Ocean‐scale prediction of whale shark distribution

Abstract

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.

Trends in sightings and environmental influences on a coastal aggregation of manta rays and whale sharks

“…For instance, a decline in whale shark sightings along the eastern coast of South Africa between 1993 and 1998 (Gifford 2001) was included in the successful proposal for listing the species on Appendix II of the Convention on International Trade in Endangered Species (CITES 2002). However, with the benefit of hindsight, the substantial variability in sighting data from this area in summer months (Cliff et al 2007) and seasonal changes in their oceanic distribution (Sequeira et al 2012) makes it difficult to attribute these earlier data to a genuine population decline. Even with comparatively robust datasets, such as for whale sharks at Ningaloo Reef in Australia, scientific consensus on population trends has proven difficult to attain due to differences in the underlying assumptions of the models, insufficient data to test which approach is more robust, and the potential influence of environmental variability (Wilson et al 2001, Meekan et al 2006, Bradshaw et al 2007, Holmberg et al 2008, 2009, Sleeman et al 2010a).…”

Feeding habitat of the whale shark Rhincodon typus in the northern Gulf of Mexico determined using species distribution modelling

“…The habitat of other large pelagic species, such as Atlantic bluefin tuna Thunnus thynnus and swordfish Xiphias gladius, has been shown to vary considerably between feeding and spawning periods throughout the year in the Mediterranean (Tserpes et al 2008, Druon et al 2011. In the Indian Ocean, seasonal habitat distribution of whale sharks Rhincodon typus has been modelled using long-term fisheries-based datasets (Sequeira et al 2012).…”

Spatial and temporal patterns of nature-based tourism interactions with whale sharks (Rhincodon typus) at Ningaloo Reef, Western Australia

“…3). Whale sharks at Ningaloo have been found to favour the warmer waters and have been observed in waters between 24 and 32 C (Sleeman et al, 2007;Sequeira et al, 2012). In 2010, 2011, the average monthly sea 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64surface temperatures at North Ningaloo remained close to or above 24 C throughout the year.…”