No abstract

Field and experimental studies were undertaken in four European countries on clawed lobster (Homarus gammarus) ecology and recruitment. The aims were to assess: (a) abundance of early benthic phase (EBP) lobsters and other benthic species at cobble sites, (b) the effect of these species on EBP growth and survival, and (c) influence of these factors on recruitment and/or viability of restocking. Suction sampling of cobble sites revealed a wide diversity and abundance of potential competitors but no EBP lobsters. Hatchery-produced EBPs were therefore used for small-scale mesocosm experiments. In nature, predation on EBP was rapid without shelter, whereas in-vitro mortality, growth, and behaviour experiments showed that cover potentially increases survival. Scarcity per se may not completely explain the apparently absence of EBP, given that not a single EBP lobster was located either during this study or during any other of the extensive benthic investigations. The present paper discusses the implications of their apparent absence and whether it arises because EBPs are very scarce, cannot be captured by suction sampling, are not within lobster habitat, or occupy a specialized niche within adult habitat outside the range of current sampling methods.

This study examined the role of predation in restricting early benthic phase (EBP) lobsters to shelter-providing substrata. In the field, the survival of animals provided with cover in the form of cobble and gravel substrata was significantly higher than unsheltered controls. Small benthic fish, particularly gobies Pomatoschistus minutus and rockling Ciliata mustela were the primary predators subtidally while crabs Carcinus maenus appeared to be the dominant intertidal predator. Predatory attack primarily occurred within minutes of the lobsters being deployed. The study reinforces the role played by predation in restricting EBP European lobsters to shelter-providing substrata.

Short-term effects of fishing on benthos from a mud patch in the northwestern part of the Irish Sea were investigated in 1994-1996 by means of samples taken both before and shortly after (ca. 24 h) fishing activity. No quantitative historical benthos data are available for the period prior to commencement of the fishery, although limited qualitative data exist. Therefore, studies of medium to long-term effects involved sampling the fauna of areas around wrecks (i.e., unfished pseudo-control sites) for comparison with fished grounds. Attempts were made to calculate the short, medium, and long-term impact of the fishery on the benthos and surrounding environment. Direct (short-term) effects were not quantifiable at a heavily fished offshore site (75 m depth); however, some changes were visible in a less fished, shallow (35 m depth) site. Medium to long-term effects were more discernible at the offshore site. Only minor changes were observed at the inshore location, suggesting that it is fishing intensity per se, rather than the direct impact from passage of the gear, that constitutes the major factor controlling long-term negative trends in the benthos of the Irish Sea Nephrops grounds.

ABSTRACT1. The distribution of effort for the most frequently used mobile demersal gears in the Irish Sea was examined and their potential to disturb different benthic communities calculated. Fishing effort data, expressed as the number of days fished, was collated for all fleets operating in the Irish Sea in 1994. For each gear, the percentage of the seabed swept by those parts of the gear that penetrate the seabed was calculated.2. For all gears, the majority of fishing effort was concentrated in the northern Irish Sea. Effort was concentrated in three main locations: on the muddy sediments between Northern Ireland and the Isle of Man (otter and Nephrops trawling); off the north Wales, Lancashire and Cumbrian coast (beam trawling); the area surrounding the Isle of Man (scallop dredging).3. In some areas, e.g. between Anglesey and the Isle of Man, the use of scallop dredges and beam trawls was coincident. A comparative experimental study revealed that scallop dredges caught much less by-catch than beam trawls. Multivariate analysis revealed that both gears modified the benthic community in a similar manner, causing a reduction in the abundance of most epifaunal species.4. Although beam trawling disturbed the greatest area of seabed in 1994, the majority of effort occurred on grounds which supported communities that are exposed to high levels of natural disturbance. Scallop dredging, Nephrops and otter trawling were concentrated in areas that either have long-lived or poorly studied communities. The latter highlights the need for more detailed knowledge of the distribution of sublittoral communities that are vulnerable to fishing disturbance. OBritish Crown