When I refer to the skate as one of my study organisms, I tend to receive a blank stare. To be fair, as someone whose interest in research was sparked by popularized megafauna such as the great white shark, I understand that reaction. After all, when it comes to shark cousins, the ray takes center stage. Most people have heard of the unfortunate incident involving the legendary television personality and conservationist Steve Irwin, or hummed along to the songs of the aptly-named Mr. Ray in Finding Nemo. However, over the course of my career as a marine scientist and conservationist, I’ve had the unique pleasure of encountering one of the shark’s lesser-known cousins: the flapper skate (Dipturus intermedia). Specifically, I’ve become fascinated by the story of the animal that may become the first to be fished commercially to extinction.
Sharks, rays, and skates are all members of a subclass of cartilaginous fish (Chondrichthyes) known as Elasmobranchii. Though most sharks have a very distinct fish-like appearance, skates and rays possess flattened bodies and reside primarily in benthic, or seafloor, habitats. There are costs and benefits to this body shape, in that it allows for crypsis (camouflage) but constrains locomotor ability (Wearmouth & Sims, 2009). Though both of these organisms closely resemble each other, skates and rays do exhibit key differences in morphology and life history. Specifically, skates are often more triangular than rays, and possess a somewhat elongated nose. Skate tails are also stockier and host two dorsal fins near the tip, rather than a single stinging spine at the base. This is not to say that skates are without their own defense mechanism. Instead, thorny scales run laterally down each side of the tail (The Shark Trust). Furthermore, skates capture prey via small teeth, rather than the crushing plates of most rays. Though such morphological differences may seem minor, one major feature distinguishing skates from rays is their form of reproduction. Most species of ray are viviparous, which means they give birth to live young. In contrast, skates lay rectangular eggs than can be found washed up on beaches or tangled in seagrass (The Florida Museum). These are commonly referred to as “mermaid’s purses”.
From a conservation perspective, skates are arguably some of the most exploited of marine fishes (Dulvy et al. 2000). Because of their life history strategies, which include longer life spans, late maturity and fewer young, elasmobranchs in general typically exhibit rapid declines in catch rates soon after initial exploitation (Dulvy et al. 2000). Their populations simply cannot recover quickly enough to keep up with their exploitation. Even if they are not targeted by a specific fishery , many elasmobranchs are unfortunately caught as bycatch. These catches often go unreported, particularly if the species in question is protected. Even in cases where fisheries do diligently report their cartilaginous fish bounty, catch trends are generally not recorded on a species-by-species basis. Instead, sharks, skates, and rays are often reported under the aggregated category of “elasmobranch,” whether caught as a target species or unintentionally (Dulvy et al. 2000). This makes it exceedingly difficult for researchers and managers alike to understand how many of each species are being captured each year. What we do know, however, is that skate stocks seem to be in dramatic decline. Skates are targeted primarily for human consumption, specifically for their wings, and researchers have noted a negative trend in catch per unit effort (CPUE) for multiple skate species since the 1950s (Dulvy et al. 2000). This is particularly true among the larger species (Dulvy et al. 2000). In certain parts of their former range, multiple local populations have gone completely extinct, their disappearances unnoticed until skate researchers began to compare historic and current fishing records (Dulvy et al. 2000; Dulvy & Reynolds 2002).
Of the roughly 280 skate species worldwide, the flapper skate is the largest. It can reach up to 10 feet in length and weigh over 200 lbs. One of the largest benthic predators in the Atlantic, it can be found in this region of the world from inshore depths of 30 meters (90 feet) to deeper waters of over 600 meters (1800 feet) where it feeds on crustaceans and fish, including small shark species. Anecdotal evidence suggests that some fish prey may be captured at middle depths, indicating that flapper skates are active predators capable of roaming throughout the water column (Ellis et al. 2005; Wearmouth & Sims 2009). However, this species does appear to exhibit site fidelity, permanently or seasonally inhabiting specific areas (Little 1995). Like other skate species, the flapper skate is oviparous, laying up to 40 eggs at a time that will hatch after 2-5 months. If able to survive, its lifespan is thought to be over 20 years (Little 1995). Of course, it’s important to recognize that this information is largely speculative, based on the few studies conducted to date. This is because until the past decade, the flapper skate was not, in fact, recognized as a species.
Large skates were once so abundant in the northeastern Atlantic as to be referred to collectively as one species, the common skate (a name that seems all too ironic given their current circumstance). However, due to commercial fishing, this species (Dipturus batis) was upgraded to Critically Endangered status on the 2006 IUCN Red List. A few years later, a genetic, life history, and morphological study revealed that the species formerly known as Dipturus batis actually included two nominal species: the flapper skate and the blue skate (D. flossada) (Inglesias et al. 2009). This study suggested that these two distinct species, emerging from a species complex already recognized as imperiled, had been misidentified since the 1920s (Inglesias et al. 2009). Such taxonomic confusion called all previously compiled information on common skate into question. However, one fact remains: the risk of extinction for the species now recognized as flapper and blue skates is substantially higher than previously assessed.
The global distribution of the flapper skate is now restricted solely to the western coasts of Ireland and Scotland. Neither of these known locations possesses a management plan for this species. Only a single breeding site along the Irish coast has been recorded. Though researchers in Ireland and Scotland are now attempting to protect what is left of its range, it remains to be seen how effectively international policy can be successfully implemented for the flapper skate. I feel fortunate to be among the few who have actually observed these animals first-hand. Yet as a young wildlife biologist, I don’t think I’ll ever be able to shake that feeling of immense helplessness in knowing that each observation could very well be the last. It’s not often that you witness extinction right before your eyes.
Written by: Alexandra McInturf, a third-year PhD candidate at UC Davis and visiting researcher at Queen’s University Belfast. Starting in the year 2019, she will work with these two universities in collaboration with seven other institutions to begin a monitoring effort for marine megafauna in Irish and Scottish waters. Among the five species targeted for conservation-driven research efforts is the flapper skate. Learn more about her past and current work with the species here.
Cover image by: Sarah Baird, a master’s student in Ecology at UC Davis. She studies the physiology and behavior of green and white sturgeon. In addition, Sarah is working to become a scientific illustrator. To see more of her work or contact her for commissions, you may visit her website or follow her on Twitter (@scutesNbarbels).
Dulvy, N. K., Metcalfe, J. D., Glanville, J., Pawson, M. G., & Reynolds, J. D. (2000). Fishery stability, local extinctions, and shifts in community structure in skates. Conservation Biology, 14(1), 283-293
Dulvy, N. K., & Reynolds, J. D. (2002). Predicting extinction vulnerability in skates. Conservation Biology, 16(2), 440-450.
Ellis, J. R., Dulvy, N. K., Jennings, S., Parker-Humphreys, M., & Rogers, S. I. (2005). Assessing the status of demersal elasmobranchs in UK waters: a review. JMBA-Journal of the Marine Biological Association of the United Kingdom, 85(5), 1025-1048.
Iglésias, S. P., Toulhoat, L., & Sellos, D. Y. (2010). Taxonomic confusion and market mislabelling of threatened skates: important consequences for their conservation status. Aquatic Conservation: Marine and Freshwater Ecosystems, 20(3), 319-333.
Little, W. (1995). Common skate and tope: first results of Glasgow Museum’s tagging study. Glasgow Naturalist, 22, 455-466.
Wearmouth, V. J., & Sims, D. W. (2009). Movement and behaviour patterns of the critically endangered common skate Dipturus batis revealed by electronic tagging. Journal of Experimental Marine Biology and Ecology, 380(1-2), 77-87.