Movement, distribution and marine reserve use by an endangered migratory giant

Effects of climate warming on energetics and habitat of the world's largest marine ectotherm

Responses of organisms to climate warming are variable and complex. Effects on species distributions are already evident and mean global surface ocean temperatures are likely to warm by up to 4.1 °C by 2100, substantially impacting the physiology and distributions of ectotherms. The largest marine ectotherm, the whale shark Rhincodon typus, broadly prefers sea surface temperatures (SST) ranging from 23 to 30 °C. Whole-species distribution models have projected a poleward range shift under future scenarios of climate change, but these models do not consider intraspecific variation or phenotypic plasticity in thermal limits when modelling species responses, and the impact of climate warming on the energetic requirements of whale sharks is unknown. Using a dataset of 111 whale shark movement tracks from aggregation sites in five countries across the Indian Ocean and the latest Earth-system modelling produced from Coupled Model Intercomparison Project Phase 6 for the Intergovernmental Panel on Climate Change, we examined how SST and total zooplankton biomass, their main food source, may change in the future, and what this means for the energetic balance and extent of suitable habitat for whale sharks. Earth System Models, under three Shared Socioeconomic Pathways (SSPs; SSP1-2.6, SSP3-7.0 and SSP5-8.5), project that by 2100 mean SST in four regions where whale shark aggregations are found will increase by up to 4.9 °C relative to the present, while zooplankton biomass will decrease. This reduction in zooplankton is projected to be accompanied by an increase in the energetic requirements of whale sharks because warmer water temperatures will increase their metabolic rate. We found marked differences in projected changes in the extent of suitable habitat when comparing a whole-species distribution model to one including regional variation. This suggests that the conventional approach of combining data from different regions within a species' distribution could underestimate the amount of local adaptation in populations, although parameterising local models could also suffer from having insufficient data and lead to model mis-specification or highly uncertain estimates. Our study highlights the need for further research into whale shark thermal tolerances and energetics, the complexities involved in projecting species responses to climate change, and the potential importance of considering intraspecific variation when building species distribution models.

Predicting suitable habitats for foraging and migration in Eastern Indian Ocean pygmy blue whales from satellite tracking data

BACKGROUND

Accurate predictions of animal occurrence in time and space are crucial for informing and implementing science-based management strategies for threatened species.

METHODS

We compiled known, available satellite tracking data for pygmy blue whales in the Eastern Indian Ocean (n = 38), applied movement models to define low (foraging and reproduction) and high (migratory) move persistence underlying location estimates and matched these with environmental data. We then used machine learning models to identify the relationship between whale occurrence and environment, and predict foraging and migration habitat suitability in Australia and Southeast Asia.

RESULTS

Our model predictions were validated by producing spatially varying accuracy metrics. We identified the shelf off the Bonney Coast, Great Australian Bight, and southern Western Australia as well as the slope off the Western Australian coast as suitable habitat for migration, with predicted foraging/reproduction suitable habitat in Southeast Asia region occurring on slope and in deep ocean waters. Suitable foraging habitat occurred primarily on slope and shelf break throughout most of Australia, with use of the continental shelf also occurring, predominanly in South West and Southern Australia. Depth of the water column (bathymetry) was consistently a top predictor of suitable habitat for most regions, however, dynamic environmental variables (sea surface temperature, surface height anomaly) influenced the probability of whale occurrence.

CONCLUSIONS

Our results indicate suitable habitat is related to dynamic, localised oceanic processes that may occur at fine temporal scales or seasonally. An increase in the sample size of tagged whales is required to move towards developing more dynamic distribution models at seasonal and monthly temporal scales. Our validation metrics also indicated areas where further data collection is needed to improve model accuracy. This is of particular importance for pygmy blue whale management, since threats (e.g., shipping, underwater noise and artificial structures) from the offshore energy and shipping industries will persist or may increase with the onset of an offshore renewable energy sector in Australia.

Illegal Trade in Protected Sharks: The Case of Artisanal Whale Shark Meat Fisheries in Java, Indonesia

Illegal, unreported, and unregulated fishing, including that of sharks, poses a significant threat to marine ecosystems and individual species. I use data from the media, tourists, and artisan fishermen to gain insight into the trade in the world's largest fish, the whale shark (Rhincodon typus). I focus on the Indonesian island of Java where, along its south coast, whale sharks are landed and butchered on the beach in view of hundreds of people and local media. Whale sharks are typically caught in fishing nets and dragged alongside boats to the shallows, where they are butchered. The meat and oil (valued at ~USD 2000 per shark) are sold and distributed within the community. I document 58 landings of mainly immature whale sharks (2002-2022). Artisanal fishermen see the landing of whale sharks as a fortuitous event, but the species is protected, and Indonesia is a signatory to various international agreements that preclude the fishing of whale sharks. It is imperative for the conservation of whale sharks that the various parties in Indonesia adhere better to their own rules and regulations protecting this species.

Individual and Population Benefits of Marine Reserves for Reef Sharks

No-take marine protected areas (MPAs) are a commonly applied tool to reduce human fishing impacts on marine and coastal ecosystems. However, conservation outcomes of MPAs for mobile and long-lived predators such as sharks are highly variable. Here, we use empirical animal tracking data from 459 individual sharks and baited remote underwater video surveys undertaken in 36 countries to construct an empirically supported individual-based model that estimates the conservation effectiveness of MPAs for five species of coral reef-associated sharks (Triaenodon obesus, Carcharhinus melanopterus, Carcharhinus amblyrhynchos, Carcharhinus perezi, and Ginglymostoma cirratum). We demonstrate how species-specific individual movement traits can contribute to fishing mortality of sharks found within MPAs as they move outside to adjacent fishing grounds. We discovered that the world's officially recorded coral reef-based managed areas (with a median width of 9.4 km) would need to be enforced as strict no-take MPAs and up to 5 times larger to expect protection of the majority of individuals of the five investigated reef shark species. The magnitude of this effect depended on local abundances and fishing pressure, with MPAs required to be 1.6-2.6 times larger to protect the same number of Atlantic and Caribbean species, which occur at lower abundances than similar species in the western Pacific. Furthermore, our model was used to quantify partially substantial reductions (>50%) in fishing mortality resulting from small increases in MPA size, allowing us to bridge a critical gap between traditional conservation planning and fisheries management. Overall, our results highlight the challenge of relying on abundance data alone to ensure that estimates of shark conservation impacts of MPAs follow the precautionary approach.

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.

Using individual-based movement information to identify spatial conservation priorities for mobile species

The optimal design of reserve networks and fisheries closures depends on species occurrence information and knowledge of how anthropogenic impacts interact with the species concerned. However, challenges in surveying mobile and cryptic species over adequate spatial and temporal scales can mask the importance of particular habitats, leading to uncertainty about which areas to protect to optimize conservation efforts. We investigated how telemetry-derived locations can help guide the scale and timing of fisheries closures with the aim of reducing threatened species bycatch. Forty juvenile speartooth sharks (Glyphis glyphis) were monitored over 22 months with implanted acoustic transmitters and an array of hydrophone receivers. Using the decision-support tool Marxan, we formulated a permanent fisheries closure that prioritized areas used more frequently by tagged sharks and considered areas perceived as having high value to fisheries. To explore how the size of the permanent closure compared with an alternative set of time-area closures (i.e., where different areas were closed to fishing at different times of year), we used a cluster analysis to group months that had similar arrangements of selected planning units (informed by shark movements during that month) into 2 time-area closures. Sharks were consistent in their timing and direction of migratory movements, but the number of tagged sharks made a big difference in the placement of the permanent closure; 30 individuals were needed to capture behavioral heterogeneity. The dry-season (May-January) and wet-season (February-April) time-area closures opened 20% and 25% more planning units to fishing, respectively, compared with the permanent closure with boundaries fixed in space and time. Our results show that telemetry has the potential to inform and improve spatial management of mobile species and that the temporal component of tracking data can be incorporated into prioritizations to reduce possible impacts of spatial closures on established fisheries.

A Synthesis of Opportunities for Applying the Telecoupling Framework to Marine Protected Areas

The world’s oceans face unprecedented anthropogenic threats in the globalized era that originate from all over the world, including climate change, global trade and transportation, and pollution. Marine protected areas (MPAs) serve important roles in conservation of marine biodiversity and ecosystem resilience, but their success is increasingly challenged in the face of such large-scale threats. Here, we illustrate the utility of adopting the interdisciplinary telecoupling framework to better understand effects that originate from distant places and cross MPA boundaries (e.g., polluted water circulation, anthropogenic noise transport, human and animal migration). We review evidence of distal processes affecting MPAs and the cutting-edge approaches currently used to investigate these processes. We then introduce the umbrella framework of telecoupling and explain how it can help address knowledge gaps that exist due to limitations of past approaches that are centered within individual disciplines. We then synthesize five examples from the recent telecoupling literature to explore how the telecoupling framework can be used for MPA research. These examples include the spatial subsidies approach, adapted social network analysis, telecoupled qualitative analysis, telecoupled supply chain analysis, and decision support tools for telecoupling. Our work highlights the potential for the telecoupling framework to better understand and address the mounting and interconnected socioeconomic and environmental sustainability challenges faced by the growing number of MPAs around the world.

Do they stay or do they go? Acoustic monitoring of whale sharks at Ningaloo Marine Park, Western Australia

Whale sharks Rhincodon typus were monitored via acoustic transmitters at the northern end of Western Australia's Ningaloo Marine Park to establish the extent to which the species inhabits the region beyond the whale-shark ecotourism industry season, which usually extends from March to August in each year. Despite the vast majority (c. 98%) of photographic submissions of R. typus from Ningaloo Reef being between March and August, acoustic detections from the tagged R. typus at Ningaloo were recorded in all months of the year, but do not preclude the occurrence of extended absences. It is concluded that as a species, R. typus occurs year round at Ningaloo, where it generally remains in close proximity to the reef edge, but that some individuals move outside of the detection range of the array for extended periods.