Population biology of Dab Limanda limanda in the inshore coastal waters of North-West Wales, Irish Sea.

Abstract

Dab (Limanda limanda L.) is mainly distributed in the inshore coastal and offshore waters of the Northeast Atlantic. It is used as a bioindicator species and fish stock assessment studies serve as a potential proxy to the commercial fishing industry and climate change monitoring programs in the Irish Sea and North Sea. The present study provides insights on the population abundance and biology of dab collected by otter trawling from inshore coastal waters of North-West Wales, Irish Sea. Dab are found in large numbers at depths 10-25 m and gradually decrease with increasing depths (>40 m). The estimated population size and total biomass of dab are 1.96 x 106 individuals and 98.34 tonnes over a total survey area of 656km2, respectively. On average, the catch rates estimated for the depth range 15-25 m are 242 fish/hour for data collected with a mesh size of 75 mm between 2001-12 and 352 fish/hour for the smaller mesh size between 2013-19 in the study area. Total length measured for the males were from 11-30 cm and 9.9-35.1 cm for females. Majority of the distribution in the length size class 15-27 cm were females accounting for 62.9% and the males about 37.1%. Females were abundant in length class >30cms contributing upto 90%. The total-weight distribution for the males ranged from 12-310 grams and for the females from 13.8-400 grams. Most of the fish which weighed over 200 g were females (92%). Age distribution for the male ranged between 1-7 years and for the female 1-8 years. Majority of the males (57.5%) were 3 years old and the females (46.8%) were 4 years old. The L-W relationship curves can be described from the curves W=0.1711*L2.99 for male and W=0.155*L3.098 for female. The Von-Bertalanffy growth curves for the male and female are Lt = 28.5 (1-e(-0.248(t+0.522))) (R2=0.696, P<0.001) for male and Lt = 36.6 (1-e(-0.254(t-0.101))) (R2=0.814, P<0.001) for female. The Length at 50% maturity (L50) values for the male and female dab are 15.43 cm and 20.02 cm. The Age at 50% maturity (A50) values are 2.61 and 3.21 years for the male and female. The instantaneous mortality rate ‘Z’ (year-1) are estimated to be 1.378 year-1 and 1.265 year-1 for the male and female, respectively. The aim of the study is to provide information on the population studies for Dab in the Irish Sea which can be related to the ongoing global climate change.