Age, growth, reproductive biology and population dynamics of the common megrim Lepidorhombus whiffiagottis (Walbaum, 1792) from off the west coast of Ireland

Abstract

A total of 4,964 common megrim Lepidorhombus whiffiagonis, were examined from commercial catches in Divisions VII b^, off the west coast of Ireland, between April 1997 and February 2001. A sex ratio of 31.8:1 females to males was recorded, with a higher percentage (15%) of fish being male at lengths <25cm TL, while no males were recorded >45cm TL. The largest and oldest fish recorded was a 51.3cm TL female, aged 16 years and weighing 1012.61g. The smallest was a 15.1cm TL female, weighing just 18.24g. Females ranged in age from 2-16 years old, while the male age range was considerably smaller, that of 3-8 years old. Age at recruitment (tr) was determined to be at age 6 years of age for both female and male fish. Values of 0.91 and 1.43 were recorded for total mortality (Z) for female and male respectively. Three different growth models were used to describe the most accurate growth rates for the fish. Average values of 50.72cm for Loo, 0.097 for K and -4.78 for to were recorded for female fish, while Leo = 41.59cm, K = 0.138 and to = -3.062 were determined for males. Yield per recruit curves revealed that optimum yield occurred at a fishing mortality (F) of 1.2 and 1.4 for female and male megrim respectively. Five maturity stages were recorded for the species. Fecundity ranged from 26,522-640,523 oocytes. Megrim were determined to be total spawners, spawning once annually between January and early March. Estimates of 24.0cm TL and 25.0cm TL for Lso»/» were calculated for female and male histologically determined maturity at length. Maturity at age estimates for A50«/o of 2 years and 2.5 years were recorded for female male fish respectively. An overall mean prevalence of atresia (Pa) of 63.5%, and relative intensity of atresia (la) of 24.2% was determined.