A new method to assess natural history traits of seahorses

Abstract

We developed a non-invasive method to record multiple measurements and data of seahorses in situ. We tested this development over individuals from the southernmost population of Hippocampus patagonicus at San Antonio Bay, northern Patagonia, Argentina. We captured individuals along transects of 1000m parallel to the coast, determined their geographical position, sex and maturity stage. We fastened each by its trunk to a scaled measuring board with an elastic band and took a photograph at a distance of 50 cm (to measure the standard length) and a close-up one of the head to individually identify the specimens by face recognition later at the lab. We obtained a left and right set of photographs of every seahorse. After this manipulation (1-2 minutes), we released the animals and recorded the escaping behavior: 1. fast escape; 2. attachment to a near holdfast or 3. catatonic behavior. 94% of the animals recovered immediately after manipulation (1 and 2 behavior). We analyzed the photographs and identified individuals by face recognition taking into account bright spots, head contour and sex. We compared over 767 photographs and were able to recognize 112 individuals recaptured. We also compared this new technique of face recognition to the standard VIE tagging method in a total of 100 animals. Both techniques showed similar effectiveness recognizing individuals. In addition, this new method resulted inexpensive and not invasive while requiring standard equipment and training.