by Hilary Goodwin
Skates and rays are often referred to as “flat sharks”. They are the lesser known chondrichthyans, a class of fish that includes sharks, sawfish, and chimaeras. Skates and rays are part of the batoid superorder, which is composed of 574 species. That’s more species than all nine orders of sharks combined! Batoids are cartilaginous fish like sharks, but tend to inhabit soft benthic environments. In Canada, batoids range from the Northern Labrador Sea down to the Bay of Fundy and Georges Bank and can be found in a wide range of depths up to 4,000 m.
You may be surprised to learn there are 14 skate and 4 ray species in Atlantic Canada – for more details on the diversity of skates and rays, please visit the WWF Identification Guide to Sharks, Skates, Rays and Chimaeras of Atlantic Canada – http://awsassets.wwf.ca/downloads/identification_guide_to_sharks__skates__rays_and_chimaeras_of_atlantic_canada.pdf.
There are two main differences between skates and rays – where they live and how they reproduce. Skates are present at higher latitudes and in deeper waters while rays prefer shallower and warmer temperate to tropical waters. To reproduce, skates produce egg cases (oviparous) while rays produce live young (viviparous).
The Bedford Institute of Oceanography and the Department of Fisheries and Oceans (DFO) have undertaken studies on skate ageing, reproduction characteristics, and population trajectories. Without these types of studies, it is difficult to adequately manage skate populations in Atlantic Canadian waters. As skates are both targeted and caught as bycatch, they have been the more studied batoid.
Some scientists have argued that skates (Family Rajidae) are the most vulnerable of exploited marine fishes. Between 2005 and 2012, the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has assessed four species of skate, including their sub-populations – Winter skate (four sub-populations), Barndoor skate, Smooth skate (four sub-populations), and Thorny skate.
Summary of COSEWIC assessments for Atlantic skate species
Scientists estimate that Winter, Thorny, and Smooth skate populations have declined as much as 90 percent off the Eastern Scotian Shelf since 1970. Even though a sub-population species of Winter and Smooth skate have been assessed as endangered and threatened, no skate species have been listed under the Species at Risk Act (SARA). The consideration to list Winter skate under SARA in 2008 failed, and recovery targets for Winter skate have not been set.
For more information on skate fisheries, discards, and management, please tune into next month’s blog on skate management in Atlantic Canada.