I have a summer tradition. Every year, as close to the first day of summer as possible, I hop onto one of the many whale-watching tours that depart from Boothbay Harbor, Maine, and spend an afternoon on the ocean. On a good day we can end up seeing a dozen or so whales. On a great day we can see hundreds of incredible harbor seals swimming through the clear water or sunning themselves on the dozens of tiny islands dotting the horizon.

Harbor seals (Phoca vitulina) have another name: Common seals. As you might guess from that sobriquet, harbor seals are, indeed, quite common, with worldide populations somewhere in the five million to six million range. Unfortunately, not all seal species are as populous or as secure in their place in the world. Some species or subspecies are barely hanging on. Here are the four most endangered seal species and subspecies, all of which face uncertain futures.

1. Saimaa ringed seals

Seals don't get any rarer than the Saimaa ringed seals (Pusa hispida saimensis) of Finland. Only about 310 members of this subspecies remain in Lake Saimaa, the largest lake in the country, where the animals have been cut off from the ocean since the last ice age.

Saimaa ringed seals are actually doing better than they were the last time I wrote about them. Back in 2010 the population was at a low of just 260 seals. At the time, warmer winters left the seals without their usual protective ice dens. Exposure to the elements increased infant mortality and left adults unprotected from fishermen, who all too often kill the animals rather than share their catch (there even used to be a state bounty for killing the seals). Luckily colder weather the last couple of years has benefitted the seals and allowed them to breed more successfully. Meanwhile new restrictions on the use of nets in some parts of the lake have lowered the number of seals accidentally caught and killed by fishermen, and six new protected zones established this past April should provide the seals with additional safe territories.

Even with a few good years under their belt, problems remain. According to a report from Finland's Yle Uutiset, this year's pups are as much as 30 percent underweight. Scientists say the winter brought enough snow to build nests but it arrived late in the season, lowering the amount of time for parents to nurse their young pups.

2. Lacs des Loups Marins harbor seals

Placing the Lacs des Loups Marins harbor seal (a.k.a. Ungava seals, P.v. mellonae) on this list is difficult, because nobody knows exactly how many exist. Estimates range from as few as 50 to as many as 600, all of which live in freshwater lakes and rivers in Quebec, where they have been cut off from the ocean for millennia. According to Fisheries and Oceans Canada, the subspecies—which was protected in 2007—has declined due to hunting and faces risks from climate change and potential hydroelectric dams, although none are actually in the planning stages. I would say more about this subspecies, but that's about all that's available. There hasn't been any new scientific information on these seals in years.

3. Mediterranean monk seals

We now move from the cold north to the warmer south, where the critically endangered Mediterranean monk seals (Monachus monachus) live in and around the sea from which they get their name. Long the victim of commercial hunting and persecution by fishermen, these seals also lost much of their former habitat to coastal development and suffered from the effects of both pollution and ocean traffic. Today the population for this species is estimated at fewer than 600 individuals, and perhaps as low as 350.

Even that count doesn't quite convey the true risk these seals face, as those 350 to 600 animals are scattered over much of the Mediterranean, as well as two small populations in the Atlantic. About 130 seals live off the coast of Western Sahara. About 20 more can be found on the tiny Desertas Islands, a little over 400 kilometers from mainland Portugal. The three islands in the archipelago, totaling less than 15 square kilometers, are a protected nature reserve for the seals.

The future of Mediterranean monk seals will depend upon their ability to breed. The seals used to raise their pups in coastal caves, which have mostly been destroyed by modern development. That leaves pups unprotected, and mortality rates as high as 50 percent have been observed. Research has also shown that the species suffers from a genetic bottleneck, reducing their genetic diversity and creating congenital defects. This has further reduced pup survival rates and left the adults more vulnerable to disease, such as one outbreak that wiped out a third of the Western Sahara population in 1997.

Luckily Mediterranean monk seals are now protected through most of their range, but some threats remain. Most notably, Turkey's economic boom has increased fishing levels, which may put the monk seals in that region back in the crosshairs.

4. Hawaiian monk seals

Our final seal on this list also comes from the Monachus genus. Like their Mediterranean cousins halfway around the world, Hawaiian monk seals (M. schauinslandi) are also critically endangered. Much like the Mediterranean species, the seals in Hawaii suffer from low genetic variation—the lowest of any pinniped species—after a period of intense hunting in the 19th century. Coastal development in the 20th century and entanglement in fishing nets have also taken a toll. Today just 1,150 of the animals remain.

Hawaiian monk seals do enjoy a great deal of protection. Whenever a seal arrives on a Hawaiian beach, volunteers rush to set up signs and barriers to prevent people from disturbing the shy animals. But even with that assistance the seals remain controversial to fishermen, who fear the seals will take their catch, and a plan from the National Oceanic and Atmospheric Administration (NOAA) to set up new critical habitat has angered some residents . A few of the seals have been shot or bludgeoned to death in the past few years, mostly likely as a result of this pent-up resentment.

NOAA's new critical habitat rules were originally scheduled to be published a few years ago. In June 2012 the agency announced a six-month extension for publishing the new rules for critical habitat. A final action was due in December 2012. We're still waiting for it.

Next?

Most other seal species and subspecies appear to be fairly healthy. But that doesn't mean that every seal is safe. Increasingly, small populations of seals find themselves isolated and at risk, if not on the verge of being wiped out.

One of the most notable cases like this comes from Alaska, where the National Marine Fisheries Service (NMFS) is investigating whether or not the small population of freshwater seals living in Iliamna Lake deserves protection under the Endangered Species Act. Although these 250 to 350 seals are probably not a separate species or subspecies, they have never been fully studied and it appears that at some if not all of the seals never mingle with other Pacific harbor seals (P. v. richardsi). NMFS will now investigate whether or not the Iliamna Lake seals should be considered a distinct population segment and if they are at risk of extinction due to low abundance, climate change and potential mining of nearby copper-gold-molybdenum porphyry deposits (the Pebble Mine Project). NMFS is currently collecting information on the Iliamna Lake seals—a public comment period runs through July 16—after which they will conduct a status review to see if the species should be protected. We'll see what happens after that.

Photos: Maine harbor seal © John R. Platt. Saimaa ringed seal by Juha Taskinen, via NOAA Fisheries. Hawaiian monk seal by Pete Markham. Used under Creative Commons license. Illiamna Lake seals, Dave Withrow, NMFS

Previously in Extinction Countdown: