Increasing biological knowledge for better management of by-catch species: age, growth, and mortality of piper and red gurnards (Teleostei: Triglidae)

Abstract

Gurnards are a valuable by-catch of mixed demersal fisheries and are commercially important in European waters, but they are often discarded, reported under “mixed gurnards” and with incomplete biological information by spe-cies. In the present work, a total of 558 piper gurnard specimens of between 10.9 and 44.4 cm (1 to 11 years) and 425 red gurnard specimens of between 10.2 and 42.1 cm (0 to 9 years) from the northeast Atlantic (Portuguese) coast were used to study age and growth. The von Bertalanffy growth parameters for piper gurnard were estimated through the combination of whole-otolith readings and back-calculation (L∞ =44.7 cm, k=0.16 yr–1 and t0 =–2.781 yr). For red gurnard the same growth parameters were estimated using whole-otolith readings (L∞ =40.2 cm, k=0.28 yr–1 and t0 =–1.074 yr). The results indicate that the red gurnard reaches a smaller length, although it grows faster than the piper gurnard. Natural, instantaneous and fishing mortalities were estimated as well as the exploitation rate for both species. For the Portuguese coast, the red gur-nard showed a higher fishing mortality and exploitation rate than the piper gurnard, raising concerns about its sustainable management.