Australian hybrid fish story – Media jumps the shark

Pretty much everyone who has seen this today shakes their head and wonders. I’m wondering too. First, the story which is being serially regurgitated without any thought in media outlets world wide:

Please  read this excepted text from the story carefully:

In what is being hailed as the world’s first evidence of inter-species breeding among sharks, a team of marine researchers at the University of Queensland have identified 57 hybrid sharks in waters off Australia‘s east coast.

…

Ovenden speculated that the two species began mating in response to environmental change, as the hybrid blacktips are able to travel further south to cooler waters than the Australian blacktips. The team is looking into climate change and human fishing, among other potential triggers.

Pretty clear with the headline, right? There’s more examples of this, such as this one from the Business Insider which takes the cake:

Now, read the actual press release from the University of Queensland this story was based on:

World-first discovery of hybrid sharks off Australia’s east coast

A group of leading marine scientists has discovered that sharks on Australia’s east coast display a mysterious tendency to interbreed, challenging several accepted scientific theories regarding shark behaviour.

In a joint-UQ research project, scientists have discovered widespread hybridisation in the wild between two shark species commonly caught in Australia’s east coast shark fisheries.

The Australian black tip shark (Carcharhinus tilstoni) and the common black tip shark (C. limbatus) have overlapping distributions along the northern and eastern Australian coastline.

Using both genetic testing and body measurements, 57 hybrid animals were identified from five locations, spanning 2000km from northern NSW to far northern Queensland. Although closely related, the two species grow to different maximum sizes and are genetically distinct.

Dr Jennifer Ovenden, an expert in genetics of fisheries species and a member of the scientific team said this was the first discovery of sharks hybridising and it flagged a warning that other closely related shark and ray species around the world may be doing the same thing.

“Wild hybrids are usually hard to find, so detecting hybrids and their offspring is extraordinary,” Dr Ovenden said.

“To find 57 hybrids along 2000km of coastline is unprecedented.

“Hybridisation could enable the sharks to adapt to environmental change as the smaller Australian black tip currently favours tropical waters in the north.

“While the larger common black tip is more abundant in sub-tropical and temperate waters along the south-eastern Australian coastline.”

Scientists from The University of Queensland, James Cook University’s Fishing and Fisheries Research Centre, the Queensland Department of Employment, Economic Development and Innovation and the New South Wales Department of Primary Industries are now investigating the full extent of the hybrid zone and are attempting to measure hybrid fitness.

The research, co-funded by the Fisheries Research and Development Corporation, identified a mismatch between species identification using mitochondrial DNA sequence and species identification using morphological characters (length at sexual maturity, length at birth and number of vertebrae).

A nuclear DNA marker (inherited from both parents) was sequenced to confirm the hybrid status.

Dr Colin Simpfendorfer from James Cook University’s Fishing and Fisheries Research Centre said black tip sharks were one of the most studied species in tropical Australia.

“The results of this research show that we still have a lot to learn about these important ocean predators,” he said.

Media: Dr Jess Morgan on 0419 676 977.

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Important point: the press release DOES NOT contain the words “global warming” nor “climate change”.

I suspect this was the trigger for the reporter jumping the shark:

“Hybridisation could enable the sharks to adapt to environmental change as the smaller Australian black tip currently favours tropical waters in the north.

“While the larger common black tip is more abundant in sub-tropical and temperate waters along the south-eastern Australian coastline.”

So “environmental change” gets morphed into a “global warming” headline, when clearly, environmental change could be any number of things; pollution, changes in food supply, overfishing, competition, any of these (and others we don’t know about) could be factors…but “global warming” is automatically looked upon as the culprit. WUWT?

So, lets look at temperature. I asked Bob Tisdale to supply some sea temperature maps and graphs for the area. First the current available SST for Australia:

So much for the idea that the water is cooler to the southeast, and least in November. The waters of the south appear to be warming faster according to this anomaly map.

Here’s the last thirty years of sea surface temperatures from the area:

Less discerning reporters would immediately go A-Ha! The smoking gun, sea surface temperatures went up. Yes they did, and the trend is 0.135 °C/decade, and the trend line suggests Australian coastal sea temperature has increased by 0.45°C over thirty years.

But, in the last ten years (denoted by the span of the blue line) the temperatures have been pretty much flat.

Consider these points then:

1. Would you believe that one of the oldest creatures on Earth, which have managed to survive 500 million years over all sorts of temperature global temperature swings far greater,  is sensitive to SST changes of 0.15 degree per decade enough to go on a panic breeding frenzy to save itself?

2. Since these “hybrid” sharks are a recent observation, it stands to reason they didn’t exist 20 years ago, maybe even 10 years ago. In this paper, the maximum lifespan of the Australian black tip shark (Carcharhinus tilstoni) is given:

The greatest recorded ages for C. tilstoni were 12 years for females and 8 years for males…

Davenport, S.; Stevens, J.D. (1988). “Age and growth of two commercially imported sharks (Carcharhinus tilstoni and C. sorrah) from Northern Australia”. Australian Journal of Marine and Freshwater Research 39 (4): 417–433.

So clearly, this new hybrid is a recent decadal scale development, and the last ten years of temperature in the area have been essentially flat. Connecting this with “global warming” doesn’t wash.

3. Ok, back to the “speculation” part of the headline:

Ovenden speculated that the two species began mating in response to environmental change, as the hybrid blacktips are able to travel further south to cooler waters than the Australian blacktips. The team is looking into climate change and human fishing, among other potential triggers.

It seems the Blacktip Shark isn’t confined in range at all, as this 2010 paper shows (bolding mine):

Boomer, J.J., Peddemors, V. and Stow, A.J., 2010. Genetic data show that Carcharhinus tilstoni is not confined to the tropics, highlighting the importance of a multifaceted approach to species identification. Journal of Fish Biology, 77:1165–1172.

Summary

Sharks are prone to human-induced impacts, including fishing, habitat destruction and pollution. Therefore, effective conservation and management requires knowledge of species distributions. Despite the size and notoriety of sharks, distributions of some species remain uncertain due to limited opportunities for observation or difficulties with species identification.

One of the most difficult groups of sharks to identify correctly is the ‘blacktip sharks’. This group of whaler sharks are harvested in substantial numbers along the Australian east coast, including NSW, yet little is known of their distribution and resultant potential portion of the commercial shark catch.

The NSW Shark Meshing Program (SMP) research has collected genetic samples from most sharks caught for many years. Analysis of these samples to determine proportions of each species caught in the shark nets yielded the surprising discovery that the tropical Australian blacktip shark (Carcharhinus tilstoni) was regularly represented. Approximately one-third of the ‘blacktip sharks’ previously assigned to the common blacktip (C. limbatus) were identified as Australian blacktip sharks. This discovery extends the range of this tropical species over 1000km southwards into temperate waters off Sydney.

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Wikipedia even has this helpful map of the range of Carcharhinus tilsoni