The Gormanstown razor clam bed, which measured 21km² in extent in 1998, provided more than half the razor clams harvested in Europe for three years, 1999–2001. Exploitation of the bed commenced in late 1997. As a result of hydraulic dredging, the sediments have higher sorting coefficients and some larger grades were added in the form of shell fragments in the intervening years. The macrobenthos of the bed was monitored over a period of seven years, beginning one year after exploitation commenced. Throughout that time the dominant species, Ensis siliqua , which had accounted for up to 90% of the biomass in the first year of the study, declined to approximately 50% in 2005. Ensis siliqua displays the characteristics of a K-selected species: heavy standing biomass, type one survivorship curve and slow replication. Coinciding with exploitation, the bed was invaded by other deposit and suspension-feeding bivalves, notably Pharus legumen and Lutraria lutraria, whose population expansion can be traced to the early dredge fishery. The ratio of Ensis to Lutraria sampled weights was 124:1 in 1998, but it steadily advanced to 1.2:1 in 2005. Thus Lutraria , another suspension feeder, has displaced the razor clam. The Shannon-Wiener index of diversity rose as exploitation of the bed progressed, and in 2005 (eight years after dredging commenced), it had not returned to its 1998 level. However, the trend over the period was downwards, suggesting that a new stability involving a different species composition may be achieved. An age length key applied to length–frequency distributions of E. siliqua indicated that no age class older than age eleven has accounted for 10% of the population since 2001, although that was usually the case in the four preceding years.

This is an account of the changing status of palourde Tapes decussatus, which occurs in patches associated with a distinctive granulometry that are isolated along the Irish littoral. The species briefly entered the official marine landings statistics in 1975 in anticipation of a high harvest value to coastal communities. The 'clam boom', which peaked in 1975–1976 was, however, quickly followed by collapse. Later capture statistics were confused with those of a cultured species, the Manila clam Tapes semidecussatus, and these statistics are elucidated. T. decussatus is near the limit of its north–south range in Ireland, where the species is in retreat. This paper investigates nine beds in Counties Donegal, Galway and Kerry. Some had been examined thirty years previously. The density, year class frequency and growth rates of the species were measured in each to ascertain the reasons for its brief commercial performance and to assess its current status. The age of individuals ranged from 0 to 16+ years. Clam beds had a density of 17–116g m^-2; age at full recruitment was seven years in commercial samples. T. decussatus has a eulittoral range on the sea shore and is associated with sheltered coastal topography. The species lives within a poorly sorted mixed granulometry of mud, sand and gravel, which is described in quantitative terms from some sample locations and compared with two other common inshore facies: Spisula sand and fine sand associated with Ensis siliqua. T. decussatus was often found in close proximity to fresh water inflows and it can survive eutrophic conditions and toxic algal blooms. Despite its low densities, T. decussatus was the quantitatively dominant bivalve wherever it occurred. The species responds to favourable growing conditions, but throughout Ireland site-specific growth rates were very similar. There was no evidence of exceptional annual spatfalls having contributed to the populations that were examined. It is proposed that the population structures described are of a k-selected species that is long lived and replicates by low but regular annual recruitments. The majority of the biomass resides in the older age classes and these are targeted for harvest; once they have been intensively exploited, T. decussatus populations are very slow to recover.

Velvet crabs (Necora puber (L.)) are taken mainly as a by-catch in the pot fishery for large crustaceans. N. puber is negatively associated with spider crabs (Maja brachydactyla Balss) and positively associated with brown crabs (Cancer pagurus L.). In the Irish Sea, which yields small quantities of brown crabs, velvets have greater commercial significance, and they are targeted. Individuals from 28 samples of velvet crabs were described to characterise landings of the species. The female:male ratio was low, as was fecundity, which was typical of the northern European subgrouping of the species. Carapacewidth frequencies of males and females were disaggregated by a Bhattacharya plot into six groups of males and four groups of females. Females have been described as having a lower life expectancy than males in this species. An age of eight to ten years is proposed as the required age to achieve maximum size in the male. Average male and female size and weight within samples correlated highly significantly, and males were used as indicators of population structure as more information was obtained on males. Age at full recruitment of males correlated inversely with landings over a period of ten years; the mortality coefficient (Z) correlated positively with landed weights. There are no conservation measures currently in force in Ireland for this species, but it is difficult to hold in captivity, and most of the trade is live export. Hence this species is landed at 20–34% of potential landing places, only where suitable buyers are available, although the species is believed to occur in all coastal waters. Spatially discontinuous exploitation favours a sustainable velvet fishery.