Seasonal patterns in stable isotope and fatty acid profiles of southern stingrays (Hypanus americana) at Stingray City Sandbar, Grand Cayman

Abstract

Ecotourism opportunities in the marine environment often rely heavily on provisioning to ensure the viewing of cryptic species by the public. However, intentional feeding of wildlife can impact numerous aspects of an animals' behavior and ecology. Southern stingrays (Hypanus americana) provisioned at Stingray City Sandbar (SCS) in Grand Cayman have altered diel activity patterns and decreased measures of health. This study looked at seasonal changes in stable isotope (SI) and fatty acid (FA) profiles of provisioned stingrays at SCS. Plasma δ¹⁵N was higher in male stingrays (11.86 ± 1.71‰) compared to females (10.70 ± 1.71‰). Lower values for δ¹⁵N in males and females were measured in October during low tourist season, suggesting stingrays may be forced to rely on native prey items to supplement the decreased amount of provisioned squid available during this time. Plasma FA profiles were significantly different between sexes and across sampling time points, with FAs 22:6n3, 16:0, 20:5n3, 18:1n3C, 18:0 and 18:1n9T contributing to dissimilarity scores between groups. Dietary FAs primarily contributed to differences between males and females lending further evidence to differences in foraging patterns at SCS, likely due to intraspecific competition. Further, canonical analysis of principal coordinates (CAP) analysis of FA profiles suggest similar diets during peak tourist season and differences in diet between males and females during the low season. This study demonstrates alterations in feeding ecology in stingrays at SCS which is of critical importance for effective management of the SCS aggregation.

Figure 1

Box plots of δ¹⁵N and δ¹³C plasma isotopes for female and male stingrays sampled at SCS in January, April, July, and October. Significant differences between sexes within a sampling month are denoted by an asterisk (*) and numbers represent sample size. This figure was created with SigmaPlot 12.5 (Systat Software, San Jose, CA).

Figure 2

Box plots of δ¹⁵N and δ¹³C whole blood isotopes for female and male stingrays sampled at SCS in January, April, July, and October. Significant differences between sexes within a sampling month are denoted by an asterisk (*) and numbers represent sample size. This figure was created with SigmaPlot 12.5 (Systat Software, San Jose, CA).

Figure 3

Canonical analysis of principle coordinates (CAP) of male (M) and female (F) stingrays within each sampling time point (January, April, July, October) with overlaid vectors of individual fatty acids identified by SIMPER routines. This figure was created with PRIMER/PERMANOVA + version 7 (Primer-e Ltd, Aukland, New Zealand).

Figure 4

Mean (±SD) plasma δ¹³C and δ¹⁵N from male (white circle) and female (grey circle) southern stingrays at Stingray City Sandbar and potential primary prey groups (black symbols) as derived from the literature. This figure was created with SigmaPlot 12.5 (Systat Software, San Jose, CA).