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Critically reading about extinction…

Preface:

How does science get published? This is one of the key processes I want to get across to my first year graduate students. We all have an idea about the peer review process, but one of the important halmarks of intellectual maturity is critically assessing a paper, and not thinking that just because something has passed peer review that it’s flawless. There are no gospels in science and it’s our job as scientists to read each new article with a critical eye. Were the data generated in an appropriate fashion? Were the data generated appropriate to answer the question asked? Does the conclusion flow from the results? Are their obvious biases? These are important questions to ask.

On occasion scientists write a response to the article where they critically and professionally point out differences in opinion. In some cases this occurs because the scientists feel the article could be improved by thinking about the data in a different way (see for example an exchange between Hufbauer et al. and Wooten and Pfister the original paper, the response letter, and the authors response), on other occasions, the original paper fails to pass the critical review questions listed above, and scientists feel that it is important to address these inconsistencies. This is especially important to do when the results of the original study have real world implications. I recently was on a team involved with the latter form of exchange.

On the importance of extinction.

Somewhere, some time after 1952 a Caribbean Monk Seal (Monachus tropicalis) breathed it’s last breath, and with the passing of that individual a species became extinct*. The environmental philosopher Thom van Dooren writes about extinction not as a single event, but a long process that occurs over multiple generations and that has ramifications for our memory of an ecosystem. My work on historical ecology deals with memories, ecosystems and conservation and the sad demise of M. tropicalis is a haunting example of how these disciplines can co-exist.

Caribbean Monk Seal in the New York Aquarium (1910) source http://www.petermaas.nl/extinct/speciesinfo/images/cms-newyorkzoologicalsociety1910.jpg

Caribbean Monk Seal in the New York Aquarium (1910) source http://www.petermaas.nl/extinct/speciesinfo/images/cms-newyorkzoologicalsociety1910.jpg

In 2013 Julio Baisre published a paper in the journal Conservation Biology called “Shifting Baselines and the Extinction of the Caribbean Monk Seal” that argued that the extinction of M. tropicalis was a fait accompli. Specifically he argues that

This finding supports the hypothesis that in AD 1500, the Caribbean monk seal persisted as a small fragmented population in which individuals were confined to small keys, banks, or isolated islands in the Gulf of Mexico and the Caribbean Sea. This hypothesis is contrary to the assumption that the species was widespread and abundant historically. The theory that the main driver of monk seal extinction was harvesting for its oil for use in the sugar cane industry of Jamaica during the 18th century is based primarily on anecdotal information and is overemphasized in the literature

This is not simply an academic argument. Rather understanding how past reef ecosystems looked like not only helps us conceptualize the degree to which they’ve changed, but helps us understand the drivers that continue to influence ecosystem change. In the case of M. tropicalis

This paper has serious methodological problems. For example in Fig. 2 he argues that low levels of reporting during the 16th and 17th century historical sources imply that populations were reduced

fig2seal

From Basire (2013)

However we have no context for the absolute number of sources he’s citing. Do the 6 references from the 16th century that mention M. tropicalis represent 90% of the literature? 1%? Somewhere in between? Without context those numbers have very little meaning.

Additionally on page 928 Baisre mentions a lack of seal remains in archaeological remains as evidence for rarity of the seal in the wild. However, there is not always a direct one to one relationship between abundance in the fauna and abundance in the archaeological remains. Archaeological remains are the result of several filters including biases in the sampling, preservation, and interpretation of data. For example, Kirch and Jones-Day (2003) show that because chickens, sharks and dogs were foods for the elite classes they do not appear frequently in midden piles, yet there is no reason to believe that those species were particularly rare. Was M. tropicalis an elite food? I have no idea, but I do know that it’s a hypothesis that is not addressed by Baisre -one that could parsimoniously explain the observed data.

Not for commoners

Not for commoners

The last criticism we have of Baisre’s work was his discounting of the ‘anecdotal’ historical record. He discounts data which do not support his hypothesis because he claims that it does not meet the “requirements of ordinary zoological records.” Well if those records were derived from works that were formal zoological monographs, that might be fine, but they weren’t. Moreover, much of historical ecological research is predicated on extracting zoological information from non-zoological resources. For example Baisre discounts early records of seal oil and skin trade as ‘anecdotal’ yet when we dug into the archives we found examples of trade records that show hundreds of gallons of seal oil and dozens of seal skins being traded between Jamaica and London.

Fig. 1 from McClanachan et al. (2015)

Fig. 1 from McClanachan et al. (2015)

Were we doing this out of spite? No, of course not. Rather we were concerned that the previous analysis spoke to a less verdant reef system, one that could not support rich populations of apex predators. Evon Hekkala has spoken about museum collections as bearing witness to human actions, and when I look at MCZ Mammalogy 6579 a wild caught female, collected from the Yucatán on the 11th of April 1889, I see our amazing potential as humans. I see the potential to wreak damage to our ecosystem. I also see the potential to learn from our mistakes and to hopefully change our actions so hopefully in the future we do not have to rely only on museum collections to bear silent witness to today’s Caribbean reefs.

IMG_0927

MCZ Mammalogy 6579

*Because of the vagaries of federal law and sampling periodicity, the seal wasn’t officially declared extinct until 2008

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