Low seabird and marine mammal occurrences densities in the Bay of Bengal, despite intense marine productivity and longline fishing activity

At-sea observations of seabirds and marine mammals provide essential baseline information with respect to their biogeography and behaviour, facilitating marine spatial planning and management. Most of the world’s oceans... [ view full abstract ]

At-sea observations of seabirds and marine mammals provide essential baseline information with respect to their biogeography and behaviour, facilitating marine spatial planning and management. Most of the world’s oceans have been charted, yet some regions remain particularly data-poor. This is the case for, including the Bengal of Bengal, despite being a highly productive upwelling area potentially harbouring a guild of marine birds and mammals. We performed 39 days of vessel-based observations across the Bay of Bengal in 2012-2014.

We recorded 17 species of seabirds, and at least seven eight species of marine mammals. Among the sea birds, were Sooty Terns (Onychoprion fuscatus, 87% of all birds) and Wedge-Tailed Shearwaters (Ardenna pacifica, 9%) predominated, and whereas most marine mammals were Spinner Dolphins (Stenella longirostris, 59%) and Indo-Pacific Bottlenose Dolphins (Tursiops aduncus, 34%). The diversity of both birds and mammals was low compared to other tropical areas, despite this area being one of the most productive marine regions. We speculate that low top predator abundances result from long-lasting disturbance and the virtual absence of suitable reproductive breeding habitats for seabirds, coupled with overfishing of key seabird and marine mammal prey, in particular small pelagic fish.