Vinay Udyawer

First record of sea snake (Hydrophis elegans, Hydrophiinae) entrapped in marine debris.

Entanglement in derelict fishing gear and other marine debris is a major threat to the survival of large marine wildlife like cetaceans, seabirds and sea turtles. However, no previous reports of entanglement or entrapment have been recorded in sea snakes (Hydrophiinae). We report here on a sea snake (Hydrophis elegans) found with a ceramic washer encircling its body captured from the north-east coast of Queensland, Australia. The ring had constricted the body and over time caused extensive damage to the underlying tissues. A post-mortem examination showed the snake was severely emaciated as the ring restricted the passage of food to the stomach and intestine. This is the first record of mortality due to marine debris entrapment in sea snakes.

Distribution of sea snakes in the Great Barrier Reef Marine Park: observations from 10 yrs of baited remote underwater video station (BRUVS) sampling

The distributions of three species of sea snake (olive sea snake: Aipysurus laevis, spine-bellied sea snake: Lapemis curtus, and ornate sea snake: Hydrophis ocellatus) were estimated over 14° of latitude within the Great Barrier Reef Marine Park (GBRMP) using data from baited remote underwater video stations (BRUVS). A total of 2,471 deployments of BRUVS were made in a range of locations, in sites open and closed to trawl fishing. Sightings of sea snakes were analysed alongside six spatial factors [depth, relative distance across (longitude) and along (latitude) the GBRMP, proximity to land, proximity to the nearest reef, and habitat complexity] to determine the factors that most strongly influenced the distribution and abundance of sea snakes. The results showed a strong latitudinal effect on the distribution of all three sea snake species, with the highest densities and diversities occurring in central and southern GBRMP locations, while the northern Great Barrier Reef was relatively depauperate in terms of both occurrence and diversity. Shallow inshore areas were identified as key habitats for A. laevis and L. curtus, whereas deeper offshore habitats were most important for H. ocellatus. No significant difference was found in the mean number of snakes sighted per hour between sites open and closed to trawling. There was a high degree of congruence in the distribution of sea snakes estimated from the BRUVS data and results from previous trawl and underwater visual surveys, demonstrating the utility of BRUVS to estimate distribution and relative abundance in these species of sea snake at broad spatial scales in a non-extractive manner.

Diel patterns in three-dimensional use of space by sea snakes

BackgroundThe study of animal movement and use of space have traditionally focused on horizontal and vertical movements separately. However, this may limit the interpretation of results of such behaviours in a three-dimensional environment. Here we use passive acoustic telemetry to visualise and define the three-dimensional use of space by two species of sea snake [Hydrophis (Lapemis) curtus; and Hydrophis elegans] within a coastal embayment and identify changes in how they use space over a diel cycle.ResultsMonitored snakes exhibited a clear diel pattern in their use of space, with individuals displaying restricted movements at greater depths during the day, and larger movements on the surface at night. Hydrophiscurtus generally occupied space in deep water within the bay, while H. elegans were restricted to mud flats in inundated inter-tidal habitats. The overlap in space used between day and night showed that individuals used different core areas; however, the extent of areas used was similar.ConclusionsThis study demonstrates that by incorporating the capacity to dive in analyses of space use by sea snakes, changes over a diel cycle can be identified. Three-dimensional use of space by sea snakes can identify spatial or temporal overlaps with anthropogenic threats (e.g. trawling, dredging) and help develop targeted management policies that mitigate any adverse effects to ensure healthy populations of sea snakes.

Temporal and spatial activity-associated energy partitioning in free-swimming sea snakes

1. Partitioning energy between critical basal functions and activity-associated behaviours is a primary determinant of animal survival. Consequently, habitat selection is likely to be driven by the efficiency with which resources can be acquired from a heterogeneous energy landscape. 2. Determining how energy partitioning is achieved across temporal and spatial scales is particularly challenging in aquatic animals due to the logistical limitations in estimating field metabolic rates (FMR) while simultaneously examining habitat choice. 3. Here, acoustic telemetry using accelerometers alongside bimodal respirometry were used to correlate vectorial dynamic body acceleration (VeDBA) with oxygen consumption rates (VeDBA) of sea snakes (Hydrophis curtus and Hydrophis elegans) across an ecologically relevant temperature range. Subsequently, VeDBA of free-roaming snakes was used to estimate activity-associated FMR within a near-shore environment over diel, seasonal and spatial scales. 4. Diel changes in activity explained short-term patterns in FMR, whereas seasonal changes in water temperature drove long-term patterns. Spatial analyses demonstrated that activity-associated FMR was elevated in productive seagrass and mudflat habitats, indicative of a concentration of foraging efforts. 5. Our findings illustrate for the first time how sea snakes partition activity-associated FMR across time and space, providing an approach by which we can monitor the impacts of, and vulnerabilities to, natural and anthropogenic disturbances like warming and trawl fisheries.

Coming up for air: thermal dependence of dive behaviours and metabolism in sea snakes

ABSTRACT Cutaneous gas exchange allows some air-breathing diving ectotherms to supplement their pulmonary oxygen uptake, which may allow prolongation of dives and an increased capacity to withstand anthropogenic and natural threatening processes that increase submergence times. However, little is known of the interplay between metabolism, bimodal oxygen uptake and activity levels across thermal environments in diving ectotherms. Here, we show in two species of sea snake (spine-bellied sea snake, Hydrophis curtus; and elegant sea snake, Hydrophis elegans) that increasing temperature elevates surfacing rate, increases total oxygen consumption and decreases dive duration. The majority of dives observed in both species remained within estimated maximal aerobic limits. While cutaneous gas exchange accounted for a substantial proportion of total oxygen consumption (up to 23%), unexpectedly it was independent of water temperature and activity levels, suggesting a diffusion-limited mechanism. Our findings demonstrate that rising water temperature and a limited capability to up-regulate cutaneous oxygen uptake may compromise the proficiency with which sea snakes perform prolonged dives. This may hinder their capacity to withstand ongoing anthropogenic activities like trawl fishing, and increase their susceptibility to surface predation as their natural environments continue to warm. Summary: Interactions between the thermal environment, body activity and bimodal respiration show that with rising water temperatures, sea snakes may become more susceptible to fishing-related mortality through reduced apnoeic capacity.

Importance of Shallow Tidal Habitats as Refugia from Trawl Fishing for Sea Snakes

Abstract Sea snakes are an important component of bycatch in commercial and small-scale trawl fisheries in tropical waters and are highly vulnerable to fishing-related mortality. Extensive boat-based surveys were conducted to investigate the assemblage and abundance of sea snakes within a protected shallow coastal bay adjacent to productive trawl fishing grounds. Spine-Bellied Sea Snakes, Hydrophis curtus (previously Lapemis curtus), and Elegant Sea Snakes, Hydrophis elegans, were the most commonly encountered species. Based on the age structure of these two species, the bay was used primarily by juveniles. Temporal trends in age structure and sex ratios showed that H. curtus may use Cleveland Bay as a nursery ground, with gravid females entering the bay in summer months to give birth. In contrast, H. elegans appears to use the bay more consistently through the year, with ∼30% of individuals being adults. This study also showed that shallow tidal habitats, too shallow for trawl fishing, are regularly used by sea snakes and may provide refugia for vulnerable life stages. The identification and protection of such habitats may further mitigate risks to sea snake populations from trawl fishing.