High genetic structure and low mitochondrial diversity in bottlenose dolphins of the Archipelago of Bocas del Toro, Panama: A population at risk?

Abstract

The current conservation status of the bottlenose dolphin (Tursiops truncatus) under the IUCN is ‘least concern’. However, in the Caribbean, small and localized populations of the ‘inshore form’ may be at higher risk of extinction than the ‘worldwide distributed form’ due to a combination of factors including small population size, high site fidelity, genetic isolation, and range overlap with human activities. Here, we study the population genetic structure of bottlenose dolphins from the Archipelago of Bocas del Toro in Panama. This is a small population characterized by high site fidelity and is currently heavily-impacted by the local dolphin-watching industry. We collected skin tissue samples from 25 dolphins to study the genetic diversity and structure of this population. We amplified a portion of the mitochondrial Control Region (mtDNA-CR) and nine microsatellite loci. The mtDNA-CR analyses revealed that dolphins in Bocas del Toro belong to the ‘inshore form’, grouped with the Bahamas-Colombia-Cuba-Mexico population unit. They also possess a unique haplotype new for the Caribbean. The microsatellite data indicated that the Bocas del Toro dolphin population is highly structured, likely due to restricted movement patterns. Previous abundance estimates obtained with mark-recapture methods reported a small population of 80 dolphins (95% CI = 72–87), which is similar to the contemporary effective population size estimated in this study (Ne = 73 individuals; CI = 18.0 - ∞; 0.05). The combination of small population size, high degree of genetic isolation, and intense daily interactions with dolphin-watching boats puts the Bocas del Toro dolphin to at high risk of extinction. Despite national guidelines to regulate the dolphin-watching industry in Bocas del Toro and ongoing educational programs for tour operators, only in 2012 seven animals have died due to boat collisions. Our results suggest that the conservation status of bottlenose dolphins in Bocas del Toro should be elevated to ‘endangered’ at the national level, as a precautionary measure while population and viability estimates are conducted.

Peer Review #1 of "Tour boats affect the activity patterns of bottlenose dolphins (Tursiops truncatus) in Bocas del Toro, Panama (v0.1)"

“…Dolphin Bay is characterized by shallow, clear waters approximately 20 m deep, possessing variable bottom substrate including mud, coral, sea grasses, and mangroves (Kaufmann & Thompson, 2005). Because dolphins use this embayment year-round it is likely an important foraging habitat (May-Collado et al, 2017) where dolphins feed primarily on lowcalorie prey such as striped parrotfish (Scarus isiri) and dwarf round herring (Jenkinsia lamprotaenia) (Barragán- Barrera et al, 2019). Since monitoring efforts began in 2004, high sighting rates of mother-calf pairs (including two neonates observed in this study) suggest Dolphin Bay may also serve as critical habitat for females with dependent offspring.…”

“…A recent study found that resident females possess a relatively long calving cycle (~62 months) and a high calf mortality rate (46%) (May-Collado et al, 2019). Additionally, nuclear and mitochondrial DNA analyses indicate this population is isolated from others in the Caribbean, including the neighboring population of bottlenose dolphins in Costa Rica located 35 km away from the Bocas del Toro archipelago (Barragán- Barrera et al, 2017). Because the small dolphin community of Dolphin Bay shows such high site fidelity, they have become the main target for dolphin watching activities in the area, resulting in the largest dolphin watching fleet in Panama (May-Collado et al, 2012, 2019.…”

“…Peak tourism season occurs from December to May during the dry months, while the low-season occurs during the rainy season (June-November). However, up to 39 boats have been reported interacting with dolphins over a period of one-hour in Dolphin Bay during the low season for tourism, demonstrating that dolphins are exposed to high levels of boat tourism year-round (May-Collado et al, 2017). The majority of interactions between tour boats and dolphin groups in this study included 1 to 2 boats (55%), which means that our measured effect could be conservative if we assume that the effect of tour boat interactions increases with the number of tour boats present.…”

“…May-Collado et al, 2019;Barragán-Barrera et al, 2017;Sitar et al, 2016). Preliminary analysis suggests the resident population ranges from 72 to 87 dolphins, with 37 individuals exhibiting a high residency rate (38.5 to 100%) in the central dolphin-watching area known as Dolphin Bay (May-Collado et al, 2017). The dolphins use this embayment for a number of activities including foraging and socializing, and high sighting and recapture rates of females with dependent offspring also suggest it may serve as important nursery habitat for females with calves (May-Collado et al, 2019).…”

“…In Bocas del Toro, Panama, a small, genetically distinct population of coastal bottlenose dolphins is the target of the largest dolphin-watching industry in Panama (e.g. May-Collado et al, 2019;Barragán-Barrera et al, 2017;Sitar et al, 2016). Preliminary analysis suggests the resident population ranges from 72 to 87 dolphins, with 37 individuals exhibiting a high residency rate (38.5 to 100%) in the central dolphin-watching area known as Dolphin Bay (May-Collado et al, 2017).…”