Monk seals and cats - management tension

Caroline observing 2 Hawaiian monk seals at Poipu Beach, Kauai.

I am not a Hawaiian monk seal biologist.  I am interested in monk seals, I discuss monk seals in my wildlife course, and I may have even sent in a written comment on a draft monk seal management plan.  Daughter Katelin probably knows more about monk seals than I do, as evidenced by her publication:

In 2016, the Hawaiian monk seal population was estimated to be 1427 individuals.  That is not a large population, although over the past 5 years, the growth rate of the population seems to be increasing at 3% per year, with the highest growth rates on the Main Hawaiian Islands.  That’s good news.  The bad news is that the the population is still small, and threats to the population continue.

What are those threats?  NOAA lists them as follows, although they are not listed in any order of priority or importance:

•. Adult male aggression:  Some males cause injury or death to females and immature animals.

•. Climate change:  What can I say?  Much of the population exists in the Northwestern Hawaiian Islands, where many atolls and islands are less than 2 meters above sea level.

•. Food limitation:  On the Northwestern Hawaiian Islands, schools of trevally or jacks follow seals and “steal” food uncovered by seals, resulting in undernourished and emaciated seals.  You can see these jacks interact with a seal in this video.

•. Human interactions:   People interact with seals in many negative ways.  Feeding, disturbing resting seals, boat strikes, fishing line entanglement, debris ingestion, intentional shooting, hooking, habituation to humans... these can all impact seals.

•. Marine debris:  NOAA writes, “Hawaiian monk seals have one of the highest entanglement rates of any pinniped (seal or seal lion) species. Pups are proportionally entangled more frequently than older animals. Monk seals have been entangled in many types of debris, including nets, lines, straps, and rings (including hagfish or eel traps), and other miscellaneous items (e.g., bucket rims, bicycle tires, rubber hoses). Intensive efforts are undertaken by NOAA and other agencies to remove debris from beaches and nearshore waters; however, the accumulation rates in the Northwestern Hawaiian Islands appear to remain constant.”  Marine debris affects many marine species.

•. Shark predation:  Predation by Galapagos sharks is the major mortality source of nursing and newly weaned monk seals around the French Frigate Shoals.  

•. Infectious diseases, parasites, and toxins:   The isolation of Hawaiian monk seals over time has prevented them from being exposed to numerous infectious agents.  Now, given the exposure of monk seals to pathogens in the air, soil, and water surrounding the Main Hawaiian Islands, their risk of infection is greater than it has been in the past.  Disemper viruses, West NIle virus, Leptospira spp., and Toxoplasma gondii are noted as of particular concerns.  Gastrointestinal parasites are a concern for young monk seals, and some seals are being treated with dewormer.  Finally, toxins of various types, often found in seal prey or in waters around the Main Hawaiian Islands, may impact monk seal survival and vitality.

Another monk seal near Poipu Beach.  When we returned, it was gone, and there were human tracks near where it was lying.  Disturbance?

Obviously, 2 things become apparent.  First, monk seal biologists are involved in research that is focused on numerous issues affecting Hawaiian monk seal survival.   From sharks to entanglement to Toxoplasma, teams of biologists have either completed, are in the process of completing, or are proposing numerous studies to identify threats.  Second, 1 threat doesn’t seem to trump another, although some threats (like shark predation and food limitation) seem to be focused on particular locations or age classes. 

Kudos to the monk seal biologists with NOAA and their staff.  I have to admit that my bucket list includes a trip with seal, honu, and marine bird biologists to the Northwestern Hawaiian Islands.   In 2012, I started to make plans to volunteer on French Frigate Shoals, and when that didn’t work (timing), I considered volunteering at the Midway Atoll National Wildlife Reguge.  That didn’t work either, for 2 reasons.  The Great Recession of 2009 resulted in the MIdway volunteer program being put on hold, and then a bike wreck while training for the Honolulu triathlon resulted in breaking my collarbone in 5 places.  Both of those issues are now resolved, but I’m not on sabbatical.  Alas, my dream goes on!

Cats (of a group of 6) observed at Kikiaola Boat Harbor, Kauai. 

So here is the point of this blog entry.  As I talk with people about cats on Oahu, the storyline is cats and seals and toxo, cats and seals and toxo.  I have seen for myself the discussion evolve away from cat predation on birds (still an important issue), to cats as the source for Toxoplasma gondii infections killing Hawaiian monk seals (and some other species).  The recommendation to protect Hawaiian monk seals?  Well, that is where things get interesting... it depends on who you talk to. 

There’s a NOAA-produced document (a 2 page handout) on the Hawaii Department of Lands and Natural Resources website that states, “While toxoplasmosis is a source of mortality, it currently does not appear to be a significant threat at a population level.”  The recommendations? 

•  Do not release unwanted cats into the wild.
•. Do not let your domestic cat roam outside.
•. Support programs to spay and neuter cats.

It’s really hard to criticize these recommendations, whether or not monk seals were part of the conversation.  I do note that in the book, Cat Wars, there’s a comment that studies indicate 40-70% of cat owners let their cats roam outside.  I suspect this includes wildlife biologists and conservation ecologists, perhaps at a lesser rate.  

The document also notes, “Any effort to remove or control feral cat colonies reduces the risk of [Toxoplasma gondii] transmission, and provides an overall benefit to Hawaiian monk seal conservation.”

I have problems with the absolute nature of this statement.

Depending on who you talk to, there are hundreds of thousands of cats on the landscape on Oahu, let alone the other populated islands.  If I removed the 9-100 cats from the Keehi Boat Harbor, I submit that it would be impossible to ever measure a decrease in the oocysts in the nearshore environment, and, according to NOAA’s document, “It is nearly impossible to determine the cat colony that may have been the source of the eggs so distance or proximity of cat colonies to the coast does not denote greater or lesser risk of transmission to monk seals.”  The risk may be mathematically reduced, but realistically, who can tell?

And of all those cats, I suspect that most do not exist in colonies, although the number probably isn’t trivial.

These Keehi cats may produce millions of oocysts, but that means there are trillions of oocysts going into the water from other sources. And I am trying to understand the natural history of the parasite here.  Some material I am reading indicates that infected cats shed oocysts for only a few days of their entire life, and young cats probably have the active infection.  So why wouldn’t a key goal be to reduce all births by the Keehi cats?  A small population of non-shedding, sterilized cats would seem to produced little harm except from a nusiance perspective, and if politically and socially it would be acceptable, it seems an alternative to removal.  I’m not against removal per se, but since that proposal is also problematic (discussed later, I hope), there is need to look for solutions.


  1. Interesting situation and great observation about cats. Based on what you have presented, I agree that preventing, as much as possible, the birth of more kittens could be an effective method of controlling the spread of toxoplasmosis. A solid TNR-maintain program could be beneficial. I've seen great success with TNR in reducing the number of feral cats over time when done correctly.


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