Oceans and Coasts

The Giant Guitarfish Project

Team members: Evan Nazareth, Elrika D'souza, Rohan Arthur

Project timeline: 2019 - Ongoing

Giant guitarfish; close relatives of sharks and stingrays can reach lengths of three meters and live for at least 18 years. Like many sharks and rays their populations drastically declined over the last few decades. Primarily due to over fishing and other anthropogenic disturbances.

Efforts to protect such large, mobile and long-lived species are often hindered by the difficulty in implement conservation efforts across large home ranges. However, giant guitarfish, give birth to live young, and studies show that these young (pups) spend their early life in shallow coastal waters before venturing into deeper seas. While, coastal waters are often the most exposed to fisheries, development, and pollution, focused conservation and management strategies at these sites could be an effective way of protect the pups and in turn the species.

Given that the Andaman Islands are situated in a heavily fished region and the rapid development along its coastline, it is imperative that such sites be identified and protected before they are lost.

The first phase of this project utilized Local Ecological Knowledge of coastal communities in the Andamans to collect baseline data on giant guitarfish distribution and relative abundance across the islands and identify potential threats to the species. A total of 175 interviews were conducted at 33 locations across seven islands. The finding of this revealed the widespread distribution of juvenile giant guitarfish aggregating sites across the islands. Highlighting the significant role that island’s coastline plays in harbouring this species, especially during it's crucial early life.

Amidst the pandemic and resulting travel restrictions, we use to the time stuck at one location to test out the effectiveness of different sampling methods in detecting juvenile giant guitarfish. We conducted visual line transects on foot along the shore and deployed Baited Remote Underwater Video Systems (BRUVS) at the same site. After almost 3 months of data collection using these two methods, we concluded that visual line transect surveys were more effective at detecting giant guitarfish and stingray pups in shallow coastal waters than BRUVS. Using this information, we adopted this method of sampling as we proceeded with our study.

Based on observation of stingrays using many of the same spaces as giant guitarfish pups, we expanded our focus to document stingrays as well. We are currently trying to understand what habitat characteristics lead to certain coastal areas supporting high abundance of giant guitarfish and rays while other sites do not. We are also evaluating the level of human disturbances at these sites and how they could be influencing the presence of giant guitarfish and rays.

With these findings we hope to map out locations across the islands where giant guitarfish and stingray pups are found and the level of human disturbances at each of these sites. These maps could enable conservationists to prioritise areas and determine conservation strategies based on the level and types of threats these species are exposed to at each site.