1Department of Zoology and Institute for Coastal and Marine Research, Nelson Mandela University, Port Elizabeth, South Africa
2South African National Biodiversity Institute, Cape Town, South Africa
3Ezemvelo KZN Wildlife, Congella, Durban, South Africa
4Department of Environment, Forestry, Fisheries: Directorate: Oceans and Coasts, Cape Town, South Africa
Long-distance, ocean-traversing migrations are well documented for leatherback (Dermochelys coriacea) sea turtles (e.g., Luschi et al., 2003, Benson et al., 2011), and are also a paramount driver of leatherback conservation challenges; over such expansive distances, turtles are exposed to many threats in multiple jurisdictions and on the high seas (Wallace et al., 2011). Many populations are still in peril (Wallace et al., 2011), with indications that key pressures limiting population recovery are often offshore (Harris et al., 2018). Therefore, beach protection alone is not a guarantee for conservation success (Nel et al., 2013). Marine Protected Areas (MPAs) can be effective in protecting turtles in areas where they aggregate, like feeding or courtship areas. This provides strong motivation for considering migration and foraging distributions of leatherback and other turtles as countries embark on Marine Spatial Planning (MSP) initiatives or MPA expansion programs. These could be used in concert with other conservation measures, particularly in the South Western Indian Ocean (SWIO) where leatherbacks are Critically Endangered (Wallace et al., 2013).
The protection of migratory species is especially complex in developing nations, which face pressing needs to use natural assets for food security, job creation and security, poverty alleviation, and tourism, while conserving natural biodiversity. South Africa, for example, has implemented a National Development Plan which prioritises the expansion of an ocean-based economy. It aims to combine biodiversity protection with sustainable development and expansion of marine livelihoods through Operation Phakisa (www.operationphakisa.gov.za). As part of this framework, South Africa expanded its existing ocean protection with 20 new MPAs (DEA, 2019), which increased the protected proportion of ocean territory around mainland South Africa from 0.4% to 5.4% (Sink et al., 2019). Representative protection of ecosystem types, spectacular features, key life history areas and distributions of focal species such as leatherback turtles, were part of the motivation, design, and zonation of these new MPAs.
Nominations for two of the new MPAs in particular were based on the seasonal presence of leatherback turtles. iSimangaliso Wetland Park is a key nesting site for the SWIO loggerhead (Caretta caretta) and leatherback management units (Nel et al., 2013), with ~120 km of protected nesting beaches and originally 5 km of protected internesting area offshore. The more extensive internesting movements of leatherbacks (Harris et al., 2015) are now protected by a new iSimangaliso MPA extending 186km alongshore, and ~20-33km offshore (DEA, 2019; Figure 1). Another new MPA, the highly productive Agulhas Front MPA, (colloquially called the “Turtle Tuckshop”), was also in part proclaimed as leatherbacks seem to forage in oceanic frontal areas (Harris et al., 2018) with the uThukela, shelf edge and seamount–associated MPAs also recognised as potentially important for turtles.
In a complementary initiative, South Africa has been revising its Ecologically or Biological Significant Marine Area (EBSA) network as part of the Marine Spatial Management and Governance Programme (MARISMA 2014-2020) under Operation Phakisa. EBSAs are spatially discrete areas that perform important ecosystem services and/or host unique or vulnerable biodiversity relative to adjacent marine areas. They were conceptualised by the Convention on Biological Diversity (CBD) and are considered helpful to guide countries’ efforts to achieve their Aichi biodiversity targets (UNEP-CBD, 2012). To be inscribed as an EBSA, a site must meet at least one of the seven EBSA criteria (UNEP-CBD, 2009), including importance for life-history stages and/or importance for threatened species. South Africa’s revised network includes 23 EBSAs (MARISMA Project, 2020), and for some of these EBSAs, sea turtle presence contributed to the sites meeting these two criteria. EBSAs are not legally binding, but the CBD encourages countries to implement improved conservation and protection measures to secure the special biodiversity features within them. All South Africa’s new MPAs reside partially in EBSAs, and in combination they are key to marine spatial planning (MSP) processes, ensuring the protection of important biodiversity features, including leatherback turtles.
Previous satellite telemetry studies have indicated three migratory paths for post-nesting leatherback females: northerly into the Mozambique Channel, south-westerly into the South Atlantic, and a south-easterly migration into the open waters of the SWIO (Harris et al., 2018; Robinson et al., 2018). Less attention has been given to the “exceptions” that seemed to be aimless “wanderers”. Several leatherback turtles from these previous tracking studies seem to be have meandered along the coast, but satellite transmissions terminated before they reached an identified foraging ground or returned for the next season’s nesting.
Sea turtle nesting beaches in South Africa are well protected in the new iSimangaliso MPA, but the leatherback population is still small with 60-70 females nesting per season (Nel et al., 2013). An important task that remains to protect and conserve SWIO leatherbacks is thus to identify foraging areas, especially in relation to existing or future MPAs that may not only provide protection to turtles but also sufficient productivity and diversity to sustain their foraging needs. It would also be relevant to ascertain the mode by which leatherbacks benefit from MPAs, as their gelatinous diet seem to have unidentified origins. Jellyfish distributions shift interannually and seasonally but seem to attain highest densities in shallow water (<200m), with high zooplankton abundances, and proximity of hard substrate for polyps to attach (Flynn et al., 2011). It is, therefore, possible to identify spatial areas with high current or topographic advection driving local productivity and consequently jellyfish abundance. If these conditions are combined with a network of sites with reduced threats because of, for example, displaced fisheries, leatherback turtles may benefit.
The aim of this paper is, thus, to inspect the distribution of leatherback turtles from the SWIO and evaluate the conservation role of the new South African MPAs and EBSAs in protecting leatherback turtles.
Satellite deployment and tissue sampling
Three leatherback turtles that nested on the beaches within iSimangaliso MPA were fitted with Sirtrack/LOTEK FastGPS/Argos satellite tags (model F6H 473A) between 12-15th January 2020. One turtle was a neophyte (or previously untagged turtle) and the other two were remigrants that had nested in previous seasons. Turtle Jackie (flipper tag: ZA1471E; satellite tag: 196916) was the neophyte flipper tagged by Jackie Raw in December 2019. Turtle Michaela (named after volunteer, Michaela King) with flipper tag NN145 and satellite tag 196913 nested for the first time in 2012 and nested again in 2020. From tag scars, it was suggested that Turtle Tamsyn (named after MPA GIS expert, Tamsyn Livingstone; flipper tag: ZA1708C; satellite tag: 196915) had also nested previously but in an unknown year due to both flipper tags being lost. All three turtles left the beach with a satellite tag directly attached to the dorsal ridge, and two metal flipper tags applied to the trailing edge of the rear flipper.
Epibionts and body shape are proxies of body condition whereas blood metabolomics provide a clinical indication of health (Nolte et al., 2020). Size was, therefore, measured, and blood samples were collected from the femoral rete system in the rear flippers (following Dutton, 1996) using a 20-gauge needle and heparin-coated vacutainers that were kept on ice and processed for packed cell volume (PCV) and total solids (TS) at the field station following Perrault et al. (2012) as early indicators of health.
Tagging of leatherback turtles in 2020 had mixed success: two of the three satellite tags failed within 10 days while the third tag transmitted until 2nd July 2020 (Figure 1). Published tracks (Figure 2) from the same rookery from satellite tags deployed in the nesting seasons of 2011-13 (Robinson et al., 2016), and between 2006-2014 (Harris et al., 2018) were, therefore, added for further comparisons.
The satellite tag deployment (196915) on Tamsyn was active for 170 days. During that time, she made a southward journey in the Agulhas Current but, unlike most of her predecessors (e.g., Figure 2) that tended to move directionally south-westwards with the current, Tamsyn made several “small” clockwise loops (Figure 1), each lasting 10-20 days. During these excursions she swam south with the current and returned along the coast in a northerly direction. The only exception was one anticlockwise rotation where she left the shelf off East London, and then returned back to the coast further north. Her last transmission, after visiting the southern-most MPA (#24; South Western Indian Seamounts), was back up to East London to the Amathole (#32) and Amathole Offshore (#33) MPAs and the Algoa to
Figure 1. Satellite track of Tamsyn the turtle (black line) between 15th January and 19th June 2020 relative to all MPAs and EBSAs in South Africa’s mainland marine territory, with an enlarged insert showing the tracks of Michaela and Jackie near the nesting beaches in iSimangaliso. The -500m isobath is plotted as a dashed grey line to show the split between the shelf edge and slope. For more information on South Africa’s MPAs see: www.marineprotectedareas.org.za, and for more information on the EBSAs see: https://cmr.mandela.ac.za/EBSA-Portal/South Africa. Note that some MPAs comprise more than one area, e.g., 24, 32 and 33.
Figure 2. Leatherback migration tracks recreated from Robinson et al. (2016) and Harris et al. (2018), coloured by the migration corridor each individual followed, and overlaid with Tamsyn’s track.
Amathole EBSA. The total longshore coastal distance covered until 19th June was ~1,400km but the track length was seven times longer with a swimming distance of 10,069km. The satellite tag deployment (196915) on Tamsyn was active for 170 days. During that time, she made a southward journey in the Agulhas Current but, unlike most of her predecessors (e.g., Figure 2) that tended to move directionally south-westwards with the current, Tamsyn made several “small” clockwise loops (Figure 1), each lasting 10-20 days. During these excursions she swam south with the current and returned along the coast in a northerly direction. The only exception was one anticlockwise rotation where she left the shelf off East London, and then returned back to the coast further north. Her last transmission, after visiting the southern-most MPA (#24; South Western Indian Seamounts), was back up to East London to the Amathole (#32) and Amathole Offshore (#33) MPAs and the Algoa to Amathole EBSA. The total longshore coastal distance covered until 19th June was ~1,400km but the track length was seven times longer with a swimming distance of 10,069km.
While Tamsyn travelled along the east coast of the country and offshore to the shelf edge and waters overlying the slope and sea mounts south of St Francis Bay, she traversed ten coastal and two offshore MPAs. The journey started in iSimangaliso MPA (#41) with GPS transmissions received from every coastal MPA except Dwesa-Cwebe (#34; although there were transmissions on either side and hence it was inferred that she travelled through), Sardinia Bay (#30) and Tsitsikamma (#27; Figure 1). She also visited every EBSA east of Mossel Bay (i.e. north to south: Delagoa Shelf Edge, Canyons and Slope; KwaZulu-Natal Bight and uThukela River; Protea Banks and Sardine Route; Algoa to Amathole; Kingklip Corals; and Shackleton Seamount Complex) except Tsitsikamma-Robberg along the south coast. Her track also confirms high use of the shelf, shelf edge and slope waters along the eastern seaboard of South Africa (Figure 1).
At this stage we do not know the final foraging destination of these three sea turtles, as the three tags failed before they started the return journeys for the next nesting season. However, the proxy indicators of condition and health suggest that all three animals (irrespective of being a coastal or pelagic feeders) were in good condition with carapace lengths exceeding 160cm. The neophyte turtle (Jackie) was the longest of the three, but the girth of Tamsyn (and so body condition) was substantially more than the other two turtles. The blood metrics, particularly packed cell volume supported the good condition for Tamsyn with a value of 43%, which is ‘normal’ although slightly better than the other two females (Table 1). She laid a clutch of 100 eggs at the time of tagging (which is the mean for the iSimangaliso population), whereas the other two females had slightly larger clutches (Table 1).
Table 1. Tagging information, blood results, and body condition of tracked turtles. CCL- curved carapace length; CCW- curved carapace width; PCV- packed cell volume; TS- total solids. Neophytes- first time observed to nest; Remigrants- tagged or with tag scars.
|Turtle||Satellite Tag | Flipper tag||Date | Distance#||Nesting status||CCL | CCW (cm)||Eggs* | Blood PCV % : TS g/dl|
|Michaela||196913 | NN145||15 Jan 2020 | 69 km||Remigrant||161.2 | 115.0||136 | 32 : 4.2|
|Tamsyn||196915 | ZA1708C||12 Jan 2020 | 43 km||Remigrant||164.4 | 122.0||100 | 43 : 4.3|
|Jackie||196916 | ZA1471E||15 Jan 2020 | 51 km||Neophyte||165.4 | 113.2||124 | 31 : 3.2|
The aim of this paper was to review the post-nesting distribution of leatherback turtles from iSimangaliso and to reassess likely migratory routes between feeding and nesting grounds. Although the sample size of this study is small, it provides a valuable comparison with previous tagging studies (and the first blood metrics), and thus adds to a baseline dataset to measure future performance of these MPAs and EBSAs for leatherback turtles. The conservation measures for the SWIO leatherbacks to date have been centred around long-term beach protection exceeding 55 years, but despite these efforts, the population has remained Critically Endangered (Nel et al., 2013; Wallace et al., 2013). The MPAs and spatial protection measures intended to be implemented in the EBSAs through the MSP process may be a “game changer” for this species.
Our results suggest that the location of the areas with spatial protection (MPAs and new measures proposed within EBSAs) are better suited for sea turtles than previously recognised. The new MPA not visited by Tamsyn ironically is the Agulhas Front “Turtle Tuckshop”. However, the other two published studies indicated the popularity of this MPA with post-nesting females with a number of tracks circling through the Agulhas Front, probably en route to the Atlantic or SWIO foraging grounds, particularly those turtles migrating further offshore (Figure 2).
The unusual migration path of Tamsyn is not due to poor body condition or disease; she is an average-sized individual for South African leatherbacks, which range from 159.3-196.3cm for neophytes and remigrants (Le Gouvello et al., 2020), with apparently normal blood metrics. These are the first baseline PCV and TS data for South Africa, which are comparable with published studies from Florida and Georgia (Perrault et al., 2012), Gabon (Deem et al., 2006) and Bioko (Honavar et al., 2011). PCV for nesting females in Florida (n=59) were (mean±SD) (range) 38±4.4% (27-50) and direct captures for Georgia (n=18) 42±7% (24-49), with Gabon (n=28) 36±5.4% (28-56) and Bioko (n=55) at 36.4±5.09% (27.8-44.9). TS (g/Dl) for Gabon (mean±SD) were 4.0±0.7 (range 2.3-5.4) and Bioko (n=54) at 5.08±0.1 (3.6-6.56). The PCV for Tamsyn was thus on the higher end of the mean range for nesting turtles, whereas the other two were on the low end but within one SD. Jackie, the neophyte, had a low TS value with the remigrants both in the mean range of nesting females from the Pacific (Harris et al., 2011). There is still much to learn from the metabolomics, but the combination of foraging location and nesting condition suggest that the eastern seaboard is an adequate foraging ground if leatherbacks do indeed remain along this coast.
It is generally assumed that post-nesting females return to the same foraging grounds from which they come (Marcovaldi et al., 2010), which suggests that turtles with similar distributions as Tamsyn may spend a substantial amount of time along the eastern seaboard. These MPAs, therefore, seem to be attractive to some migrating leatherbacks. The mode of attraction is intriguing and not entirely clear, as the preferred food of leatherbacks are planktonic drifters and thus there seems little dependence on the (spatially predictable) benthic biodiversity as other turtle species would. However, highly productive shelf, shelf-edge and deeper waters, now encompassed in MPAs and EBSAs, may include productive upwelling zones that seem to provide at least an interim destination (or half-way stop) for post-nesting females to replenish. This south-eastern edge of the African continent is characterised by the edge of the Agulhas Bank forcing the Agulhas Current offshore, and a combination of log-spiral bays and rocky headlands with strong summer north-easterly winds. The result is wind- and current-driven coastal upwelling (Goshen et al., 2012) and potential retention of zooplankton accumulations along the coast and in bays. These oceanographic features are similar to those described in Benson et al. (2011) including current boundaries, stationary fronts and coastal retention areas aggregating prey, and so attracting Pacific leatherbacks to coastal foraging grounds.
The residence duration of leatherbacks on the Agulhas shelf seems to differ among the studies (Figure 2) suggesting interannual differences in behaviour that are most likely dependent on oceanic conditions of any given year, and the foraging destination from which the turtles have come. Both Robinson et al. (2016) and Harris et al. (2018) clearly demonstrated migratory routes to the north, southwest and southeast. Tamsyn, however, seems to be following a different post-nesting migration strategy, remaining well within South Africa’s marine territory. This indicates that there is likely an undocumented fourth post-nesting migration/foraging route (or interim stop-over) for leatherbacks in the SWIO, but detailed analysis of oceanographic and track data is required to confirm the drivers and conditions under which the eastern Agulhas Bank is a preferential foraging destination.
Tamsyn the leatherback turtle frequented 12 of 13 MPAs on the South African eastern seaboard. This data set, although preliminary, suggests that South Africa’s expanded MPA network is likely to contribute to the protection of leatherback turtles during nesting, migratory and foraging stages. It is the first time that FastGPS tags were used for South African leatherbacks, providing better spatial resolution than available from traditional Argos tags, especially for data points close to inshore. This improvement in accuracy has contributed to better determining the potential value of the MPAs and the delineation of EBSAs for protecting post-nesting females, with this area also potentially being a distinct foraging ground. It is necessary to review these data periodically because the new MPAs may aid in the recovery of SWIO leatherbacks and other, more coastally distributed, sea turtles.
Ethics approval (A180SCI-ZOO-006) and national research permits (RES2019/05 and RES2020/102) were obtained prior to conducting the field research. Funding for the field component of this study was provided by the Pew Charitable Trust as a Marine Fellowship to RN. The MPA expansion project was also partly funded by Pew as a Marine Fellowship to KJS. LRH is supported by the MARISMA Project, funded by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety through its International Climate Initiative, and implemented by GIZ (Deutsche Gesellschaft für Internationale Zusammenarbeit GmbH) in partnership with the Benguela Current Commission and its contracting parties. Special recognition is given to Tamsyn Livingstone for creating countless versions of the maps for the MPA expansion project until the final version was accepted. Special thanks are extended to the unpaid volunteers that assist each season with the field component of turtle monitoring (like Jackie Raw and Michaela King).
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