Divers for the Environment June 2021

Page 24

FEATURE CREATURE

FEATURE CREATURE INDIAN OCEAN HUMPBACK DOLPHIN (SOUSA PLUMBEA) FEATURE IUCN RED LIST 2017 PHOTOGRAPHY DR. ADA NATOLI

RED LIST CATEGORY & CRITERIA: ENDANGERED Scientific Name: Sousa plumbea Synonym: Delphinus plumbeus (G. Cuvier, 1829) Common Names: English: Indian Ocean Humpback Dolphin French: Dauphin à bosse Afrikaans: Boggelrugdolfyn Arabic: Dukhs Hindi: Fukariyo, Gada/Gad/Gaadha reda, Goonu, Kadal ongi, Kadal panni, Paru vedan, Sori vedan, Thella thoralu TAXONOMIC NOTES Sousa plumbea has been recognised as a species since taxonomic revision of the genus Sousa in 2014 (Committee on Taxonomy 2014, Jefferson and Rosenbaum 2014). Previously this species was lumped with the Indo-pacific humpback dolphin (Sousa chinensis) but animals occurring in the Indian Ocean from South Africa to India are now recognised as taxonomically distinct from those that occur further east, based on genetics, skeletal morphology, external morphology and colour. There is uncertainty about the taxonomic affinities of the humpback dolphins that occur 24

DIVERS FOR THE ENVIRONMENT | JUNE 2021

in the Bay of Bengal and future studies will confirm whether S. plumbea actually occurs east of the southern tip of India. JUSTIFICATION In the places where studies have occurred, Indian Ocean Humpback Dolphin subpopulations were found to be small: always fewer than 500 and generally fewer than 100 individuals in discrete, or semi-isolated areas. Humpback dolphins have one of the most specific habitat preferences and restricted distributions of any marine megafauna, and both of these characteristics are well known to reduce the resilience of species to environmental change and anthropogenic threats and to increase their extinction risk (Davidson et al. 2011, Dulvy et al. 2014, Purvis et al. 2000). Indian Ocean Humpback Dolphins are concentrated in coastal waters within 2 km of shore and they are often sighted only a few hundred metres from land. This distribution places them in exactly the same location as the majority of small-scale fishing effort prevalent throughout their range in the same nearshore habitat. As a result, humpback dolphins encounter large numbers of coastal

gillnets and are at high risk of entanglement. High and clearly unsustainable mortality rates have been reported from several areas and frequent encounters with fishing gear can be inferred from the high degree of scarring and injury – for example, 41% of individuals in Pemba, Tanzania bore gear-related scars (Braulik unpub. data). Although information on population size, threats and mortality is available only for portions of the species range, there are strong reasons to suspect and infer that the threats will be similar or possibly even more intense elsewhere. The deaths of only 4.2 individuals per year from a population of 100 would result in a 50% decline (Moore 2015). The available evidence on the studied subpopulations in South Africa and all indications from elsewhere in the range suggest that mortality rates are consistently at or above the rate that would result in a 50% decline in 75 years (three generations). The species’ preferred habitat and small populations overlap in both space and time with several ubiquitous and pervasive threats that are increasing in severity, leaving no refuges for these dolphins. The


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Articles inside

DAN Europe Physician's Field Experience Regarding Diving After COVID-19

10min
pages 104-106

What you Should Know About Diving After COVID-19

6min
pages 102-103

Diver Propulsion Vehicle Review: SUEX VRT

3min
pages 78-81

How Eight Pacific Island States Are Saving the World's Tuna

10min
pages 34-39

Diving & COVID-19: A Focus in the MENA Region

12min
pages 48-53

Ria Deseado and the Majestic Penguin Island

9min
pages 94-101

Digital Online’s Results

8min
pages 82-93

Star International School Mirdif’s Quest to Becoming Ocean Ambassadors

4min
pages 70-73

My Buddy The Freediving Instructor

6min
pages 74-77

Green Fingered Divers

13min
pages 64-69

The SSI Service Centre’s Revamp in the UAE

13min
pages 58-63

UAE Dolphin Project Update Relaunching the Report a Sighting Campaign

3min
pages 54-57

Entangled – www.entangled-film.com

10min
pages 28-33

Masbango (Bigeye Mackerel)

6min
pages 40-47

Feature Creature

22min
pages 24-27

In Memoriam: Carina Escudero

3min
page 21

From the Start, to Fred’s Stride

3min
pages 18-19

Bringing Back Kelp Forests in the Monterey Peninsula

2min
page 20

PADI Meets with Maldivian Ministry to Confirm Protection of Sharks

2min
page 17

Diveheart & Tourism Malaysia Attend the Moscow International Dive Show 2021

1min
page 15

Introducing the All-New PADI Dive Guides

2min
page 16

Safety First: Know Your Equipment

1min
page 14

EAD Records a Remarkable Increase in the Sustainable Fishing Index

4min
page 11

EAD & The National Aquarium Team up to Rescue Endangered Loggerhead Turtle

2min
page 9

EAD & The National Aquarium Start Receiving & Rehabilitating Rescued Animals

3min
page 8

The National Aquarium

2min
page 10

Be Resilient and Agile

2min
page 5

Abu Dhabi Media to Air EAD’s New Documentary: Our Sea, Our Future

5min
pages 12-13

EAD Joins Forces with the National Aquarium to Protect the Wildlife in Abu Dhabi

3min
page 7

Nemo Diving Center Introduce Their New Location with a Clean-up Event

2min
page 6
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