ALBERT

Description: Demersal fisheries generate large quantities of unwanted by-catch. Nephrops norvegicus is the most important shellfish resource in UK waters and although the fishing effort has increased considerably over past decades the ecological effects of this fishery have yet to be evaluated. This study provides a baseline assessment of the composition and fate of invertebrates regularly discarded in the Clyde Nephrops fishery. Monthly sampling on local fishing boats revealed that only 18% of the catch is landed, invertebrates accounting for up to 90% of the discards. Crustaceans (Liocarcinus depurator, Munida rugosa) and echinoderms (Asterias rubens, Ophiura ophiura) were the most important groups discarded. Monthly damage assessments of invertebrates collected from commercial trawlers showed the severity and frequency of damage was mainly correlated with species-specific morphological and behavioural characteristics: almost all O. ophiura and some 40%-60% of the crustaceans incurred injury. By contrast, damage was low in more flexible invertebrates such as A. rubens (30%) or hard-shelled animals such as Pagurus bernhardus (14%) and Aequipecten opercularis (2%). Biochemical analyses of haemolymph samples taken from trawled and emersed crustaceans revealed significant increases in ammonia, glucose and lactate concentrations along with a decrease in pH. Recovery started after 4 h. Longer-term survival experiments showed that post-trawling mortality was 100% for O. ophiura 14 d after trawling; by contrast, almost all hermit crabs and whelks survived. Experimental ablation of appendages and autotomy increased L. depurator post-trawling mortality significantly (78% and 26%) cf. creel-caught controls (8%). Asterias rubens with multiple arm loss showed 〉90% mortality 21 d after trawling possibly due to an increased risk of infection with Vibrio metschnikovii. While mortality figures for most species doubled over the last 14 d of the experiment, most previous studies covered monitoring periods of only 〈5 d and may have underestimated discard mortality. Traps baited with crustacean and echinoderm discards deployed at sea attracted a number of species. While whelks and A. rubens were found in significantly higher numbers in traps baited with crustaceans, P. bernhardus was more attracted to A. rubens bait. The two amphipods Orchomene nanus and Scopelocheirus hopei occurred in high numbers (n=2745) and preferred traps baited with crustaceans. These findings are discussed with respect to their ecological significance and relevance to fisheries management.

Description: Despite over a century of exploitation of fish in European waters, scientists know surprisingly little about the precise distribution of the major commercially exploited fish species, and their habitat requirements. This is the first European study that aims to identify essential fish habitats of commercially important fish species (cod, haddock, whiting, plaice, sole, plaice, lemon sole) in the Irish Sea and the English Channel (UK). Areas of the seabed that harbour the highest densities of these species were identified and mapped using an existing database spanning 12 years data from national stock assessments. Demersal fishers observe samples from the sea floor every time they haul their nets, which far exceed the sampling schemes that scientists can afford or mobilise. Experienced fishers may have decades of observations to bring to bear and keep detailed records of exactly where and when they fish and how much they catch. Although the ultimate goal of fishing is to provide income from the catch, rather than to test scientific hypotheses, many fishers seek to understand the very questions about the seabed that motivate our study. Therefore, we decided to liase with the fishing industry to refine our broad scale fish maps for future survey. Information was gathered in a pilot study through questionnaires filled in at a fishing exhibition. Through a process of informal presentations and meetings, fishermen have helped us to refine our studies by pinpointing fishing grounds of importance for the fish species in question. The co-operation with fishers has not only added to the credibility of the study and any management decisions that may depend on its findings, but has also highlighted once more the vast amount of knowledge that can be gained from this declining species.

Description: The Clyde Sea Nephrops fishery produces ca. 25,000ty1 discards with invertebrates accounting for up to 90% of the number of animals discarded. Trawling and handling of the (by-)catch often results in physical injury, the extent of which was previously unknown.Damage sustained by invertebrate discards was assessed following commercial trawling (of 62-270min duration) and sorting on deck. Brittlestars Ophiura ophiura were most vulnerable with 100% incurring damage, followed by squat lobsters Munida rugosa (57%) and starfish Astropecten irregularis (56%). Harder-shelled species such as hermit crabs Pagurus bernhardus and queen scallops Aequipecten opercularis sustained fewer injuries (14 and 2%, respectively). Shell chipping, loss and damage of limbs were the most frequent types of injury incurred. The severity and frequency of damage was mainly correlated with species-specific morphological and behavioural characteristics. Vessel type, tow duration and animal size had a major influence on damage to the epibenthic invertebrates caught. While damage may potentially be repaired, survival is adversely affected and sublethal effects might significantly impair fitness of frequently trawled individuals and populations.

Description: The Clyde Sea Nephrops fishery produces large amounts of invertebrate discards. Of these, up to 80% (by numbers) are echinoderms, including the starfishAsterias rubens and the brittlestar Ophiura ophiura. The short- and longer-term mortality of these species was determined after trawling in order to gain reliableestimates of trawl-induced mortality. Short-term mortality was assessed after trawling and periods of aerial exposure on deck, and ranged from 0-31%, with A.rubens showing lower mortality. Mortality of haphazardly collected echinoderms of various sizes and degrees of damage was monitored over one month todetermine longer-term mortality. The effects of injury on starfish survival were also examined, as were the effects of trawling and aerial exposure on O. ophiurasurvival and A. rubens righting time. Injured A. rubens had a significantly higher long-term mortality (22-96%) than controls (4%). Trawling and aerial exposuresignificantly increased righting times of A. rubens, implying susceptibility to stress and an increased risk of predation. Moribund A. rubens developed white lesionscontaining bacteria (Vibrio metschnikovii and Acinetobacter sp.) and mortality rates only stabilised in the third week after trawling. In contrast, all trawled O. ophiuradied within 14d. Immediate re-immersion in sea water resulted in lower, but nevertheless high, mortality (91%). Our results suggest that post-trawling mortality ofdiscarded echinoderms has been underestimated in the past.

Description: Arm damage and loss were examined in starfish Asterias rubens that had been caught in a variety of towed commercial fishing gears deployed on different sea bed types. Between 7 and 38% of starfish in each catch lost one or more arms and arm loss was positively correlated with the volume of the catch for two of the fishing gears examined. Subsequent monitoring of damaged animals showed that arms were autotomised for at least 3 weeks following capture. Mortality was highest in starfish with damaged or missing arms, compared with those that appeared intact after fishing. Arm regeneration was delayed in a small proportion of the animals caught by commercial gears. In a parallel study, 17% of starfish caught by a 4 m beam trawl had a damaged ambulacral ossicle at the point of autotomy (cf none from a control group that were allowed to autotomise slowly). There was no difference in regeneration rates between the animals caught by commercial gears and a control set (caught by a small trawl and forced to autotomise an arm in the laboratory) once the animals that delayed regeneration were excluded from the dataset. After 1 year under laboratory conditions the starfish had, on average, regenerated the missing arm to 75% of the length of the other four arms. During this time period the lengths of the undamaged arms increased by c. 50%. The implications of this study for using arm loss in starfish as an indicator of fishing disturbance are discussed.