Diving into the diet of provisioned smooth stingrays using stable isotope analysis

Area of Science:

• Marine biology
• Ecology
• Fisheries science

Background:

• Recreational fishing generates waste, impacting aquatic ecosystems.
• The dietary effects of this waste on marine species are understudied.
• Smooth stingrays (Bathytoshia brevicaudata) consume fishing discards and are fed commercial baits in tourism.

Purpose of the Study:

• To assess the diet of smooth stingrays exposed to recreational fishing discards and commercial baits.
• To understand how these resources alter stingray foraging patterns.
• To evaluate the nutritional impact of 'stingray feeding' tourism.

Main Methods:

• Stable isotope analysis (carbon δ13C and nitrogen δ15N) was used.
• Bayesian stable isotope mixing models were employed.
• Diets were compared between a discard-only site and a provisioning site.

Main Results:

• Invertebrate contribution to stingray diets was limited at both sites.
• A benthic teleost fish, a common recreational catch, was the dominant dietary component.
• Commercial baits had a negligible impact on stingray nutrition at the provisioning site.

Conclusions:

• Smooth stingrays show a reduced reliance on invertebrates and increased reliance on teleost fish when provisioned.
• The source of the dominant teleost fish (discard or natural prey) requires further investigation.
• Recreational fishing discards significantly influence stingray diets, while tourism feeding has minimal nutritional effects.