Using opportunistic data to study the distribution and abundance of a warm water elasmobranch at the northern edge of its range

Abstract

Detecting changes in the distribution and abundance of marine species that are cryptic or occurring in very low abundances is difficult, but essential for assessing their status and informing management. One way of quantifying these changes is through the collation of opportunistic records. We reconstruct the population trajectory and distribution of the common stingray Dasyatis pastinaca around Great Britain, using opportunistic records, mostly obtained by recreational anglers. We tested if D. pastinaca declined in abundance and body size in response to fishing and if their distribution has shifted northwards in response to warming seas. We obtained 518 records covering the period 1838–2020. After correcting for observation effort, D. pastinaca catches reported by anglers showed no long-term trend over 50 years, but decreased from 1970 to 1995 and an increase in abundance since 1995. While records of species occurrence were found around much of Great Britain, nearly all were from south of 54◦ latitude, and records have contracted southwards since 2000. No trend in maximum size through time was detected. In conclusion, we did not find support for the hypothesized declines in abundance and body size or a northward shift in distribution of D. pastinaca and instead found a southward contraction.