Member profile - Mark Rosenstein

Like most people, when I see an unfamiliar species of fish, I ask myself, “What fish is that?” Sometimes this question reminds me of once visiting a rural community hall and meeting a gentleman who’d recently retired. He told me his hobby was birdwatching. Interested in hobbies, I asked, “Do you keep a journal of observations”. “No” was the reply. “Do you have any bird books”. “No”. “Do you travel to other places to see different birds?” “No”. His hobby was to sit on the back porch, throw seeds and watch the birds eat.
While an inexpensive hobby, it seemed to be on the lower end of the scale for engagement with the natural environment. With Australasian Fishes we are fortunate to have many people who deeply engage the natural world. More importantly, their personal curiosity has led to active intellectual pursuits which has made the project, a strong, accurate database of Australian and New Zealand marine fish. These individuals not only ask themselves, “What fish is this?” but strive to answer that question, driven by their scientific curiosity.
Well known to our community is Sascha Schultz, a project leader, who frequently responds to our question, “What fish is that?” and finds the answer. Perhaps a less familiar name but another leader in the project is Mark Rosenstein, aka maractwin, ranked 146 in observations for Australasian Fishes, recording 44 photos of 38 species of fish. While this may seem a bit far down the league tables of observations, his contributions are remarkable for two reasons. 1. Mark lives 16,259 kilometres from Australia, in the New England region of the United States. 2. Mark also is ranked at #2 position in fish identification for Australasian Fishes, supplying, at the time of this writing, 16,595 identifications! This impressive record is only a small part of Mark’s passion for the natural environment. To date he has logged a total of 36,003 observations for iNaturalist, recording 4,829 species. Most impressive of all is that Mark has provided 259,745 identifications for iNaturalist. His travels are remarkably widespread, with observations recorded all over the globe. Clearly, on the other end of the spectrum from sitting in the back yard and feeding birds. Including Australasian Fishes, Mark participates in 90 iNaturalist projects covering extremely diverse flora and fauna across the globe, demonstrating a fascination for the natural environment, which has helped our project and many more across the globe. Marks answers our top questions.
Question: Your work in the natural environment is diverse, however, you participate in many fish related projects, tell us about your interest in fish?
Answer: “I’m not an ichthyology professional, this is just a hobby for me. I first became interested in coral reefs watching Jacques Cousteau on TV while growing up. After college I got into saltwater aquariums and had these for many years, including reef tanks with live coral. At some point I realized that I should get certified for scuba so that I could see the real thing, not just the poor copy on life support in my aquariums.
While on dive boats the other divers would sometimes comment on the boobies, terns, etc. that were flying around. They all just looked like seagulls to me, but at some point, I guess I started paying attention, and eventually became a birder. I liked bird watching because it used a lot of the same skills as fish watching, but I could do it every day from home, rather than just a couple of times a year during trips. Then after a decade of birding, I realized that if I switched my primary focus to butterflies and dragonflies, I could sleep in and just go on hikes at mid-day. In the mean time I was spending enough time in the tropics diving that I got rid of the aquariums at home because I preferred to see the real thing, and the aquariums only ever had mechanical failures when I was away and a friend was watching them for me.
My professional work was in computers—specifically web programming of large database driven sites. When I heard about iNaturalist, it was a good fit. I quickly started spending way too much time there. I’ve learned a lot on the site by not just posting my own observations, but by looking at many observations of others, and identifying what I can.”
Question: Tell us about your diving, and how did you become interested in photography?
Answer: I pretty much always take my camera while scuba diving. On those rare dives when I don’t, it feels like I am missing an important piece of gear. On the typical dive I take 50-100 images. I try to get at least one photo of each species I see during a trip. I photograph the common species as well as the more unusual ones. About half the shots I take are useful as identification shots. Maybe 20% are really good pictures of fish, and I hope to get one or two pictures a day that are publishable shots that a non-fish geek would enjoy.
I’m nearly always on scuba, even when I’m exploring a very shallow bay or mangroves. It gives me more flexibility to get close to subjects. I actually started photographing fish in aquariums before I started diving. In 1993 I created what was probably the first web site about aquarium keeping, and started putting together a catalogue of all of the fish commonly found in the aquarium trade. Fiji is my favourite place to dive. I’m there about once a year. As an American, it is perhaps the easiest place to get to in the South Pacific. The people are friendly and speak English. There’s no malaria and little crime. And the reefs are healthy and very colourful. On my eighth or ninth trip there, my regular dive buddy commented that I had probably photographed every fish in Fiji. That, along with my propensity to try to name everything I see on the reef prompted her to suggest that I make a field guide. While it wasn’t a serious suggestion the first time, that eventually became a goal, and four years later I did publish Fiji Reef Fish.
Question: You are a veteran iNaturalist user, with an incredible record of observations and identifications. What advice would you offer the less experienced members of our project?
Answer: “Don’t be afraid to post your photos on iNaturalist even if they aren’t very good. Sometimes it is surprising what can be identified even in a poor photo. If there is something you really want identified that isn’t very distinctive (think drab damselfishes or silvery fish lurking in the gloom) be sure to write a description of the habitat (how deep were you? in a lagoon or on an outer reef?) and anything you remember from the sighting. And if you post a photo with more than one fish in it, be sure to mention in your description which fish you are asking to have identified.
If you want to learn fish identification, don’t just post your own photos and see what gets identified. Look through other people’s observations. When I’m not too busy with other things, I try to review every fish that gets posted to iNaturalist. Some fish that I haven’t seen in real life, but have seen dozens of posted observations, I begin to feel I know well enough to start identifying for other people. But I try to read about new species in a trusted source, such as a printed field guide or Fishbase. Google is not a trusted source, as there are a great many misidentified pictures on the net. And if you do start identifying observations, don’t be afraid to make mistakes. Even the leading taxonomists who are on the site sometimes make mistakes; if you don’t then you’re either not doing many identifications or are incredibly lucky. But I do pay attention to site notifications and fix my mistakes when they are pointed out. And learn from that, so you don’t make the same mistakes again.”
Question: Tell us how you've developed your skills in nature ID and could you give some advice to those of us who probably guess a little too much.
Answer: “Part of my skill at identification is having a good memory for these things. I can’t remember the name of a person I just met or what I had for lunch, but tell me a number or the scientific name of a creature, and I’ll probably remember that. And I remember patterns really well, so quickly figure out the subtle differences among similar species.
Figuring out a tricky ID has several parts. First, know approximately what it is: a terminal phase wrasse, a trevally, etc. Second, either know or have a reference that can tell you what the local choices are for that sort of creature. I think a lot of people fail by not having a decent field guide; they do a net search and pick the first thing that looks similar. But if you have a field guide, and find the right section, you can look and discover that there are a few very similar choices Then read about those, to learn what the differences are between them. You might be lucky and have a photo that shows the necessary field marks to tell which of several similar species it is. Or you might have to leave an observation at the family or genus level. But if you remember those field marks, next time you can try to get them in the photo.
I’m also not afraid to write in books. My field guides are all full of annotations. I correct mistakes. I put in hints for separating similar species. I write in additional species to beware of. These days I have some of my most used guides in electronic form on my laptop and I make annotations in those too.”
Listening to Mark, I feel inspired to locate that retired birdwatcher, and encourage him to buy a field guide. Perhaps with a little more effort, he can move his hobby up to a level where people like Mark, residing on the other side of the planet, will assist in identification and understanding of these backyard visitors. Mark firmly believes that the greatest strength of iNaturalist, is the willingness of those with specialist knowledge to share with others. Mark sees this as a two-way street, where project participants learn of the species they encounter and professional researchers gain access to information and data on fish they are currently studying or describing. It is a large marketplace of scientific information, where thousands go to share, for both the advancement of scientific knowledge to just to learn, “What fish is that?”
This journal post was written by Australasian Fishes member, Harry Rosenthal. Thank you Harry! :)
Posted on September 26, 2019 02:13 AM by markmcg markmcg


I've known about Mark for a long time through his fish identifications but I found this bio really fascinating, especially his advice to users. I tend to follow his advice when underwater - take as many photos as possible and post all except the absolute dreadful [Some may think some of my posted ones ARE dreadful!]. Many thanks Mark, for all your help.

Posted by nyoni-pete almost 5 years ago

@maractwin Thank you Mark. Thank you. You've been an inspiration, and a supportive rock. I'm (mostly) happy to have a crack at an ID because I know people like you are out there to correct me, when, inevitable; my view turns out to be wrong.

I suspect you do not realise just how many people out there contribute to iNat because of you ID'ing their observations and providing feedback. Communities such as this rely on central nodes that support and aggregate. Big thank you to a Super-duper node!

Posted by sascha_schulz almost 5 years ago

Great article, I joined iNat because Parks Canada used it for an amphibian count I volunteered to help with in Banff National Park, but I stayed and continue to contribute because of @maractwin and people like him that are willing to spend their own time and use their expertise to help educate people like myself regarding species ID's. I hope that I am contributing to the scientific community in some small way with the observations, but if not I have certainly learned a lot from people like @maractwin , so thank you and keep doing what you do. Its important to recognise these contributions.

Posted by anthonywood almost 5 years ago

Thanks for all of the nice comments. I'm on my way to Fiji now, and will probably be off the next for the next few weeks.

Posted by maractwin almost 5 years ago

Great to get to know Mark. I bought Mark's Fiji book for the Auckland Museum library. Even though we have plenty of guide books for the regional Pacific around NZ, this one complements the rest. Mark focuses on the distinguishing features, which is essential for our identification work during our surveys. Thanks for your passion, Mark!

Posted by tomtrnski almost 5 years ago

@maractwin ---Thanks for your avid participation, Mark. You've certainly been a big inspiration to me to photograph and post more, and your expertise is highly appreciated!

Posted by desertnaturalist almost 5 years ago

Hi Mark - it is great to learn more about you. You have identified many of the fish that I was unable to - Thank you

Posted by fiftygrit almost 5 years ago

Hi Mark R,
This comment is rather retrospective, but I particularly like your self assessment about being unable to remember the name of a person you just met, while having a good memory for (e.g.) fish patterns and markings. Our heads work in mysterious ways, as individuals nobody is identical-not even identical twins- but you've touched upon what is clearly a defining attribute that unites a significant percentage of the more devoted iNat users, so I think it is worth emphasis.
Great bio in all other respects too!

Posted by davemmdave over 4 years ago

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