BioBrevia: In Living Reef Colour

Giant Carpet Anemone (Stichodactyla gigantea), seen here with one of its typical symbiotic partners, the Common Clownfish (Amphiprion ocellaris)

William Saville-Kent worked widely in Australian waters, but found his greatest scientific and artisitc interests in tropical coral reefs, particularly the Great Barrier, off the Queensland coast. The Giant Carpet Anemone (Stichodactyla gigantea), seen here with one of its typical symbiotic partners, the Common Clownfish (Amphiprion ocellaris), was originally named for Saville-Kent as Discosoma kenti, so it was only fitting that he devoted an entire plate to it in his groundbreaking 1893 book The Great Barrier Reef of Australia: its Products and Potentialities. The book was notable for being the first major scientific work to use photography for documenting nature. The black and white photographs are great, but it is his wonderful illustrations that really bring the book to life. Saville-Kent was the first to capture the truly breathtaking, the absolutely flabbergasting, and the singularly bizarre colour schemes of reef organisms. The colours of Saville-Kent's animals are no exageration, as anyone who has dived or snorkeled on a tropical reef knows, nature spared nothing when colouring the animals of the world's coral seas. Here's just a sampling of some of the beautifully detailed plates from The Great Barrier Reef:

BioBrevia: The Trout

Brown Trout (Salmo trutta)

Illustration: Knepp Timothy (Wikimedia Commons)

For your listening pleassure, Franz Schubert's Trout Quintet (a.k.a. Piano Quintet in A major, D. 667). This was the second of Schubert's works to be named after that venerable European fish, the Brown Trout (Salmo trutta). The first was the song Die Forelle (D. 550), German for The Trout, an allegorical piece warning young women away from the depredations of male suitors, framed as a struggle between angler and fish. The quintet's fourth movement is a series of variations on Die Forelle, thus the transference of the name between the two works. The kind of information that can nail a daily double on Jeopardy...

Fish of the Forgotten North

Lake Cisco (Coregonus artedi)

Illustration: Ellen Edmonson and Hugh Chrisp (Wikimedia Commons)

Ontario's far north, that area above an imaginary line running from Woodland Caribou Provincial Park in the west to Natogami Lake in the east, comprises 42% of the province. At 451,920 square kilometres, that's a huge area. It's bigger than the UK. It's bigger than Romania. It's bigger than all three maritime provinces combined. Big, but easy to overlook if you're not one of the 0.2% of Ontarians who live there, or one of the lucky southerners who has visited this intractable miasma of forest, muskeg and tundra. Most southerners never give a moment's thought to the province's far north, nor its 1210 km of saltwater coastline. But there it sits, in all its subarctic glory, even if it is more or less forgotten by the vast majority of Ontarians.

If you've lived, worked or played in Ontario's far north, you know that in reality it's anything but forgettable. It's vast, and wild. It's a place where wildfires are often allowed to rage unchecked, where the forces of nature rule. Roads are few and mostly winter access only. Settlements are small, scattered and have only limited access to outside resources. In the dead of winter the forests are eerily silent and temperatures can be devastatingly cold. In summer the land bursts with life, which would be paradisaical if it weren't for the uncounted hordes of biting flies. Wildlife abounds, but given the immensity of the landscape, can be difficult to find. In the far north, the rest of the world seems very far away.

I've been lucky enough to enjoy two visits in recent years: once to the vast and sweeping tundra-treeline ecotone of Hudson Bay's Polar Bear Provincial Park; and once to the coastal wetlands, forested ridges and tidal flats of southern James Bay. But even after two visits chasing Nelson's Sparrows (Ammodramus nelsoni), Yellow Rails (Coturnicops noveboracensis), Northern Fulmars (Fulmarus glacialis), Smith's Longspurs (Calcarius pictus), Polar Bears (Ursus maritimus), Arctic Foxes (Vulpes lagopus), Caribou (Rangifer tarandus), Melissa Arctics (Oeneis melissa), Azure Darners (Aeshna septentrionalis), 'Hudson Bay' American Toads (Anaxyrus americanus copei) and dozens of other unusual (for Ontario) species, I've come to realize that there's one aspect of the far north's natural history that I still have almost no knowledge of: the marine fishes.

Ontario's Hudson Bay coast is home to very few people and is visited by fewer still. Cree hunters built these cairns in Polar Bear Provincial Park. Ice still lingers offshore in this June photograph.

Photo: Mark Conboy

Ontario's saltwater coast represents the southernmost extension of Hudson and James Bays, which together form the largest discrete body of water on Earth that completely freezes in winter and completely thaws in summer; ice cover lasts from December to May or June. As in any northern waters, ice plays a significant role in the lives of fish.

Marine fish live in a supercooled world, a world of liquid ice, in a sense. That's because saltwater has a freezing point of roughly -1.9 degrees Celsius. But that's an extremely challenging environment for fish to live in, requiring a whole suite of enzymes and other molecules that can function below the temperatures experienced by organisms in more benign environments. Furthermore, fish have a freezing point which is slightly above that of seawater. As a result, fish that are living in seawater could actually freeze solid before the water that surrounds them does. Some species get around this problem by migrating to deeper waters where ice doesn't form, owing to increased water pressure. A descent below 30 metres depth is usually sufficient to avoid freezing.

Other fish remain near the surface and have developed another strategy to avoid freezing: antifreeze proteins. Antifreeze proteins bind to rudimentary ice crystals, essentially coating them, and inhibiting further growth of those crystals. There are at least half a dozen known antifreeze proteins at work in arctic and antarctic fish. Because the proteins inhibit the growth of ice crystals, fish can live in shallow supercooled environments without the risk of turning into fishcicles.

Rivers such as Ontario's Winisk, Severn, Attawapiskat, Albany, and Moose are just as influential as ice is in determining the region's ecology. The estimated 750 cubic kilometres of freshwater that these and other rivers in Manitoba, Nunavut and Quebec pour into the bays annually, drastically lowers salinity levels across this relatively small oceanic basin. Consequently, fish diversity in the bays is a mixture of truly marine species and normally freshwater species that can live in the much reduced salinity.

Rivers bring such a tremendous amount of freshwater into the bays that one Canadian engineer has devised the Great Recycling and Northern Development Canal, an ill-conceived megaproject that calls for the construction of a dam across the mouth of James Bay to keep saltwater out, while allowing the ample inflow from rivers to eventually turn the bay into a massive freshwater lake. A canal would then be constructed to carry water south into the Great Lakes where it would be used to bolster water supplies in other parts of the continent. Such a scheme would irrevocably affect the region's ecology and would be an environmental disaster of nearly unparalleled proportions, but the fact that such a project would even be conceived of serves to underscore just how much freshwater enters the bays every year.

There are perhaps as many as 61 fish species in the bays, with about 53 of those known from southeastern Hudson Bay and James Bay; about half of them are strictly marine, while the rest are amadromous, spending at least part of their lives in freshwater or brackish estuaries. How many species regularly occur off Ontario's coast is a little unclear, but there are at least 20.

Indeed, when it comes to Ontario's saltwater coast, there is a lot that remains unclear. Relatively little is known about fishes in our forgotten north, because research has been rather limited. That's not to say that no research has been conducted. Early twentieth century expeditions were sent to Hudson Bay to determine any potential for establishing commercial fisheries there. No such potential was found. Even today, when it seems humans have managed to exploit virtually every corner of the Earth, there is still no true marine fishery in the bays. A small amount of commercial fishing, mainly limited to Arctic Char (Salvelinus alpinus) occurs along the Nunavut and Nunavik (northern Quebec) coasts. These harvests are relatively small, more akin to subsistence fisheries than full-scale commercial harvests, and are confined to rivers, not the bays themselves. The lack of a commercial fishery in the bays is probably one of the major reasons for the research deficit. But one area where there has been particular research interest is in understanding the impacts of hydroelectric development on amadromous species, particularly on the Quebec side of James Bay.

We do have a good understanding of which species are most common and widespread and which species are of prime ecological importance. Of the truly marine species, Arctic Cod (Arctogadus glacialis), Capelin (Mallotus villosus) and Pacific Sand Lance (Ammodytes hexapterus) are among the most significant. Arctic Cod have long been a food source for people living on the Belcher Islands off the coast of Quebec (the Belcher Islands are actually part of Nunavut, and so are all other islands in Hudson and James Bays), but have apparently never represented a significant subsistence fishery off the Ontario coast. Another cod, the similar but non-gregarious Greenland Cod (Gadus ogac) occurs in eastern James Bay but, interestingly, seems to be more or less absent from the Ontario coast. Belcher Islanders have also traditionally harvested Capelin where they spawn off shallow beaches, but again this species has never been harvested in significant quantities off the Ontario coast. Pacific Sand Lance have the curious behaviour of burying themselves in the benthos where they can even survive above the low tide line. Arctic Cod, Capelin and Pacific Sand Lance all school in large numbers and are the ecological cornerstones of Canada's arctic and subarctic marine environments, representing a significant food source for other fish, mammals and seabirds. Their importance off the Ontario coast is probably similar to elsewhere in the bays, but the extent to which that has been studied seems to be very limited.

Twohorn Sculpin (Icelus bicornis), Fourhorn Sculpin (Myoxocephalus quadricornis), Arctic Sculpin (Myoxocephalus scorpioides), and Shorthorn Sculpin (Myoxocephalus scorpius) are also marine inhabitants of Ontario's coast. Interestingly, there is a documented case of a young male Polar Bear (Ursus maritimus) diving for and catching Fourhorn Sculpin and Arctic Charr, making those the only two species the only fish for which Polar Bears have actually been documented to hunt; they normally focus on seals.

The Arctic Alligatorfish (Aspidophoroides olrikii) sounds formidable in name but only ever reaches a maximum length of 10 cm and feeds on tiny prey such as amphipods and ostracods. The woefully named Lumpfish (Cyclopterus lumpus) was long thought to be a primarily benthic species, with its suction cup-like pelvic fin and lack of swim bladder, but in reality it also seems to spend a great deal of time in the water column. Lumpfish, at one time were part of a fishery in Newfoundland and Labrador, where considerable numbers were taken for their nutritious row. The species has declined considerably in eastern Canada and is not fished as heavily anymore. Although it is fished in Greenland, it has never become a commercial species in Hudson or James Bays. Similar to the Lumpfish is the Leatherfin Lumsucker (Eumicrotremus derjugini). The lumpsucker is a true bottom-dweller, and it too is without a swim bladder but has a suction cup-like pelvic fin for anchoring to the bottom as an adult and to seaweed mats or other drifting debris as a juvenile. There's also the relatively little known, but widespread Variegated Snailfish (Liparis gibbus) and the Fourline Snakeblenny (Eumesogrammus praecisus). No sharks penetrate into southern Hudson Bay or James Bay, only the Greenland Shark (Somniosus microcephalus) reaches the northern parts of Hudson Bay and the deeper waters of the Hudson Strait.

A juvenile Lumpfish (Cyclopterus lumpus) using its suction cup-like pelvic fin to adhere to a piece of seaweed.

Photo: Hans Hillewaert (Wikimedia Commons)

The list of truly marine species is relatively short. But marine fish are only part of the piscean picture. In James Bay in particular, anadromous freshwater species form a significant portion of the diversity. Anadromous species spend at least part of their life cycle in freshwater, usually rivers, and part of their life at sea (or in large lakes, such as with many Great Lakes species). Lake Cisco (Coregonus artedi), Lake Whitefish (Coregonus clupeaformis), Round Whitefish (Prosopium cylindraceum) and Longnose Sucker (Catostomus catostomus) are commonly found in James Bay for at least part of their life cycles. Burbot (Lota lota) and Lake Trout (Salvelinus namaycush) are less common. Seldom do any of these species use saltwater in most other parts of their range. But in James Bay, the low salinity levels from river inflows means that these normally freshwater fish can survive. But all of these species become rarer in Hudson Bay, where salinity increases to intolerable levels.

Among anglers, perhaps the most notable of Ontario's northern amadromous fish is Brook Trout (Salvelinus fontinalis). Not normally thought of as an ocean fish, but rather one of streams, rivers and cold lakes, there are some populations that are amadromous (in the maritime provinces they're called salters). Both the typical permanently freshwater form and the amadromous form can be found in Ontario's Hudson Bay Lowlands, but of course, its only the salters that reach the bays themselves. These trout spend the first 2-4 years of their life in freshwater, before going to sea for 2-4 months, and then returning to freshwater to spawn. While at sea, Ontario salters lose their bright red colours, becoming silvery. Their vibrant colours return once they retreat to freshwater. The related Arctic Char also has permanently freshwater and anadromous forms throughout much of its range, though only the anadromous form is thought to occur in Ontario, and then only rarely.

Other freshwater species are found in James Bay from time to time, including Walleye (Sander vitreus), White Sucker (Catostomus commersonii), Slimy Sculpin (Cottus cognatus), Spoonhead Sculpin (Cottus ricei), Brook Stickleback (Culaea inconstans), Threespine Stickleback (Gasterosteus aculeatus), and Ninespine Stickleback (Pungitius pungitius). The latter two species are confined primarily to estuaries where the concentration of saltwater is lower still.

Unfortunately Hudson and James Bays have not been spared the scourge of introduced species. In a somewhat misguided attempt to artificially establish commercial and recreational salmonid fisheries, the eggs and fingerlings of Pink (Oncorhynchus gorbuscha) and Chum Salmon (Oncorhynchus keta) were introduced into several rivers in southern Hudson Bay and James Bay in 1955-56. Luckily none of the fish survived to found breeding populations. Another introduction to Hudson Bay has been the Rainbow Smelt (Osmerus mordax). Introduced for some confounded reason into river systems in northwestern Ontario, this species has spread into Manitoba and southern Hudson Bay. Rainbow Smelt are anadromous and gregarious. They consume the same planktonic and invertebrate prey as many native species, resulting in direct resource competition. Smelt themselves become prey for a multitude of other larger predatory species but many fishers claim that commercial and sport fish that feed on smelt spoil more quickly and taste poorly. Rainbow Smelt are not harvested in Hudson Bay or its tributaries, as they are in Atlantic Canada and on the Great Lakes.

There's still a great deal to learn about the fish of Ontario's saltwater coast. Perhaps the ever growing interest in arctic and subarctic ecosystems and the challenges they face from climate change will stimulate new research initiatives in our forgotten north. Until then, the vast northern coastline will remain as wild and elusive as ever.

Isla de Pequeños Carnívoros: Cozumel

Splendid Toadfish (Sanopus splendidus) are endemic to the coastal reefs of Isla Cozumel

Photo: Randall McNeely

Rough and wild was the 30 minute ferry crossing from the Mexican mainland to Isla Cozumel. The boat, big enough to hold a couple hundred passengers, lurched its way across the 19 km wide channel, tossing about on the waves as though it was a mere canoe. Suspecting, based on the crew's cavalier attitude, that this was par for the course, I sat back and enjoyed the dramatic heave-to of the waves and veils of spray that blasted from the bow. The ride reminded me more of the North Atlantic than the western Caribbean. Despite the waves, our capable Mexican captain brought us dockside without incident. Half-domesticated Brown Pelicans (Pelecanus occidentalis) and skeins of undomesticated tourists lined the wharf. The pelicans were a welcome sight, and so were the Ruddy Turnstones (Arenaria interpres) that foraged among the feet of passersby, like some kind of maritime pigeons. I had stilled myself for tourists, but the sight of half a dozen massive cruise ships anchored nearby caused me to recalibrate my expectations. Cozumel, like Playa del Carmen, the mainland port from which I sailed, is a tourist trap, attracting sun-seekers from all over the north to hotels and resorts, including some that (disappointingly, but not surprisingly) have their own private pods of captive dolphins! But, I wasn't on the island for a luxury vacation, and I certainly wasn't heading to play with the caged cetaceans. Instead, I was in search of something far more interesting and far more worthwhile: Cozumel's unique endemic species.

Isla Cozumel amounts to only about 10% of Quintana Roo's land area, but it holds an estimated 40% of the state's animal diversity; and a great deal of that diversity is found only on Cozumel.

The Cozumel Harvest Mouse (Reithrodontomys spectabilis), Pygmy Raccoon (Procyon pygmaeus), and Dwarf Coati (Nasua nelsoni) are all endemic. So is the enigmatic Cozumel Fox (Urocyon sp.), a very rare species, presumably similar to its mainland counterpart the Grey Fox (Urocyon cinereoargenteus), but it has never actually been scientifically described. Both the Cozumel Emerald (Chlorostilbon forficatus) and the Cozumel Vireo (Vireo bairdi) are endemic. A third endemic bird, the Cozumel Thrasher (Toxostoma guttatum) is exceedingly rare, indeed almost extinct. The Cozumel Whiptail (Aspidoscelis cozumela) is the only endemic reptile. The coral reefs which fringe the island's shores are home to the endemic, Splendid Toadfish (Sanopus splendidus). There is also the very unusual cave-dwelling sea star Copidaster cavernicola, and at least three endemic species of crustaceans: Agostocaris bozanici, Yagerocaris cozumel, and Bahadzia setodactylus.

The fun doesn't stop there. Isla Cozumel is also home to endemic subspecies of Common Opossum (Didelphis marsupialis cozumelae), Coues' Rice Rat (Oryzomys couesi cozumelae), White-footed Mouse (Peromyscus leucopus cozumelae), Collared Peccary (Pecari tajacu nanus), Great Curassow (Crax rubra griscomi), House Wren (Troglodytes aedon beani), Blue-grey Gnatcatcher (Polioptila caerulea cozumelae), Black Catbird (Dumetella glabrirostris cozumelana), Yucatan Woodpecker (Melanerpes pygmaeus pygmaeus), Golden-fronted Woodpecker (Melanerpes aurifrons leei), Yucatan Flycatcher (Myiarchus yucatanensis lanyoni), Brown-crested Flycatcher (Myiarchus tyrannulus cozumelae), Bright-rumped Attila (Attila spadiceus cozumelae), Rufous-browed Peppershrike (Cyclarhis gujanensis insularis), Yellow Warbler (Setophaga petechia rufivertex), Rose-throated Tanager (Piranga roseogularis cozumelae), Western Spindalis (Spindalis zena benedicti) and Northern Cardinal (Cardinalis cardinalis saturata). In addition, three subspecies are near-endemic: Both the Roadside Hawk (Buteo magnirostris gracilis) and the Yellow-faced Grassquit (Tiaris olivacea intermedius) are found on Cozumel as well as Holbox Island, off the Yucatan's north coast. The Bananaquit (Coereba flaveola caboti) is found on Cozumel and some other islands off the Yucatan Peninsula.

Why does Cozumel have so many endemic species and subspecies? What makes this relatively dry, rocky, hurricane swept, Caribbean Thatch Palm (Thrinax radiate) clothed, 486 sq km island such a hotspot of biodiversity? I've always wondered...

It's not unusual for islands to possess unique fauna. It's by virtue of their isolation that islands tend be relatively depauperate in total species, but of the ones that do occur there, a good many may be endemic. Madagascar and only Madagascar boasts lemurs. Tasmania has its eponymous Devil (Sarcophilus harrisii). Eil Malk has a lake teeming with Stingless Golden Jellyfish (Mastigias papua etpisoni). Isla Socorro has the Socorro Mockingbird (Mimus graysoni). Santa Cruz Island has the Island Scrub Jay (Aphelocoma insularis). The main islands of New Zealand have the Lesser Short-tailed Bat (Mystacina tuberculata). Indeed, most of these islands have pantheons of endemic species. From Galapagos to Borneo, from Sri Lanka to South Georgia, islands are hotbeds of endemicity. But many (not all, but many) islands that have particularly rich endemic diversity are rather isolated. Oceanic or microcontinental islands, those disconnected from the nearest continental shelf, are so isolated that when a wayward bird or reptile comes ashore, they are not likely to be joined by others of their kind. When there's no gene flow between an island and the mainland, a host of evolutionary processes like founder effect, genetic drift, and good old fashion natural selection, cause island colonists to diverge in form and behaviour from their continental ancestors.

Cozumel, as far as islands go, is not very isolated from the mainland. Though only 19 km wide, the channel that separates Cozumel from continental Quintana Roo, is also some 900 m deep. That's deep enough to ensure that ever since the island first rose out of the sea some 200,000 years ago, it has never had a physical connection (a land bridge, if you like) to the mainland. Cozumel has been completely submerged by the ocean during times of high water (it's highest point is only about 10 m above sea level), but it's never been connected to the mainland, not even during periods of low sea levels, such as during the last ice age. It's not nearly as isolated as a typical oceanic island, but then again, some of the most diverse islands on Earth are not particularly isolated either: Borneo, Sumatra and New Guinea, for example. Evidentially, it doesn't take extreme distance, just a certain degree of isolation, to promote island endemicity.

Take the carnivores of Cozumel, for instance. There's the endemic Pygmy Raccoon and the Dwarf Coati. As their names suggest, they're small compared to their mainland relatives. Dwarf Coatis, for example, are only about 75% the size of mainland White-nosed Coatis (Nasua narica). The very rare (apparently not a single museum specimen exists) Cozumel Fox is also a dwarf, being essentially a reduced version of the mainland's Grey Fox. Why does the Cozumel carnivore fauna have a decidedly dwarfish aspect? In fact, dwarfism extends beyond the carnivores; the island's Collared Peccaries, Great Curassows, and Cozumel Thrashers are all miniaturized when compared to their mainland counterparts. So what's the deal, why evolve towards smallness?

A general pattern among island fauna the world over is that big creatures get smaller on islands, while little creatures get bigger. Biogeographers call this Foster's Rule. Think of the Komodo Dragon (Varanus komodoensis), a supersized monitor lizard. Or consider the diminutive White-tailed Deer (Odocoileus virginianus clavium), the so-called Key Deer, of the Florida Keys. Big things get small, small things get big. I'd love to call it a law of nature, but it's not: as far as rules go, Foster's is one that's fraught with exceptions.  As David Quammen tells us in his wonderful exploration of island biogeography, Song of the Dodo, "Many kinds of animal are likely to grow larger on islands, yes, except under exceptional circumstances, which instead make them grow smaller. But to the exceptional circumstances there are other exceptions, which might again make them grow larger or, on the other hand, smaller". But even setting aside those exceptions, and their exceptions too, it can be difficult to say exactly what leads to dwarfism (or gigantism for that matter).

In general terms, it seems that on islands animals shrink when resources are scare (exceptions abound). Cozumel is relatively dry, having only localized permanent fresh surface water. It's relatively rocky. And it's prone to catastrophic disturbance in the form of hurricanes. Potential prey for predatory raccoons, coatis and foxes would also be rather small in size - birds, whiptails, insects, and seashore creatures like crabs. No need to be large to subdue small prey. Perhaps these factors could lead to dwarfism, if being small made coping with island life more efficient. By way of interest, there is a fourth carnivore (in this case a carnivore that eats mostly fruit, go figure) on Cozumel, but it's not endemic: it's the Kinkajou (Potos flavus), a species that is widespread in the neotropics, though reportedly becoming rather rare on Cozumel. The providence of the Kinkajou is questionable, with some suggesting that it was only recently introduced to the island by humans. Kinkajous on Cozumel are not dwarfs.

Western Spindalis (Spindalis zena)

Photo: Laura Gooch

Most of Cozumel's endemic species and subspecies seem to have an ancestral affinity with the Yucatan Peninsula. One particular exception is the very striking Western Spindalis, a tanager-like songbird that, along with a suite of similar congeners, occurs across the Greater Antilles. I found a few Western Spindalises along the overgrown roads of an abandoned subdivision project on a pleasantly overcast morning. Well, it was pleasant right up until two highly aggressive, but thankfully also very stupid, feral dogs put the run on me for the better part of a kilometre. Nonetheless, I saw the birds, and was rather happy to do so, partly because of their unique distribution (it's the only place in Mexico where they regularly occur) and because of the interesting taxonomic quandary they present. All spindalis species, there are four of them, were once classified as conspecific. Now they've been split, with separate species on Puerto Rico, Hispaniola and Jamaica, in addition to the widespread Western Spindalis. As for their general placement among the other passerines, there's still some debate. I'm intrigued by incertae sedis, species whose place in the taxonomic order is confused at best, or just simply unknown. For many years, the spindalises were considered to be tanagers, indeed the whole complex of species and subspecies was called the Stripe-headed Tanager. But genetic and traditional comparative taxonomic approaches tell us that spindalises are not tanagers. We don't yet know where to place them instead though. If they're not tanagers, what are they? Time will tell, I'm sure, but for the present I was quite content to stare at a mystery, until I heard those damned dogs coming for me!

Feral dogs aren't just a problem for birders, but they're also a problem for the endemic island wildlife. Introduced species threaten Cozumel's biodiversity. There are the usual culprits, that afflict island ecosystems all over the world: Domestic Dogs (Canis familiaris) and Domestic Cats (Felis catus), as well as House Mice (Mus musculus) and rats. The newest threat on Cozumel though, seems to be the Boa Constrictor (Boa constrictor). Boas are found on the mainland, in fact not far from the port of Playa del Carmen I saw a pair of Northern Caracaras (Caracara cheriway) ripping apart a massive road killed Boa Constrictor. But boas never made it Cozumel on their own. They were apparently released from the set of some B-rated movie about 40 years ago. The boas reproduced quickly, feeding on the island's birds, laying waste to Cozumel's once abundant, and not uncommon, Yellow-lored Parrots (Amazona xantholora).

Another island bird that has declined precipitously is the Cozumel Thrasher, but the degree to which boas are to blame is uncertain in this case. The thrasher, once an iconic Cozumel bird, was locally common until Hurricane Gilbert came ashore in 1988. After that, the thrashers virtually disappeared. Researchers searched throughout the 90's, seeing only a handful of thrashers and even capturing some of the last survivors. Subsequent storms seemed to push the already small population even closer to the brink. The last definitive sight record was of a single bird in 2006, but since then there have been no confirmed observations. If not totally extinct, the thrasher is most certainly functionally extinct. That is to say, even if there are a few remaining survivors, they are unlikely to ever re-establish a viable breeding population.

Many biologists and naturalists have asked, why did Hurricane Gilbert and subsequent storms, such as 1995's Hurricane Roxanne knock back the thrasher population so severely? After all, didn't this endemic species evolve to deal with the catastrophic habitat alterations that result from the hurricanes and tropical storms which sweep the island periodically? Perhaps, on pristine Cozumel, before the introduction of cats, mice, rats and boas, the thrasher population would have been able to recover from a devastating hurricane. Just maybe, the toll taken by so many non-native predators in addition to the effects of hurricanes (not to mention other possible adverse factors such as anthropogenic habitat changes, or even an unidentified invasive disease), was too much for the thrasher to endure.

Those feral dogs that ruined my spindalis watching, were something of a blessing in disguise. They forced me to relocate, and it just so happened that I came upon a cenote, and one that was guarded by a rather large and statuesque American Crocodile (Crocodylus acutus) to boot. Cenotes are water-filled sinkholes, and they're often part of complex subterranean karst (cave) networks. The cenotes on Cozumel are sort of like islands within the island, because they are really the only permanent sources of surface freshwater. Cozumel certainly isn't a desert island, it's covered in vegetation, and rainfall is frequent, if not sometimes torrential. But the limestone bedrock and thin soils drain rainwater very rapidly, making cenotes the only reliable surface waters. Most of Cozumel's cenotes, including Aerolito, the one I'd stumbled upon, connect to one another through a series of erosion-carved tunnels. The cave system also connects to the ocean, meaning that most of Cozumel's cenotes are anchialine in nature: they contain both fresh- and saltwater. Because freshwater is less dense than saltwater, the lower reaches of Cozumel's cenotes are salty, while the surface waters are fresh.

I wandered around the Red Mangroves (Rhizophora mangle) which fringed the cenote, watching for more crocodiles and hoping to find the Pygmy Raccoons that left their tracks in the mud. Sure enough, after a little stealthy tracking and mud up to my knees, I spotted one endemic raccoon among the tangle of strut-like mangrove roots. It recalled a slightly smaller, slightly greyer Northern Raccoon (Procyon lotor), the species with which I am familiar back home. Happy with that, I turned my attention to the Great-tailed Grackles (Quiscalus mexicanus), those large and gregarious blackbirds, as they worked their way through the trees, and within centimetres of the basking croc. Brazen or calculating, I wondered? Small fish swam in the clear cenote waters, colourful and plentiful. When a Mexican couple appeared, I left them to enjoy the cenote and its guardian crocodile. It wasn't until after I returned to town and began reading, that I began to understand just how impressive this cenote actually was.

American Crocodile (Crocodylus acutus)

Photo: Mark Conboy

Without some pretty serious dive training there aren't too many options for exploring cenotes. Aerolito, as one of the largest cenotes on Cozumel attracts the attention of cave divers, who can travel more than a kilometre underground through chambers and tunnels decorated with stalagmites and stalactites. Luckily YouTube provides a glimpse of what the cenote looks like deep underground. The décor is nice, but the video shows only a single example of the supposed abundance of organisms that apparently inhabit Aerolito. Including the endemic sea star, Copidaster cavernicola (unfortunately not the species featured ever so briefly at 2:03 in the video). Endemic crustaceans live here too. Both freshwater and brackish water fishes swim here. Aerolito is sort of like an underground estuary, with its mixing of freshwater and saltwater ecosystems.

Don't let the tourist trap reputation of Cozumel turn you off from the island's wondrous natural history. The island's diving is noteworthy (unfortunately I didn't have time to get offshore on this trip), but the lesser known facets of Cozumel, the dwarfed carnivores, the endemic species, and the deep cenotes, are all worth putting up with the crush of Hawaiian shirts and Bermuda shorts. Cozumel is a surprise, waiting to be discovered. Just watch out for the dogs.

BioBrevia: Introducing the Ninja Lanternshark

The newly described Ninja Lanternshark (Etmopterus benchleyi)

Photo: From Vasquesz et al 2015

A new species of lanternshark, whimsically named the Ninja Lanternshark (Etmopterus benchleyi), has been described in a paper by Vasquez et al in the Journal of the Ocean Science Foundation. Like the lanternsharks I've written about previously, the Ninja Lanternshark can glow, but it seems to have only a limited number of photophores.

In Praise of the Freshwater Drum

Freshwater Drum (Aplodinotus grunniens)

Illustration: WPClipart

I wish to say a few words about an odd fish, the Freshwater Drum (Aplodinotus grunniens). Here's a species that I too seldom see alive, but I do find washed up dead, on the shores of Lake Erie with some regularity. Indeed, just this evening I watched a Great Black-backed Gull (Larus marinus) rip apart a smoldering drum carcass, its heavy bill effortlessly shearing the hard overlapping ctenoid scales that smaller scavengers like Ring-billed Gulls (Larus delawarensis) would have had difficulty penetrating. As fascinating as is the process of death and decay, it's the living Freshwater Drum that I'm here to endorse.

A drum's thick scales help protect it from attack by the parasitic native Silver Lamprey (Ichthyomyzon unicuspis) and the highly invasive non-native Sea Lamprey (Petromyzon marinus). Using suction cup-like mouths, lampreys attach themselves to large fish, chewing through their host's scales to the soft tissue below, using a toothed tongue. A lamprey feeds on the blood of its host, sometimes for months at a time. This can be severely detrimental to the host, resulting in reduced reproductive success, or ultimately even death. Freshwater Drum enjoy the advantage of being a among the most well-armored Great Lakes fish, a significant advantage in a world teaming with raspy-tongued parasites.

Besides their boilerplate scales, drum are oddballs among Great Lakes fish for other reasons, and their name, Freshwater Drum, makes it plain. This is the only species of totally freshwater-dwelling drum. All of the other 160 or so drums and croakers (family Sciaenidae) are marine. No other native Great Lakes fish has such a salty pedigree, though the Burbot (Lota lota) comes close, with only one other member of the cod family (Gadidae) found in freshwater - the Atlantic Tomcod (Microgadus tomcod). The name drum, and the specific moniker grunniens, which means "grunting", refers to the sounds that this species makes during mating, and, indeed, when handled by anglers. Drums don't vocalize in the conventional way most mammals or birds do, by issuing vibrations in the throat, instead their sounds are produced by muscular manipulating of the swim bladder. As far as I know, this is the only Great Lakes fish that makes sounds.

Freshwater Drum eggs contain a large oil globule that allows them to float on the water's surface, something totally unique among North American freshwater fish. Most other freshwater fish lay their eggs in nests, like sticklebacks and sunfish, or  stick their eggs to vegetation or other debris, as Yellow Perch (Perca flavescens) do. Some ichthyologists have suggested that planktonic eggs may be particularly good at dispersing long distances, perhaps having played a role in helping Freshwater Drum to attain the greatest natural latitudinal distribution of any fish in North America; they range from the northern reaches of Manitoba's mighty Nelson River to southern Mexico and Guatemala.

From a simple examination of a fish's mouth, it's possible to hypothesize something about its foraging ecology. For example, a Brook Silverside (Labidesthes sicculus) sports an upturned mouth for taking surface-dwelling prey, and don't forget the aforementioned parasitic lampreys with their suctioning and rasping mouthparts. Silversides and lampreys have highly modified external mouthparts, and while Freshwater Drums have extraordinary internal mouth parts. They're highly adapted for crushing the shells of hard-bodied prey. Most perciform fish have two sets of jaws, the external ones which we can plainly see, and a set of internal ones, and it's a drum's internal ones, the pharyngeal jaws, that set them apart. Drum pharyngeal arches are unique among Great Lakes fish in that they are fused together and are covered with large molar-like teeth, adaptations for processing hard foods, namely mollusks and crayfish. No other fish in the Great Lakes has such highly modified arches, though some other species, like Pumpkinseed (Lepomis gibbosus) and Yellow Perch, do feed on mollusks, they don't have the same crushing adaptations. Drums grind native and non-native mollusks, alike, including Zebra (Dreissena polymorpha) and Quagga Mussels (Dreissena bugensis), on those molar-like teeth using powerful muscles which are supported by a series of bone struts on their robust skulls.

Once in a while, while wandering along the beach, I find a polished and intact drum arch washed up on shore, a reminder that there is a thick-scaled, croaking, planktonic egg-laying, mussel-crushing, freshwater version of a marine fish, beneath the Lake Erie waves. Fascinating!

BioBrevia: A Bird's-Eye View of Sockeyes

Spawning Sockeye Salmon (Oncorhynchus nerka)

Photo: William Rosmus (Wikimedia Commons)

Photographer Jason Ching gives us a bird's-eye view of a big Sockeye Salmon (Oncorhynchus nerka) run on Lake Iliamna, Alaska’s largest lake. The imagery is beautiful, the fish abundant, and the resulting temptation to go see the run for oneself is real. Check out the video here.

Bioluminescent Biters

Smooth Lanternshark (Etmopterus pusillus)

Photo: Brandi Noble (Wikimedia Commons)

Bioluminescence, the production of light by organisms, is a marvelous ability possessed by a broad range of species including troglodytic glow worms, forest fireflies, thumb-sized click beetles, Caribbean zooplankton, parasitic fungi and even lowly bacteria. There are hundreds of bioluminescent species on land and in water, but arguably, the phenomenon finds its finest (and trippiest) expression in the murky ocean depths.

Deep sea organisms live in a dark world, with little or no sunlight penetration. But its not a world entirely without light, thanks to bioluminescence. Most deep sea organisms utilize bioluminescence for communication, warning, or hunting, by combining a light-emitting luciferin pigment (the most common of which is coelentarazine) with an oxidative luciferase enzyme; the result, as luciferin reacts with oxygen, is the production of light.

Perhaps the most famous of these deep sea illuminators are the anglerfishes, diverse array of whimsically named species from a suite of different families, including goosefishes, frogfishes, handfishes, sea toads, footballfishes, dreamers, whipnoses and seadevils. Typical anglerfish, let's take the Humpback Anglerfish (Melanocetus johnsonii), which is perhaps better known as the Black Seadevil, thanks to its meteoric rise to fame on YouTube in 2014, features a light-producing organ called a esca, which is mounted on a specialized ray called an illicium. The esca hangs in front of the anglerfish's generously-toothed and highly destendable mouth, and illuminates with the help of bioluminescent symbiotic bacteria. The light serves to attract potential prey and mates.

Beyond anglerfish, there is a ensemble of other bioluminescent deep sea denizens, including squid, snails, worms, jellies, an astounding diversity of zooplankton, and many more fish. Among the more unique are the loosejaws (Malacosteus spp.), which produce a red bioluminescence. Red light cannot be seen by most of the loosejaw's prey and so this flashlight-wielding predator has a distinct hunting advantage - it can see its prey, but its prey can't see it. Most bioluminescent deep sea organisms haven't received much scientific study, but one group that has are the lanternsharks (Etmopterus spp.), and they've proven even more interesting than your average bathypelagic swimmer.

Lanternsharks (family Etmopteridae), are a diverse lineage found all over the world's oceans, most of them living between 200 and 5000 m deep. As their name suggests, lanternsharks are bioluminescent, but they aren't the only sharks that sparkle and shine: cookiecutter sharks (Isistius spp.), Viper Dogfish (Trigonognathus kabeyi), Pygmy Shark (Euprotomicrus bisinatus), and Taillight Shark (Euprotomicroides zantedeschia), for example, do so too. But it is among the 40 species (others probably await discovery) of lanternsharks that bioluminescence is most pronounced. In fact, their bioluminescence may have played an important role in promoting the great diversity of Etmopterus we see in the world's oceans today.

Most of the lanternsharks have bioluminescent organs (photophores) on their bellies and their sides, although some species don't seem to have any at all. Sadly, the only lanternshark that occurs in Canadian waters, Great Lanternshark (Etmopterus princeps), doesn't glow, though, strangely, it lives deeper than many of the other etmopterids, down to 4500 m, where having some bioluminescent abilities ought to be highly advantageous. But for those species that do light up the abyssal depths, they do so in a three of different ways. Their bellies are covered in photophores that glow a dull blue and are used as a form of camouflage called counter-illumination. Most lanternsharks are less than a metre long, thus potential prey for many larger fish. Even in the near-complete darkness of the deep sea, the large sensitive eyes of many predatory fish can detect the silhouettes of their prey swimming above them, but the subtly glowing bellies of lanternsharks makes their silhouettes invisible against the faint background of blue light emanating from above. Lanternsharks, in effect, hide in plain sight. Many surface dwelling fish have a similar but less sophisticated adaptation called counter-shading, wherein their bellies are a light shade to match the sky above, thus making them more difficult for predators to spot from below.

Other sets of  photophores lines the flanks of lanternsharks  and some species have them on their backs as well. These photophores, rather than acting as camouflage, make their bearers more obvious, either as aposmatic (warning) signals to potential predators or as advertisements to potential mates. We're all familiar with aposmatic colours, bees and wasps for example, are patterned black and yellow to announce to predators that they shouldn't be messed with, lest they deliver a painful sting. In a similar fashion, lantersharks have generously large spines at the base of both dorsal fins, and at least one species, the Velvet Belly (Etmopterus spinax), illuminates its spines to advertise this formidable defense mechanism. The researchers who made this discovery facetiously called the illuminated spines lightsabers.

Green Lanternshark (Etmopterus virens). The dark patch on the belly is a concentration of bioluminescent photophores used in counter-illumination, while the linear dark patches near the base of the tail are photophores used in species recognition. Each dorsal fin sports a spine at its lead edge. 

Photo: Brandi Noble (Wikimedia Commons)

Lanternsharks also employ bioluminescence when advertising to potential mates. The band of photophores along the flanks and tail base are unique for each species. This novel adaptation may have allowed Etmopterus to rapidly diversify into more species than almost any other shark genus. Species-specific photophore patterns act as a means of genetic isolation, keeping species from hybridizing. Just as bird species tell each other apart by the differences they display in plumage, lanternsharks distinguish between members of their species (potential mates) and other species (non-suitable mates) by the unique light patterns each produces. A lanternshark's light display isn't terribly bright, it doesn't shine like a spotlight through the pelagic depths, instead it's more subdued, often visible from only a few metres away. But it's enough to do the trick, especially when aided by special ocular adaptations that make lanternshark eyes extremely sensitive. What to a human observer may seem like a meagre glow emanating from the flank of a Splendid Lanternshark (Etmopterus splendidus), may actually appear to be a magnificent lightshow to the sharks themselves.