Charles A. Gray

User-level device drivers: Achieved performance

Running device drivers as unprivileged user-level code, encapsulated into their own process, has often been proposed as a technique for increasing system robustness. However, in the past, systems based on user-level drivers have generally exhibited poor I/O performance. Consequently, user-level device drivers have never caught on to any significant degree. In this paper we demonstrate that it is possible to build systems which employ user-level device drivers, without significant performance degradation, even for high-bandwidth devices such as Gigabit Ethernet.

Horizontal and vertical trends in the distributions of larval fishes in coastal waters off central New South Wales, Australia

Larval fishes were sampled across six transects perpendicular to a 50 km section of the coast off Sydney, Australia, in April/May and August/September 1990. Samples were collected at the surface and at depth (20 to 30 m) at three locations across each transect; over the 30, 70 and 100 m depth contours. There was a large level of heterogeneity in the horizontal and vertical distributions of most taxa examined, and no general pattern of distribution was evident for the whole assemblage. Classification analyses revealed that the major differences between assemblages were related to depth. Horizontal trends in the distributions of the abundant taxa were evident in the inshore-offshore direction, but not longshore. Seven taxa belonging to the families Gobiidae, Labridae, Sillaginidae, Sparidae, Ambassidae, Clupeidae and Clinidae/Tripterygiidae were most abundant inshore, whereas 4 taxa of the families Cepolidae, Percichthyidae, Cheilodactylidae and Gonorynchidae were generally more abundant offshore and 24 taxa showed no discrete horizontal trends across transects. More taxa and individuals were generally caught at depth than at the surface and this was evident across all transects. Twenty taxa were more numerous at depth, whereas 4 taxa, the Cheilodactylidae, Gonorynchidae, Mullidae and Scorpididae, were most abundant at the surface and 11 taxa showed no difference in densities between depths. Ontogenetic differences in the distributions of some larvae were evident. The mean size of larval Liza argentea (Mulgilidae) caught was greater offshore than inshore, and greater at the surface than at depth. In contrast, larger Pseudocaranx dentex (Carangidae) occurred in greater numbers at depth than at the surface. The data emphasise that the assemblages of larval fishes in coastal waters off central New South Wales cannot be modelled as a single unit, which concurs with the findings in other temperate and tropical vaters. Furthermore, the data denote the need to spatially stratify sampling in these waters in order to assess seasonal changes in these assemblages.

Rain reverses diel activity rhythms in an estuarine teleost

Activity rhythms are ubiquitous in nature, and generally synchronized with the day–night cycle. Several taxa have been shown to switch between nocturnal and diurnal activity in response to environmental variability, and these relatively uncommon switches provide a basis for greater understanding of the mechanisms and adaptive significance of circadian (approx. 24 h) rhythms. Plasticity of activity rhythms has been identified in association with a variety of factors, from changes in predation pressure to an altered nutritional or social status. Here, we report a switch in activity rhythm that is associated with rainfall. Outside periods of rain, the estuarine-associated teleost Acanthopagrus australis was most active and in shallower depths during the day, but this activity and depth pattern was reversed in the days following rain, with diurnality restored as estuarine conductivity and turbidity levels returned to pre-rain levels. Although representing the first example of a rain-induced reversal of activity rhythm in an aquatic animal of which we are aware, our results are consistent with established models on the trade-offs between predation risk and foraging efficiency.

Marine genetic swamping: hybrids replace an obligately estuarine fish.

Populations of obligately estuarine taxa are potentially small and isolated and may lack genetic variation and display regional differentiation as a result of drift and inbreeding. Hybridization with a wide‐ranging marine congener should introduce genetic variation and reduce the effects of inbreeding depression and genetic drift. However, high levels of hybridization can cause demographic and genetic swamping. In southeastern Australia hybridization occurs between obligately estuarine Black bream (Acanthopagrus butcheri) and migratory marine Yellowfin bream (Acanthopagrus australis). Here, we surveyed genetic variation at eight microsatellite loci and the mitochondrial control region of juvenile fish from five coastal lagoons (including temporal replication in two lagoons) (total n = 970) to determine the frequency and persistence of hybridization, and its likely consequence for the estuarine restricted A. butcheri. Of 688 juvenile fish genotyped 95% were either A. australis (347) or hybrids (309); only 5% (32) were A. butcheri. Most hybrids were later generation hybrids or A. butcheri backcrosses, which are likely multi‐generational residents within lagoons. Far greater proportions of hybrid juveniles were found within two lagoons that are generally closed to the ocean (>90% hybrid fish within generally closed lagoons vs. 12–27% in permanently or intermittently open lagoons). In both lagoons, this was consistent across multiple cohorts of fish [79–97% hybrid fish (n = 282)]. Hybridization and introgression represent a major threat to the persistence of A. butcheri and have yet to be investigated for large numbers of estuarine taxa.

Evolutionary impacts of hybridization and interspecific gene flow on an obligately estuarine fish

For free‐spawning estuarine taxa, gene flow among estuaries may occur via hybridization with mobile congeners. This phenomenon has rarely been investigated, but is probably susceptible to anthropogenic disturbance. In eastern Australia, the estuarine Black Bream Acanthopagrus butcheri and marine Yellowfin Bream Acanthopagrus australis have overlapping distributions and the potential to hybridize. We used surveys of microsatellite and mtDNA variation in 565 adults from 25 estuaries spanning their distributional range to characterize the species and their putative hybrids. Hybrids were widespread (68% of estuaries) and hybrid frequencies varied greatly among estuaries (0–58%). Most (88%) were classed as advanced generation backcrosses with A. butcheri and displayed A. butcheri mtDNA haplotypes. We found most hybrids in the three estuaries within the zone of sympatry (57%). Our study highlights the underemphasized importance of estuaries as sites of hybridization and suggests that hybridization is driven both by opportunity for contact and human activity.

Optimal positioning and design of behavioural-type by-catch reduction devices involving square-mesh panels in penaeid prawn-trawl codends

Two experiments were done in the oceanic penaeid prawn-trawl fishery in New South Wales to investigate (i) the optimal positioning of behavioural-type by-catch reduction devices (BRDs) involving square-mesh panels; and (ii) the relative performances of two industry-developed square-mesh panels against a composite square-mesh panel developed by scientists. In the first experiment, three codends, each containing one square-mesh panel (located on the tops of the codend at distances of 0.7, 1.2 and 1.6 m anterior to the last row of meshes respectively) significantly reduced the catches of some small fish and total discards compared with a control codend that held no BRD. Rates of reduction significantly increased with proximity of the square-mesh panel to the end of the codend. There was, however, a significant reduction in catches of prawns from the codend containing the square-mesh panel at 0.7 m. Based on these results, the optimal position for these sorts of BRDs was determined to be at 1.2 m anterior to the last row of meshes. In the second experiment, at this position, two codends containing industry-developed plastic and metal square-mesh panels were less effective in excluding by-catch than a codend containing the composite square-mesh panel. The results are discussed in terms of species-specific differences in behavioural responses and swimming ability and the future development and testing of behavioural-type BRDs in penaeid prawn trawls.

Influence of Pollutants and Oceanography on Abundance and Deformities of Wild Fish Larvae

Publisher Summary This chapter reviews the oceanographic features that can concentrate fish larvae and pollutants and lead to exposure regimes of greater concentration and longer duration than expected based on simple diffusion models. Pollutants can lead to decreased viability of larvae, resulting from morphological deformities. Field studies provide a powerful way to study the interaction between oceanographic processes and biological effects. Pollutants diffuse from point sources and do not consider accumulation of pollutants in oceanographic features such as fronts. Fish eggs, larvae, and prey are an order of magnitude higher in linear oceanographic features (LOFs) and other features such as thermoclines where pollutants also accumulate. Plumes affect larvae spawned near to and at great distances from outfalls due to long-shore currents. Reversing currents and multiple plumes result in multiple exposures to pollutants, thus, increasing the chances of deleterious effects to larvae. On scales < 10 km it is possible with current reversal that larvae affected by pollutants may be found at considerable distances from point sources of pollution.

Utility of morphological data for key fish species in southeastern Australian beach‐seine and otter‐trawl fisheries: Predicting mesh size and configuration

Abstract Samples of 16 key fish species targeted by oceanic prawn trawlers and oceanic and estuarine beach seiners in southeastern Australia were measured for up to 10 morphological dimensions that included: total (Wt) and eviscerated weights (EWt); total (TL), fork (FL), natural (NL), standard (SL), dorsal standard (DSL), and anal standard lengths (ASL); and maximum body height (MH), width (MW), and girth (MG). All partial lengths were indexed against TL to provide linear relationships and, where there were sufficient data, tested for intra‐specific sexual dimorphism. Nearly all species that were sexed demonstrated at least some morphological divergence, and especially for transverse measures; probably owing to different reproductive conditions. Sex‐specific or combined regressions of DSL and ASL and transverse measures versus TL were used to identify the most appropriate: (1) partial length for compliance purposes; and (2) mesh sizes and configurations for the different fishing gears used. Using relevant data describing the smallest commercial‐sized fish species (stout, Sillago robusta and red spot whiting, S. flindersii— 150mm TL) retained in prawn trawls, a new square‐mesh codend (made from 35‐mm mesh hung on the bar) was designed and constructed. The selectivities of this square‐mesh codend and a conventional diamond‐mesh design (40‐mm mesh) were then modelled and compared in a case study. The conventional codend was demonstrated to be non‐selective for the sizes of eastern king prawns and red spot whiting targeted. In contrast, the square‐mesh codend selected red spot whiting across narrow selection ranges (18.88–15.67 mm) and at lengths of 50% retention (143.39–146.32mm TL) that closely corresponded to the estimated maximum mesh opening. The square‐mesh codend also improved selection for eastern king prawns, without impacting on commercial catches. Based on these results, similar predictions were made for appropriate mesh sizes and configurations in oceanic and estuarine beach seines; both of which were demonstrated to comprise minimum mesh sizes that would be non‐selective for the sizes of all targeted fish.

Strategies for Improving the Selectivity of Fishing Gears

Few fishing methods and gears are entirely selective for the targeted species and their sizes. The majority of gears have incidental catches (collectively termed ‘bycatch’) that vary from isolated occurrences in some hook-and-line fisheries to large numbers of juveniles of key species in trawl fisheries. Of primary concern is the contribution that the mortalities of such bycatches may have on subsequent stocks. Over the past 20 years, extensive efforts have been directed towards addressing this issue by modifying problematic fishing gears (especially trawls) and practices. Whilst this work has facilitated considerable reductions in bycatches (up to 80% in some cases), very few (if any) of the changes made to existing gears are 100% effective. There remains, therefore, a substantial mortality of unwanted individuals in most fisheries. To work more comprehensively towards the ultimate goal of achieving perfect selectivity, we propose that, in addition to conventional methods used in recent decades to modify fishing gears, a more lateral approach should also be adopted involving completely alternative gears. Specifically, we propose a strategy that: (1) examines the boundaries of what is realistically achievable in modifying poorly selective gears using established bycatch reduction protocols; and (2) determines the utility of alternative gears that, because of their design and/or operation, have selective mechanisms which could be applied to problematic gears. In this paper, the logic involved in the first approach is discussed and data supporting the benefits of the second approach are presented. Reducing the discarding of small prawns Project No. 2001/031 88 NSW Dept of Primary Industries The issue of bycatch From the earliest evidence of fishing more than 90 000 years ago (Yellen et al. 1995) to the present day, humans have exponentially advanced their harvesting methods. The clear focus of these developments has been to maximize the catches of an ever-increasing diversity of targeted species, with little or no regard for the incidental catches (termed ‘bycatch’, sensu Saila 1983). A progression from simple harpoons, hooks and traps deployed from the shore, through nets set from boats, to the industrial factory trawlers of developed countries has culminated in technology which, in many cases, far exceeds the sustainability of local resources. This excess was evident at the end of the 20 century by the collapse of many commercially-important stocks, a plateau in the world’s total landed wild catch (at less than 100 million tonnes) and the volumes of bycatch discarded in pursuit of targeted catches (Alverson et al. 1994). While recognition of the potentially negative impacts of unchecked fishing technology date back to the 14 century (Dyson 1977), it is only during the last few decades that coordinated attempts have been directed towards improving the selectivity of fishing gears (Kennelly and Broadhurst 2002). Relevant reviews of the published literature suggest that nearly all fishing gears and methods have received at least some attention (e.g. gillnets – Hamley 1975; longlines – Løkkeborg and Bjordal 1992; traps – Mahon and Hunte 2001), although the majority of effort has been directed towards benthic trawl fisheries (e.g. Kennelly 1995) and especially those targeting shrimp (Andrew and Pepperell 1992; Broadhurst 2000). This has occurred in response to the disproportional ratio of retained-to-discarded catches and the amount of unwanted catch discarded each year by shrimp trawlers; estimated to represent between 30 and 60% of the total world harvest of wild fisheries resources (Alverson et al. 1994). While the absolute volume of bycatch associated with shrimp trawling clearly makes it one of the most the most problematic fishing methods, many other gears including fish trawls, seines, gillnets, traps and longlines have, in recent times, been identified as having significant selectivity issues and have consequently been associated with prolonged calls for improvements coming from a variety of environmental groups, recreational fishers, interacting commercial fisheries and the general public. Solving bycatch problems During the past 2 decades, problems surrounding the issue of bycatch has shifted the focus of fishing gear technology from catching as much of the target species as possible (with little regard for collateral impacts) to improving selectivity, both in terms of the species targeted and their desired sizes (Kennelly and Broadhurst 2002). In many cases, the successful development and adoption of solutions to improve selection in problematic gears can be summarized in a simple framework (see also Kennelly and Broadhurst 1996; Kennelly 1997; Broadhurst 2000) which involves industry and researchers each applying their respective areas of expertise to the particular problem. This framework comprises five key steps: (1) quantifying bycatches (mostly via observer programs), (2) identifying the main bycatch species and their sizes of concern, (3) developing alterations to existing fishing gears and practices that minimize the mortality of these species, (4) testing these alternatives in appropriately-designed field experiments and (5) gaining acceptance of the new technology throughout the particular fishery and interested stakeholders. The protocol for completing the framework is quite straightforward and has been described with numerous examples by Kennelly and Broadhurst (1996), Kennelly (1997) and Broadhurst (2000). The crucial and most difficult step (3 above) is the actual development of appropriate solutions that improve the selectivity of existing fishing gears for the targeted catch and so reduce unwanted bycatch. Depending on the type of gear and its particular problems, solutions may involve simple adjustments to operational procedures and/or existing components of the gear, like changing the size and/or shape of meshes or hooks. Alternatively, for many towed gears, more complicated modifications that include physical bycatch reduction devices (BRDs) may need to be invented or modified from other fisheries (Broadhurst 2000). Owing to their relative complexity, these types of modifications frequently require detailed adjustment and reassessment to exclude specific sizes of individuals or species, yet maintain targeted catches (Kennelly and Broadhurst 2002). Project No. 2001/031 Reducing the discarding of small prawns NSW Dept of Primary Industries 89 While the above framework summarizes several successful attempts at addressing the problems of bycatch in different fisheries throughout the world (Kennelly 1997), in many cases the established protocols for improving inherently problematic gears has restricted fishing technologists in terms of working towards the ultimate goal of perfect selectivity. A reason for this is that to ensure the industry adoption and acceptance of modified designs that reduce bycatch (i.e. step 5 above), nearly all researchers have aimed to achieve 100% retention of the targeted species (during step 3). Theoretically, it should be possible to dramatically improve the selectivity of most fishing gears, provided some concomitant sacrifice in their overall efficiency is permitted. The issue would then become what is an acceptable loss of the targeted catch in order to improve selectivity and reduce bycatch. An extreme solution for achieving ‘perfect selectivity’ may be to reorder the above logic and, using traditional gears and established bycatch reduction methods, approach a 100% exclusion rate of unwanted catch at any cost to the desired catch. This approach could be appropriate in tightly-regulated fisheries where there is imminent threat of closure due to discarding. Reductions in gear efficiency could also be offset via some compensatory increases in the value of the targeted catch through ‘eco-labeling’. This sort of strategy would not be feasible, however, in the vast majority of countries and especially those where artisanal fisheries represent the main source of income for communities. For these fisheries, bycatch reduction clearly needs to be maximized with minimal impact on the efficiency of the gear for the targeted catch. Maximizing gear development within existing bycatch reduction frameworks To approach maximum bycatch reduction with no loss of the targeted catch (during step 3 of the framework described above), there needs to be a general estimate of what is achievable for particular gears. As a starting point, this requires an assessment of the limits of established modifications for improving selectivity. For many conventional towed gears, different sizes and/or shapes of mesh are among the simplest alterations and their utility is often (or at least should be) defined first. Under the framework proposed by Broadhurst (2000), this involves testing beyond what might intuitively be appropriate, so that the limits of a particular range of mesh sizes or shapes can be quantified and defined. If the solution to reducing particular bycatch species of concern is not apparent within the boundaries of the simple alterations tested, then more complex modifications (including physical BRDs) warrant examination. Specific designs of BRDs should also be tested to define their limits. For example, if mechanical-sorting grids are required to exclude organisms larger than the targeted species, then a range of configurations that include very narrow and wide bar spacings and small and larger profiles or angles of orientation should be examined (e.g. Broadhurst et al. 2004b). Similarly, because factors like relative water flow strongly influence the performance of BRDs that operate by exploiting differences in the behavior of species (Broadhurst et al. 1999a), these sorts of modifications need to be tested at different positions throughout the gear (e.g. Broadhurst et al. 2002). Coherent hypotheses encompassing the full range of key factors influencing the performance of mod

Growth and reproductive biology of tarwhine Rhabdosargus sarba (Sparidae) in eastern Australia

The growth and reproductive biology of the commercially and recreationally important sparid fish, tarwhine (Rhabdosargus sarba), was examined from the coastal waters of New South Wales (NSW), south-eastern Australia. Previ- ous research on this species in other parts of the world has yielded conflicting results concerning its growth and reproductive biology. Age estimates were made by counting opaque zones in otolith sections. The method was validated by marking the otoliths of captive fish with alizarin complexone, and also by marginal increment analyses using otoliths from wild-caught fish. Both sexes grew at a similar rate. Von Bertalanffy growth function parameters were: L∞ = 26.40 ± 0.40 cm fork length (FL), k = 0.39 ± 0.02 year −1 and to =− 0.56 ± 0.09 years. The maximum estimated age was 16.5 years. Spawning occurred from May to August with a peak in July. Both sexes matured at a similar size (L50 = 19.44 ± 0.15 cm FL), which was larger than the current minimum legal length in NSW. Ovotestes were identified in adult tarwhine and were confirmed by histological analyses. Results of this study provided evidence that tarwhine are likely to be rudimentary hermaphrodites in eastern Australia and are more similar in growth rate, maximum size/age, and reproductive biology to tarwhine from Western Australia than those from other parts of the world.