Movement and predation: a catch-and-release study on the acoustic tracking of bonefish in the Indian Ocean

Tourism generated through bonefish (Albula spp.) fishing contributes to the economies of many isolated tropical islands and atolls. However, little research has been conducted on bonefish in the Indian Ocean. This study aimed to contribute to the understanding of bonefish ecology in the Indian Ocean by quantifying the spatial and temporal movements of Albula glossodonta at a near-pristine and predator-rich atoll in the Seychelles; however, to achieve this, an analysis to identify the occurrence of possible post-release predation bias was first necessary. An acoustic telemetry study was initiated at the remote St. Joseph Atoll, within an array of 88 automated data-logging acoustic receivers. Thirty bonefish were surgically implanted with Vemco V13 acoustic transmitters and tracked for one year. Only 10% of the tagged bonefish were detected for longer than two weeks. A comparison of the final 100 h of movement data from fish detected for less than two weeks to the movement data of the fish detected for longer periods revealed distinct differences in area use and significant differences in the average daily distance moved, speed of movement and frequency of detections. This suggested that mortality in the form of post-release predation was at least 43% of tagged fish. The three surviving bonefish were tracked for 210 to 367 days. These individuals remained in the atoll and showed high use of the marginal habitats between the shallow sand flats and the lagoon. A generalised linear mixed model identified that water temperature, diel cycle and tide were significant predictors of bonefish presence in the lagoon. The high post-release mortality highlights that catch-and-release is likely not as benign as previously believed and management and policy should be adjusted accordingly

Stingray Habitat Use Is Dynamically Influenced by Temperature and Tides

Abiotic factors often have a large influence on the habitat use of animals in shallow marine environments. Specifically, tides may alter the physical and biological characteristics of an ecosystem while changes in temperature can cause ectothermic species to behaviorally thermoregulate. Understanding the contextual and relative influences of these abiotic factors is important in prioritizing management plans, particularly for vulnerable faunal groups like stingrays. Passive acoustic telemetry was used to track the movements of 60 stingrays at a remote and environmentally heterogeneous atoll in Seychelles. This was to determine if habitat use varied over daily, diel and tidal cycles and to investigate the environmental drivers behind these potential temporal patterns. Individuals were detected in the atoll year-round, but the extent of their movement and use of multiple habitats increased in the warmer NW-monsoon season. Habitat use varied over the diel cycle, but was inconsistent between individuals. Temperature was also found to influence stingray movements, with individuals preferring the deeper and more thermally stable lagoon habitat when extreme (hot or cold) temperature events were observed on the flats. Habitat use also varied over the tidal cycle with stingrays spending a higher proportion of time in the lagoon during the lowest tides, when movement on the flats were constrained due to shallow waters. The interplay of tides and temperature, and how these varied across diel and daily scales, dynamically influenced stingray habitat use consistently between three species in an offshore atoll.</jats:p

Movement and predation: a catch-and-release study on the acoustic tracking of bonefish in the Indian Ocean

Tourism generated through bonefish (Albula spp.) fishing contributes to the economies of many isolated tropical islands and atolls. However, little research has been conducted on bonefish in the Indian Ocean. This study aimed to contribute to the understanding of bonefish ecology in the Indian Ocean by quantifying the spatial and temporal movements of Albula glossodonta at a near-pristine and predator-rich atoll in the Seychelles; however, to achieve this, an analysis to identify the occurrence of possible post-release predation bias was first necessary. An acoustic telemetry study was initiated at the remote St. Joseph Atoll, within an array of 88 automated data-logging acoustic receivers. Thirty bonefish were surgically implanted with Vemco V13 acoustic transmitters and tracked for one year. Only 10% of the tagged bonefish were detected for longer than two weeks. A comparison of the final 100 h of movement data from fish detected for less than two weeks to the movement data of the fish detected for longer periods revealed distinct differences in area use and significant differences in the average daily distance moved, speed of movement and frequency of detections. This suggested that mortality in the form of post-release predation was at least 43% of tagged fish. The three surviving bonefish were tracked for 210 to 367 days. These individuals remained in the atoll and showed high use of the marginal habitats between the shallow sand flats and the lagoon. A generalised linear mixed model identified that water temperature, diel cycle and tide were significant predictors of bonefish presence in the lagoon. The high post-release mortality highlights that catch-and-release is likely not as benign as previously believed and management and policy should be adjusted accordingly

Environmental DNA biomonitoring in biodiversity hotspots: A case study of fishes of the Okavango Delta

The Okavango Delta is the largest freshwater wetland in southern Africa and a recognized biodiversity hotspot and UNESCO World Heritage Site. The region is extremely rich in floral and faunal diversity, including a fish fauna of ~90 species in 15 families, that also support recreational and subsistence fishing. Anthropogenic pressures and invasive species threaten the unique biodiversity and ecosystem services that the Delta provides, necessitating biomonitoring tools that can provide broad community-level diversity insights. Here, we utilize environmental DNA metabarcoding of aquatic eDNA using the MiFish 12S rRNA primers, to investigate fish communities and also sequenced 211 mtDNA 12S barcodes for 74 species across 36 genera of fishes from the region. Metabarcoding recovered 11 of 15 families, with 40 species detected across 23 genera, representing ~50% of known diversity, with the mtDNA 12S fragment able to delineate all genera (except for the cichlid genera Serranochromis and Pharyngochromis that comprised a single clade) and most species, except for some in the Clarias, Enteromius, Labeo, Lacustricola, and Petrocephalus genera. Generally, abundant and wide-spread taxa such as Clarias spp. and Marcusenius altisambesi, amongst others, were often detected in the surveys, with other species, including Zaireichthys kavangoensis, Schilbe intermedius, and Labeo sp. detected less frequently. Dissolved oxygen, temperature, and dissolved organic solids were positively correlated with community diversity, highlighting the influence of environmental factors in shaping fish communities in the region. Further, there was strong variability in the eDNA signal across only 1000 m, suggesting that future surveys need to consider spatio-temporal aspects of sample collection. Our study highlights the potential of eDNA metabarcoding for surveying aquatic biodiversity in the Okavango Delta, particularly within the context of baseline biodiversity inventories, that underpin conservation and management initiatives. As such, we provide a number of recommendations that can help structure future sampling efforts in the region

The twilight of the Liberal Social Contract? On the Reception of Rawlsian Political Liberalism

This chapter discusses the Rawlsian project of public reason, or public justification-based 'political' liberalism, and its reception. After a brief philosophical rather than philological reconstruction of the project, the chapter revolves around a distinction between idealist and realist responses to it. Focusing on political liberalism’s critical reception illuminates an overarching question: was Rawls’s revival of a contractualist approach to liberal legitimacy a fruitful move for liberalism and/or the social contract tradition? The last section contains a largely negative answer to that question. Nonetheless the chapter's conclusion shows that the research programme of political liberalism provided and continues to provide illuminating insights into the limitations of liberal contractualism, especially under conditions of persistent and radical diversity. The programme is, however, less receptive to challenges to do with the relative decline of the power of modern states

Constitutivism

A brief explanation and overview of constitutivism

Philosophy of action

The philosophical study of human action begins with Plato and Aristotle. Their influence in late antiquity and the Middle Ages yielded sophisticated theories of action and motivation, notably in the works of Augustine and Aquinas.1 But the ideas that were dominant in 1945 have their roots in the early modern period, when advances in physics and mathematics reshaped philosophy

Demographic resilience of territorial island birds to extinction: the flightless Aldabra Rail Dryolimnas (cuvieri) aldabranus as an example

Since 1600, a disproportionate number of avian extinctions have occurred among  flightless and island-dwelling species. Some of these happened very rapidly, implying that such populations had low resilience to perturbation. In managing  insular populations, there is a need to be able to predict their demographic  responses to novel circumstances, such as predator introduction, not least in  order to quantify the window of time within which remedial action must be taken to minimise extinction risk. To explore how such resilience might be  quantified, we used the territorial, flightless Aldabra Rail Dryolimnas (cuvieri) aldabranus as a ‘model’ species. Endemic to Aldabra Atoll, Republic of Seychelles, this is the last remaining flightless bird in the tropical Indian Ocean. Formerly ubiquitous on Aldabra, by 1977 its range had contracted to three islands: Malabar (by far the largest population), Polymnie and Île aux Cèdres. In  1999, the species was successfully reintroduced to a fourth island (Picard),  where exponential growth of the reintroduced population was predicted to continue until it reached c. 1 000 pairs in about 2010. Despite this success, the entire world population of Aldabra Rails remains confined to four adjacent islets, with no ex situ populations, placing the species at high risk of stochastic extinction. The aims of this study were to assess whether there were any significant changes in the population size of rails in recent decades and to explore the population level consequences of the most likely stochastic event, viz. the introduction of alien predators to Malabar Island (cats being abundant on the adjacent island of Grande Terre). There have been no substantial changes in the population at Malabar Island since the 1980s, but the previous estimate of the number of breeding pairs was revised downwards from c. 4 000 to c. 3 500. We made the first assessment of the number of non-breeding birds (floaters)—in early 2000, Malabar was estimated to have c. 3 500 floaters—and explored their role as a demographic buffer to extinction using a stochastic population model. Despite the large number of floaters, a population of 60 or more cats is predicted to drive the Malabar rails to extinction within 20 years. However, in the absence of introduced predators the Malabar population is resilient to the removal of up to 100 pairs of breeding birds annually for introductions to other islands within the species’ former range. Of wider relevance, for territorial, insular species, monitoring of the floater population may provide an earlier warning of a pending population crash than monitoring of numbers breeding. OSTRICH 2011, 82(1): 1–

Dietary niche differentiation in a mesopredatory dasyatid assemblage

Most batoids are mesopredators and are often hypothesised to play important ecological roles. However, a comprehensive understanding into these roles remains limited given the paucity of information of their trophic habits. St. Joseph Atoll (5.43∘S, 53.35∘E) is a remote ecosystem that hosts a resident assemblage of dasyatids (Pastinachus ater, Urogymnus granulatus, and U. asperrimus). Both stomach contents (SC) and stable isotope samples (SI) (δ15N and δ13C) were collected in 2015 and used to investigate the trophic niches of this dasyatid assemblage and whether these niches differed inter- and intra-specifically. Dasyatid muscle samples as well as baseline samples of potential prey species and primary producers were collected for SI analyses. SC data highlighted significant inter-specific differences in diet, U. granulatus juveniles mostly consumed decapod crustaceans (Callianassidae and Portunidae) and P. ater juveniles mostly consumed bivalve molluscs. The mean species trophic positions for juveniles of all three species ranged from 2.9 to 3.6 when calculated using δ15N and from 3.4 to 3.6 when calculated using stomach content data. Analysis of δ13C showed that all juveniles were reliant upon the same carbon resources (primarily derived from seagrass beds) at the base of the food web. Diet appeared to change with size as larger individuals displayed lower δ13C and higher δ15N compared to smaller juveniles. Additionally, isotope values of the smallest individuals were similar to the largest individuals, suggesting maternal meddling. The identified patterns of inter- and intra-specific trophic niche differentiation may be indicative of competitive effects and contributes to the understanding of mesopredators in community trophic dynamics