Welcome!

September 3, 2007 at 10:57 am · Filed under Web Stuff, Creativity, Science, Family, Conservation

You've found the website of Dave Johnston.
You can reach me at:
Duke University Marine Laboratory
135 Duke Marine Lab Rd.
Beaufort, NC 28516
252 504 7593

On these pages you'll find information about work, family, friends and other things that may interest you. Use the links at right if you need further details regarding my research projects and other work/science/conservation stuff. The search function works well.

Below you'll find updates about people, papers, projects and current events in Hawaii and elsewhere. If you still can't find what you need, email me at david.johnston(at)duke.edu

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Another good week!

December 7, 2007 at 9:22 am · Filed under Science, Conservation, Monument

It was definitely a good week. This morning I got word from the editorial staff at the IWC office that our manuscript about odontocetes in American Samoa is accepted for publication in the Journal of Cetacean Research and Management. This is great news as it will provide a good baseline for future studies as well as a tool for NMFS to move forward with listing "stocks" of cetaceans in the waters of American Samoa. Currently there are no stocks recognized for this region. It will start with spinner dolphins, as the genetics are clear enough from this paper. Next up might be Rough-toothed dolphins - Steno bredanensis.

Read the rest of this entry »

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Harp seals in the Northwestern Atlantic: Did cumulative effects of harvests and climate variability lead to rapid depletion?

December 4, 2007 at 4:00 pm · Filed under Science, Conservation

So, I've been spending a lot of my spare time looking at sea ice dynamics in the North Atlantic in relation to the North Atlantic Oscillation. Ideally, this research aims to make sense of what is - and might - happen to harp seals, and other pagophilic pinnipeds, if global warming greatly effects their breeding habitats. Much of the work involves building an understanding of how decadal-scale climate variability effects sea ice availability for these animals during the breeding season. Once we've teased that out, we can start to study how longer-term or unidirectional climate change may effect these animals.

While looking at the NAO it became clear that the largely positive period during the 1980s and early 1990s was preceded by a negative stretch from the mid-1940s till the mid-70s. The most consistent portion of this negative period occurs during the late 50s and sixties. A graph illustrating the NAO and these two contrasting periods of time is below. The curve in red is a simple spline that accounts for at least 20% of the variation in the NAO data - not perfect but it gets the point across.

Considering that sea ice concentration in eastern Canada is "in phase" with the NAO (see below), it stands to reason that this period exhibited poor ice conditions (we know that 1969 is one of the worst on record), and therefore increased seal mortality. Interestingly, the harp seal population plummeted during this negative NAO period, dropping by at least 55% during 1950 to 1970. During this time seal catches were relatively high…and it seems that the combined effects of reduced sea ice and large harvests may best explain the dramatic drop in seal numbers.

 Ari, Dave Lavigne and I are working on a note about this right now.

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Sea Ice and the NAO

November 27, 2007 at 2:24 pm · Filed under Science, Conservation

I've been with working with Ari Friedlaender and David Lavigne (see collaborators page) on a project examining sea ice dynamics in the North Atlantic and their effects on breeding pagophilic seals. Previously, we established that the mode of the North Atlantic Oscillation contributes strongly to the amount of sea ice off eastern Canada (study available here). This is an important breeding site for harp and hooded seals, and these animals depending on ice as a platform to give birth to and nurse their pups. We've recently expanded this study to look at the other breeding sites for harp seals - the West Ice and the White Sea. While the results are certainly preliminary (and soon to be presented at the CLIOTOP 2007 meeting), at right is a sneak-peek at one of the results. As we found previously, sea ice tends to be in phase with the NAO signal - meaning that when the NAO is positive, there is greater and more persistent sea ice. Interestingly, it appears that the White Sea is actually out of phase with the NAO, exhibiting lower ice concentrations when the NAO is positive. Cool stuff, and more to come.

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