It’s no surprise that the demand for shark fins is one of the causes for their overall population decline. Scientists have been working for years to understand where geographically shark fins are coming from – and from which species – to help identify regions for improved management. A report last year used data on species composition of shark fins at four markets and species distribution models (SDMs) to predict the probability of fin origin. Now a group of shark scientists has published a rebuttal, saying they disagree with the results and conclusions of the previous paper.
“We fundamentally disagree with the central assumption of the paper that there is a direct link between species distribution and shark fin origin. This assumption relies on fisheries catch being equal through the distribution of a species, which we know is not true,” the authors state in the new journal article, fittingly published on Shark Awareness Day (July 14). “An example of the dissonance caused by excluding fishing activity is northwestern Australia, where Van Houtan et al. indicate a high probability of shark fin origin for many species, despite the area being closed to commercial shark fishing since 1993, and no operational fisheries to support suggested catch. Such discrepancies have overinflated the estimated contribution of shark fins from nations as these factors have not been accounted for, leading to unrealistic conclusions about the source of fins in trade.”
Western Australia’s shark fisheries are strictly managed, with specific controls on fishing efforts being “continually adjusted in response to ongoing monitoring and assessment to ensure that shark fishing remains sustainable,” states the Government of Western Australia Department of Fisheries. As such, fishing for shark has been prohibited for 12 years in the state’s north-west due to overfishing. “The conclusion that Australia is the top contributor to the fin trade is impossible given that national shark and ray catch is less than 5000 t yr−1, a level that cannot produce sufficient fins (they account for about 5% of landed weight, approx. 250 t) to account for it being the country supplying the most fins to the trade,” the authors argue.
The researchers also state that the paper’s use of DNA data from some markets may be misleading since it assumed that all markets contributed equally to the global fin trade. “Many of the SDMs used by Van Houtan et al. were seriously flawed, with 21 of the 57 (more than 30%) having serious inaccuracies,” Raoult says, saying that the models in in the 2020 paper indicate “species occurrence well outside their established geographical distributions known from decades of fishery and research data, which are reported in widely available species guides.”
“Our model conservatively assigns a species’ catch level to the entire area in which it most probably exists,” Van Houtan replied to this critique with their team’s own publication. “Our approach does have limitations and can be further improved with additional data layers on marine protected areas [MPAs] and fishery accessibility, operator incentives, vessel tracking, and market surveys. Such additions may alter our conclusions.”
Raoult disagreed with the model, explaining that, “aside from the issues with the species distribution models that [was] used – they still have not justified the presence of species known to only occur in one ocean occurring globally – at its core the assumption that finning occurs across the range of an animal’s occurrence is flawed. The presence of a shark species in an area does not mean it gets fished and finned.” Raoult used Australia as an example; in Van Houtan’s paper the models highlights the northern parts of this country as areas where large amounts of finning occurs, but shark fisheries do not exist there. “The implication that there is a large volume of illegal fishing is not realistic,” says Raoult.
While Raoult and his team agree that opportunities exist to improve shark conservation efforts within the exclusive economic zones (EEZs) of numerous countries, they insist that the results from Van Houtan’s paper “at best show the probability of where species in the fin trade occur, not probabilities that ‘represent the top nations contributing the most shark fins to the global market.’” Van Houtan replied via Tweet: “We hope this debate drives more debate, improves predictive models, and sharks win.”
Yes, one thing both groups seem to agree on: a serious threat to sharks exists in these fin markets, and both international and local communities must ban together to protect threatened and endangered species. How stakeholders, scientists, and conservationists go about tackling this threat… that’s where we all might differ.