Rising temperatures, shrinking rays?
We know that fish often end up smaller overall if their populations have been overfished. Rising ocean temperatures with our changing climate might have the same impact. Scientists have figured this out using ‘Gill Oxygen Limitation Theory’ (GOLT), which describes how limited oxygen affects the growth of water-breathing animals. Buddhi wants to decipher this relationship for rays, which hasn’t yet been described using GOLT. She’s hoping that this way she can raise awareness about how rays will be affected in our changing world.
Buddhi Pathirana
I was raised in the rural village of Erathna, which is located at the base of the well-known Adam’s Peak and far from Sri Lanka’s coastline. My journey towards the ocean started when my Grade 4 teacher arranged a visit the Colombo Museum. I can still recall a giant skeleton dangling from the museum’s ceiling and the curator of the museum telling me it belonged to a blue whale. I just spread out my arms and tried to imagine that massive creature that couldn’t have fitted into our village creek. We stopped at the coastal park of...
The Ratio of Size at Maturity to Maximum Size of Batoids and Management Implications
The Gill Oxygen Limitation Theory has not yet been applied to batoid species. The prime objective of this research is therefore to minimise the resulting gap by interpreting the length–weight relationship and growth of both male and female rays using the theory. This will provide insight into how ocean warming affects rays.
I plan to use a scientific approach to describe how a rise in water temperature leads to ray species being smaller at maturity. The additional pressure of fishing on specific ray species needs to be addressed if the observations from this project agree with the relationship already established for marine fishes as described by the Gill Oxygen Limitation Theory.
The smaller size at maturity of many fish, including ray species, is due to over-exploitation. A rise in water temperature due to global warming may also lead to smaller sizes at maturity of various fish species. The effect of a higher temperature on the size of fish species can be explained by the Gill Oxygen Limitation Theory (GOLT), which describes how a limited supply of oxygen affects the growth of water-breathing aquatic ectotherms such as fish and aquatic invertebrates. However, according to the available literature, GOLT has not yet been applied to ray species. The fact that female rays reach a greater size than their male counterparts is explained by their lower maintenance metabolism due to a lower rate of activity. This project aims to use GOLT to study how maintenance metabolism in ray species is affected in their natural habitat. This will be useful to recommend conservation actions for these vulnerable species.
GOLT will be applied:
- To understand why there is a size difference between mature male and female rays.
- To understand how global warming affects the size of ray species at maturity.
- To raise awareness of how ocean warming affects ray species.
Summary of main research results/outcomes:
Maturation of batoids is only viable when oxygen supply and demand reach a critical point. The slope of the LmaxD/LmD ratio is used to assess this critical point, where Lmax is the maximum length, Lm is the mean size at first maturity, and D is a gill-related exponent. Although the observed ratio for batoids was lower than that of bony fish, it remained within the 95% confidence interval of the estimates (1.187 – 1.468). Hence, as batoids grow, their two-dimensional gill surfaces are unable to provide sufficient oxygen to their three-dimensional bodies, as suggested by the Gill Oxygen Limitation Theory. Therefore, if batoids are exposed to oxygen-depleted environments, resulting from global warming and marine water pollution in the long run, a decline in their reproductive potential and biomass is evident. Hence, effective approaches to minimize global warming and manage coastal zones are crucial for conserving these vital species.