Fecundity and Maturity of Orange Roughy (Hoplostethus atlanticus Collett 1889) on the Porcupine Bank, Northeast Atlantic

Abstract

The first, comprehensive analysis of the fecundity and reproductive maturity of orange roughy, Hoplostethus atlanticus, from a specific area in the Northeast Atlantic is reported. Specimens were collected from aboard vessels, targeting this species on the Porcupine Bank (ICES subarea VII), in waters of between 1400 m and 1,650 m depth. Between September and December 2002, a non-random, stratified, sampling protocol was implemented by on board fisheries biologists to collect mature female fish between 300 mm and 540 mm SL. Ovaries from 65 individuals, representing the majority of 10 mm SL size classes, formed the analytical sample. A novel, digital method of oocyte counting was developed, allowing digital images of oocytes to be annotated, counted and stored. Total fecundity ranged between 20,352 and 244,578 oocytes per female and mean total fecundity was estimated to be 97,368 oocytes per female (SD = 48,322). Relative fecundity was estimated to be 33,376 oocytes per kg (SD = 11,407). Fecundity was shown not to decrease with age. Macroscopic analyses showed that 50% of females were not mature until they reached 27.5 years and 37 cm SL. Comparison with stocks from the southern hemisphere indicate that orange roughy from the Northeast Atlantic mature at a larger size and generally have a higher mean fecundity than those found in the southern hemisphere. This may reflect differences in growth rates influenced by environmental variables and fishing pressure.