This study provides a comprehensive assessment of the dietary composition of the ambush predator Neosebastes pandus and compares the diets of 49 species from 39 studies of three benthic predatory ...families in the Scorpaeniformes: Scorpaenidae (20 species), Triglidae (19 species) and Platycephalidae (10 species). A total of 275 N. pandus were collected from the west (Rottnest Island) and south (Esperance) coasts of south‐western Australia and the percentage frequency and volumetric contribution of the stomach contents identified. Fish from the west coast consumed a greater mean number of broad taxonomic groups and were more diverse in their diet than fish from the south coast. Cephalopods, brachyurans and teleosts were the largest overall contributors to diet, with teleosts being more important to diets of west‐coast fish and polychaetes for south‐coast fish. This reflects differences in habitat between the two locations. Dietary composition also changed with increasing body size, reflecting morphological changes that allow bigger fish to capture and ingest larger, more mobile prey. Meta‐analysis of the diets of 49 species of scorpaenid, triglid and platycephalid revealed that they feed predominantly on teleosts and large crustaceans. Significant differences in diet were detected among families, with platycephalids being the most distinct and feeding more on teleosts than scorpaenids and triglids.
Portunid crabs contribute to significant commercial and recreational fisheries globally and are commonly fished in estuaries and/or marine embayments, which are amongst the most degraded of all ...aquatic ecosystems.
Portunus armatus
were collected seasonally between April and February from five locations across three systems in temperate south-western Australia. The dietary composition of crabs was quantified and compared between two estuaries (Peel-Harvey and Swan-Canning) and a sheltered marine embayment (Cockburn Sound) containing three distinct habitats: shallow seagrass, shallow sand and deep sand. Overall, crabs ingested large volumes of bivalves (both live organisms and dead shell), polychaetes, crustaceans (e.g., amphipods, small decapods), and smaller volumes of teleosts, echinoderms and plant material (seagrass, algae). Analysis of Similarities showed that dietary composition varied significantly among the five locations (two estuaries and three habitats within Cockburn Sound) and seasons, with greater location than seasonal differences in the two estuaries. Diets were most distinct in the Cockburn Sound seagrass due to greater volumes of decapods and teleosts and smaller volumes of bivalve shell consumed in this habitat. Crabs from both estuaries consumed greater quantities of bivalves than those from Cockburn Sound. Seasonal differences in both estuaries were greatest between summer and winter, with a more diverse range of prey and large quantities of bivalves ingested in summer, whereas small bivalves and bivalve shell in the Peel-Harvey and polychaetes and other crustaceans in the Swan-Canning, were consumed in greater quantities in winter. The summer diet in the Peel-Harvey Estuary in the current study was compared to that 20 years previous and with documented change in the benthic macroinvertebrate fauna. Currently, crabs consume smaller volumes of high-calorie prey, i.e., polychaetes, small bivalves and teleosts, and instead ingest greater proportions of calcareous material than previously. This marked shift in dietary composition parallels changes in benthic macroinvertebrates in the Peel-Harvey Estuary. Overall, prey availability appears to be the major factor influencing the spatial and temporal differences in
P. armatus
diets in these three coastal systems.
The demand for fish is expected to rise substantially by 2020. Although aquaculture must provide much of the additional fish, it remains to be seen whether restored or enhanced capture fisheries can ...also help fill the projected gap in supply. The key challenges for capture fisheries involve reducing fishing effort, removing excess fishing capacity and building the institutional arrangements needed to restore spawning biomass to more productive levels, and to reverse degradation of the supporting habitats. Two interventions, based largely on hatchery technology, have the potential to reduce the time needed to rebuild some severely over-exploited fisheries, or improve the productivity of other ‘healthy’ fisheries. These interventions are ‘restocking’, which involves releasing cultured juveniles to restore spawning biomass to levels where the fishery can once again support regular harvests, and ‘stock enhancement’, which involves release of cultured juveniles to overcome recruitment limitation. However, despite the potential of these interventions, few restocking and stock enhancement programmes have met expectations. The main problems have been a pre-occupation with bio-technical research at the expense of objective analysis of the need for the intervention, and failure to integrate the technology within an appropriate management scheme that has the participation and understanding of the users. The papers presented at the Special Symposium on this subject at the Seventh Asian Fisheries Forum provide a series of valuable lessons to guide objective assessment of the potential for restocking and stock enhancement. They also show how to implement these interventions responsibly and effectively where they are deemed to add value to other forms of management. Above all, these studies demonstrate that restocking and stock enhancement programmes are applied in complex human–environment systems, involving dynamic interactions between the resource, the technical intervention and the people who use it.
Octopus as predators of abalone on a sea ranch Greenwell, Claire N.; Loneragan, Neil R.; Admiraal, Ryan ...
Fisheries management and ecology,
April 2019, 2019-04-00, 20190401, Letnik:
26, Številka:
2
Journal Article
Recenzirano
This study examined the occurrence of octopus across an abalone, Haliotis laevigata, Donovan, sea ranch in south‐western Australia, to understand how octopus may be impacting abalone production. ...Commercial divers removed 654 octopus and 17,666 empty abalone shells during regular, 2 to 4‐weekly surveys over 27 months. A negative binomial generalised linear model estimated a 78% increase in empty shells per artificial abalone habitat per day, when octopuses were present, after adjusting for location and season. Of the 408 shells examined for evidence of predation, 19% had a small, slightly ovoid hole consistent with those made by octopus. The mean (± 1 SE) length of shells with boreholes (70.3 ± 2.2 mm) was significantly longer than those without (59.8 ± 0.5 mm), and boreholes were concentrated over the adductor, respiratory organs and heart. This study provides important insights into the adaptable feeding regimes of octopus and their potential to impose strong top‐down controls on sea ranching operations.
We genetically characterised larval and adult specimens of species of Echinocephalus Molin, 1858 (Gnathostomatidae) collected from various hosts found within Australian waters. Adult specimens of ...Echinocephalus were collected from a dasyatid stingray Pastinachus ater (Macleay); n = 2 from Moreton Bay, Queensland and larvae from a hydrophiine sea snake Hydrophis peronii (Duméril); n = 3 from Cape York Peninsula, Queensland, from an octopus (Octopus djinda Amor & Hart; n = 3) from Fremantle, Western Australia and from a lucinid bivalve Codakia paytenorum (Iredale); n = 5 from Heron Island, Queensland Australia. All nematode samples were identified morphologically and genetically characterised using the small subunit nuclear ribosomal DNA (SSU). Some morphological differences were identified between previous studies of Echinocephalus spp. and those observed herein but the significance of these differences remains unresolved. Molecular phylogenetic analyses revealed that larval Echinocephalus sp. from H. peronii and C. paytenorum in Australia were very similar (with strong nodal support) to larval Echinocephalus sp. infecting two fish species from Egypt, Saurida undosquamis (Richardson) (Synodontidae) and Pagrus pagrus (Linnaeus) (Sparidae). The SSU sequences of larval Echinocephalus sp. from O. djinda and adults from P. ater formed a well-supported clade with that of adult E. overstreeti Deardorff and Ko, 1983 from the Port Jackson shark, Heterodontus portusjacksoni (Meyer), as well as that of the larval Echinocephalus sp., from the common carp (Cyprinus carpio Linnaeus) from Egypt. This study extends the intermediate host range of Echinocephalus larvae by including a sea snake for the first time. Findings of this study highlight the importance of genetic characterisation of larval and adult specimens of Echinocephalus spp. to resolve the current difficulties in the taxonomy of this genus.
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•Historical morphological descriptions of larval forms of Echinocephalus provide inadequate species identification.•Larval stages of Echinocephalus species from various hosts found within Australian waters were characterised.•Intermediate host range of Echinocephalus larvae was extended to include a reptile.•Future studies should include genetic characterisation of Echinocephalus spp. to resolve taxonomic inaccuracies.
This study describes nest desertion as a probable but previously undescribed anti-predator strategy for the Australian Fairy Tern Sternula nereis nereis. Deserted nests were observed at night for up ...to nine nights following the laying of the first eggs at a colony in southwestern Australia. Nocturnal nest desertion may provide the terns with a mechanism for assessing the occurrence of potential nest predators, maintaining reproductive synchrony, and reducing the total time a colony is detectable by predators. Additionally, temporary diurnal nest desertion for up to 80 minutes was observed following the predation of an adult tern. Diurnal nest desertion may be used to reduce the risk of adult mortality and, consequently, decrease colony visibility, thereby increasing reproductive success.
For several decades, fishing sharks for their fins has provided important livelihoods for eastern Indonesian coastal communities that fish the Halmahera, Arafura and Timor Seas. Fishery and interview ...data collected in 2012-13 from three case studies on the islands of Seram, Aru and Rote were used to examine changes in shark fishers’ livelihoods over the preceding 20 years. While recent declines in catches and shark fin prices have had a substantial impact on fishers’ livelihoods, the fishery's low visibility in some areas of its geographic range and its political complexity in general have meant that government and international development agencies have largely been unaware of this impact. Many respondents remembered the Asian Financial Crisis in 1997-98 and the turn of the millennium as a time when sharks were still abundant and shark fin prices high, but were concerned about the on-going fall of shark fin prices since March 2012. High-value species, particularly guitarfish, hammerhead and sandbar sharks were most affected, losing up to 40% of their pre-2012 value. These changes, combined with the loss of fishing grounds, few attractive options for alternative income and restrictive debt relationships with shark fin bosses, have led some fishers to resort to high-risk activities such as blast fishing, illegal transboundary fishing, and people smuggling. This paper examines the multi-layered causes and consequences of fishers’ decision-making in response to adverse changes in their fishery, and explores options and obstacles to pursuing livelihoods that carry lower environmental, financial and personal risks.
•We use a transdisciplinary approach to examine shark fishing livelihoods.•Declining shark fin prices and catches have adversely affected fishers’ livelihoods.•The 2012 drop in shark fin prices caused a 40% reduction in value of some species.•Economic pressure, e.g. through debt, has led to high-risk livelihood activities.•Sustainable fisheries development must link global to local scales of governance.
Fisheries are complex social-ecological systems, where managers struggle to balance the socio-economic interests of fishing communities with the biology and ecology of fisheries species. Spatial ...closures are a popular measure to address conservation and fisheries management goals, including the protection of shark populations. However, very little research has been published on the effectiveness of shark-specific closures to protect sharks, or their impacts on fisher behavior. Situated within the global center of tropical marine biodiversity, Indonesia’s shark fishery contributes more to the international shark fin trade than any other nation. Here we evaluate the effect of shark-specific closures on sharks and other species of interest, as well as shark fishers’ responses to losing access to their former fishing grounds. We assessed shark diversity and abundance in an open access zone (OAZ) and two No-Take Zones (NTZs) of a Marine Protected Area within the recently established shark sanctuary in Raja Ampat, Indonesia, where sharks have high monetary value as a tourism attraction. Shark abundance was significantly higher in the privately managed NTZs than in the OAZ. Across all management zones, neither zone size, depth nor reef complexity explained variations in shark abundance, suggesting that governance is the main driver of successful shark conservation areas. These trends were also reflected in species targeted by small-scale reef fisheries, including snappers, emperor, groupers, tunas, mackerels, and large-bodied wrasse and parrotfish. Interviews with shark fishers who lost access to their primary fishing grounds when the shark sanctuary was established showed that while most fishers (88%) knew that sharks were protected in Raja Ampat, many were unsure about the purpose of the sanctuary. Few fishers felt that the agencies implementing fishing bans understood their livelihood needs. We found that shark fishers adapted to the loss of former fishing grounds by shifting fishing effort to other locations or diversifying their livelihoods, including illegal petrol transport. While conserving sharks for tourism can be effective, it may inadvertently result in displacing fishing effort to unprotected regions. We propose that effective shark conservation in Indonesia will need to combine strategic spatial protection with efforts to support livelihood security and diversification.
Marine ranching has been proposed as a promising solution to manage the depleted coastal fishery ecosystem in recent decades across China. Marine ranching integrates the practices of artificial ...habitat-based with aquaculture-based enhancement. Assessing the ecological carrying capacity of target species for enhancement is a precondition for determining the optimal numbers for release, particularly for those species whose habitat restrictions have been eliminated through the construction of artificial habitats in the marine ranch. A responsible approach to stock enhancement aims not only to increase total yield and stock abundance but also to consider any potential effects on ecosystem structure and function. A time-dynamic, ecosystem model was constructed using Ecopath with Ecosim for the Laizhou Bay (Bohai Sea) marine ranching ecosystem in the nearshore waters of northern China. Two sedentary target species with potential for stock enhancement, i.e., the carnivorous red snail
Rapana venosa
and the detritivorous sea cucumber
Apostichopus japonicus
, were selected to simulate and estimate their ecological carrying capacities and project their overall effects on the ecosystem. Ecological carrying capacity was defined as the maximum standing stocks of the target species that would not cause “unacceptable” impacts on the ecosystem function and resilience, i.e., not cause any other group’s biomass to fall below 10% of its original biomass. The ecological carrying capacities estimated for
R. venosa
and
A. japonicus
were 623.46 and 200.57 t·km
−2
, respectively, corresponding to 7.8 and 5.0 times higher than their current standing stocks. Simulations of
R. venosa
enhancement showed distinct effects of increased target species abundance on other functional groups and ecosystem properties. An increase in red snail biomass caused negative impacts on the biomass of most other functional groups and ecosystem indicators, such as Finn’s cycling index, transfer efficiency, and Kempton’s Q index. In contrast, the simulated
A. japonicus
enhancement had relatively few impacts, and the biomasses of most other functional groups and ecosystem indicators did not change or changed very slightly (<5%). The current model framework provides a means of estimating the ecological carrying capacity in commercial-scale stock enhancement practices and avoiding potential ecological risks for marine ranching in northern China.
Most studies of delphinid‐trawler interactions have documented the surface behavior of dolphins feeding on discarded bycatch, but not their subsurface behavior around demersal trawl gear. Using video ...cameras mounted inside trawl nets, we recorded the subsurface behavior of common bottlenose dolphins (Tursiops truncatus) in a demersal fish trawl fishery in northwestern Australia. Footage from 36 trawls across the fishery was analyzed to determine the extent of dolphin‐gear interactions and the behavior of dolphins inside the nets. Interaction rates were high, with dolphins present inside and outside the nets during 29 and 34 trawls, respectively, and for up to 99% of the trawl duration. The proportion of foraging behaviors exhibited inside the nets was higher than the proportions of traveling and socializing behaviors. Twenty‐nine individuals were identified inside the net, seven of which returned repeatedly within and between trawls and fishing trips, but were observed primarily in the same localized areas in which they were first recorded. Our results suggest that entering trawl nets may be a frequently occurring, yet specialized behavior exhibited by a small subset of trawler‐associated dolphins. We propose that gear modifications, not spatial or temporal adjustments to fishing effort, have the greatest potential to reduce dolphin bycatch.
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