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Whale Sharks Choose To Aggregate At Specific Locations – Why Bathymetry Matters

Why do whale sharks choose to aggregate at certain locations - and what does this mean for conservation?

Whale sharks (Rhincodon typus) are known to aggregate in a number of coastal locations around the world, but scientists don’t quite understand why they choose these specific sites. Until now.

A recent global study examines whether bathymetry is an important driver of coastal aggregation locations for R. typus. Scientists hypothesized that bathymetry’s effect on primary productivity and prey availability would be important determinants to why whale sharks aggregate in specific sites.

Scientists tested their theory by conducting an extensive literature review of whale shark aggregations, taking into account all coastal areas within R. typus’ range. They then compared these aggregations with different bathymetric characteristics – to see which characteristics were most associated with aggregation sites.

The Results? Aggregation sites are shallow, in close proximity to deep water, and were significantly steeper than non-aggregation sites.

So Why Do Whale Sharks Aggregate And Why?

The big finding here are that these three characteristics are associated with a phenomenon called upwelling. Upwelling occurs where cold, deep, nutrient-rich waters rise suddenly towards the surface. The result is a huge nutrient base for life to grow, meaning more prey for whale sharks who are massive filter feeders.

The researchers believe that the proximity of aggregations to shallow areas such as reefs could also be an important factor why whale sharks thermoregulate after deep dives to feed. These findings increase our understanding of whale shark behaviour and may help guide the identification and conservation of further aggregation sites.

More Information: Joshua P. Copping et al. Does bathymetry drive coastal whale shark (Rhincodon typus) aggregations? PeerJ (2018) https://peerj.com/articles/4904/

Journal Reference: PeerJ