The energetic cost of protogynous versus protandrous sex change in the bi-directional sex-changing fish Gobiodon histrio

To investigate the relative cost of protogynous versus protandrous sex change we induced sex change in each direction in Gobiodon histrio (Gobiidae) and then compared growth, body condition and biochemical condition between sex-changed and non-sex-changed fish in treatment and control groups. Sex change in each direction was induced by establishing pairs of adult males and pairs of adult females on isolated coral colonies. Heterosexual pairs were used as controls. For both males and females, growth and body condition did not vary between fish that changed sex and those that did not. The relatively low cost of sex change, compared to the likely costs of searching for a mate of the correct sex, appears to explain the evolution of bi-directional sex change in coral-dwelling gobies. Lipid concentrations in the liver of males and females that changed sex were reduced by similar amounts (34% and 41%, respectively) compared to male and female controls that did not change sex. Therefore, changes in biochemical condition were approximately equal for fish that sex change in each direction and cannot explain the unequal frequency of sex change in each direction in natural populations of G. histrio

Otolith increment widths and lipid contents during starvation and recovery feeding in adult Ambassis vachelli (Richardson)

Adult Ambassis vachelli (Richardson) were used to test the effects of starvation and recovery feeding on otolith increment widths, Fulton's K and levels of carcass and viscera lipid. Three laboratory treatments (fed throughout the experiment; fed for 41 days then starved for 37 days, starved for 41 days then fed for 37 days), were compared. Fish were also collected from the field throughout the experiment to assess the natural fluctuations of variables examined in this study. Starvation and recovery induced significant changes in Fulton's K and lipid contents and were permanently recorded in the widths of otolith increments. Although changes in increment widths did occur in a predictable way, changes in increment widths due to starvation and recovery feeding were not of the same magnitude as changes in lipid levels. Thus, the widths of otolith increments may be determined by feeding regime, but increment widths vary in a more conservative fashion than do lipid levels. Increment widths in field fish showed similar variations compared to fish in the laboratory. Condition and lipid levels, as well as results from a canonical discriminant analysis, indicated that field fish were exposed to intermediate feeding environments, compared to the fed and starved regimes in the laboratory

Effects of feeding history on the growth characteristics of a reef fish at settlement

A feeding experiment was conducted on the pelagic stages of the tropical goatfish Upeneus tragula (family Mullidae) to examine how food quantity affects growth characteristics and potential success at settlement. Pelagic goatfish were collected from aggregation rafts 3 nautical miles west of Lizard Island on the northern Great Barrier Reef during December 1990. Three tanks in each of four feeding regimes were stocked with 25 pelagic goatfish between 20 and 23 mm standard length (SL). The four feeding regimes were: fed ad lib. (fed): fed once per day (f1pd); starved every second day (stld); starved for 3 d and re-fed (st3d). Fishes were fed 36 to 48 h old Artemia sp. nauplii (Ocean Star strain). Fish were removed from tanks when they underwent metamorphosis, changed pigmentation and settled to the bottom of the tanks. Morphology, muscle development, time taken to settle and biochemical condition were examined. Growth attributes of the treated fish were compared to fish which settled within 24 h of capture (field). All attributes examined were significantly influenced by the feeding treatments. Fish within the fed and st3d treatments were significantly larger and heavier than fish in the less well-fed treatments (f1pd, st1d). Similarly, concentrations of total lipid, carbohydrate and protein in the settled fish were significantly higher in the fed and st3d treatments compared with the st1d and f1pd treatments. For all these morphological and biochemical attributes the st1d and f1pd fish did not significantly differ from the field fishes, but did differ from the fed and st3d fishes. Water content was significantly higher in the f1pd, st1d and field fishes compared with the fed and st3d fish. Furthermore, the average time taken to settle followed the pattern: fed (14d)<st3d (16d)<st1d (22d)<f1pd (24d). Muscle development mirrored the patterns in fish length between treatments, being more developed in the fed treatment and least well developed in the st1d treatment. Feeding rate differed significantly between treatments and changed through the experiment for all but the fed treatment. Feeding rate decreased slightly for the f1pd and st1d treatments over the experimental period, but increased rapidly for the st3d treatment. The experiment suggests that U. tragula are physiologically well suited to exploiting a patchy food source, and that food availability within the pelagic stages can have a major influence on the growth characteristics of this reef fish at settlement. The ramifications of this finding are discussed in relation to survival and success once fish have recruited to the reef population

Spawning migrations and local movements of a tropical sparid fish

Between June 1994 and September 1996, a mark–recapture study was conducted in the Hinchinbrook Channel area of tropical northeastern Australia to investigate the movements of the sparid fish Acanthopagrus berda. A total of 962 A. berda were tagged, 922 within a single estuary system, Deluge Inlet. No movements among estuaries were detected. Of the fish tagged in Deluge Inlet, 12.9% were recaptured. Two movement regimes were detected: local movements (mostly <500 m) during non-spawning times, and longer migrations (up to 3.12 km) during spawning seasons, to and from a spawning site at the estuary mouth. Although there appeared to be a major spawning aggregation in the mouth of Deluge Inlet, ripe female A. berda were present in upstream sites, indicating that spawning probably occurs there also. This contrasts to the situation in South Africa, where A. berda is reported to spawn only close to estuary mouths. Differences such as this highlight our limited knowledge of variations in the reproductive biology of widespread species such as A. berda

Temporal population dynamics of the swarming shrimp, Acetes sibogae australis, in a tropical near-shore system

Acetes sibogae australis, a small swarming crustacean, is an important component of near-shore systems in eastern Australia. It is considered that densities of A. s. australis are highly variable. However, this variability has never been tested on a fine temporal scale. In this study, densities of A. s. australis within swarms, as well as swarm length and width, were recorded once a week for seven months at one locality in Townsville, Australia, and once a fortnight for seven months at two other localities in the region. Length frequency of a sub-sample of individuals caught at each sample time was also recorded. Density of A. s. australis fluctuated significantly during the seven months, with numbers per replicate varying between 0 and 1000 individuals. Swarm width and length were significantly correlated with density, contributing to large-scale differences in overall abundance. Length frequencies revealed at least three dominant cohorts present during the seven months, although appearance and disappearance of these did not correspond to density changes. Patterns recorded were similar at the three spatially separate localities. The large fluctuations in A. s. australis abundance over time are likely to have important effects on the near-shore system of Townsville

Age-based demography and reproduction of hapuku, Polyprion oxygeneios, from the south coast of Western Australia: implications for management

The hapuku, Polyprion oxygeneios, inhabits deep (>100 m) continental slope waters of Western Australia. In all, 1352 P. oxygeneios were collected from the waters along the south coast of Western Australia (ca. 35°S) from 2004 to 2008. The species is gonochoristic, and spawns during the austral winter (May-September). Ages were estimated from counts of opaque zones from thin-sectioned sagittal otoliths. Classification analysis of the outer margin of sectioned otoliths indicated that a single opaque zone is deposited annually. Female P. oxygeneios (n = 630; 535-1114 mm total length, TL) ranged in age from 2 to 35 years and males (n = 691; 521-1004 mm TL) from 2 to 52 years. von Bertalanffy growth models for male and female P. oxygeneios were statistically, but not biologically, different (<5 difference in mean and estimated lengths-at-age). Estimates of the lengths and ages at which 50% of the females and males in the population reached sexual maturity were 760 and 702 mm TL and 7.1 and 6.8 years. The instantaneous rate of natural mortality (M) was estimated to be 0.09. Estimates of the instantaneous rate of fishing mortality (F) were low (0.01-0.05). Harvest rates in 2005 and 2006 were close to estimated sustainable levels. Monitoring of any future increases in catch and effort in continental slope waters in both State- and Commonwealth-managed fisheries is required in order to assess impacts to stock sustainability. Sustainable management would also benefit from improved understanding of possible pan-oceanic recruitment of the species among southern hemisphere populations

Status of demersal finfish stocks on the west coast of Australia

Assessments of the key indicator species for the West Coast Demersal Scalefish Resource (WCDSR; West Australian dhufish Glaucosoma hebraicum, Snapper Pagrus auratus and Baldchin groper Choerodon rubescens) in 2007 and 2009 demonstrated that the stocks were experiencing overfishing. Thus, between late 2007 and early 2010, substantial changes were made to the management of the commercial and recreational fisheries that exploit the WCDSR. These were designed to reduce catches of the entire suite of demersal scalefish species (and of each indicator species) by both the commercial and recreational sectors in the West Coast Bioregion (WCB) by at least 50 % of the 2005/06 levels (the catch benchmark), to allow stocks to recover. The current (third) stock assessment of indicator species for the demersal scalefish suite was based on age data collected between 2008/09-2010/11 for G. hebraicum and P. auratus and 2007/08-2010/11 for C. rubescens and on catch statistics for the commercial and recreational fishing sectors (including charter fishing) from 2008-2012. The assessment compared estimates of fishing mortality (F) for the most recent period with several previous time periods and against internationally accepted biological reference points to determine whether there was evidence of any stock recovery. The sampling period for this assessment included the period when major changes were being made to management in the WCB of commercial and recreational/charter fishing for demersal species. As each of the indicator species is relatively long-lived, it is expected that it will take at least 10 years from these management changes before their stocks show strong signs of recovery, and that it may take substantially longer before they fully recover (~15-20 years). Catches of the demersal suite of species in the WCB by the commercial sector and of the top 15 species taken by the recreational sector have been reduced to less than the catch benchmark. Although catches of all indicator species have been reduced, those of two indicator species, P. auratus and C. rubescens, have not been reduced below the catch benchmark by all sectors

Case 3267: Cherax tenuimanus Smith, 1912 and Cherax cainii Austin in Austin & Ryan, 2002 (Crustacea, Decapoda, PARASTACIDAE) proposed conservation of usage of the specific names

The purpose of this application, under Article 75.6 of the Code, is to conserve the specific name Cherax tenuimanus Smith, 1912 in its accustomed usage, for a species of freshwater crayfish or ‘marron’, important in the aquaculture industry, particularly in Australia. It has long been recognised that there are two subspecies of C. tenuimanus; in 2002 Austin elevated these to species level and proposed the name Cherax cainii for one. Based on the supposed location of Smith’s (1912) type series of C. tenuimanus, Austin applied the name C. tenuimanus to geographically isolated marron found only in a small catchment in Western Australia, and applied his new name C. cainii to all other marron in Australia and elsewhere. This switching of names is causing confusion since almost all usage of the name C. tenuimanus refers to marron occurring outside the area of Smith’s type series. It is proposed that all previous type fixations for the names Cherax tenuimanus Smith, 1912 and Cherax cainii Austin in Austin & Ryan, 2002 be set aside and neotypes designated for both species to maintain the accustomed usage of the name Cherax tenuimanus

The need for a broad perspective concerning fisheries interactions and bycatch of marine mammals

Fisheries bycatch is a worldwide issue. In many developed nations, including Australia, major research, development, management and fishery innovations have significantly reduced bycatch rates, interactions, and mortalities, and have reduced the risks and impacts imposed by fisheries. There is negligible risk to the sustainability of bycatch species from fisheries in many cases. However, societal perceptions of bycatch of marine mammals are such that the bycatch or mortality of a single individual can threaten the ongoing operations of an otherwise sustainable fishery. Developed nations now find themselves at a crossroads, whereby there is an ever-increasing demand for seafood while their fisheries and catches are more regulated and declining. This can result in either (1) the importing of more seafood from countries with little or no bycatch monitoring or mitigation plans and thus effectively exporting any bycatch issues; or (2) increasing production in other industries such as agriculture resulting in other environmental impacts and risks. Using Western Australia fishery examples, the paper identifies the need for a wider dissemination of information on the risks of fishing on marine mammal sustainability. Separating sustainability risks from social acceptability, collecting and collating all relevant information including the development of robust observer programs, and exploring costs and benefits of all options may provide a framework for informed public debate around managing marine mammal–fishery interactions

Independent observations of catches and subsurface mitigation efficiencies of modified trawl nets for endangered, threatened and protected megafauna bycatch in the Pilbara Fish Trawl Fishery

Mitigation of endangered, threatened and protected (ETP) species is a challenge in many commercial fisheries globally and independent observer programs are often implemented to determine accurate estimates of interaction rates. However, interactions with ETP species may be extremely rare requiring very high and therefore costly levels of observer coverage to provide adequate statistical rigor for such programs. The Pilbara Fish Trawl (Interim Managed) Fishery (PFTF) has a long history of developing and adopting mitigation measures that have resulted in very low capture rates of ETP megafauna, i.e. dolphins, turtles, sea snakes and sawfish. However, there has been uncertainty over the potential for unaccounted mortality of ETP megafauna from subsurface expulsion in poor condition through escape hatches in the PFTF trawl nets (particularly air breathing species). To examine this issue, all trawl vessels in the PFTF (n = 3) were fitted with dual-lens above water and subsurface within-net camera systems from June to December 2012. Above water cameras recorded continuously (except during malfunctions) and all video files were stored in read only folders and encrypted with passwords to prevent tampering. At the end of each trip these secure folders containing the video files were transferred onto external hard drives by Department of Fisheries staff for later analysis. The observer coverage rates of 85.2% of trawl catches above water (n = 1,916 trawls observed), and 71.7% of day-trawls (n = 774 trawls observed) and 53.9% of day-trawl hours (n = 1,013 h observed) below water, far exceeded that stipulated in the Bycatch Action Plan (22%) and levels achieved from previous studies from the PFTF. Captures of ETP megafauna were rare, despite very high levels of attendance in and around trawl nets by bottlenose dolphins (> 75% of trawls). All observed catches of ETP species were reported in statutory logbooks and these catches were consistent with previous data since exclusion grids were mandated in March 2006. Therefore, there was no evidence to suggest that captures of ETP species were being unreported by commercial fishers. About two thirds of all megafauna, including chondrichthyans, were expelled from escape hatches during trawling, with the majority of megafauna expelled relatively quickly (< 10 min). This resulted in more than half of the trawl catches containing no megafauna (51.4%). A total of 705 megafauna individuals were observed to exit the nets through an escape hatch during trawling. Of these megafauna, only one bottlenose dolphin was observed to exit these trawls in poor condition. A large turtle was observed to persist in a trawl for an extended period (60.1 min). However, despite its condition being inconclusive upon exiting, its duration in the net was well within the breath holding capabilities for marine turtles. Thus, the subsurface expulsion of megafauna in poor condition was extremely rare. No megafauna were observed to exit through the top opening escape slit. However, an upward excluding grid with a top opening escape hatch resulted in a higher proportion of escapement for most chondrichthyans. The loss of targeted scalefish through escape hatches occurred during less than 3% of trawls. Extensive subsurface observations determined that current mitigation strategies are highly effective for sea snakes, turtles and chondrichthyans (except sawfish), and that further investigation in the forward sections of trawl nets may provide useful information to improve mitigation strategies for dolphins and sawfish. The very low rates of mortalities of these ETP megafauna by the PFTF were considered to pose a negligible risk to their sustainability based on 1) these rates likely to be less than their natural mortality rates (e.g. at least 371 bottlenose dolphins stranded from 1981-2010), 2) they appear abundant in Western Australian waters despite large scale mortalities from historic foreign fishing (e.g. 13,459 cetacean mortalities from Taiwanese fishing from 1981-86), and 3) they have wide distributions and are highly mobile