Scientists challenge research showing SA’s white shark population is stable

Monitoring locations (solid circles) within South Africa that were used to develop the sightings-per-unit-effort or catch-per-unit-effort abundance indices. (Source: Heather D. Bowlby, Matt L. Dicken, Alison V. Towner, Sarah Waries, Toby Rogers, Alison Kock – Decline or shifting distribution? A first regional trend assessment for white sharks (Carcharodon carcharias) in South Africa).

By Julia Evans

12 Mar 2024

An international team of marine biologists and local conservationists have challenged an academic article which suggests South Africa’s white shark population remains stable and has redistributed eastwards to flee predation from orcas. The team is mainly concerned that this will detract from the likely urgent need to conserve the great white shark in SA, which faces multiple threats, including shark nets and longline fisheries.

In September 2023, an article published in the journal Ecological Indicators titled “Decline or shifting distribution? A first regional trend assessment for white sharks in South Africa”, authored by several renowned marine biologists, as well as researchers at SANParks, Shark Spotters and the KwaZulu-Natal Shark Board, supported claims that as of 2020 (the latest available data) shark populations have remained stable since 1991 when white sharks were officially protected from exploitation in SA.

This study also suggested that the notable disappearance of white sharks from their typical aggregation sites in False Bay and Gansbaai was related to two orcas who had been hunting them since 2015 and that they had moved to the Eastern Cape.

white sharks White shark photographed in Gansbaai, Western Cape. This species has been seen only sporadically in its typical aggregation sites, like Gansbaai, since 2017. (Photo: Dr Sara Andreotti)

However, a rebuttal article was recently released in the same journal, challenging the claims that the white shark population remains stable and sounding the alarm on the likely need to ramp up conservation efforts for white sharks in SA.

Dr Enrico Gennari, lead author of the rebuttal article and a marine ecologist from the Oceans Research Institute in Mossel Bay specialising in white sharks, told Daily Maverick, “I would be very happy to be wrong. It would mean that the white sharks are okay.”

The problem, Gennari said, was that they could not afford to be right and carry on as normal.

Gennari, who is also a research associate at the Department of Ichthyology and Fisheries Science at Rhodes University, acknowledged the reputability of the scientists – many of whom he has worked with on other studies – but stressed the potential ramifications of accepting that the white shark population in SA is stable.

Gennari co-authored a study in 2022 – with the lead author of the article he’s rebutting – that used simulation modelling and found that even 10-20 mortalities would affect the stability of the white shark population in South Africa.

“I was quite surprised that the year after that paper, there was another one saying [the white shark population] is stable. But that is normal in science,” noted Gennari.

Gennari said that at first he wouldn’t have bothered to write a rebuttal article, but he said concerns started when some officials of the Department of Forestry, Fisheries and Environment (DFFE) took the 2023 article as absolute truth, and Gennari worried that this would deprioritise white shark conservation in SA.

“That to me was a big alarm bell … it was very quick,” said Gennari, explaining that he wanted to publish the reasons why the other paper could not prove that white sharks were stable and that a precautionary approach was needed.

However, the scientists who wrote the 2023 article say that their research does underscore the importance of conservation and points to the need to get more data to track the status of populations, but that as of 2020, white shark populations were stable.

Alison Kock, a marine biologist and co-author of the 2023 study, told Daily Maverick that their article also addressed the concern that there was no evidence to show that white shark populations had increased since they were formally protected in 1991 – “something we would have expected after more than two decades of protection”.

She added: “We also emphasise the need to understand ecological drivers and mortality sources better, and recommend more representative monitoring to track changes in the abundance of white sharks in South Africa in the future.”

Gennari said the rebuttal emphasised that existing data warranted immediate action rather than waiting for additional years of data collection.

“Otherwise we might run the risk of just describing extinction,” he said.

Gennari said they had asked the researchers from the 2023 study for the data so they could re-analyse it. The article states that data will be made available on request.

“But we were presented with a legal document that surprised us because it isn’t part of an open-access approach to research,” said Gennari, adding that this was another reason they wanted to look into this.

The DFFE was approached for comment on 7 March and on 13 March told Daily Maverick that they noted the 2023 study and the recent rebuttal.

“The original study is an analysis of the best available data in South Africa using the most comprehensive suite of abundance indices compiled to date,” department spokesperson Peter Mbelengwa said.

Mbelengwa said the authors of the original study concluded that there is no evidence of a white shark population decline across the entire South African range, which is in line with previous findings during the National Plan of Action (NPOA) review.

“Since then, more evidence has become available to suggest that the white shark population has shifted eastward, and no additional verifiable evidence has been presented that white sharks are in further decline,” he said.

Mbelengwa added: “The rebuttal challenges some of these findings based on uncertainties and sparse data but fails to present alternative analyses or evidence for a white shark decline that is verifiable scientifically.”

Are sharks migrating east?

The 2023 article noted a general shift of white sharks from the Western Cape to the Eastern Cape, based on several reports of human-shark incidents.

Researchers also suggested that environmental or operational factors affecting the abundance of white sharks should be explored at a regional level in future studies.

But the rebuttal article took issue with their methods and objected to the presentation of the two data sets, arguing that it could not support the claims made about population stability or redistribution of South Africa’s white sharks.

Dr Sara Andreotti, a co-author of the rebuttal article and a marine biologist from the Department of Botany and Zoology at Stellenbosch University, told Daily Maverick that the 2023 article compared very different data sets.

In the Western Cape, they used shark sightings. In the Eastern Cape, they used reports from four anglers and the white sharks killed in the shark nets and drumlines (baited hooks) deployed by the KZN Sharks Board.

Gennari took issue with the 2023 article interpreting percentage changes without considering absolute numbers.

“If the entire population was indeed regionally stable and those observed simply moved from west to east, one would have expected the number of white sharks in Algoa Bay [Eastern Cape] to be tenfold higher,” the rebuttal researchers write.

Wilfred Chivell, the CEO of ecotourism operator Marine Dynamics and founder of the affiliated Dyer Island Conservation Trust, who has worked with some of the scientists cited in both papers, but wasn’t part of either article, told Daily Maverick that he did not agree with the methodology and findings in the 2023 paper right from the start.

Chivell said that his organisations had been studying white sharks for almost two decades, through tagging and tracking, behavioural surveys, movement and foraging ecology, environmental parameter monitoring, as well as population and fin cam studies.

“There is NO evidence that the white sharks that we identified and knew moved to the Eastern Cape and further north,” said Chivell. “None of these sharks were ever seen again, not here and not on the east coast.”

Movement happened before orcas

The number of shark sightings in the Western Cape has declined to fewer than 10 per year recently, raising concern.

The 2023 study proposed a theory that the disappearance of white sharks from False Bay and Gansbaai in Western Cape, their typical aggregation sites, was related to the recent appearance of a pair of killer whales (orcas), that specialise in hunting large, coastal sharks.

Gennari agreed that some white sharks were moving east because of orcas, but he emphasised that the decline in white sharks in these areas started around 2011-2012, before the appearance of the orcas.

The famous orcas appeared only in 2015 in the Western Cape, and the first noted killing of a white shark was in 2017.

Chivells said that Marine Dynamics, which has been monitoring the orcas since their first appearance in Kleinbaai, Gansbaai, in 2017, said he “agrees that they cause a flight response of the great whites. But that they are solely to blame or causing all white sharks to move eastwards is incorrect.”

Andreotti said that while she was not denying that orcas could play a temporary role in displacement, “I am worried that too much attention has been given to these sporadic events (about 10 in total since 2017), forgetting about the continuous depletion of white sharks due to human-related threats.”

Human threats

The controversy doesn’t solely revolve around natural factors like orca predation.

Human-induced threats, such as the lethal shark control programme of the KwaZulu-Natal Sharks Board (shark nets and drumlines) and the demersal shark longline fishery contribute significantly to the decline in white shark numbers.

Gennari emphasises that these threats are within human control and require immediate attention.

Gennari notes that one of the authors of the 2023 article, Dr Matt Dicken, is part of the KZN Shark Board’s lethal shark control programme. For the past 40 years, the programme has killed an average of around 30 white sharks every year.

Dicken, who is the KZN Sharks Board head, previously told Daily Maverick, “The data used by Enrico [Gennari] is incorrect… We don’t kill that many white sharks — as such, the paper’s conclusions are wrong.”

Yet Dicken was co-author of a paper which reported that 1,317 white sharks were captured in the KZN shark nets and drumlines between 1978 and 2018 and only 16% were released alive, meaning an average of 28 white sharks were killed per year.

Gennari says he is currently working on research that estimates that at least 40 white sharks have been killed by the longline fisheries industry per year since 2005, peaking around 2010-2012 – the same time the decline started happening in the Western Cape.

Longline fisheries unintentionally catch white sharks as bycatch because they are fishing for the same prey as white sharks. What makes matters worse, the demersal shark longline fishery received a new permit this year that includes targeting and killing critically endangered and endangered species.

“It’s like allowing the commercial exploitation of black rhinos in the hundreds,” said Gennari.

“Out of 200 chondrichthyan species occurring in South Africa, white sharks constitute the species with the highest protection level, in terms of regulations under the Marine Living Resources Act,” said the DFFE’s Mbelengwa.

Mbelengwa said several protection measures have been added since the NPOA II was published, including: A reduction of the demersal shark longline effort from six to one vessel, a proposed electronic monitoring system, aimed at augmenting physical observer coverage, new handling protocols for incidental shark captures in several fisheries, a change in size limit to avoid capture of large (and very small) sharks and a reduction in catch of pelagic sharks in the longline fishery of more than 80%.

He added that the DFFE regularly reviews and updates permit conditions in all its fisheries to be in line with international best practice.

“Moreover, the department banned recreational drone fishing, one of the emerging threats to white shark conservation.”

Gennari emphasised that the two threats might not be the only reasons for the decline, but that these threats alone kill almost 10 times more white sharks than what researchers know the orcas have killed in seven years, and are the only threats that that we, as humans, can do something about.

Chivell agreed that these two threats have a massive impact on the decimation of our shark populations, saying, “The KZN Sharks Board is indiscriminately killing sharks, dolphins and sea turtles every day.”

Kock acknowledges the critique and commits to evaluating the feedback, emphasising the ongoing importance of research and management efforts for white shark conservation.

The 2023 study also noted that research needs to be directed toward management focused on reducing anthropogenic sources of mortality within their southwest Indian Ocean range.

A vulnerable population

Whether the scientists agree on the stability of white shark populations or not, they both agree that conservation is important

“Given their [white sharks] relatively small population sizes and vulnerability to human impacts, ongoing research and management efforts are crucial for white shark conservation,” said Kock.

In the absence of an official population study – it would also help protect sharks if they were classified as endangered – the latest population estimates pin white sharks at only 500 to 1,000 individuals left, and there’s evidence the average female size of white sharks in SA is decreasing.

Genetic studies also suggest a high level of inbreeding.

Gennari said his main concern is not the rebuttal of the 2023 paper, but that there is enough evidence now to suggest that the white shark’s stability is under threat.

Since 2019, the Oceans Research Institute in Mossel Bay has tagged 21 white sharks with internally implanted 10-year tags. By 2023, only three white sharks (14%) of the tagged individuals were still detected, indicating an 86% disappearance.

While not completely representative, this data sheds light on a concerning trend.

The controversy serves as a wake-up call for scientists, policymakers and the public alike, highlighting the delicate balance between conservation and human activities that threaten the survival of these majestic creatures.

“We might be running out of time,” warned Gennari. DM

This article was updated at 12pm on 13 March 2024 to include a response from the Department of Forestry, Fisheries and Environment.

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South Africa

Are sharks migrating east?

Movement happened before orcas

Human threats

A vulnerable population