Human Error of Species Classification Can Result in Species Extinctions.

The Common skate ( Dipturus batis ) was once widely distributed in the North Sea, Celtic Sea, and surrounding Rockall (SNH, 2019). It is one of the largest skates and can reach up to 250cm and weigh up to 100 kg (Neat et al, 2014). The skate reaches sexual maturity at approximately 11 years of age, and the females are capable of laying up to 40 eggs per year (Walker and Hislop, 1998). The Common skate have frequently been caught by accident by fishermen since the 1900’s. A study by Walker and Hislop (1998) showed that the Common skate was regularly caught until the late 1950’s but after that seemed to have disappeared completely from their catch data.

The Common skate was heavily overfished in this period, but we have learned that there is a more complex explanation to the situation. The bycatch that was caught unintentionally by fishermen was supposed to be accurately classified according to what species they belong to and for that information to then be archived. However, since the 1920’s, more than one species have been classified as the Common skate ( D. batis ) (Wiley-Blackwell, 2009).

In 2006 The IUCN Red List of Threatened Species listed the Common skate ( D. batis ) as ‘Critically Endangered’ due to its significant loss in distribution and population (Wiley-Blackwell, 2009). Dr. Iglesias was one of the first scientists to question which species belonged to D. batis and more importantly, which one of them had been listed by IUCN (Wiley-Blackwell, 2009). It was not until 2009 that researchers found that the name Common skate ( D. batis ), actually belonged to two distinct species; the Flapper skate ( D. intermedia ) and the Blue skate ( D. flossada ) (Wiley-Blackwell, 2009).

Even today, there is still confusion about what the common name is and what the species name is for the identified Flapper skate and Blue skate (Figure 2).

The confusion in classification of the two species has over time led to incorrect catch records and ultimately made us unaware of the status of the species. The distribution of the two species have been significantly limited, and today the skates are only occasionally found in the northern North Sea (Neat et al. 2014). According to Wiley-Blackwell (2009), due to the inaccurate information that has been recorded over several decades, it is believed that the Flapper skate is actually the most endangered species of the two and is threatened by extinction.

The Flapper skate is particularly vulnerable because it is a larger and more slow growing species. Their size makes them more vulnerable to being caught in fishing nets and their growth rate limits their ability to reproduce quickly enough to make up for the mortality numbers. Even their large-sized eggs are vulnerable to bottom-dwelling fishing equipment that scoops them up (Walker and Hislop, 1998, SNH, 2010).

Since the discovery of the two distinct species, conservation measures have been put in place to allow for recovery. Both species became illegal to fish in 2009 commercially, and all fisheries have been instructed to immediately release the species if caught (SNH, 2010). For the Flapper skate, it has been suggested that Marine Protected Areas (MPA’s) should be put in place to protect the remaining population from fisheries (Neat et al. 2014).

The inaccurate classification and catch record by the fishermen that considered the two species as one may have caused irreversible impacts, particularly for the Flapper skate. We have learned that accurate identification, classification and catch records are critical for our understanding of the conservation status of a species. Even though implementations have been put in place since the discovery in 2009, it might be too late for the Flapper skate to recover and avoid extinction.

References:
Neat, F., Pinto, C., Burrett, I., Cowie, L., Travis, J., Thorburn, J., Gibb, F. and Wright, P.J., 2015. Site fidelity, survival and conservation options for the threatened flapper skate (Dipturus cf. intermedia). Aquatic Conservation: Marine and Freshwater Ecosystems , 25 (1), pp.6-20.

SNH. 2019. Flapper Skate . Scottish Natural Heritage. Available at: https://www.nature.scot/plants-animals-and-fungi/fish/sea-fish/flapper-skate.

Walker, P.A. and Hislop, J.R.G., 1998. Sensitive skates or resilient rays? Spatial and temporal shifts in ray species composition in the central and north-western North Sea between 1930 and the present day. ICES Journal of Marine Science , 55 (3), pp.392-402.

Wiley-Blackwell. 2009. "Is 80-year-old mistake leading to first species to be fished to extinction?". ScienceDaily. Available at: https://www.sciencedaily.com/releases/2009/11/091117191048.htm.