Page 44 - Atlas Sea Birds Ver1

2.1.2 Population trends and conservation status of sea turtles in
northern KwaZulu-Natal

Author: S Bachoo

Abstract:
Two species of sea turtle nest in austral summers on Indian Ocean beaches in northern KwaZulu-Natal (KZN), which are protected within
the iSimangaliso Wetland Park World Heritage Site: Loggerhead (Caretta caretta) and Leatherback (Dermochelys coriacea). The KZN
turtles contribute to the South-West Indian Ocean subpopulations of these species, which are classified as Near Threatened and Critically
Endangered, respectively. Numbers of both species increased in KZN after the mid-1960s. In the 2021/22 breeding season, overall counts
of nests were 4,551 for Loggerheads and 493 for Leatherbacks. Most nests of Loggerhead Turtles occurred between the Mozambique
border and Black Rock, whereas those of Leatherback Turtles were spread from the border to Sodwana Bay. There was one record of a
Green Turtle (Chelonia mydas) nesting in KZN in 2014.

Introduction:
Two sea turtles, Loggerhead (Caretta caretta) and Leatherback (Dermochelys coriacea), nest annually between October and March along
the northeast coast of KwaZulu-Natal (KZN) in the iSimangaliso Wetland Park World Heritage Site. Consistent, dedicated monitoring of
tracks of these species exiting the ocean on sandy beaches (emergences) and of nests laid has taken place every breeding season since
1965/66 in the area from the mouth of Kosi Bay estuary (3.2 km south of the Mozambique border) to the Bhanga Nek research station
(16 km south of the Mozambique border, Figure 1). This is known as the Index Area (Nel and Bachoo 2011). Counts of these parameters
were made exclusively by foot patrol on each night of breeding seasons by turtle monitors walking the beaches from 19h00 to 24h00 and
by a sunrise patrol the following morning. Tracks counted by monitors were clearly marked when first encountered to avoid their being
recounted. These time-series allow assessments of trends in numbers of Loggerhead and Leatherback turtles in northeast KZN. Together
with counts made over a wider area, from the border with Mozambique in the north to Sodwana Bay in the south, they provide information
on numbers of these species nesting in KZN that is relevant to assessments of the conservation status of these species and their sub-pop-
ulations in the South-West Indian Ocean (SWIO). There was a solitary record of a Green Turtle (Chelonia mydas) nesting in KZN in 2014.
Population trends and distribution

Counts of emergences and of nests can both be used The large increase in the 1990s and 2000s was ascribed
to gauge trends in turtle populations. It is thought that to protection afforded to hatchlings in KZN since 1965/66,
emergences may provide better estimates than nests of which some subsequently returned to nest (Nel 2014).
as they are less dependent on effort, equipment and It was initially thought probable that Loggerhead Turtles in
interpretation (Nel 2014). Within the index area, for each northern KZN take 12–15 years to reach nesting maturity
species the two measures of abundance were strongly (Hughes 1989), but it has since been established that the
positively correlated for 1965/66–2021/22: Loggerheads (N average age at sexual maturity for this loggerhead turtle
= 57, r = 0.969, P < 0.001); Leatherbacks (N = 57, r = 0.989, subpopulation is around 36 years (Tucek et al. 2014). This
P < 0.001). This lends confidence to their use as proxies of is in line with populations elsewhere that attain maturity
trends in abundance for both species off northern KZN. at 10–39 years (Avens and Snover 2013). The KZN
For Loggerheads and Leatherbacks each index is shown Loggerheads may also have benefitted from increased
below. protection of beaches in Mozambique after 1996 and
the collapse of a trawl fishery for prawns (Haliporoides
Loggerhead Turtle triarthurus) and associated species off the east coast of
KZN (Nel 2014). Loggerhead Turtles are catholic feeders
that eat jellyfish at the sea surface, feed on mussels close
Numbers of emergences and nests of Loggerhead Turtles
recorded in the Index Area from 1965/66–2021/22 are inshore and dive to catch benthic prawns, rock lobsters and
shown in Figure 2. The trends are similar and indicate molluscs (Hughes 1989). Turtles that are caught in trawls
increases in the 1960s, plateaux in the 1970s and 1980s, face a risk of serious injury or drowning (IUCN 2020).
increases again in the 1990s and 2000s, peaks from 2011–
2014, decreases until 2016/17 and subsequent recoveries
towards the peaks. Numbers of emergences were < 700 in
three seasons in the 1960s, fluctuated around c. 1,500 in
the 1970s and 1980s, rose to above 4,000 from 2010/11–
2013/14, dropped to c. 2,500 in 2016/17 and then increased
to c. 3,800 in 2021/22. Numbers of nests were < 500 in
three seasons in the 1960s, fluctuated around c. 750 in
the 1970s and 1980s, rose to above 2,500 from 2011/12–
2013/14, dropped to slightly more 1,500 in 2017/18 and
recovered to 2,554 by 2021/22 (Figure 2). The slightly
depressed numbers of emergences and nests in 2020/21
resulted from reduced monitoring that season attributable
to the COVID-19 pandemic. A Loggerhead Turtle in KZN (photo J Tucek)

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