Multivariate analysis of biologging data reveals the environmental determinants of diving behaviour in a marine reptile

Diving behaviour of 'surfacers' such as sea snakes, cetaceans and turtles is complex and multi-dimensional, thus may be better captured by multi-sensor biologging data. However, analysing these large multi-faceted datasets remains challenging, though a high priority. We used high-resolution multi-sensor biologging data to provide the first detailed description of the environmental influences on flatback turtle (Natator depressus) diving behaviour, during its foraging life-history stage. We developed an analytical method to investigate seasonal, diel and tidal effects on diving behaviour for 24 adult flatback turtles tagged with biologgers. We extracted 16 dive variables associated with three-dimensional and kinematic characteristics for 4128 dives. K-means and hierarchical cluster analyses failed to identify distinct dive types. Instead, principal component analysis objectively condensed the dive variables, removing collinearity and highlighting the main features of diving behaviour. Generalized additive mixed models of the main principal components identified significant seasonal, diel and tidal effects on flatback turtle diving behaviour. Flatback turtles altered their diving behaviour in response to extreme tidal and water temperature ranges, displaying thermoregulation and predator avoidance strategies while likely optimizing foraging in this challenging environment. This study demonstrates an alternative statistical technique for objectively interpreting diving behaviour from multivariate collinear data derived from biologgers.

Fish-habitat associations on a subsea pipeline within an Australian Marine Park

Subsea pipelines have been installed in all major hydrocarbon basins across the globe to support the offshore Oil & Gas (O&G) industry. These artificial structures provide hard substratum that can be colonised and utilised by sessile and mobile organisms. The present study utilises industry-collected remotely operated vehicle (ROV) video to assess fish species richness and abundance, and marine growth type, extent and complexity along sections of a subsea gas pipeline, in 56-82 m depth, that traverses the Australian Commonwealth Montebello Marine Park (MMP). A total of 7493 fish from 81 species and 33 families were recorded from 606 analysed 10 m transects spaced across sections of the pipeline. Of these 81 species, 27 are considered fishery-target species in the Pilbara Demersal Scalefish fishery (PDSF), with select commercial fishing activities permitted with authorisation within the Marine Park. A moderate abundance (175) of sub-adult red emperor (Lutjanus sebae), a fishery-indicator species, were observed along the pipeline. Eleven different categories of marine growth habitat were observed, with the pipeline possessing quite uniform coverage of encrusting marine growth (coralline algae, bryozoans, ascidians, etc.) with patchy occurrences of more structurally complex sponges and black/octocoral forms. Fish species richness and abundance of the commercially targeted Moses' snapper (Lutjanus russellii) were correlated positively with increasing cover of sponges. The pipeline itself had very few spans and was never more than fractionally buried. Despite the somewhat homogenous habitats, depths, and position of the pipeline relative to the seafloor, presence of a field joint indent had a positive influence on the abundance of some common and commercially important fish species. This study demonstrates the ecological value of ROV footage obtained during industry inspection operations that were conducted for reasons unrelated to the determination of ecological information. The pipeline offers a corridor of hard bottom habitat within a marine park that facilitates epibiotic growth and the presence of reef-associated species in a region characterised by sandy sediments. Results indicate the potential importance of subsea O&G infrastructure as a habitat for fish, and in consequence, potentially also as structures with value to fisheries.

Migratory corridor linking Atlantic green turtle, Chelonia mydas, nesting site on Bioko Island, Equatorial Guinea to Ghanaian foraging grounds

This study uses satellite telemetry to track post-nesting movements of endangered green turtles (Chelonia mydas) (n = 6) in the Gulf of Guinea. It identifies a migratory corridor linking breeding grounds of Atlantic green turtles nesting on Bioko Island, Equatorial Guinea, to foraging grounds in the coastal waters of Accra, Ghana. Track lengths of 20–198 days were analyzed, for a total of 536 movement days for the six turtles. Migratory pathways and foraging grounds were identified by applying a switching state space model to locational data, which provides daily position estimates to identify shifts between migrating and foraging behavior. Turtles exhibited a combination of coastal and oceanic migrations pathways that ranged from 957 km to 1,131 km. Of the six turtles, five completed their migration and maintained residency at the same foraging ground near the coastal waters of Accra, Ghana until transmission was lost. These five resident turtles inhabit heavily fished waters and are vulnerable to a variety of anthropogenic threats. The identification of these foraging grounds highlights the importance of these coastal waters for the protection of the endangered Atlantic green turtle.

Twenty years of turtle tracks: marine turtle nesting activity at remote locations in the Pilbara, Western Australia

Little is known about the biology and ecology of marine turtles in the Pilbara region of Western Australia and most potential habitat is unconfirmed and, therefore, undescribed. Understanding basic biological parameters at a regional level is critically important for effective long-term management. We used the ‘track census’ methodology to identify reproductive habitat and assess species-specific abundance of adult flatback (Natator depressus), green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles at 154 locations in the Pilbara region of Western Australia. Between 1992 and 2012, potential nesting habitat was assessed via either ground or aerial ‘snapshot’ (single visit) or ‘census’ (more than one night) surveys and additional information obtained using the Expert Elicitation Method. Species-specific abundance (tracks night–1 ± s.d.) was varied; green turtles were most abundant, nesting at fewer locations (n = 47) but in greater numbers (1200.5 ± 62.0) than flatback or hawksbill turtles and primarily (93%) at island locations. Flatback turtle nests were more widely distributed (n = 77) than those of green or hawksbill turtles, yet abundance (877.4 ± 29.5) was lower than that of green and greater than that of hawksbill turtles. Activity was primarily (76%) island-based and activity on the mainland coastline was concentrated close to Mundabullangana and Cemetery Beach. Hawksbill turtle abundance (314.1 ± 17.1) was lowest and the least widespread (n = 43), concentrated primarily in the Onslow and Dampier subregions with no activity recorded in the Port Hedland subregion or on the mainland coastline. The findings provide information with which the Federal government can meaningfully assess the status and distribution of EPBC Act–listed species where habitat overlaps with areas zoned for development. We highlight the urgent need for the Federal Government to regulate the process by which we accumulate data to support data quality and provide meaningful information to enhance efficacy in state and Federal management of species of concern.