Sandra Irwin

Stocking density, growth and growth variation in juvenile turbot, Scophthalmus maximus (Rafinesque)

Abstract Although high stocking densities of turbot have been achieved in culture using supplementary oxygenation, this rearing strategy ignores the possibility that high densities may interfere with behavioural interactions between individuals and thereby affect biomass gain. This study describes the effect of stocking density on the growth of juvenile turbot populations. Groups of juvenile turbot were reared at four different densities (initial densities: 0.7, 1.1, 1.5 and 1.8 kg/m 2 ) for 45 days. Treatment density had a significant effect on turbot growth rates over the experimental period. Fish held at the highest density showed lower growth rates and mean weights at the conclusion of the study than fish held at lower densities. The dispersion in fish weights was also affected by stocking density. The variation in fish weights was greatest in the highest density group and as stocking densities increased the growth of some individuals was suppressed. It is concluded that growth of juvenile turbot can be significantly increased and more homogeneous weights achieved by stocking the fish at lower densities than previously reported.

Effects of diet transition regimen on survival, growth and lipid composition of intensively reared Atlantic cod, Gadus morhua, larvae

Replicated groups of Atlantic cod were rearedfor up to 40 days in 100 l tanks stocked at adensity of 75 eggs l−1. Larvae weretransferred from rotifers, Brachionusplicatilis, to either fresh-hatched orenriched Artemia nauplii on each of days5, 15 and 25 post-hatch (ph). Rotifers wereprogressively withdrawn over a 5 day period.The type of Artemia offered(fresh-hatched, enriched) did not affectsurvival or growth rates at any of the 3transfer ages. Larvae transferred toArtemia from day 5 ph suffered a highincidence of swimbladder over-inflation andhigh mortality during metamorphosis (< 1%survival to day 36 ph). Cod in the day 15 and day25 transfer groups did not differ significantlyin weight-specific growth rate or size on day40 ph (mean standard length 13.8 mm, dry weight3.8 mg). Highest mean survival rates to day 40ph (18.1%) and lowest mortality followingtransfer to nursery tanks were also observed inthe day 25 transfer groups. Fish that receivedArtemia from day 5 ph containedcirca twice as much total lipid per unit bodyweight and had a 30% higher triacylglycerol(TAG) content compared to all other groups.Ratios of the essential fatty acidsdocosahexaenoic acid (DHA), eicosapentaenoicacid (EPA) and arachidonic acid (ARA) alsodiffered according to age-at-transition.DHA:EPA ratio exceeded 1 only in codtransferred to Artemia on day 25 ph.Based on these findings, it is recommended thatintensively reared Atlantic cod should continueto receive rotifers until completion ofmetamorphosis.

The value of plantation forests for plant, invertebrate and bird diversity and the potential for cross-taxon surrogacy

As the area of plantation forest expands worldwide and natural, unmanaged forests decline there is much interest in the potential for planted forests to provide habitat for biodiversity. In regions where little semi-natural woodland remains, the biodiversity supported by forest plantations, typically non-native conifers, may be particularly important. Few studies provide detailed comparisons between the species diversity of native woodlands which are being depleted and non-native plantation forests, which are now expanding, based on data collected from multiple taxa in the same study sites. Here we compare the species diversity and community composition of plants, invertebrates and birds in Sitka spruce- (Picea sitchensis-) dominated and Norway spruce- (Picea abies-) dominated plantations, which have expanded significantly in recent decades in the study area in Ireland, with that of oak- and ash-dominated semi-natural woodlands in the same area. The results show that species richness in spruce plantations can be as high as semi-natural woodlands, but that the two forest types support different assemblages of species. In areas where non-native conifer plantations are the principle forest type, their role in the provision of habitat for biodiversity conservation should not be overlooked. Appropriate management should target the introduction of semi-natural woodland characteristics, and on the extension of existing semi-natural woodlands to maintain and enhance forest species diversity. Our data show that although some relatively easily surveyed groups, such as vascular plants and birds, were congruent with many of the other taxa when looking across all study sites, the similarities in response were not strong enough to warrant use of these taxa as surrogates of the others. In order to capture a wide range of biotic variation, assessments of forest biodiversity should either encompass several taxonomic groups, or rely on the use of indicators of diversity that are not species based.

Breeding bird communities of second‐rotation plantations at different stages of the forest cycle

Capsule Early stages of the plantation forest cycle have distinct bird communities and bird density was significantly higher in the second rotation than in the first for a given age class. Aims To characterize the bird communities in Irish second-rotation plantations and to compare them with those of first-rotation plantations. Methods Point counts were used to survey 20 plantation forests in four age classes (Pre-thicket; Thicket; Mid‐rotation; and Mature) in the breeding season of 2007. distance software was used to generate bird densities. Ordination, indicator species analysis, and glm were used to analyse the bird communities. Results Bird communities of Pre‐thicket and, to a lesser extent, Thicket age classes were distinct from those of more mature forests. Bird communities of Mid‐rotation and Mature age classes were indistinguishable from each other and were therefore combined into a single age class (Closed canopy). Pre‐thicket held significantly lower total bird density, but significantly higher migrant bird density, than this Closed canopy age class. Bird density was significantly higher in the second rotation in all age classes except for Pre‐thicket, but migrant density was significantly higher in Pre‐thicket in the second rotation. There was no difference in species richness between the first and second rotation. Conclusions Differences between rotations are probably due to changes in vegetation structure, and the increase in second‐rotation forests in Ireland is likely to be a positive development for bird communities. Especially encouraging is the higher migrant bird density in second‐rotation Pre‐thicket, as some of these species are in decline throughout Europe. However, the largest differences in population density between rotations were exhibited by common species and such species will likely benefit most from future increases in the area of second‐rotation plantation forests.

The relationship between individual consumption and growth in juvenile turbot, Scophthalmus maximus

The development of feeding hierarchies was investigated in juvenile turbot, Scophthalmus maximus (Rafinesque) held at two rearing densities for 82 days. Individual biometrics were measured on five occasions and a diet labelled with ballotini glass beads was used in combination with a noninvasive radiographic technique to estimate consumption rates. The results demonstrate that the inclusion of the radio-opaque glass beads in the diet did not significantly reduce consumption by turbot. A significant relationship was found between individual consumption and growth of juvenile turbot. A weight differential within groups increased with time and was largely explained by inter-individual variation in food consumption. This differential was driven by an uneven distribution of food within groups, where individuals of a higher weight than the group average consistently consumed a greater than average share of the group meal, and showed less day to day variation in consumption than their smaller counterparts. The results demonstrate that in captive turbot groups, size hierarchies are mediated, at least in part, through inter-individual differences in food consumption.

Adaptation and validation of a radioimmunoassay kit for measuring plasma cortisol in turbot.

Levels of cortisol in fish blood provide quantitative information on the degree of stress induced by a variety of stressors. It is also useful in describing the social status of individual fish within groups. The commercial production of radioimmunoassay (RIA) kits, such as the DPC Coat-A-Count radioimmunoassay kit, has considerably reduced the effort required for cortisol measurement. These kits employ human plasma based cortisol standards which are not compatible for use with non mammalian species such as fish e.g. turbot, Scophthalmus maximus (Rafinesque), blood due to the interference effect of lipids and steroid binding proteins present in the plasma. In this study the DPC kit was used following the removal of these lipids and steroid binding proteins from the plasma using an ethanol-hexane extraction. Excessive variability in the cortisol values obtained using this method deemed it unsatisfactory in overcoming the problem of incompatibility. A second modification of this technique that was tested involved the preparation of turbot specific standards for use in the preparation of modified standard curves. Using this method, an accuracy of 93.4% was achieved, as opposed to 79.6% using the kit human plasma based standards, and 47.1% using samples following lipid removal using an ethanol-hexane extraction. Based on analysis of accuracy, precision and reproducibility it is concluded that commercially available cortisol kits are suitable for use with turbot plasma, but a number of minor modifications are necessary.

Implications of afforestation for bird communities: the importance of preceding land-use type

Afforestation of open habitats is one of the principal land-use changes underway in Europe and elsewhere in the world at present, and it can have a considerable impact on local biodiversity. The sustainable expansion of global forest plantations requires an understanding of the factors that determine the ecological impacts of afforestation. This study set out to determine the importance of preceding land-use type in determining the outcomes of afforestation for bird communities. Paired comparisons of 5-year-old exotic conifer plantations and matching non-forested sites were studied in areas of low (peatland), intermediate (wet grassland) and high (improved grassland) management intensity. Afforestation resulted in an overall increase in total bird density in all three habitat types. The effects of forest planting on bird conservation were found to be positively related to prior management intensity at the site. The density of bird species of conservation concern increased in response to the planting of intensively managed grassland sites, but decreased in response to afforestation of peatlands and of grasslands under intermediate management intensity. This study shows that plantation forests can, in some contexts, offer opportunities for bird conservation, and the findings highlight the trade-offs that are an integral part of land-use change. Therefore, where afforestation planning includes consideration of its impact on bird communities, planting should take place predominantly on sites of low biodiversity value, such as agriculturally improved grasslands. Furthermore, the preservation of sites of high conservation value within areas of afforestation would confer advantages on bird communities.

The influence of a native tree species mix component on bird communities in non‐native coniferous plantations in Ireland

Capsule Norway Spruce plantations with Scots Pine as a secondary tree species had higher bird densities than pure Norway Spruce. Shrub cover was the most important structural variable, influencing bird density, species richness and Simpson’s diversity. Aims To investigate whether incorporating a native tree component into non‐native coniferous plantations had any effect on bird communities or vegetation structure. Methods Birds were surveyed in plantations of Norway Spruce mixed with Oak and Scots Pine, each paired with a plantation of pure Norway Spruce. distance was used to generate bird densities. Bird density, species richness and Simpson’s diversity were compared between each mix type and pure Norway Spruce. glms were used to investigate relationships between structural components of plantations and bird data. Results Bird communities of mixed plantations differed only slightly in their composition from pure Norway Spruce. Bird density was significantly higher in Scots Pine mixes than in Oak mixes or pure Norway Spruce. Neither species richness nor Simpson’s diversity differed significantly between the plantation types. Some vegetation components differed between the plantations and shrub cover was positively associated with bird density, species richness and Simpson’s diversity. The presence of rides also increased bird density. Conclusions There is a positive effect on bird communities of including a native tree species in non‐native coniferous plantations, but the magnitude of the effect is small. The influence of shrub cover on birds suggests that forest management may play an important role in determining the utility of plantations for birds. We recommend the establishment of mixed tree species plantations where possible, although, in the case of Oak mixes, the Norway Spruce appeared to suppress growth of the Oak and thus may be restricting its effect on birds. Changes in management, such as planting Oaks in clumps or heavier thinning of the coniferous component, could address this problem.

Mercury and organochlorine content of Dipper Cinclus cinclus eggs in south-west Ireland: trends during 1990–1999

A sample of 124 deserted/infertile dipper (Cinclus cinclus) eggs was collected in south-west Ireland during six seasons (1990-1994 and 1999) and analysed for mercury and organochlorines. Mercury was detected in three of the 6 years but no trend was observed. DDT occurred above the limit of detection in only two eggs, one each in 1993 and 1994. In contrast, two derivatives of DDT (DDE and TDE) were found much more commonly. DDE occurred in over 87% of eggs, while TDE contamination was less widespread and reached a maximum of 60% in 1993, with none detected in 1991 or 1999. There was no trend in occurrence of DDE or TDE across years. PCB contamination was present consistently over the 10-year period, with little change in the proportion of contaminated eggs collected over time. In all years, the lowest recorded occurrence of total PCBs was 69% expressed on a formulation basis as Arochlor 1254. PCB congeners 138, 153 and 180 dominated. The congener pattern was similar across years with the exception of 1990 when congener 118 dominated. A distinct trend of high values of contaminants was observed in 1990 and 1993. In 1990, PCB 118 was the dominant contaminant, while in 1993, HEOD, DDE, PCB 138 and PCB 153 were primary contributors to the observed result. Other contaminants (HCB, PCB 101, gamma-HCH, PCB 170 and PCB 180) showed little obvious patterns between years and occurred at relatively low levels. No pattern was observed in contaminants when eggs were grouped according to river or altitude. These data provide a baseline for organochlorine contamination levels in Irish freshwater ecosystems against which future trends can be assessed.

Mouth morphology and behavioural responses of cultured turbot towards food pellets of different sizes and moisture content

Abstract The importance of food pellet size and texture in pre-capture selectivity and subsequent ingestion by juvenile turbot, Scophthalmus maximus (Rafinesque), was investigated. Measurements of mouth parts and body lengths were taken to investigate their relation to preferred pellet sizes. Two fish size classes, with mean lengths of 123.9±2.5 mm and 161.3±2.9 mm were tested. Behavioural responses of individual fish offered pellets of five different diameters (2.0, 3.5, 5.0, 8.0 and 13.0 mm) and two moisture levels (10.9% and 28.3%) were investigated. Responses were classed as follows: no reaction; orientation; incomplete approach; complete approach and capture, and scored accordingly. A broad range of acceptable pellet sizes was observed in both fish size groups. In the smaller sized group, acceptable pellet diameters ranged between 4.0% and 6.5% of total fish length, or 40% of mouth gape. This decreased to 20% of mouth gape, or between 2.2% and 5.0% of total fish length in the larger fish group. Juvenile turbot demonstrated an ability to accurately select pellets within the acceptable range and pellets outside this range were largely ignored, eliciting few pre-capture behaviours.