Does bathymetry drive coastal whale shark (Rhincodon typus) aggregations?

Area of Science:

• Marine Biology
• Oceanography
• Ecology

Background:

• Whale shark (Rhincodon typus) aggregations occur globally, but the drivers for these specific locations remain unclear.
• This study investigates the role of bathymetry in influencing coastal aggregation sites for whale sharks.
• The research considers the impact of bathymetry on primary productivity and prey availability.

Purpose of the Study:

• To determine if bathymetry is a significant factor in whale shark aggregation site selection.
• To understand how underwater topography influences prey distribution and, consequently, whale shark presence.
• To provide insights for identifying and conserving whale shark aggregation sites.

Main Methods:

• Identified whale shark (Rhincodon typus) aggregation sites through a comprehensive literature review.
• Compared global bathymetric data at aggregation sites versus randomly selected non-aggregation areas.
• Utilized generalized linear models (GLMs) to identify key bathymetric features influencing aggregation presence.

Main Results:

• Aggregation sites were significantly shallower and closer to deep water (mesopelagic zone) than non-aggregation sites.
• Steeper seafloor slopes were characteristic of aggregation sites.
• Three bathymetric variables explained up to 88% of the deviation in aggregation site presence.

Conclusions:

• The identified bathymetric features promote upwelling, increasing primary productivity and attracting prey species.
• Increased prey availability in these specific bathymetric areas is the primary driver for whale shark aggregations.
• Proximity to shallow areas may also facilitate thermoregulation for whale sharks after deep feeding dives, aiding conservation strategies.