Complexity of Species Extinction

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The Complexity of Species Extinction: Can Conservation Learn From The Past?

Written by Matthew Scott

Last month the vaquita received a lot of attention. NOAA announced plans to corral the last 30 or so of this severely endangered species and place them in sea pens. They will use specially trained navy dolphins to assist in capturing the most endangered porpoise in the world and transport its members to San Filipe where the species will hopefully recover to the point they can be released back into their natural habitat. This multi-million dollar plan to save a species from human-caused extinction illustrates how complex extinction can be. Not just because we have the ability to engineer recovery of species on the brink but because when it comes to studying illusive cetaceans, a lot of time and money is needed simply to assess numbers in populations and perform genetic analysis, all research essential in order to determine stock size and vulnerability. The vaquita is not the first cetacean to reach this level of human-caused vulnerability. The Baiji river dolphin’s story was remarkably similar, a spices that is now extinct.

When does a species become extinct? This might be an obvious question, the official definition of ‘a species or family having no living members’ would be similar to the definition of extinction you had in mind, I’m sure. In practice this is a little more difficult. First of all, what makes a species a species? Although this seems rather philosophical it has major implications for extinction rates. The other more obvious question to ask is, well…how do we know every member of a species has died out? Nobody knows the exact number of individuals there are of any species of cetacean. Extrapolation can be done using statistical models based on survey efforts but this is not an exact number. We may have a very good idea about how many orca there are in the southern resident population but this is because orca are comparatively easy to distinguish and there have been continuous studies of them dating back to the 70’s. So back to my question, if we do not know how many individuals there are even in most populations (let alone species) then how do we say a species has gone extinct?

Firstly, let’s address the species question. What makes a species a species? The working definition is a group of individuals that actually or potentially interbreeds in nature to produce viable offspring. You can test the relatedness of species using molecular techniques. In principle this is rather straightforward among cetaceans, if you think of humpback whales and grey whales they look completely different and it would be easy to recognize and keep track of the offspring of the two or conduct genetic analyses on them. In practice, however, with other species it is not so obvious. For example, until recently medium sized rorquals were thought to be one of two species, Bryde’s whale or sei whale.  Surprisingly, as recently as 2003 a new species was discovered called Omura’s whale and there is now enough molecular genetic evidence to know this species is probably more closely related to the blue whale than Bryde’s whale. At present, genetic data is not sufficient to say exactly how many species there are however we know there are at least 3-4 genetically distinct types of medium sized roquals. Looking at the pictures of a Bryde’s and sei whale below it is easy to see why they would be assumed to be the same species. The only visible difference is their size at full maturity that separates them, with the sei whale being larger. You can see why the species question is relevant in this discussion; it becomes the foundation for the next question because once we identify a species we can look for the number of individuals in that species.

As mentioned above, this becomes more complex when dealing with marine organisms. Let us look at a case study to illustrate the point. The baiji (or Yangtze) river dolphin is thought of by most researchers as being extinct since 2006 despite the IUCN Red List, the authority on species extinction, classifying it as merely critically endangered. Inhabiting the Yangtze and Quintang rivers, sightings of the baiji have ceased in the Quintang river since the 1950’s. Between 1971 and 2000 estimates of total population numbers went from 400 in the 1970’s, to approximately 300 in 1985-86, to 13 in 1997-99. This represented a steady decline of the population. Non-selective and illegal fishing practices would later be the main culprit in the extinction of the baiji. To address a lack of information on the species a multi-national research team was deployed to conduct a 5 week, two vessel, 1669km survey of the Yangtze river in 2006. They used line-of-sight and acoustic recorders to look for the illusive dolphins and listen for their clicks and whistles. At the end of the survey they were forced to come to the conclusion the baiji was functionally extinct because they didn’t see or hear a single one.Blog 7- Fig 4

I mentioned the definition of extinct above as being ‘a species having no living members’. The last confirmed stranding of a baiji was in 2001 and the last picture was taken in 2002. Despite the 2006 extensive survey, there have been reports of sightings after 2002 leading all the way up to when the survey was being conducted in 2006. Between 2005 and 2006 4 baiji sightings were reported by local fishermen and 2 baiji were reported by Local Marine Affairs staff. During the 2006 survey effort a retired school teacher saw some baiji 60-70m from shore. The animals were identified as baiji rather than the other cetacean that inhabits the Yangtze river, the finless porpoise, by the presence of a dorsal fin. So the question becomes, when you have a survey design that is as comprehensive as possible however still mentions the possibility of a few surviving baiji coupled with sporadic unconfirmed sightings, how certain can you be that every living member has died out and that a species has officially become extinct?Blog 7- Fig 5.jpg

I realize this is picking at threads; however it is a good illustrator of the complexities involved in conservation as well as cetacean science. To be able to speak in certainties is the most persuasive thing for activist attempts however conservation attempts are often shrouded in gray.

To come full circle, the conservation efforts and subsequent extinction of the baiji echo those being made today for the vaquita. Both have non-specific fishing practices to blame for their decrease in numbers, both have years of surveys watching the species decline, and both have the plan to relocate the remainder of the species to semi-artificial habitat to preserve them from their own toxic habitat. While in the case of the baiji the efforts culminated with a final survey that found no viable population to preserve, hopefully the fate of the vaquita will be different. There are approximately 30 vaquita as of 2016 so the effort will depend more on the success of the trained navy dolphins and the ability of the vaquita to survive in transit than on the researcher’s ability to find any of the species.

I will leave you with the final sentence from the researchers that found no baiji in 2006: ‘The baiji’s probable extinction serves as a potent reminder to conservationists that even large charismatic and nominally protected animals are still in grave danger of being lost; species cannot be expected to save themselves, and intervention may need to be swift and decisive’.

Further reading

First human caused extinction of a cetacean specie?- http://rsbl.royalsocietypublishing.org/content/3/5/537

NOAA vaquita overview- https://swfsc.noaa.gov/textblock.aspx?Division=PRD&ParentMenuId=676&id=21081