Diel variation in spawning orange roughy (Hoplostethus atlanticus, Trachichthyidae) abundance over a seamount feature on the north‐west Chatham Rise

Abstract

The diel variation in abundance of an orange roughy (Hoplostethus atlanticus Collett) spawning aggregation on a deepsea seamount on the Chatham Rise known as “Graveyard” was studied using acoustics. A 4‐day survey was carried out using a Latin cube statistical design. The acoustic data was echo‐integrated and analysis of variance was carried out to estimate the effects of day, time of day, and transect path. The estimated biomass of the spawning aggregation did not display any significant diel variation. We conclude that this result validates the current practice of acoustically surveying orange roughy on this seamount without considering diel effects. The aggregation fluctuated in abundance over the survey period, suggesting that turnover offish was occurring. Differences in roughy biomass with transect orientation indicate the importance of randomised radial transects for these surveys.