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.

Description: The Clyde Sea Nephrops fishery produces large amounts of invertebrate discards. Of these, as much as 89% are decapod crustaceans, including the swimmingcrab Liocarcinus depurator (Linnaeus, 1758), the squat lobster Munida rugosa (Fabricius, 1775) and the hermit crab Pagurus bernhardus (Linnaeus, 1758). Theshort-term mortality of these species was assessed following trawling and periods of aerial exposure on deck (16-90min), and ranged from 2-25%, with Pagurusbernhardus showing the lowest mortality. Two experiments were performed to determine the longer-term survival of trawled decapods compared to those withexperimentally ablated appendages. Deliberately damaged decapods had a significantly lower longer-term survival (ca. 30%) than controls (72-83%). Survival oftrawled Liocarcinus depurator that had been induced to autotomize two appendages was slightly lower (74%) compared with intact creel-caught animals (92%).Mortality rates stabilised about 10d after trawling. Our results suggest that post-trawling mortality of discarded decapod crustaceans has been underestimated in thepast, owing to inadequate monitoring periods. Copyright 2001 International Council for the Exploration of the Sea

Description: Crustacean discards experience stress during commercial fishing operations, due to increased exercise while in the trawl and aerial exposure during sorting of the catch. Physiological stress and recovery were assessed following trawling of two ecologically important decapod species, regularly discarded in the Clyde Nephrops fishery. Haemolymph samples taken from trawled swimming crabs, Liocarcinus depurator, and squat lobsters, Munida rugosa, had significantly higher concentrations of ammonia (0.308 and 0.519 mmol l super(-1)), D-glucose (0.14 and 0.097 mmol l super(-1)) and L-lactate (6.2 and 0.87 mmol l super(-1)) compared with controls, indicating an impairment of ammonia excretion and a switch to anaerobic metabolism. Concurrently, the haemolymph pH of trawled squat lobsters was low (7.47) compared with controls (7.75); however, the reverse trend was found in L. depurator. Initially elevated lactate (7.98 mmol l super(-1)) and glucose (0.73 mmol l super(-1)) concentrations of trawled and emersed (1 h) L. depurator were restored, 4 h after re-immersion along with pH (7.54). Crabs that had been emersed for 1 h had significantly higher concentrations of glucose (0.2 mmol l super(-1)) and lactate (5.14 mmol l super(-1)), and had more acidic blood (7.64) than L. depurator subject to 1 h of exercise, indicating that anoxia was the main cause of physiological stress. Crabs and squat lobsters lost 7% and 9% of their initial body wet weight following 1 h of emersion, although blood osmolarities did not change significantly. While all animals survived aerial exposure in our experiments, sorting of the catch on commercial boats takes up to 300 min, which could lead to mortality or sub-lethal chronic biochemical changes that could compromise fitness.