Global attempts to offset declines in fishery populations through stock enhancement have had varied levels of success due to the absence of preliminary studies to determine which habitats best ...support release species and the mechanisms controlling their distribution. Habitat preference was examined as a possible mechanism driving distribution of postlarval Penaeus plebejus, a current candidate prawn for stock enhancement in Australia. Occupancy of complex (artificial macrophyte) and simple (bare sand and mud) habitats by postlarvae was compared in the presence and absence of a choice between the habitats. Predation mortality was also compared amongst these habitats. P. plebejus settled into the different habitats randomly during the night, but actively selected macrophyte over the simple habitats during the day. Mortality caused by the predatory fishes Centropogan australis and Acanthopagrus australis was higher in simple habitats than in complex habitats, but was similar across habitats when large penaeid prawns, Metapenaeus macleayi (which are tactile rather than visual feeders), were used as predators. Postlarvae may select macrophyte habitats during the day to lower predation risk, but because nighttime foraging efficiency is reduced in their predators, which are primarily visual hunters, this may preclude the need of postlarvae to obtain shelter in macrophyte habitats at night. Predation mortality of stocked P. plebejus may be minimized by releasing postlarvae directly into macrophyte habitats. Studies such as these must precede all stock enhancement attempts because they identify optimal release strategies and allow ecological and financial costs of enhancement to be weighed against projected benefits, and thereby assess the practicality of enhancement as a management option.
Densities of nekton were estimated by comparing catch rates of two previously uncompared gear types, a beam trawl and a seine net, by day and night in a shallow seagrass (
Zostera capricorni) habitat ...in Moreton Bay, Queensland, Australia. A total of 39,676 fish and crustaceans representing 42 species was caught. The catch rates of nekton were 1.4–68.1 times higher at night than in the day for 8 of the 17 common species, and were 1.4–9.2 times higher in seines than trawls for 11 of the common species. None of the common species had higher catch rates in the day than the night, or in the trawls than the seines. For some species there was no significant difference in catch rates amongst the sampling combinations. Night-time seine collections had a greater proportion of larger individuals than day and trawl samples. The differences in catch rates and size of nekton are probably a consequence of both gear avoidance and the movement of nekton out of seagrass during the day. Catch rates were estimated more accurately and precisely with the seine than the trawl, with higher catch rates at night. An analysis of the overall composition of the catch (based on presence/absence data) by multi-dimensional scaling separated the samples into four main groups: day-trawl, night-trawl, day-seine and night-seine. The results suggest that seine nets are a better choice for determining the relative proportion of species in a seagrass habitat, and estimating the density of most species. Such sampling should also be done by day and night, or by night alone.
Baited remote underwater video (BRUV), with its non-destructive nature and ease of replication, is an effective and widely used method to record the relative abundance and behavior of aquatic fauna. ...However, the effectiveness of BRUVs for investigating the structural and functional diversity of mobile fauna on artificial reefs has not been fully evaluated. In China artificial reefs form an important component of very extensive marine ranching systems along the coast. This study used BRUVs and baited fish traps (traps), a traditional and popular fishing gear in the coastal waters of northern China, over six months to quantify the mobile fauna around artificial reefs and adjacent natural substrate (“control”) and compared the richness, abundance, community composition and functional diversity of reefs and control areas and BRUVs and traps. A significantly greater number of species and relative abundance was recorded using BRUVs than traps. Significant differences in faunal composition were detected between the two methods (BRUVs, traps), the two habitats (artificial reef, control) and the seven sampling occasions. Measures of functional diversity were also all significantly higher using data derived from BRUVs than traps. The weighted average analysis of functional traits revealed that those related to feeding and space use were more diverse from BRUVs. These results indicate that BRUVs provided a more complete representation of the mobile fauna than traps and show great potential for fishery-independent monitoring of marine ranching in China.
•First use of baited remote underwater videos (BRUVs) for investigating the community dynamics of mobile fauna in China.•Higher number of species and relative abundance recorded on BRUVs than in fish traps.•Measures of community function: richness, evenness, and divergence were greater using BRUVs.•Broader range of functional traits and IUCN-listed threatened species recorded on BRUVs.
► The Ecospace model was used to evaluate the effects of different management options, such as spatial closures on fished species (e.g. western rock lobster, dhufish, pink snapper) and the trophic ...interactions in the ecosystem. ► The fishing closures in Jurien Bay can lead to increments in the abundance of exploited resources, while without some closures, the biomass of all key target species was predicted to decline under the current levels of fishing. ► The changes in biomass resulting from the spatial closures, evaluated by Ecospace, varied greatly between species. They were much more effective for relatively sedentary species such as dhufish and pink snapper than migratory species such as sharks. ► The largest increases in biomass for exploited species was predicted when spatial closures were combined with additional fisheries management controls in fished areas.
An Ecospace model, was developed to investigate the potential impacts of spatial closures on key species and the food webs in the Jurien Bay Marine Park (JBMP), central Western Australia (823km2). The model comprised 80 functional groups (more than 200 species). The JBMP is a multiple use-marine park with several types of zoning and the effects of these on rock lobster biomass, mortalities and landings were explored using five Ecospace scenarios as baselines: (1) no-take Sanctuary Zones covering 4% of the total area; area of Sanctuary Zones changed to (2) 25%, (3) 50%; (4) 0%, i.e. No Sanctuary Zones; and (5) combining 25% of no-take areas with a 50% reduction in fishing mortality of the main targeted species. The results suggest that the introduction of the current management zones with 4% of the area in Sanctuary Zones produced a modest increase of ∼5% in the biomass of western rock lobster after 20 years, even with stable fishing effort. However, Western Rock Lobster biomass increased by ∼20% when the Sanctuary Zones covered 25% of the Park. Similar trends were observed for exploited fish species such as pink snapper, dhufish, and small sharks with their biomasses predicted to increase by up to 30% as the area of sanctuary zones increase from 4% to 50%. The largest predicted increases in biomass for the main target species were found when the protection from the sanctuaries (25%) was combined with a 50% reduction of fishing pressure. The catch of finfish species improved up to 70% (e.g. pink snapper) when a 25% of no-take area simulated was combined with a 50% reduction of fishing mortality during 20 years. To test the effects of habitat structure on the effectiveness of these fishing closures, a set of four scenarios were developed. We relocated the current 4% of sanctuaries, which are mainly associated with a reef-seagrass habitat, to the other three major habitats (reefs, seagrass and sand). The predicted fish biomass was higher when sanctuaries were placed on high structured habitats, such as reefs and seagrass-reefs (10–90%) than seagrass and sandy areas.
Small-scale fisheries (SSF) provide crucial contributions to livelihoods, food and nutrition security, and the well-being of coastal communities worldwide. In Indonesia, 2.5 million households are ...involved in SSF production, yet these households are characterised by high poverty rates and vulnerability due to declining ecosystem health and climatic change. In this study we applied the Sustainable Livelihoods Framework to analyse the characteristics and immediate and longer-term outcomes of 20 SSF livelihood-focused intervention programs implemented in coastal communities across the Indonesian Archipelago over the last two decades. Projects covered a wide range of spatial scales, funding providers and key participants. Factors supporting positive program outcomes included application of inclusive and holistic approaches to sustainable livelihoods, implemented and supported over appropriate time frames; use of participatory capacity development methodologies and locally-situated project facilitators; and collaborative engagement with local government, non-government organisations and private-sector actors. However, it was impossible to identify evidenced successes from a longer-term sustainability perspective. Short project timeframes, absence of baseline or monitoring data, pressure for satisfactory reports to donors, and limited post-project evaluation, together with invisibility of women’s work and non-commercial exchanges, affected the adequacy of assessments. Given the lack of post-project assessment among projects studied, a thorough review of longer-term project impacts is recommended, guided by the Sustainable Livelihoods Framework, to evaluate sustained improvements in livelihoods outcomes and environmental sustainability. This would support best-practice design and implementation of SSF livelihood-focused interventions, disseminated beyond academia, to influence policy and development to achieve socio-economic equity and environmental goals.
•Fishing households are particularly vulnerable to poverty and environmental degradation.•Many livelihood interventions have been attempted to improve fisheries dependent households and coastal communities.•There has been inadequate post-project impact evaluation in small-scale fisheries (SSF) livelihood-focused interventions.•Interventions engaging communities in partnership with government and non-government agencies appear to have greatest impact.•Assessment of long-term socio-ecological effectiveness of SSF livelihood-focused interventions across Indonesia is needed.
In Shark Bay, Western Australia, bottlenose dolphins Tursiops sp. carry conical sponges Echinodictyum mesenterinum on their rostra in the only documented cetacean foraging behaviour using a tool ...('sponging'). In this study, we examined the influence of various ecological factors on live sponge distribution and the occurrence of sponging in parts of the western gulf of Shark Bay. We assessed sponge distribution and seagrass cover along 12 transects of approximately 11 km length, by recording sponges and seagrass in a total of 1380 quadrats (1 x 1 m), of which 56 quadrats contained conical sponges. The occurrence of sponging dolphins ('spongers') was documented along 10 of these 12 transects. The distribution of conical sponges was negatively correlated with the distribution of seagrass: no conical sponges were observed in water depths of 12 m. A digital elevation model, created from the sample depth data, identified channels in the region. Binary logistic and Poisson log-linear generalised linear models showed that water depth and bathymetric features including channel, substrate and slope were significant in predicting the occurrence and the mean number of conical sponges, as well as that of seagrass. Conical sponge distribution was positively correlated with the distribution of sponging, indicating that ecological factors influence where sponging occurs. The greater number of spongers found in this region may be explained by the larger area of habitat suitable for conical sponges in the western than the eastern gulf of Shark Bay.
Sharks are apex predators that influence the behavioural ecology of a range of prey species. Unsuccessful predation attempts from sharks are evidenced by fresh bites and scars, and these wounds ...provide indirect measures of predation pressure. To better understand the predatory dynamics of sharks on bottlenose dolphins, we investigated the frequency, sex and age class differences, seasonality and annual trends, and location (open vs. sheltered waters) of shark predation attempts on Tursiops aduncus off Bunbury, south-western Australia. Over seven years from 2007 to 2013, standardised boat-based, photographic-identification dolphin surveys (n = 600) were conducted year-round over 540 km2 in open coastal and sheltered waters (bay, estuary and river). The overall frequency of shark predation attempts on dolphins (calves, juveniles and adults) was 16.9% (58 of 343). Shark bites were categorised as Open (n = 25, 40.9%), Intermediate (n = 16, 26.2%) and Scars (n = 20, 32.8%). Scarring frequencies did not differ significantly between sexes or among age classes. Bites increased in frequency from 2009 to 2013, coinciding with sustained warm water temperatures from 2011 La Niña conditions, resulting in 34% of Open and Intermediate bites being recorded in 2013. The frequency of Open bites differed among seasons, with bites more prevalent during the summer of 2012/13. The proportion of dolphins with shark bites was significantly greater for individuals residing in the sheltered waters (24.7%, 19 of 77) compared to open waters (13.4%, 34 of 253). Our findings provide knowledge into predator-prey dynamics of marine top predators by quantifying temporal and spatial incidences of failed predation attempts of sharks on bottlenose dolphins in temperate, south-west Australia.
•The frequency of shark predation attempts on dolphins was 16.9% (58 of 343).•Scarring frequencies did not differ significantly between sexes or among age classes.•Bites increased in frequency by year from 2009 to 2013.•The frequency of bites differed temporally, with most occurring in summer 2012/2013.•The proportion of dolphins with bites in sheltered waters was significantly greater than for dolphins in coastal waters.
We used a regional, ecosystem mass-balance model (Ecopath with Ecosim) to evaluate the possible changes in flows of mass and energy between the benthic and pelagic components of the marine ecosystem ...of Jurien Bay in temperate Western Australia (∼30°S, ∼115°E). The effects of varying the biomass of western rock lobster in the system were examined by simulating changes in commercial and recreational fishing mortality as well as recruitment-driven changes in the abundance of lobster puerulus (the first post-larval stage). The model comprised 80 functional groups (more than 200 species). A simulated closure of the commercial lobster fishing was predicted to lead to an increase in lobster biomass of 160% after 20 years, with changes in biomass of up to 20% of the main prey and predators of lobster. Since 2006/2007, the puerulus settlement (recruitment to the benthos) of western rock lobster has declined to the lowest levels recorded in the fishery. The model predicted that under 2005 levels of fishing effort, a simulated depletion of 90% of puerulus biomass resulted in an ∼17% reduction in the biomass of adult lobster biomass after 20 years (i.e. by 2025). In general, the model predicts that the variations in lobster biomass, whether induced from fishing mortality or declining puerulus settlement, have relatively small effects on the biomass of the main predators and prey of lobster in the marine park. The relative biomass of adult rock lobster and their associated predators and prey was more sensitive to fishing than to variations in recruitment.
The fish faunas of eight estuaries along 130 km of the south coast of Western Australia were sampled seasonally for one year, during which Beaufort Inlet became markedly hypersaline (salinities up to ...122 and > 100 for six months). These conditions were caused by a combination of low amounts of saline river flow, the bar of this shallow estuary remaining closed for 27 months and high rates of evaporation. Fish faunas in the nearshore, shallow and offshore, deeper waters of Beaufort Inlet were depauperate compared to nearby estuaries. The number of fish species declined as salinity increased, with the highly euryhaline, estuarine-resident atherinid Atherinosoma elongata being the only species to survive throughout the study. The cosmopolitan flathead mullet Mugil cephalus survived for the next longest period, living in salinities in excess of 100 for at least four months and in a maximum salinity of 122. This is the highest known salinity in which a marine-spawning fish species has been found globally. This finding provides support for the cryptic species complex hypothesis pertaining to M. cephalus and that individuals in south-western Australia may be a seperate species. The survival of these species for a relatively protracted time reflects the fact that they are euryhaline and have a suite of adaptations that allow them to occupy environments from freshwater to extreme hypersaline conditions. The longer occurrence of M. cephalus in the extreme salinities than Acanthopagrus butcheri and Aldrichetta forsteri, is likely also related to their primary diet of detritus, particulate organic matter and diatoms, all of which are abundant in Beaufort Inlet. In contrast, piscivorous and zoobenthivorous fish were depauperate and in low abundances, which may reflect limited food resources during hypersaline conditions, and/or more reduced euryhalinity by these species. Clearly, hypersalinity has a marked effect on the faunas and thus ecosystem functioning of estuaries, and with declines in rainfall and hotter temperatures projected in future climate change scenarios, more estuaries are likely to become increasingly hypersaline.
•Salinities in Beaufort Inlet reached 122 due to low ‘freshwater’ flow and bar closure.•Fish and invertebrate fauna depauperate, exacerbated by multiple fish kills.•Protracted occurrence of Mugil cephalus in salinities > 100.•Detritus provided abundant food source for M. cephalus assisting survival.•Highest salinity in which a marine-spawning fish species has been recorded.
The mechanisms that drive density dependence are rarely studied in the applied context of population management. We examined the potential for competition for food and shelter and the resulting ...demographic density dependence to influence how well populations of the eastern king prawn Penaeus plebejus Hess can recover following marine stock enhancement programmes in which captive-bred juveniles are released into the wild. Specifically, manipulative laboratory experiments were used to quantify the differential effects of competition for food and competition for shelter on survival of wild and captive-bred P. plebejus as densities were increased and as each category of P. plebejus (wild or captive-bred) was supplemented with the alternate category. Increasing population densities when food and shelter were limited lowered survival for both categories. When food was limited, survival of both categories was unaffected by addition of the alternative category. Adding wild P. plebejus to their captive-bred counterparts when shelter was limited under laboratory conditions resulted in significantly higher mortality in captive-bred individuals. In contrast, adding captive-bred P. plebejus to wild individuals under these conditions did not affect wild P. plebejus. We conclude that if the current results can be extended to wild conditions, competition for shelter may lead to the loss of captive-bred P. plebejus, thereby reducing the intended outcomes of stock enhancement. This highlights the importance of investigating interactions between wild and captive-bred animals prior to stock enhancement to predict long-term outcomes and identify situations where stock enhancement could be an effective response to the loss of populations or recruitment limitation.
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