The distribution and abundance of larval mackerel, Scomber scombrus L., horse mackerel, Trachurus trachurus (L.), hake, Merluccius merluccius (L.), and blue whiting, Micromesistius poutassou (Risso, 1826) in the Celtic Sea and west of Ireland during the years 1986, 1989 and 1992

Abstract

Mackerel, horse mackerel, hake and blue whiting larvae were studied from plankton samples collected, as part of time-series egg surveys, from off the west of Ireland and the Celtic Sea in 1986, 1989 and 1992. In May/June 1992, there was a higher abundance of mackerel larvae west of the Shelf, than east of the Shelf Break, in the Celtic Sea and particularly west of Ireland, with Scomber scombrus absent from many of the on-Shelf samples. This distribution reflected and corroborated the trend indicated by the egg survey. Mackerel larvae were more abundant and widespread in 1989 than in 1992, despite the fact that egg production was 19% higher in 1992 than in 1989, possibly indicating high mortalities of eggs and/or larvae. Mackerel larvae were widespread in July, but not as abundant as in previous months. Horse mackerel larvae appeared to be more widespread and abundant in 1989 than in other years. Maximum abundances were recorded close to, or on, the Continental Shelf Break. There was not a significant correlation between the level of larval abundance and sea surface temperatures. Hake larvae were not very widespread or abundant and occurred mainly between 48°30′ and 51°30′N. Length distributions indicated that larvae spread from the Shelf Break, eastwards onto the Shelf as the spawning season progressed, and by late June the majority of larvae were located over the Shelf. Distribution of blue whiting larvae was sporadic and abundances were low, with most of the larvae being recorded in early April.