Population biology of grey gurnard (Eutrigla gurnardus (L.); Triglidae) in the coastal waters of Northwest Wales

Abstract

The grey gurnard Eutrigla gurnardus (L.) has been identified by ICES as a potential commercial species in the NE Atlantic with recommendations made to derive information on population biology for stock assessment purposes. However, data on the population biology of this species is limited. In this study, data on the age, growth and maturity of grey gurnard were collected by otter trawling in the coastal waters of northwest Wales and Eastern Anglesey. Total length (TL) of fish sampled ranged between 2.1–33.0 cm (male) and 1.9–36.9 cm (female) with the majority of female (70.8%) fish between 11 and 20 cm TL and male fish (70.5%) between 11 and 18 cm TL. The percentage of fish >20 cm TL was larger for females (30.4%) compared to males (17.6%). Total weight (TW) for female and male grey gurnard in the stratified subsample ranged from 1.9 to 499.9 g for females and 2.1–390.0 g for males, with the majority of female (66.3%) and male (76.1%) fish between 10 and 60 g. TL/TW relations for male and female fish and both sexes combined were: TW = 0.006TL³.⁰⁷, TW = 0.007TL³.⁰³ and TW = 0.007TL³.⁰⁵ respectively. Age structure (based on otolith reading) ranged between 0.5 and 7.5 years old for females and 0.5 to 5.5 years old for male with the majority of female (41.7%) and male (46.0%) fish aged as 1.5 years old. The age structure of female and male grey gurnards was significantly different with the majority of older fish (>2.5 years) being female. The von Bertalanffy growth functions were calculated as Lₜ = 32.4[1 − e⁻⁰.²⁴⁽ᵗ ⁺ ¹.⁴¹⁾] for males, Lₜ = 45.9[1 − e⁻⁰.¹⁶⁽ᵗ ⁺ ¹.³⁷⁾] for females and Lₜ = 44.0[1 − e⁻⁰.¹⁸⁽ᵗ ⁺ ¹.²⁰⁾] for both sexes combined. Instantaneous rates of total mortality were similar for males and females and the combined Z value 1.00 year⁻¹ with the natural mortality rate estimated as 0.33 year⁻¹. The size at 50% maturity (L₅₀) was estimated to be 25.3 cm TL for males, females and for both sexes combined. Age at 50% maturity (A₅₀) was 3.2 years for both males and females. The results of this study provide the first information on the population biology of E. gurnardus in the Irish Sea, the first detailed study in the NE Atlantic since 1985 and helps to address the data gap identified by ICES in knowledge of the population biology of this species.