. Biological responses in Lake Indoon have implications for natural populations living in estuaries with modified salinity regimes. 5. The ecological, social and economic impacts potentially arising from the introduction of fish to Lake Indoon, which is an important migratory bird habitat and a recreational amenity for local residents and tourists, illustrate the complexities of fish translocation and the need for rigorous assessment before stocking to identify potential costs and benefits

Seabird bycatch in a sardine purse seine fishery

Limited understanding of seabird bycatch in purse seine fisheries has been highlighted as a key information gap in assessments of seabird bycatch in fisheries globally. This study documents the bycatch of breeding flesh-footed shearwaters (Ardenna carneipes) in a sardine purse seine fishery on the southern coast of Western Australia. Fishery-dependent bycatch records from 2009/2010 to 2017/2018 showed a strong peak in the mortality rate per fishing trip during March and April, closely associated with the final stage of chick rearing. Observers during those peak months in 2007, 2008, 2017, and 2018 recorded 171 mortalities during 222 trips at per trip rates (± 95% confidence limits) ranging from 0.59 (0.25–1.17) in 2017 to 1.10 (0.56–1.96) in 2007. Zero mortalities were recorded on at least 70% of trips in any year, suggesting infrequent formation of net folds that can trap birds. Total annual mortalities estimated for 2016/2017 and 2017/2018 were 123 (52–251) and 172 (91–302), respectively. Although within a sustainable anthropogenic limit of 495 (369–660) estimated from conservative application of the potential biological removal method, the extent of other anthropogenic mortalities is unknown. Further research on the effect of distance of breeding colonies from fishing operations is required