A stochastic model for estimating sustainable limits to wildlife mortality in a changing world.

Human-caused mortality of wildlife is a pervasive threat to biodiversity. Assessing the population-level impact of fisheries bycatch and other human-caused mortality of wildlife has typically relied upon deterministic methods. However, population declines are often accelerated by stochastic factors that are not accounted for in such conventional methods. Building on the widely applied potential biological removal (PBR) equation, we devised a new population modeling approach for estimating sustainable limits to human-caused mortality and applied it in a case study of bottlenose dolphins affected by capture in an Australian demersal otter trawl fishery. Our approach, termed sustainable anthropogenic mortality in stochastic environments (SAMSE), incorporates environmental and demographic stochasticity, including the dependency of offspring on their mothers. The SAMSE limit is the maximum number of individuals that can be removed without causing negative stochastic population growth. We calculated a PBR of 16.2 dolphins per year based on the best abundance estimate available. In contrast, the SAMSE model indicated that only 2.3-8.0 dolphins could be removed annually without causing a population decline in a stochastic environment. These results suggest that reported bycatch rates are unsustainable in the long term, unless reproductive rates are consistently higher than average. The difference between the deterministic PBR calculation and the SAMSE limits showed that deterministic approaches may underestimate the true impact of human-caused mortality of wildlife. This highlights the importance of integrating stochasticity when evaluating the impact of bycatch or other human-caused mortality on wildlife, such as hunting, lethal control measures, and wind turbine collisions. Although population viability analysis (PVA) has been used to evaluate the impact of human-caused mortality, SAMSE represents a novel PVA framework that incorporates stochasticity for estimating acceptable levels of human-caused mortality. It offers a broadly applicable, stochastic addition to the demographic toolbox to evaluate the impact of human-caused mortality on wildlife.

La mortalidad de la fauna causada por humanos es una amenaza continua para la biodiversidad. El análisis del impacto a nivel poblacional de la captura pesquera incidental y otras causas humanas de la mortalidad de la fauna comúnmente ha dependido de métodos determinísticos. Sin embargo, las declinaciones poblacionales con frecuencia se aceleran por los factores estocásticos que no son considerados en dichos métodos convencionales. A partir de la ecuación de extirpación biológica potencial (EBP) de extensa aplicación diseñamos una nueva estrategia de modelación poblacional para estimar los límites sustentables de la mortalidad causada por humanos y la aplicamos en un estudio de caso de los delfines nariz de botella afectados por la captura en una pesquería australiana de arrastre demersal. Nuestra estrategia, denominada mortalidad antropogénica sustentable en ambientes estocásticos (MASAM) incorpora la estocasticidad ambiental y demográfica, incluyendo la dependencia que tienen las crías por sus madres. El límite MASAM es el número máximo de individuos que pueden extirparse sin causar un crecimiento poblacional estocástico negativo. Calculamos un EBP de 16.3 delfines por año con base en la mejor estimación de abundancia disponible. Como contraste, el modelo MASAM indicó que sólo podían extirparse entre 2.3 y 8.0 delfines anualmente sin ocasionar una declinación poblacional en un ambiente estocástico. Estos resultados sugieren que las tasas reportadas de captura incidental no son sustentables a largo plazo, a menos que las tasas reproductivas sean sistemáticamente más altas que el promedio. La diferencia entre el cálculo determinístico del EBP y los límites de MASAM mostró que los enfoques determinísticos pueden subestimar el verdadero impacto de la mortalidad de la fauna causada por humanos. Lo anterior resalta la importancia de integrar la estocasticidad al evaluar el impacto de la captura incidental y otras causas humanas de la mortalidad como la caza, las medidas letales de control y las colisiones con turbinas de viento. Aunque el análisis de viabilidad poblacional (AVP) se ha utilizado para evaluar el impacto de la mortalidad causada por humanos, MASAM representa un marco novedoso de AVP que incorpora la estocasticidad para estimar los niveles aceptables de mortalidad causada por humanos. Este enfoque ofrece una adición estocástica de aplicación generalizada para las herramientas demográficas usadas para evaluar el impacto de la mortalidad causada por humanos sobre la fauna.

Regional differences in the feeding of the ambush predator Neosebastes pandus and comparisons of diets in the Scorpaenidae, Triglidae and Platycephalidae.

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.

Genetic isolation between coastal and fishery-impacted, offshore bottlenose dolphin (Tursiops spp.) populations.

The identification of species and population boundaries is important in both evolutionary and conservation biology. In recent years, new population genetic and computational methods for estimating population parameters and testing hypotheses in a quantitative manner have emerged. Using a Bayesian framework and a quantitative model-testing approach, we evaluated the species status and genetic connectedness of bottlenose dolphin (Tursiops spp.) populations off remote northwestern Australia, with a focus on pelagic 'offshore' dolphins subject to incidental capture in a trawl fishery. We analysed 71 dolphin samples from three sites beyond the 50 m depth contour (the inshore boundary of the fishery) and up to 170 km offshore, including incidentally caught and free-ranging individuals associating with trawl vessels, and 273 dolphins sampled at 12 coastal sites inshore of the 50 m depth contour and within 10 km of the coast. Results from 19 nuclear microsatellite markers showed significant population structure between dolphins from within the fishery and coastal sites, but also among dolphins from coastal sites, identifying three coastal populations. Moreover, we found no current or historic gene flow into the offshore population in the region of the fishery, indicating a complete lack of recruitment from coastal sites. Mitochondrial DNA corroborated our findings of genetic isolation between dolphins from the offshore population and coastal sites. Most offshore individuals formed a monophyletic clade with common bottlenose dolphins (T. truncatus), while all 273 individuals sampled coastally formed a well-supported clade of Indo-Pacific bottlenose dolphins (T. aduncus). By including a quantitative modelling approach, our study explicitly took evolutionary processes into account for informing the conservation and management of protected species. As such, it may serve as a template for other, similarly inaccessible study populations.

Qualitative mathematical models to support ecosystem-based management of Australia's Northern Prawn Fishery.

A major decline in the catch of the banana prawn [shrimp], Penaeus (Fenneropenaeus) merguiensis, occurred over a six-year period in the Weipa region of the northeastern Gulf of Carpentaria, Australia. Three main hypotheses have been developed to explain this decline: (1) prawn recruitment collapsed due to overfishing; (2) recruitment collapsed due to a change in the prawn's environment; and (3) adult banana prawns were still present, but fishers could no longer effectively find or catch them. Qualitative mathematical models were used to link population biology, environmental factors, and fishery dynamics to evaluate the alternative hypotheses. This modeling approach provides the means to rapidly integrate knowledge across disciplines and consider alternative hypotheses about how the structure and function of an ecosystem affects its dynamics. Alternative models were constructed to address the different hypotheses and also to encompass a diversity of opinion about the underlying dynamics of the system. Key findings from these analyses are that: instability in the system can arise when discarded fishery bycatch supports relatively high predation pressure; system stability can be enhanced by management of fishing effort or stock catchability; catch per unit effort is not necessarily a reliable indicator of stock abundance; a change in early-season rainfall should affect all stages in the banana prawn's life cycle; and a reduced catch in the Weipa region can create and reinforce a shift in fishing effort away from Weipa. Results from the models informed an approach to test the hypotheses (i.e., an experimental fishing program), and promoted understanding of the system among researchers, management agencies, and industry. The analytical tools developed in this work to address stages of a prawn life cycle and fishery dynamics are generally applicable to any exploited natural. resource.

Genetic characterisation of Echinocephalus spp. (Nematoda: Gnathostomatidae) from marine hosts in Australia.

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.

A two-phase approach to elicit and measure beliefs on management strategies: Fishers supportive and aware of trade-offs associated with stock enhancement.

Understanding fisher beliefs and attitudes towards specific management strategies can help inform and improve fisheries management, and thus stock sustainability. Previous studies highlight a lack of fisher awareness regarding environmental issues influencing the systems they utilise and the negative impacts of specific strategies, such as stock enhancement. Our study used a two-phase approach to first elicit and then measure the strength of common fishers' beliefs and associated attitudes regarding stock enhancement. Specifically, this research focused on recreational fishers of an estuarine crab fishery (Portunus armatus) in south-western Australia. The results demonstrate that recreational fishers believe stock enhancement could have strong positive outcomes, but also recognise that this management strategy could lead to some negative outcomes, though the latter are perceived as less likely to happen. This contrasts with previous research on fisheries stocking and demonstrates the value of using the two-phase approach to clarify fishers' perceptions of particular management approaches. To reduce fisher dissatisfaction with management actions, careful communication on the benefits and costs of stock enhancement is recommended. Our study highlights the significance of integrating social sciences into fisheries research, and the need to better understand fishing community beliefs to ensure effective management of the fishery.

Cat Gets Its Tern: A Case Study of Predation on a Threatened Coastal Seabird.

Domestic cats have a cosmopolitan distribution, commonly residing in urban, suburban and peri-urban environments that are also critical for biodiversity conservation. This study describes the impact of a desexed, free-roaming cat on the behavior of a threatened coastal seabird, the Australian Fairy Tern, Sternula nereis nereis, in Mandurah, south-western Australia. Wildlife cameras and direct observations of cat incursions into the tern colony at night, decapitated carcasses of adult terns, dead, injured or missing tern chicks, and cat tracks and scats around the colony provided strong evidence of cat predation, which led to an initial change in nesting behavior and, ultimately, colony abandonment and the reproductive failure of 111 nests. The death of six breeding terns from the population was a considerable loss for this threatened species and had the potential to limit population growth. This study highlights the significant negative impacts of free-roaming cats on wildlife and the need for monitoring and controlling cats at sites managed for species conservation. It also provides strong evidence against the practice of trap-neuter-release programs and demonstrates that desexed cats can continue to negatively impact wildlife post-release directly through predation, but also indirectly through fundamental changes in prey behavior and a reduction in parental care.

Microplastics: No Small Problem for Filter-Feeding Megafauna.

Microplastic pollution can impact filter-feeding marine megafauna, namely mobulid rays, filter-feeding sharks, and baleen whales. Emerging research on these flagship species highlights potential exposure to microplastic contamination and plastic-associated toxins. Research and its wide communication are needed to understand the magnitude of the issue and improve marine stewardship.

Preliminary estimates of the abundance and fidelity of dolphins associating with a demersal trawl fishery.

The incidental capture of wildlife in fishing gear presents a global conservation challenge. As a baseline to inform assessments of the impact of bycatch on bottlenose dolphins (Tursiops truncatus) interacting with an Australian trawl fishery, we conducted an aerial survey to estimate dolphin abundance across the fishery. Concurrently, we carried out boat-based dolphin photo-identification to assess short-term fidelity to foraging around trawlers, and used photographic and genetic data to infer longer-term fidelity to the fishery. We estimated abundance at ≈ 2,300 dolphins (95% CI = 1,247-4,214) over the ≈ 25,880-km2 fishery. Mark-recapture estimates yielded 226 (SE = 38.5) dolphins associating with one trawler and some individuals photographed up to seven times over 12 capture periods. Moreover, photographic and genetic re-sampling over three years confirmed that some individuals show long-term fidelity to trawler-associated foraging. Our study presents the first abundance estimate for any Australian pelagic dolphin community and documents individuals associating with trawlers over days, months and years. Without trend data or correction factors for dolphin availability, the impact of bycatch on this dolphin population's conservation status remains unknown. These results should be taken into account by management agencies assessing the impact of fisheries-related mortality on this protected species.

Macroalgae inhibits larval settlement and increases recruit mortality at Ningaloo Reef, Western Australia.

Globally, many coral reefs are degraded and demonstrate reduced coral cover and increased macroalgal abundance. While negative correlations between macroalgae and coral recruitment have commonly been documented, the mechanisms by which macroalgae affects recruitment have received little attention. Here we examined the effect of macroalgae on larval settlement and the growth and survival of coral recruits, in a field experiment over nine months. Exclusion treatments were used to manipulate herbivory and macroalgal biomass, while settlement tiles measured coral settlement and survival. After nine months the volume of macroalgae was up to 40 times greater in the caged treatments than in controls and the settlement of coral larvae on the undersides of tiles within caged plots was 93% lower than in the uncaged treatments. The growth and survival of coral recruits was also severely reduced in the presence of macroalgae: survival was 79% lower in caged treatments and corals were up to 58% smaller with 75% fewer polyps. These data indicate that macroalgae has an additive effect on coral recruitment by reducing larval settlement and increasing recruit mortality. This research demonstrates that macroalgae can not only inhibit coral recruitment, but also potentially maintain dominance through a positive feedback system.

Patterns of dolphin bycatch in a north-western Australian trawl fishery.

The bycatch of small cetaceans in commercial fisheries is a global wildlife management problem. We used data from skippers' logbooks and independent observers to assess common bottlenose dolphin (Tursiops truncatus) bycatch patterns between 2003 and 2009 in the Pilbara Trawl Fishery, Western Australia. Both datasets indicated that dolphins were caught in all fishery areas, across all depths and throughout the year. Over the entire datasets, observer reported bycatch rates (n = 52 dolphins in 4,124 trawls, or 12.6 dolphins/1,000 trawls) were ca. double those reported by skippers (n = 180 dolphins in 27,904 trawls, or 6.5 dolphins/1,000 trawls). Generalised Linear Models based on observer data, which better explained the variation in dolphin bycatch, indicated that the most significant predictors of dolphin catch were: (1) vessel--one trawl vessel caught significantly more dolphins than three others assessed; (2) time of day--the lowest dolphin bycatch rates were between 00:00 and 05:59; and (3) whether nets included bycatch reduction devices (BRDs)--the rate was reduced by ca. 45%, from 18.8 to 10.3 dolphins/1,000 trawls, after their introduction. These results indicated that differences among vessels (or skippers' trawling techniques) and dolphin behavior (a diurnal pattern) influenced the rates of dolphin capture; and that spatial or seasonal adjustments to trawling effort would be unlikely to significantly reduce dolphin bycatch. Recent skipper's logbook data show that dolphin bycatch rates have not declined since those reported in 2006, when BRDs were introduced across the fishery. Modified BRDs, with top-opening escape hatches from which dolphins might escape to the surface, may be a more effective means of further reducing dolphin bycatch. The vulnerability of this dolphin population to trawling-related mortality cannot be assessed in the absence of an ongoing observer program and without information on trawler-associated dolphin community size, broader dolphin population size and connectivity with adjacent populations.

Mechanism for the small-scale movement of carbon among estuarine habitats: organic matter transfer not crab movement.

In theory, carbon is highly mobile in aquatic systems. Recent evidence from carbon stable isotopes of crabs (Parasesarma erythrodactyla and Australoplax tridentata), however, shows that in subtropical Australian waters, measurable carbon movement between adjacent mangrove and saltmarsh habitats is limited to no more than a few metres. We tested whether the pattern in crab delta13C values across mangrove and saltmarsh habitats was explained by crab movement, or the movement of particulate organic matter. We estimated crab movement in a mark-recapture program using an array of pitfall traps on 13 transects (a total of 65 traps) covering an area of 600 m2 across the interface of these two habitats. Over a 19-day period, the majority of crabs (91% for P. erythrodactyla, 93% for A. tridentata) moved <2 m from the place of initial capture. Crab movement cannot, therefore, explain the patterns in delta13C values of crabs. delta13C values of detritus collected at 2-m intervals across the same habitat interface fitted a sigmoidal curve of a similar form to that fitting the delta13C values of crabs. delta13C values of detritus were 2-4 per thousand more depleted in saltmarsh (-18.5+/-0.6 per thousand), and 4-7 per thousand more depleted in mangroves (-25.9+/-0.1 per thousand) than delta13C values of crabs recorded previously in each habitat. Assimilation by crabs of very small detrital fragments or microphytobenthos, more enriched in 13C, may explain the disparity in delta13C values. Nevertheless, the pattern in delta13C values of detritus suggests that crabs obtain their carbon from up to several metres away, but without themselves foraging more then a metre or so from their burrow. Such detailed measurements of carbon movement in estuaries provide a spatially explicit understanding of the functioning of food webs in saltmarsh and mangrove habitats.