Don’t Panic! The reality of monk seal recovery in the main Hawaiian Islands (Part 1)

by Charles Littnan

Since monk seals, a species native and unique to Hawaii, reestablished themselves on Niihau in the 1970’s there has been a slow return of the seals to the rest of the main Hawaiian Islands (MHI).  This recolonization became more noticeable in the last decade particularly for residents of the more western MHI’s (Kauai, Oahu, Molokai) where seals are more abundant.  The current MHI population of monk seals is somewhere between 150 – 200 animals and is growing at about 6.5% per year.


Monk seal at Ko Olina.

While this return to the MHI and continued growth of the seal population are good news for the seal, there is no doubt that the overlap of seals and people are causing some growing pains for ocean users, managers, and the seals themselves.  Everyone is shifting to a new reality and we are still pretty early in that process. There are also a number of understandable concerns about the return of seals to the MHI.  Some of the more common questions include, but are not limited to:  How will this affect my access to beaches?  How will this affect my fishing catch or my ability to bring food to my family?

But also with this change comes confusion, angst, animosity, and other unpleasant feelings which stoke fears of what things could look like in the MHI with an increase of seals.  Some of this confusion is due to a lack of information, but some may be due to people intentionally trying to instill fear in their community.  We’ve heard tales of a swarm of monk seals sweeping over the MHI with comparisons made to situations in California (see below).  Imagine not being able to find a few square feet to roll out your blanket on the sand for a Saturday BBQ because of a mass of snoozing monk seals at your local beach. Or imagine having to carefully thread your way through a small gang of furry sausages and trying not to ding them with the tail of your board as you tiptoe to your favorite surf break.  I agree that would be awful, but thankfully, that is not going to happen in Hawaii …ever.

These exaggerated ideas of a population explosion are getting in the way of important conversations needed to address the public’s concerns and of attempts to  find solutions to conflict between seals and people.  What might help everyone to understand what the future of monk seals in the MHI might look like, is a little bit of perspective.   This is a topic that has lots of interesting things to talk about so I have broken it up into a couple of blogs.

For the first piece we will just look at how many seals we are planning for as part of natural seal growth in the MHI and how this compares to another place that has some experience with recently increasing seal populations: California.  I will start with California, which has a number of seal and sea lion species that reside part-time or full-time along the coastline.  For this exercise, I am only going to focus on seals that occur consistently in California in significant numbers: harbor seals, elephant seals, Steller sea lions, and California sea lions (Table 1).

Table 1:  Global and statewide population sizes for pinnipeds in California.

Common Name

Scientific Name


Total Global Population Size


Population in California

California sea lion Zalophus californianus



Harbor seal Phoca vitulina



Northern elephant seal Mirounga angustirostris



Steller sea lion Eumetopias jubatus



Estimate of total seals in CA:


Currently, there are almost 400,000 seals and sea lions in California. Four. Hundred. Thousand.  That is lot of seals and a whole lot of human-seal management problems, which will be touched on in the next blog.  But one important thing to note is that even with that massive population of seals in California, the ecosystem still functions; people still use the beach; people dive, surf, fish, recreate etc.

So, with that as a reference point, what does a recovered population of monk seals in the MHI look like?  What is the number of seals managers are projecting in the future?


That’s right.  The target MHI population size for the Hawaiian Monk Seal Recovery Plan is 500 individuals, or about 2.5 to 3 times the current population.  A graphical representation comparing the two states:


Or, for those of you who prefer densities, here is another example of the very different situations between the states.  The total lengths of coastline are similar between California (840 miles) and Hawaii (750 miles); however, the average number of seals per mile of coastline is dramatically different.  There are an average of 472 seals for every mile of coast in California. When the monk seal population reaches 500 seals there will be an average of 0.7 seals every mile.

Of course, seals don’t haul out evenly and some species aggregate in large numbers.  Pier 39 in San Francisco is a great example often raised in our Hawaii public meetings.  In January 1990, small groups of sea lions (from 10 – 50) started hauling out on available dock space at Pier 39, taking advantage of plentiful herring and the marina’s protected environment.  The population grew to more than 300 within a few months and now each winter the population can increase to  ~900 sea lions.  Most of the sea lions that haul out at Pier 39 are male, and many, but not all, leave during the summer months.   The image below shows sea lions at Pier 39 and is often presented as the inevitable outcome of monk seal growth in the MHI…but is it?


Picture of the California sea lions hauled out on docks at Pier 39, San Francisco. Aggregations of mostly male sea lions can top 900 individuals at times. Sometimes monk seal populations in the MHI top 9 individuals. As a side note, there are more sea lions in this photo than there are monk seals in all of the MHI.

Monk seals, even at their peak population will not aggregate in the way that sea lions (or harbor seals) do.  Monk seals tend to occur in groups of only 1 or 2 individuals, though on rare occasion, and in remote areas, you may see groups between 5-10 animals.  This more solitary existence of monk seals relative to sea lions is due in part to differences in the species’ social structures and reproductive behaviors.  Some seal species’ reproductive cycles are driven by the environment.  It is safest for mothers to give birth and suckle their offspring in spring and summer, during good weather, and so females time their cycle to the seasons.  This means that most females in a population are coming to shore around the same time and, therefore, are ready to mate around the same time as well. This encourages males to come ashore to gain access to those reproductive females.  Large numbers of animals vying for access to females lead to complex social interactions and dominance hierarchies being formed and voila…you have the makings of a colony!  These social aggregations stretch outside the breeding season as well, which is why you see situations like Pier39 with young males hanging out en masse.

Monk seals on the other hand, are very different.  Due to their tropical environment, monk seals are not as tightly constrained by seasons.  They can give birth at anytime during the year (though most births are still between March and August) and thus a female can be ready to mate any time.  So it is in a male’s best interest to keep swimming and looking for a potential female.  This creates a much weaker social structure and discourages the formation of colonies.  So when you see larger numbers of seals in one location in the MHI it is probably due to the fact it is some place they aren’t chronically harassed.  It is more a desire to rest and be safe, than a need to socialize that encourages these small groupings.


A rare “large” group of monk seals on a remote coast of Molokai. If monk seals aggregate in the MHI it is generally in places that are remote and difficult for humans to access and harass them.

So the fear that our beaches will be over run by monk seals is not founded in fact.  Monk seal numbers may go over 500 but they will never be in the thousands, much less the hundreds of thousands.  And when we do reach our 500 seal mark for the MHI, their biology and reproductive behavior will prevent dense aggregations appearing anywhere.

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