Senegalese sole (Solea senegalensis) is a flatfish of high commercial importance in Southern Europe that has been a promising species for diversifying Mediterranean aquaculture since early 1980's. It has failed to reach successful farming development due to lack of full control over spawning, poor fry quality and high mortality during the weaning stage. Furthermore, optimization of production has not been possible due to high heterogeneity in growth rates within cultured stocks that result in high body size variance at harvest. Among the several aspects needing wider knowledge in order to reach optimization of sole aquaculture, the ongrowing stage from juveniles to the commercialization size has been overlooked until the last years. It includes the relationships between individual growth and rearing parameters as stocking density, or the size composition of stocks. It is also important to evaluate growth according to the feeding rhythms, offering feed at adequate times for this species. Not less important is to assess the genetic variability of farmed stocks, and compare it to the wild populations, as a stepping stone to link genetic traits to the performance of aquaculture stocks. The aims of this thesis were to take an individual-based approach to growth, and growth sexual dimorphism, of Senegalese sole reared at high and low densities, with different levels of initial size variation, and under different feeding strategies. Moreover, the level of genetic variability of this species was compared between farmed and wild stocks through molecular genetic markers, and their sibship relationships were also assessed. Three experiments were conducted, involving a) rearing soles under high density (180% of bottom coverage) and low density (60% of bottom coverage); b) rearing soles under the same high and low densities, but also under homogeneous or heterogeneous initial size composition; c) rearing soles under a medium/high initial density (130% of bottom coverage) fed either during nocturnal hours, similar to their natural feeding rhythms, or during daylight hours. Additionally, the genetic variability of a farmed sample was compared to its wild donor population. Stocking density affects growth of Senegalese sole in two ways. First, sudden and steep increases in density could lead to poorer or no growth of fish until re-acclimatization to new high density conditions. Second, it seems that there is a sizedependent component on how stocking density affects growth, with smaller fish (sub-adults) growth being suppressed by high stocking density. Size composition of reared Senegalese sole does not affect individual growth. Sole doesn¿t show aggressive behavior and apparently, competition between individuals is low and size independent. Grading Senegalese sole does not guarantee the improvement of growth, and if so, it would be in high density conditions. Senegalese sole females grow faster than males, but after attaining certain body weight (between 40 and 80 g). It could be hypothesized that sexual maturation may be involved in the onset of sexual growth dimorphism in this species. Besides being an eminently nocturnal species, Senegalese sole fed during the light phase may yield specific growth rates and feed conversion ratios that are comparable to those of fish fed during the dark phase, suggesting the feasibility of feeding during normal business hours in commercial facilities. There is a loss in genetic variability in a single generation of Senegalese sole rearing, as evidenced by lower values of mitochondrial haplotypic diversity and nuclear diversity in the farmed sample compared with the wild donor population. Comparing wild Atlantic and Mediterranean samples suggests a limited gene flow between the populations inhabiting these basins. An accurate knowledge of the genetic composition of farmed stocks is essential both for maintaining the cultured stocks and for potential future restocking purposes. Castelldefels 17/ / El llenguado senegalès (Solea senegalensis) és un peix pla de gran importància comercial al sud d'Europa. El seu cultiu no està totalment desenvolupat, en part degut a l'alta heterogeneïtat en les taxes de creixement dins de les poblacions cultivades, que donen lloc a una alta dispersió de talles en arribar a la mida comercial. Els objectius de la tesi van ésser l'aproximació individual al creixement, i al dimorfisme sexual del creixement, del llenguado cultivat a altes i baixes densitats, amb diferents nivells de dispersió de talles inicial i sota diferents estratègies alimentàries. D'altra banda, el nivell de variabilitat genètica d'aquesta espècie es va comparar entre les poblacions de cultiu i salvatges a través de marcadors genètics moleculars, i es van avaluar les seves relacions de parentiu. Es van dur a terme tres experiments, implicant a) el cultiu de llenguado a alta densitat (180% de cobertura del fons del tanc) i baixa densitat (60% de cobertura); b) el cultiu de llenguado sota les mateixes densitats, però també sota condicions d'homogeneïtat o heterogeneïtat de talles inicials; c) cultiu de llenguado a densitat mitja/alta (130% de cobertura) alimentats durant les hores nocturnes, de manera semblant als seus ritmes alimentaris naturals, o durant les hores diürnes. Addicionalment, es va comparar la variabilitat genètica d'una mostra de cultiu amb la seva població salvatge donant. La densitat de cultiu afecta el creixement del llenguado senegalès de dues maneres. En primer lloc, els augments sobtats i pronunciats de la densitat podrien conduir a un creixement pobre o nul fins la re-aclimatació a les noves condicions d'alta densitat. En segon lloc, sembla que hi ha una component mida-dependent de com la densitat de cultiu afecta el creixement, amb els peixos més petits (sub-adults) experimentant una supressió del seu creixement degut a l'alta densitat. La composició de talles del llenguado senegalès de cultiu no afecta el creixement individual. El llenguado no mostra un comportament agressiu i, pel que sembla, la competència entre els individus és baixa i independent de la mida. La classificació de talles en el llenguado no garanteix la millora del seu creixement, i si és així, seria en condicions d'alta densitat. Les femelles de llenguado senegalès creixen més ràpid que els mascles, però després d'assolir cert pes corporal (entre 40 i 80 g). Es podria hipotetitzar que la maduració sexual pot estar implicada en l'aparició de dimorfisme sexual en el creixement d'aquesta espècie. A pesar de ser una espècie eminentment nocturna, el llenguado senegalès alimentat durant les hores de llum pot experimentar taxes de creixement específiques i ràtios de conversió de l'aliment que són comparables a les dels peixos alimentats durant les hores nocturnes, el que suggereix la viabilitat de l'alimentació durant les hores normals de treball a les instal·lacions comercials. Hi ha una pèrdua de la variabilitat genètica en una sola generació de cultiu de llenguado senegalès, com s'evidencia pels valors més baixos de diversitat haplotípica mitocondrial i diversitat nuclear de la mostra de cultiu en comparació amb la població salvatge donant. La comparació de mostres salvatges de l'Atlàntic i del Mediterrani suggereix un flux limitat de gens entre les poblacions que habiten en aquestes conques. Un coneixement exacte de la composició genètica de les poblacions de cria és essencial per al manteniment de les poblacions cultivades, i per a possibles programes de repoblació en el futur.

The phenomena of resistance compensation to temperature and heat death in the freshwater crayfish Austropotamobius pallipes has been studied, with particular regard to muscle membranes. The lipid composition of whole muscle was analysed by conventional chromatographic techniques. The principle phospholipids present were choline phosphoglycerides (50%), ethanolamine phosphoglycerides (25%) and serine/inositol phosphoglycerides (10%). Temperature acclimation had no effect on the phospholipid composition. The fatty acid composition of various phospholipid classes were also analysed by GLC and were found to be highly unsaturated. Total phospholipid extracts from animals acclimated to 4 C (18 hr light photoperiod) contained as lightly greater proportion of unsaturated fatty acids, compared to extracts from 25 C acclimated crayfish. The acidic phospholipids showed the greatest changes. Acclimation to 4 C with 8 hr light photoperiod conditions caused incorporation of a still greater proportion of unsaturated fatty acids into membrane phospholipids. This daylength effect, however, was not associated with a change in the thermal resistance of the whole animal. The overall activity of the Ca(^2+) stimulated ATPase of crayfish sarcoplasmic reticulum was unaffected by thermal acclimation, although warm-acclimated crayfish yielded significantly more microsomal protein per gram muscle weight. The kinetics characteristics of enzyme activity were independent of temperature up to 28 C. Incubation at 35 C (a lethal temperature) caused a decline in enzyme-substrate affinity. Thermal acclimation had no effect upon these characteristics. Arrhenius plots of enzyme activity for preparations isolated from both acclimated groups were linear. The activation energy for the enzyme from each acclimation group was similar (approximately 15 Kcals. Mole(^-1) ; 62,8 KJ. Mole(^-1)).The process of inactivation of the Ca(^2+)-stimulated ATPase at lethal temperature was also studied. High KC1 media protected the enzyme from inactivation, although dilution, and addition of BSA and calcium had no effect. Inactivation in low KC1 media, was a first order process. Acclimation had no significant effect upon the rate of inactivation. The proposed role of membranes in the phenomenon of resistance compensation has been discussed in the light of this and other data. An ultrastructural and histological study of a Microsporidian parasite of crayfish muscle is also presented.

The general biology and population dynamics of the fresh water crayfish, Austropotamobius pallipes, were studied in a man- made aqueduct in Northumbrla. The paucity of ecological knowledge of this species; the threat of the pathogenic crayfish 'plague' fungus, which has destroyed many European crayfish stocks; and several features of this aqueduct which made it particularly suitable for a population study inspired this investigation. The latter features were: the population was delimited to a known area (ca. 0.25 ha.); immigration was unlikely and the water level could be artificially manipulated allowing the collection of many crayfish by hand. Two sampling methods, hand-collection and funnel traps, and two marking schemes, one date-specific and one individual-specific were used to monitor the population. Over 4,500 crayfish were numbered and over 6,000 given a date- specific mark between March 1974 and June 1977. Moulting and growth were followed and found to occur only between late June and mid-September; this was limited by higher summer water temperatures. A potential life span of I0-I3 years was projected. Fecundity was estimated for individuals and the whole population. No recognizable 'home range' was observed. An attempt was made to describe crayfish diel activity patterns and trophic interrelationships. The effects of a protozoan parasite were observed under natural conditions. It was demonstrated that hand- collection provided relatively unbiased mark-recapture estimates of population size; trap samples seriously underestimated this parameter. The density of crayfish of body length ≥ 26 mm. was estimated as 8+/m(^2) in the summiers of 1974 and 1975 and to have varied between 10.4/m(^2) and 3.8/m(^2) from June 1976 to May 1977. Annual production (ca. 170.5 Kg./ha.) and mean annual biomass (ca. 409.7 Kg./ha.) were estimated in 1976.

The brown crab or European edible crab Cancer pagurus is one of the most economically important crab species in European waters with landings of 49 263 t in 2013. C. pagurus is also one of the most important commercial species in the United Kingdom with landings of 28 778 t in 2013 worth approximately £33.5M at first sale. The global capture production of brown crab has increased markedly during the last two decades. Despite this, the crab fishery is relatively data poor in terms of the ecology and catch characteristics of this species, particularly in the Irish Sea. The aims of this study were to provide the information to fill science gaps needed to inform sustainable brown crab fisheries in the Isle of Man. This was done by studying the population structure, reproductive ecology and catch characteristics of the brown crab fishery, and by examining the impacts of scallop fisheries on brown crabs, as well as assessing the by-catch composition of the brown crab pot fishery. A combination of sampling techniques was used to collect data which included: baited pots between Spring 2012 and Summer 2013, dredge, trawl and shore surveys. The catch per unit effort (CPUE) of crabs caught in traps was strongly influenced by environmental (i.e., temperature, season, area) and fishery specific factors (i.e., pot volume). This study compared fishery dependent data (FDD) and fishery independent data (FID) to assess the CPUE estimates. Both of these data sources gave similar results which indicated that fisher-based surveys provide good quality information for future monitoring of the population provided that environmental and gear effects are accounted for. This study also determined the total exploitation rate of brown crab using both commercial and recreational fisheries data. The latter contributed only a small percentage of total mortality which is largely due to strict controls on total recreational fishing effort. Observations of the distribution of brown crabs around the Isle of Man indicated the presence of a reproductive migration. Ovigerous crabs were generally found in offshore areas. These egg carrying females varied in size from 134 to 215 mm CW and each individual carried an estimated 0.4-3.0 million eggs. However, examination of behavioural maturity indicated that the earliest presence of sperm plugs was at 110 mm CW while functional maturity was 134 mm CW. There appears to be a predictable trend across Europe in the minimum size of egg bearing which appears to be related to water temperature. Based on quantitative data collected throughout the dredge surveys the potential impact of scallop dredging on the brown crab population was estimated in terms of by-catch, damage and mortality estimates. This study indicated that female crabs were particularly vulnerable to scallop dredging around the North-West coast of the island in November when fishing effort was highest in this area. Estimates of the potential mortality associated with scallop dredging led to a lower and higher estimate of a potential annual crab by-catch mortality of between 11 t and 17 t respectively (assuming 45% mortality of the crab by-catch), which represented 2.2 - 3.4% of the commercial landings of brown crab for the Isle of Man. Thus at present levels of fishing (up until 2014) this would seem to contribute a relatively small proportion of total mortality to the crab population. Nevertheless, an extension of the scallop dredging closed season until the end of November in the area of the Targets fishing ground might be a useful conservation measure if scallop dredging activity were to increase in the future. By-catch in pot fisheries is poorly studied in general. A total of 43 by-catch species were found in crustacean pots lifted around the Isle of Man and the velvet swimming crab Necora puber was the most abundant by-catch species. This study identified significant spatial differences in the CPUE of by-catch species; the highest by-catch CPUE was recorded around the west coast of the Isle of Man. However, seasonal changes in by-catch were less important. There was a significant negative relationship between the two target species (brown crab and European common lobster). However, there was no significant relationship between by-catch composition and target species (a combination of crab and lobster) composition.

Variation in recruitment is known to affect species demography and population dynamics. There is scant information, however, on how variation in recruitment influences community composition and processes. In the rocky intertidal, mytilid mussels have long been recognised as an important foundation species which can influence the dynamics of the entire community. Although numerous studies have demonstrated the effects of recruitment and post-recruitment processes on structure and dynamics of mussel populations, as well as the effect of mussels as a habitat engineering on community of rocky shores, the understanding of how variation in mussel recruitment might affect community level structure and processes remains unclear. In this Ph.D. research project I used the mussel Mytilus edulis L. as a model species to investigate the effects of variation in recruitment and post-recruitment processes on adult abundance and distribution on rocky shores around the Isle of Anglesey, North Wales, an area known for intense spatial variation in recruitment. I also examined how community composition of key taxa varied in relation to the presence of mussel-modified habitat. Particular emphasis was placed on how mussel-modified habitat influences the abundance and distribution of the dominant canopy-forming fucoid algae Fucus serratus L. which occupies a similar position on the low shore as mussel beds.Recruitment appeared to be a determinant of adult abundance and distribution at the mesoscale (1000s of metres) but not at the smaller, within-shore scale (10s of metres). The relative abundance of adult mussels among three geographically defined coastlines of Anglesey (west, north, and east) reflected the abundance of the recruits. The absence of mussel beds on the west coast of the island can be explained by a combination of low levels of recruitment, poor food supply, probably poor environmental condition, and intense predation. At the community level, community composition varied according to the existence of mussel-modified habitat at different scales. The difference was significant at 1000s of metre scale, significant in one of the two years studied at 100s of metre scale, and not significant at 10s of centimetre scale. Abundance of sessile taxa on primary substrates was lower where mussel habitat dominates, while abundance of mobile species except limpets was higher in the presence of mussel habitat. For mussel-fucoid interactions, mussel habitat influenced fucoids of different life-history phases in different ways. A negative effect of mussel-modified habitat on fucoids was profound in adults but the effect was context-dependent in juveniles and can be positive at settlement. There was a greater number of large fertile fucoids growing directly attached to rock than on mussel shells. This suggests that mussel dominated habitat may have a significant impact on reproductive output in fucoid populations as the abundance of reproducing thalli was reduced. Overall, a series of surveys and experiments in my thesis demonstrates that recruitment of the foundation species M. edulis is an important determinant for community composition on rocky shores.

No description available.

Scallops are currently the 3rd most valuable species in UK fisheries, with a first sale value of over £60 million per annum. Scallops are a non-quota species and landings have more than doubled in the last eight years. Forty percent of king scallop (Pecten maximus) landings into the UK originate from the English Channel. Despite the economic importance of this fishery there has never been a full stock assessment of scallops in English waters and there is a general paucity of scientific data for stocks in the English Channel. Existing management measures are not aligned with the biological structure of the stock, or based on robust science. The aims of the study were to provide data to assess the sustainability of the king scallop fishery through identifying the maximum spatial extent and distribution of fishing effort in the English Channel and defining scallop population structure by the degree of larval connectivity between spatially segregated scallop beds. The environmental impacts of the dredge fishery were investigated through quantifying bycatch and the impact of the dredge fishery on the habitats and communities present across scallop fishing grounds. The activity and spatial extent of the inshore and offshore scallop fleets indicated that although scallop fishing has occurred across a large proportion of the English Channel, fishing behaviour is sporadic and is concentrated in areas that are characterised by consistent scallop abundance. Economic and legislative drivers have altered historical fishing patterns in recent years. The patchiness of fishing behaviour, coupled with the nomadic nature of the fleet suggest that closure of areas that are infrequently fished could provide ecosystem benefits and potential benefits for the wider fishery while having minimal impact on fleet behaviour. Despite the well documented environmental impacts of scallop dredges, it is important to understand the environmental context in which fishing occurs as well as the predicted recovery timescales for benthic communities. Within the context of the English Channel king scallop fishery, species diversity and benthic community composition are constrained primarily by natural physical disturbance. It was not possible to detect community level response to a gradient of scallop fishing intensity against a background of environmental forcing. This could be due to historical fishing activity (40+ years) that may have changed the community to a stable altered state that continues to reflect the background environmental gradient across the English Channel. Bycatch in the English Channel was low compared to other towed mobile fishing gears and compared to other scallop dredge fisheries in the UK. Bycatch composition varied over local and broad spatial scales. The fishery affected a limited number of bycatch species of ecological importance and low biomass of such species were present, indicating that the population impacts of the dredge fishery on these species are likely to be minimal. Discards of commercial species also varied significantly with location and were higher in the eastern English Channel. Three reproductively distinct populations of scallops have been identified in the English Channel, indicating the largest appropriate management units. Large scale oceanographic currents maintain larval connectivity across much of the English side of the Channel; however complex hydrodynamic processes within Falmouth Bay suggest that larval dispersal is prevented at localised spatial scales in this location. The population in the Baie de Seine is reproductively isolated from the eastern English Channel, however larvae may disperse west, to the Baie St Brieuc and southern Cornwall, via residual currents. Improving the management, sustainability and public perception of the English Channel king scallop dredge fishery is a priority for the UK scallop industry. This thesis addresses fundamental gaps in the scientific data to inform future management and the sustainable exploitation of the fishery.

The fisheries sector in Malawi is a major protein source. However, catches have decreased in all water bodies, including rivers. This has been attributed to unsustainable fishing, dam building, and degradation of spawning habitats through increases in siltation. A better understanding of the biology of riverine species may help to promote management and conservation. Research in this thesis initially focusses on migratory behaviour of three species in the genus Opsaridium within the Lake Malawi catchment. Using new micro satellite markers I demonstrate that the endemic large-bodied lake-river migratory species mpasa (Opsaridium microlepis) and sanjika (Opsaridium microcephalum) show weak spatial genetic structure among breeding grounds, consistent with a lack of natal homing. These results suggest conservation initiatives aimed at improving spawning runs in individual rivers could have broader catchment-level benefits. I also demonstrate that the small-bodied exclusively riverine non-endemic dwarf sanjika (Opsaridium tweddleorum) shows strong population genetic structuring among rivers, suggesting each population represent an individual conservation unit. I then present an overview of the evolution of Opsaridium taking a multigene phylogenetic approach and broader taxon sampling. The results demonstrate the three Malawi species have not radiated within the lake catchment, but instead each lineage has independently colonised the system from neighbouring drainages. These results suggest that riverine faunas assemble from multiple colonisation events, rather than within-catchment speciation. I then take a community-level approach to investigate factors that influence riverine fish community structure in Malawi, using geographical variables, locally-measured environmental variables and bioclimatic variables from global-scale databases. The results demonstrate that all sets of variables contribute to structuring, suggesting both historical dispersal limitation and present day habitat contribute to spatial structure of fish diversity. Together, this thesis provides evidence for processes have shaped genetic and species diversity of river fishes in Malawi, which should inform conservation and management of these important resources.

The European native oyster (Ostrea edulis) was once abundant across Europe; however, due to a combination of overfishing and disease, many of these populations collapsed during the early 1900s and now there are few natural populations left in Britain or Ireland. One such remaining population is located in Loch Ryan, Scotland which supports a small fishery, currently landing up to 25 tonnes of oysters per annum. The Loch Ryan fishery has been privately owned and managed by the Wallace family since 1701, when they were given the rights to fish in a Royal Charter by King William III. Unique access to historical documents enabled an examination of management techniques, landings and population structure since 1874. Assessment of the leases over the last 87 years suggested that the owners are willing to expend resources on regulating tenant behaviour. The current landings data indicated that the fishery has recovered from the lowest historical catch levels in the 1950s, to a catch similar to that observed before the 1913 population crash (at the highest sustainable catch of 20 tonnes p.a.). The pooled annual sex ratio (male: female) was 3:2 for 2013 and 2:1 for 2014, which was significantly different to the presumed ideal 1:1 ratio. However, the sex ratio for individual months was not significantly different to a 1:1 ratio, with only 3 months (over the two years) showing a significantly skewed ratio. This investigation aimed to ensure sustainable fishing practice in Loch Ryan and, by using this site as a case study, inform the management of other fisheries - both public and private - by emphasising the importance of learning from experience. In conclusion, this study presents results which demonstrate that a collapsed fishery can be restored to produce sustainable high catches, if controlled management is applied over a prolonged period of time.

Freshwater pearl mussel (Margaritifera margaritifera) population declines in Northern Ireland led to an ex situ breeding programme being established on the Ballinderry River in 1998 by the Ballinderry Rivers Trust. If the causes of the initial threats or declines have been remedied it is recommended that captive- bred individuals are returned to their natural habitat to help avoid domestication by not retaining them in captivity for extended periods. Mussel silos (upwelling mussel housing system) were found to be a useful intermediate release method with a mean survival rate of 81%. Differences of survival between various size classes led to the recommendation that mussels should be maintained in the hatchery environment until they are approximately 10 mm to maximise potential survival. M. margaritifera populations in Northern Ireland are regarded as overaged and reproductively non­functional. Therefore, to delay their extinction, artificial mussel populations were assembled using translocated wild adults and captive bred juveniles which would have the potential to become self­recruiting. Recovery by observers and survival varied strongly across sites with the majority of mussels moving from their initial release site during the course of the study. Broodstock for captive breeding has been maintained in the Ballinderry Fish Hatchery since 1998. Despite rotation of the broodstock in 2010 in an attempt to maintain genetic diversity in captive bred juveniles significant levels of inbreeding remain. Individuals recently discovered in the Ballinderry catchment showed distinct differences in allele frequencies from the current hatchery broodstock. It is recommended that such individuals should be used for broodstock rotation to genetic diversity in future generations. Juvenile bivalves often use pedal feeding until the ctenidia are fully developed. Serial sections of juvenile mussels suggest that mussels 4 mm long are in transition from pedal to filter feeding because, although a ventral food groove is present, the outer demibranch of the ctenidium is only beginning to form and there are no labial palps. Mussels 8 mm long have all the features found in adult mussels, including palps suggesting they are predominantly filter feeders at this stage.