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.     

Association of the whale shark Rhincodon typus with the cannonball jellyfish Stomolophus meleagris

This study describes the first record of the whale shark Rhincodon typus association with the cannonball jellyfish Stomolophus meleagris in the Gulf of California, Mexico. Whale sharks were observed swimming and feeding among swarms of jellyfish, suggesting competition and predatory behaviour given the overlap in food preferences between both species. This finding is relevant because of the species‐wide distribution and the importance of these interactions, which should be considered in conservation strategies of R. typus and management of cannonball jellyfish fisheries.     

A new record of whale shark Rhincodon typus in Brazilian waters: a report of association with Caranx crysos

In May 2011, a Rhincodon typus was sighted on the continental shelf of the central Brazilian coast, in the vicinity of a gas platform. During the video record, an interspecific following association was observed between a Caranx crysos school and the R. typus.     

Distribution and feeding habitat characterization of whale sharks Rhincodon typus in a protected area in the north Caribbean Sea

The relationship between the distribution of the whale shark Rhincodon typus and hydrobiological variables in the Caribbean Sea during 2005–2009 was analysed. Monthly trips were made to the R. typus aggregation area during the months when this species is present in the region (May to September) to record sightings and hydrological data and to collect samples to determine nutrients, chlorophyll a (Chl a) and zooplankton biomass. A total of 2104 R. typus were counted and three zones of high abundance were identified: Cabo‐Catoche, Contoy (both within the Whale Shark Biosphere Reserve, WSBR) and the zone knows as Afuera. The zones of greatest R. typus density within the WSBR were characterized by high Chl a concentrations (median: 1·1 mg m^?3, interpercentile range: 0·5–1·8 mg m^?3) and high nutrient concentrations, such as ammonium (median: 2·5 µmol l^?1, interpercentile range: 0·5–6·4 µmol l^?1), due to the influence of local upwelling. A generalized additive model (GAM) was used to explore the relationship between R. typus distribution and the environmental variables inside WSBR. Zooplankton biomass was the most influential environmental variable, supporting the close relationship between R. typus distribution and biological productivity. Copepods were the dominant zooplankton group within the WSBR. In the Afuera zone, there were large R. typus aggregations (>80 individuals) associated with zooplankton dominated by fish eggs and significantly higher mean ± s.d. biomass (3356·1 ± 1960·8 mg m^?3) compared with that recorded inside the WSBR (103·5 ± 57·2 mg m^?3). The differences among zones generated changes in R. typus distribution patterns and provided opportunities to develop local management strategies for this species.     

Population structure and residency of whale sharks Rhincodon typus at Utila,Bay Islands,Honduras

There were 479 reported whale shark Rhincodon typus encounters between 1999 and 2011 at the island of Utila, which forms part of the Meso‐American Barrier Reef System (MBRS) in the western Caribbean Sea. The majority of R. typus were found to feed on small bait fish associated with various tuna species. Ninety‐five individual R. typus, ranging from 2 to 11 m total length (L_T), were identified through their unique spot patterns. A significant male bias (65%) was present. There was no significant difference between the mean ± s.d . L_T of female (6·66 ± 1·65 m) and male (6·25 ± 1·60 m) R. typus. Most R. typus were transient to Utila, with 78% sighted only within a single calendar year, although some individuals were sighted in up to 5 years. Mean residency time was modelled to be 11·76 days using maximum likelihood methods.     

Population structure of a whale shark Rhincodon typus aggregation in the Red Sea

The presence of whale sharks Rhincodon typus were recorded around Shib Habil, a small, coastal reef off the Red Sea coast of Saudi Arabia, from 2010 to 2015. A total of 267 suitable photographs resulting in the identification of 136 individuals, were documented from 305 encounters. Sharks were divided evenly between the sexes with no evidence of temporal or spatial segregation. All individuals were immature based on size estimates and, for males, juvenile clasper morphology. Scars were reported for 57% of R. typus with 15% showing evidence of propeller trauma. Estimates of population size and patterns of residency were calculated by modelling the lagged identification rate. Multiple models were run simultaneously and compared using the Akaike information criterion. An open population model was found to best represent the data and estimates a daily abundance between 15 and 34 R. typus during the aggregation season, with local residence times ranging from 4 to 44 days. Residence times away from Shib Habil range from 15 to 156 days with a permanent emigration–death rate between 0·07 and 0·58 individuals year^?1. These results are broadly similar to those from other aggregations of R. typus, although the observed sexual parity and integration found at this site is unique for the species and needs further study.     

Whale shark Rhincodon typus strandings in the Gulf of California,Mexico

The present study analyses whale shark Rhincodon typus stranding in the Gulf of California, Mexico, reported by the public, scientists, authorities and artisanal fishermen. A total of 14 strandings were documented during the period 2001–2018. The total length of R. typus ranged from 350–1,102 cm, with a sex ratio of 3.5:1 (males: females). This study highlights potential stranding areas, the need for better stranding protocols to assist R. typus recovery and the importance of samples from dead animals for scientific research.     

Northernmost record of a whale shark Rhincodon typus from the Sea of Okhotsk

The whale shark Rhincodon typus is the world's largest fish and it occurs in tropical, subtropical and warm temperate waters. Here, the northernmost record of R. typus is reported, when it was found in the Sea of Okhotsk for the first time. This occurrence can be explained by the unusually high sea surface temperature during the summer of 2012.     

The first record,tagging and release of a neonatal whale shark Rhincodon typus in Taiwan

On 27 October 2013, a Rhincodon typus was apparently chased by a group of Caranx ignobilis into nearshore waters near Green Island (Ludao), east of Taiwan. A fisherman brought it back to port where it was kept in a small sea pen until release. The R. typus was 78 cm total length, and was tagged and released on 29 October 2013.     

Acoustic telemetry reveals cryptic residency of whale sharks

Although whale sharks (Rhincodon typus) have been documented to move thousands of kilometres, they are most frequently observed at a few predictable seasonal aggregation sites. The absence of sharks at the surface during visual surveys has led to the assumption that sharks disperse to places unknown during the long ‘off-seasons’ at most of these locations. Here we compare 2 years of R. typus visual sighting records from Mafia Island in Tanzania to concurrent acoustic telemetry of tagged individuals. Sightings revealed a clear seasonal pattern with a peak between October and February and no sharks observed at other times. By contrast, acoustic telemetry demonstrated year-round residency of R. typus. The sharks use a different habitat in the off-season, swimming deeper and further away from shore, presumably in response to prey distributions. This behavioural change reduces the sharks'' visibility, giving the false impression that they have left the area. We demonstrate, for the first time to our knowledge, year-round residency of unprovisioned, individual R. typus at an aggregation site, and highlight the importance of using multiple techniques to study the movement ecology of marine megafauna.     

Movement Patterns of Juvenile Whale Sharks Tagged at an Aggregation Site in the Red Sea

Conservation efforts aimed at the whale shark, Rhincodon typus, remain limited by a lack of basic information on most aspects of its ecology, including global population structure, population sizes and movement patterns. Here we report on the movements of 47 Red Sea whale sharks fitted with three types of satellite transmitting tags from 2009–2011. Most of these sharks were tagged at a single aggregation site near Al-Lith, on the central coast of the Saudi Arabian Red Sea. Individuals encountered at this site were all juveniles based on size estimates ranging from 2.5–7 m total length with a sex ratio of approximately 1∶1. All other known aggregation sites for juvenile whale sharks are dominated by males. Results from tagging efforts showed that most individuals remained in the southern Red Sea and that some sharks returned to the same location in subsequent years. Diving data were recorded by 37 tags, revealing frequent deep dives to at least 500 m and as deep as 1360 m. The unique temperature-depth profiles of the Red Sea confirmed that several whale sharks moved out of the Red Sea while tagged. The wide-ranging horizontal movements of these individuals highlight the need for multinational, cooperative efforts to conserve R. typus populations in the Red Sea and Indian Ocean.     

Regional movements of satellite‐tagged whale sharks Rhincodon typus in the Gulf of Aden

To gain insight into whale shark (Rhincodon typus) movement patterns in the Western Indian Ocean, we deployed eight pop‐up satellite tags at an aggregation site in the Arta Bay region of the Gulf of Tadjoura, Djibouti in the winter months of 2012, 2016, and 2017. Tags revealed movements ranging from local‐scale around the Djibouti aggregation site, regional movements along the coastline of Somaliland, movements north into the Red Sea, and a large‐scale (>1,000 km) movement to the east coast of Somalia, outside of the Gulf of Aden. Vertical movement data revealed high occupation of the top ten meters of the water column, diel vertical movement patterns, and deep diving behavior. Long‐distance movements recorded both here and in previous studies suggest that connectivity between the whale sharks tagged at the Djibouti aggregation and other documented aggregations in the region are likely within annual timeframes. In addition, wide‐ranging movements through multiple nations, as well as the high use of surface waters recorded, likely exposes whale sharks in this region to several anthropogenic threats, including targeted and bycatch fisheries and ship‐strikes. Area‐based management approaches focusing on seasonal hotspots offer a way forward in the conservation of whale sharks in the Western Indian Ocean.     

Behavioural response of a whale shark during the passage of a typhoon

During a behavioural survey of a tagged whale shark (Rhincodon typus) conducted in 2019 in the waters off Kagoshima, Japan, a typhoon passed close to the area under surveillance. As the typhoon approached, monitoring of the shark's movements indicated that it dived to depths of up to 90 m, and during this period, the authors recorded the effects of the typhoon-induced waves. They also detected changes in the vertical thermal structure of the waters, possibly due to the disturbance caused by the typhoon.     

Why are there no really big bony fishes? A point-of-view on maximum body size in teleosts and elasmobranchs

The most massive teleost, the ocean sunfish(Mola mola), is an order of magnitude smaller than the largest cartilaginous fish,the whale shark (Rhincodon typus), and issignificantly smaller than several other extantelasmobranch species. Possible reasons for this discrepancy in maximum size include:anatomical, physiological, ecological, and life-history/ontogenetic constraints. Weexamined life-history traits and growth ratesas the most likely constraints on maximum teleostsize. For pelagic fishes there appear to be two life-history strategies: producing few,large, live young or many, tiny eggs. We propose that this dichotomy is an evolutionaryvestige of the freshwater origins of teleosts, and is the basis of the limitation onmaximal body size in teleosts.     

Mismatch between fishway operation and timing of fish movements: a risk for cascading effects in partial migration systems

Habitat fragmentation is a growing problem worldwide. Particularly in river systems, numerous dams and weirs hamper the movement of a wide variety of species. With the aim to preserve connectivity for fish, many barriers in river systems are equipped with fishways (also called fish passages or fish ladders). However, few fishways provide full connectivity. Here we hypothesized that restricted seasonal opening times of fishways can importantly reduce their effectiveness by interfering with the timing of fish migration, for both spring‐ and autumn‐spawning species. We empirically tested our hypothesis, and discuss the possible eco‐evolutionary consequences of affected migration timing. We analyzed movements of two salmonid fishes, spring‐spawning European grayling (Thymallus thymallus) and autumn‐spawning brown trout (Salmo trutta), in Norway's two largest river systems. We compared their timing of upstream passage through four fishways collected over 28 years with the timing of fish movements in unfragmented river sections as monitored by radiotelemetry. Confirming our hypothesis, late opening of fishways delayed the migration of European grayling in spring, and early closure of fishways blocked migration for brown trout on their way to spawning locations during late autumn. We show in a theoretical framework how restricted opening times of fishways can induce shifts from migratory to resident behavior in potamodromous partial migration systems, and propose that this can induce density‐dependent effects among fish accumulating in lower regions of rivers. Hence, fragmentation may not only directly affect the migratory individuals in the population, but may also have effects that cascade downstream and alter circumstances for resident fish. Fishway functionality is inadequate if there is a mismatch between natural fish movements and fishway opening times in the same river system, with ecological and possibly evolutionary consequences for fish populations.     

Spatial and temporal patterns of genetic variation in the widespread antitropical deep‐sea coral Paragorgia arborea

Numerous deep‐sea species have apparent widespread and discontinuous distributions. Many of these are important foundation species, structuring hard‐bottom benthic ecosystems. Theoretically, differences in the genetic composition of their populations vary geographically and with depth. Previous studies have examined the genetic diversity of some of these taxa in a regional context, suggesting that genetic differentiation does not occur at scales of discrete features such as seamounts or canyons, but at larger scales (e.g. ocean basins). However, to date, few studies have evaluated such diversity throughout the known distribution of a putative deep‐sea species. We utilized sequences from seven mitochondrial gene regions and nuclear genetic variants of the deep‐sea coral Paragorgia arborea in a phylogeographic context to examine the global patterns of genetic variation and their possible correlation with the spatial variables of geographic position and depth. We also examined the compatibility of this morphospecies with the genealogical‐phylospecies concept by examining specimens collected worldwide. We show that the morphospecies P. arborea can be defined as a genealogical‐phylospecies, in contrast to the hypothesis that P. arborea represents a cryptic species complex. Genetic variation is correlated with geographic location at the basin‐scale level, but not with depth. Additionally, we present a phylogeographic hypothesis in which P. arborea originates from the North Pacific, followed by colonization of the Southern Hemisphere prior to migration to the North Atlantic. This hypothesis is consistent with the latest ocean circulation model for the Miocene.     

Ocean‐scale prediction of whale shark distribution

Aim Predicting distribution patterns of whale sharks (Rhincodon typus, Smith 1828) in the open ocean remains elusive owing to few pelagic records. We developed multivariate distribution models of seasonally variant whale shark distributions derived from tuna purse‐seine fishery data. We tested the hypotheses that whale sharks use a narrow temperature range, are more abundant in productive waters and select sites closer to continents than the open ocean. Location Indian Ocean. Methods We compared a 17‐year time series of observations of whale sharks associated with tuna purse‐seine sets with chlorophyll a concentration and sea surface temperature data extracted from satellite images. Different sets of pseudo‐absences based on random distributions, distance to shark locations and tuna catch were generated to account for spatiotemporal variation in sampling effort and probability of detection. We applied generalized linear, spatial mixed‐effects and Maximum Entropy models to predict seasonal variation in habitat suitability and produced maps of distribution. Results The saturated generalized linear models including bathymetric slope, depth, distance to shore, the quadratic of mean sea surface temperature, sea surface temperature variance and chlorophyll a had the highest relative statistical support, with the highest percent deviance explained when using random pseudo‐absences with fixed effect‐only models and the tuna pseudo‐absences with mixed‐effects models (e.g. 58% and 26% in autumn, respectively). Maximum Entropy results suggested that whale sharks responded mainly to variation in depth, chlorophyll a and temperature in all seasons. Bathymetric slope had only a minor influence on the presence. Main conclusions Whale shark habitat suitability in the Indian Ocean is mainly correlated with spatial variation in sea surface temperature. The relative influence of this predictor provides a basis for predicting habitat suitability in the open ocean, possibly giving insights into the migratory behaviour of the world’s largest fish. Our results also provide a baseline for temperature‐dependent predictions of distributional changes in the future.     

Population structure of the dusky pipefish (Syngnathus floridae) from the Atlantic and Gulf of Mexico,as revealed by mitochondrial DNA and microsatellite analyses

Aim To elucidate the historical phylogeography of the dusky pipefish (Syngnathus floridae) in the North American Atlantic and Gulf of Mexico ocean basins. Location Southern Atlantic Ocean and northern Gulf of Mexico within the continental United States. Methods A 394‐bp fragment of the mitochondrial cytochrome b gene and a 235‐bp fragment of the mitochondrial control region were analysed from individuals from 10 locations. Phylogenetic reconstruction, haplotype network, mismatch distributions and analysis of molecular variance were used to infer population structure between ocean basins and time from population expansion within ocean basins. Six microsatellite loci were also analysed to estimate population structure and gene flow among five populations using genetic distance methods (F_ST, Nei’s genetic distance), isolation by distance (Mantel’s test), coalescent‐based estimates of genetic diversity and migration patterns, Bayesian cluster analysis and bottleneck simulations. Results Mitochondrial analyses revealed significant structuring between ocean basins in both cytochrome b (Φ_ST = 0.361, P < 0.0001; Φ_CT = 0.312, P < 0.02) and control region (Φ_ST = 0.166, P < 0.0001; Φ_CT = 0.128, P < 0.03) sequences. However, phylogenetic reconstructions failed to show reciprocal monophyly in populations between ocean basins. Microsatellite analyses revealed significant population substructuring between all locations sampled except for the two locations that were in closest proximity to each other (global F_ST value = 0.026). Bayesian analysis of microsatellite data also revealed significant population structuring between ocean basins. Coalescent‐based analyses of microsatellite data revealed low migration rates among all sites. Mismatch distribution analysis of mitochondrial loci supports a sudden population expansion in both ocean basins in the late Pleistocene, with the expansion of Atlantic populations occurring more recently. Main conclusions Present‐day populations of S. floridae do not bear the mitochondrial DNA signature of the strong phylogenetic discontinuity between the Atlantic and Gulf coasts of North America commonly observed in other species. Rather, our results suggest that Atlantic and Gulf of Mexico populations of S. floridae are closely related but nevertheless exhibit local and regional population structure. We conclude that the present‐day phylogeographic pattern is the result of a recent population expansion into the Atlantic in the late Pleistocene, and that life‐history traits and ecology may play a pivotal role in shaping the realized geographical distribution pattern of this species.     

Genetic structure of populations of whale sharks among ocean basins and evidence for their historic rise and recent decline

This study presents genetic evidence that whale sharks, Rhincodon typus, are comprised of at least two populations that rarely mix and is the first to document a population expansion. Relatively high genetic structure is found when comparing sharks from the Gulf of Mexico with sharks from the Indo‐Pacific. If mixing occurs between the Indian and Atlantic Oceans, it is not sufficient to counter genetic drift. This suggests whale sharks are not all part of a single global metapopulation. The significant population expansion we found was indicated by both microsatellite and mitochondrial DNA. The expansion may have happened during the Holocene, when tropical species could expand their range due to sea‐level rise, eliminating dispersal barriers and increasing plankton productivity. However, the historic trend of population increase may have reversed recently. Declines in genetic diversity are found for 6 consecutive years at Ningaloo Reef in Australia. The declines in genetic diversity being seen now in Australia may be due to commercial‐scale harvesting of whale sharks and collision with boats in past decades in other countries in the Indo‐Pacific. The study findings have implications for models of population connectivity for whale sharks and advocate for continued focus on effective protection of the world's largest fish at multiple spatial scales.     

Whale sharks Rhincodon typus get cleaned by the blue-streak cleaner wrasse Labroides dimidiatus and the moon wrasse Thalassoma lunare in the Philippines

Cleaning interactions are essential for healthy marine ecosystem communities. This study reports the first documentation of the whale shark Rhincodon typus cleaning behaviour in the Indo-West Pacific by two wrasse species, the blue-streak cleaner wrasse Labroides dimidiatus and the moon wrasse Thalassoma lunare in Cebu, Philippines. This study documented 36 cleaning interactions with 14 individual whale sharks. The cleaning interactions appear opportunistic rather than targeted by the sharks, unlike that observed in other species of elasmobranchs. Further work should focus on understanding the drivers of these unique cleaning interactions.