Bycatch and strandings programs as ecological indicators for data-limited cetaceans

An integrated approach of using strandings and bycatch data may provide an indicator of long-term trends for data-limited cetaceans. Strandings programs can give a faithful representation of the species composition of cetacean assemblages, while standardised bycatch rates can provide a measure of relative abundance. Comparing the two datasets may also facilitate managing impacts by understanding which species, sex or sizes are the most vulnerable to interactions with fisheries gear. Here we apply this approach to two long-term datasets in East Australia, bycatch in the Queensland Shark Control Program QSCP, 1992–2012) and strandings in the Queensland Marine Wildlife Strandings and Mortality Program StrandNet, 1996–2012). Short-beaked common dolphins, Delphinus delphis, were markedly more frequent in bycatch than in the strandings dataset, suggesting that they are more prone to being incidentally caught than other cetacean species in the region. The reverse was true for humpback whales, Megaptera novaeangliae, bottlenose dolphins, Tursiops spp.; and species predominantly found in offshore waters. QSCP bycatch was strongly skewed towards females for short-beaked common dolphins, and towards smaller sizes for Australian humpback dolphins, Sousa sahulensis. Overall, both datasets demonstrated similar seasonality and a similar long-term increase from 1996 until 2008. Analysis on a species-by-species basis was then used to explore potential explanations for long-term trends, which ranged from a recovering stock (humpback whales) to a shift in habitat use (short-beaked common dolphins)

Ghost fishing in the pot fishery for blue swimmer crabs Portunus pelagicus in Queensland, Australia

Blue swimmer crabs (Portunus pelagicus) are an economically important crab caught in baited traps throughout the Indo-west Pacific and Mediterranean. In Australia they are traditionally caught using rigid wire traps (approximate to pots) but there has been a recent increase in the use of collapsible pots constructed from polyethylene trawl mesh. Two experiments were conducted in Moreton Bay, Queensland, to determine the ghost fishing potential of lost crab pots on both target and bycatch species and to evaluate the differences between traditional and contemporary pot designs. A lost contemporary, collapsible trawl mesh pot will catch between 3 and 223 R pelagicus per year after the bait has been exhausted, while a traditional wire mesh pot would catch 11-74 crabs peryear. As most fishers now use the collapsible trawl mesh pots, ghost fishing mortality could be as high as 111,811-670,866 crabs per year. Bycatch retention was also higher in contemporary designs. Periods of strong winds appeared to increase the ghost fishing potential of lost pots. The use of escape gaps, larger mesh sizes and construction options that allow for the deterioration of entrance funnels to minimise ghost fishing are recommended to reduce environmental impacts

Surviving the effects of barotrauma: assessing treatment options and a ‘natural’ remedy to enhance the release survival of line caught pink snapper (Pagrus auratus)

A new technique to ameliorate the effects of barotrauma was tested based on observations of pink snapper, Pagrus auratus (Forster), inadvertently piercing their everted stomach with their teeth and releasing trapped swim bladder gases. This technique was termed buccal venting and involved piercing the everted stomach protruding into the buccal cavity or out of the mouth with a 16-gauge hypodermic needle (a practice previously not encouraged). Short-term (~3 days) survival of buccal-vented fish was not significantly different from laterally vented fish nor untreated controls. Both buccal and lateral venting techniques were shown to cause no harm and allowed fish to return to depth. The short-term (1–3 days) post-release survival of line caught snapper was 88% with no significant difference in survival across three depth ranges tested (37–50, 51–100 and 101–180 m). Survival of sublegal pink snapper ( 0.05) from that of legal-sized fish (≥35 cm TL). Healing of the swim bladder was observed in 27% of pink snapper dissected after ≤3 days in captivity, and healing of stomachs was observed in 64% of pink snapper that had been buccal vented. Relatively high post-release survival rates of line caught pink snapper may offer some protection for snapper stocks where high fishing pressure and legal size restrictions result in the majority of the catch having to be released

Short-term survival of discarded pearl perch (Glaucosoma scapulare Ramsay, 1881) caught by hook-and-line in Queensland, Australia

Post-release survival of line-caught pearl perch (Glaucosoma scapulare) was assessed via field experiments where fish were angled using methods similar to those used by commercial, recreational and charter fishers. One hundred and eighty-three individuals were caught during four experiments, of which >91% survived up to three days post-capture. Hook location was found to be the best predictor of survival, with the survival of throat- or stomach-hooked pearl perch significantly (P < 0.05) lower than those hooked in either the mouth or lip. Post-release survival was similar for both legal (≥35 cm) and sub-legal (<35 cm) pearl perch, while those individuals showing no signs of barotrauma were more likely to survive in the short term. Examination of the swim bladders in the laboratory, combined with observations in the field, revealed that swim bladders rupture during ascent from depth allowing swim bladder gases to escape into the gut cavity. As angled fish approach the surface, the alimentary tract ruptures near the anus allowing swim bladder gases to escape the gut cavity. As a result, very few pearl perch exhibit barotrauma symptoms and no barotrauma mitigation strategies were recommended. The results of this study show that pearl perch are relatively resilient to catch-and-release suggesting that post-release mortality would not contribute significantly to total fishing mortality. We recommend the use of circle hooks, fished actively on tight lines, combined with minimal handling in order to maximise the post-release survival of pearl perch

Assessment of genetic structure among Australian east coast populations of snapper Chrysophrys auratus (Sparidae)

Snapper Chrysophrys auratus is a high-value food fish in Australia targeted by both commercial and recreational fisheries. Along the east coast of Australia, fisheries are managed under four state jurisdictions (Queensland, Qld; New South Wales, NSW; Victoria, Vic.; and Tasmania, Tas.), each applying different regulations, although it is thought that the fisheries target the same biological stock. An allozyme-based study in the mid-1990s identified a weak genetic disjunction north of Sydney (NSW) questioning the single-stock hypothesis. This study, focused on east-coast C. auratus, used nine microsatellite markers to assess the validity of the allozyme break and investigated whether genetic structure exists further south. Nine locations were sampled spanning four states and over 2000 km, including sites north and south of the proposed allozyme disjunction. Analyses confirmed the presence of two distinct biological stocks along the east coast, with a region of genetic overlap around Eden in southern NSW, ~400 km south of the allozyme disjunction. The findings indicate that C. auratus off Vic. and Tas. are distinct from those in Qld and NSW. For the purpose of stock assessment and management, the results indicate that Qld and NSW fisheries are targeting a single biological stock.

Stock assessment of Australian east coast snapper, Chrysophrys auratus Predictions of stock status and reference points for 2016

Snapper, Chrysophrys auratus, is a valuable commercial, recreational and charter fish species throughout its temperate/subtropical range along Australia’s east coast. East coast snapper form a single genetic stock in ocean waters between Mackay (21.50S) in northern Queensland and about Eden (380S) in southern New South Wales. Fish in this eastern coast stock have been recorded to live for up to 41 years, with maturity occurring at four years of age. This is the first assessment for the whole east coast stock. This comprehensive snapper stock assessment includes commercial, recreational and charter data sets from both New South Wales and Queensland (up to 2016). The assessment grouped the dynamics of the fishery into four fishing sectors: namely, 1) New South Wales commercial trap fishing, 2) New South Wales commercial and charter line, 3) Queensland commercial and charter line and 4) New South Wales and Queensland recreational. Changes in management arrangements through time were incorporated

Assessment of genetic structure among Australian east coast populations of snapper Chrysophrys auratus (Sparidae)

Snapper Chrysophrys auratus is a high-value food fish in Australia targeted by both commercial and recreational fisheries. Along the east coast of Australia, fisheries are managed under four state jurisdictions (Queensland, Qld; New South Wales, NSW; Victoria, Vic.; and Tasmania, Tas.), each applying different regulations, although it is thought that the fisheries target the same biological stock. An allozyme-based study in the mid-1990s identified a weak genetic disjunction north of Sydney (NSW) questioning the single-stock hypothesis. This study, focused on east-coast C. auratus, used nine microsatellite markers to assess the validity of the allozyme break and investigated whether genetic structure exists further south. Nine locations were sampled spanning four states and over 2000 km, including sites north and south of the proposed allozyme disjunction. Analyses confirmed the presence of two distinct biological stocks along the east coast, with a region of genetic overlap around Eden in southern NSW, ~400 km south of the allozyme disjunction. The findings indicate that C. auratus off Vic. and Tas. are distinct from those in Qld and NSW. For the purpose of stock assessment and management, the results indicate that Qld and NSW fisheries are targeting a single biological stock.

Assessment of the blue swimmer crab (Portunus armatus) fishery in Queensland

The blue swimmer crab (BSC) fishery in Queensland has undergone considerable change since its development in the middle of the 20th century. In the last 30 years the fishery has progressed to being fully fished with the expansion of crab-pot fisheries to areas outside of Moreton Bay. After the implementation of the Fisheries (East Coast Trawl) Management Plan 1999, the reported harvest from the trawl sector decreased significantly, with the commercial and recreational crab-pot sectors now accounting for the majority of the reported blue swimmer crab harvest. The commercial pot fisheries outside Moreton Bay also developed rapidly in the late 1990s. Concerns have been raised by a number of crab-pot fishers about poor economic viability under current management rules and reduced catch rates from a number of Moreton and Hervey Bay areas. This research and publication was requested by fisheries management to assess reasons for declining catch rates and profits, including evidence associated with overfishing, crab reproduction and disease, and flood events. The analyses undertaken during the current study suggested that the blue swimmer crab population was not overfished to the point where the spawning biomass was significantly reduced. However, the current levels of population size of male legal crab and fishing effort were not suitable to produce acceptable levels of catch rates for economic profit or angling quality. Analysis of the reproductive characters of the blue swimmer crab from fished areas of Moreton Bay has shown no significant changes in key indicators since research was conducted in the mid 1980’s. Similarly, the levels of fertilization of immediate post-moult female crabs have remained unchanged in the past 30 years. There was no evidence of declines in fertilization rate as all females assessed had >90% of eggs successfully developing. There was evidence to suggest a decline in the size of females, despite the fact that females are not legally fished. The levels of parasitism and disease were found to be low and have not changed significantly in the last 30 years. Levels of parasitism by Sacculina granifera have declined. Environmental factors have been shown to influence blue swimmer crab fisheries in both Cockburn Sound and Shark Bay in Western Australia, but we found no conclusive evidence to support similar effects in Queensland. Declining catch rates appear to be related to overly competitive fishing, resulting in a smaller population size of male legal crab. Increases in the number of pots used by fishers in all regions is likely a result of escalating costs of fishing, particularly fuel, impacting on profits due to declining beach price relative to inflation. To cure this state, the data and analyses indicate that effort reduction is required in order to significantly improve catch rates and generate economic profits. A range of maximum economic yields were calculated for the Moreton and Hervey Bay regions, so that a meaningful upper limit on license numbers and total allowable fishing effort can be evaluated. Effort reductions of 50% to 70% may be required in order to maximise vessel based profit. The evaluation of raising the minimum legal size (MLS) in order to reduce fishing pressure indicates that this would have a negative impact on fishery economics