Deirdre Brophy

A comparison of otolith microchemistry and otolith shape analysis for the study of spatial variation in a deep-sea teleost, Coryphaenoides rupestris

The study of the morphological and chemical characteristics of otoliths have recently been proposed as complementary tools for fish stock identification. However, their effectiveness remains to be fully assessed, especially in species whose life history is still poorly understood. The relative efficiency of otolith microchemistry and otolith shape analysis in discriminating samples of the deep-sea macrourid Coryphaenoides rupestris collected in different areas in the North Atlantic was examined. Otolith microchemistry based on LA/ICP-MS found significant differences in the concentrations of lithium, manganese and barium among sample sites. This allowed for very high classification accuracy (92%), when using discriminant function analysis. Otolith shape analysis based both on linear shape measurements and elliptical fourier analysis revealed a contrasting weak discrimination, with only 43% classification success. Otolith microchemistry appears to be a more effective tool in identifying individual fish from different locations. The implications for the study of population structure are discussed taking into account the limitations of the methodologies employed.

The influence of pre-recruitment growth on subsequent growth and age at first spawning in Atlantic herring (Clupea harengus L.)

Calculation of the spawning stock biomass for fisheries management requires information on the numbers or proportions of fish in each age- or length-group that are mature each year. This study was conducted to determine the relationship between growth and age of first reproduction in herring stocks around Ireland. Measurements of otolith size at the onset of the first annulus (O1) were used to compare growth during the first year of life between 1-, 2-, and 3-group spawning herring collected from spawning grounds in the Celtic Sea over a period of 3 years. The 1-group spawning fish had significantly greater mean O1 measurements, and hence showed faster growth on average during the first year of life than 2- or 3-group spawning fish. Fish that exhibited slow growth during the first year were absent from the adult spawning population at age 1, but occurred at similar levels in the samples of 2- and 3-group spawning fish. Regression of O1 radius on fish length at capture showed that growth during the first year of life had a small but significant effect on subsequent growth up to age 3. The relationship between pre-recruitment growth and subsequent growth and age at first spawning has implications for recruitment patterns of juveniles from different nursery areas and for the lifetime fecundity of population components with differential growth.

The feeding ecology of 0 year-group turbot Scophthalmus maximus and brill Scophthalmus rhombus on Irish west coast nursery grounds

On sandy beach nursery grounds along the west coast of Ireland, 0 year-group turbot Scophthalmus maximus were found to consume six types of crustaceans, in addition to polychaetes. The 0 year-group brill Scophthalmus rhombus fed almost exclusively on mysids, even though nine taxonomic prey groups were identified in the sediment across the investigated beaches. Both species avoided non-motile organisms such as gastropods and bivalves, which were present in high abundances in the sediment and their growth and condition was not significantly related to the quantity or type of prey consumed, temperature or salinity. A high incidence of feeding was detected for both species over the duration of the study, suggesting that food was not limiting on west of Ireland nursery grounds. Temporal partitioning of settlement was detected between S. maximus and S. rhombus, indicating that inter-specific competition for food does not occur between these two flatfish species on west of Ireland nursery grounds.

Macrobenthic prey availability and the potential for food competition between 0 year group Pleuronectes platessa and Limanda limanda

This study describes the feeding habits of plaice Pleuronectes platessa and dab Limanda limanda during early juvenile development and relates differences between nursery grounds and sampling years to spatial and temporal variabilities in macrobenthic prey availability. The main prey taxa of both species were copepods, bivalves, amphipods, polychaetes and oligochaetes and size-related variation in diet was found. Despite considerable similarity in the prey items, differences in food composition between the two species were observed and spatial variability in diet confirmed their opportunistic feeding behaviour. A high degree of dietary overlap was found in June and decreased steadily throughout the season. The prey composition in the guts of both species largely reflected the composition of the main macrobenthic taxa in the sediment. The overall data suggest that resources were not limiting in the littoral sandy nursery areas in the west of Ireland and no indications were found that exploitative competitive forces upon the benthic prey assemblages occurred between P. platessa and L. limanda. Feeding success, Fultons K condition and dietary overlap, however, showed spatial and temporal variations, and were probably affected by the availability and density of macrobenthic prey.

Otolith shape variation provides a marker of stock origin for north Atlantic bluefin tuna (Thunnus thynnus)

Two stocks of bluefin tuna (Thunnus thynnus) inhabit the north Atlantic; the western and eastern stocks spawn in the Gulf of Mexico and the Mediterranean Sea respectively. Trans-Atlantic movements occur outside spawning time whereas natal homing maintains stock structure. Commercial fisheries may exploit a mixed assemblage of both stocks. The incorporation of mixing rates into stock assessment is precluded by uncertainties surrounding stock discrimination. Otolith shape descriptors were used to characterise western and eastern stocks of Atlantic bluefin tuna in the present study and to estimate stock composition in catches of unknown origin. Otolith shape varied with length and between locations and years. Within a restricted size range (200–297-cm fork length (FL)) the two stocks were distinguished with an accuracy of 83%. Bayesian stock mixture analysis indicated that samples from the east Atlantic and Mediterranean were predominantly of eastern origin. The proportion assigned to the eastern stock showed slight spatial variation; however, overlapping 95% credible intervals indicated no significant difference (200–297cm FL: central Atlantic, 73–100%; Straits of Gibraltar, 73–100%; Morocco, 50–99%; Portugal 64–100%). Otolith shape could be used in combination with other population markers to improve the accuracy of mixing rate estimates for Atlantic bluefin tuna.

FIN-RAY COUNT VARIATION IN 0-GROUP FLATFISH: PLAICE ( PLEURONECTES PLATESSA (L.)) AND FLOUNDER ( PLATICHTHYS FLESUS L.) ON THE WEST COAST OF IRELAND

During the autumns of 2005 and 2006, 0-group plaice (Pleuronectes platessa (Linnaeus)) and flounder (Platichthys flesus Linnaeus) were collected from beaches in Galway and Kerry on the west coast of Ireland by beach seining and push netting. Characteristics used to identify adult flatfish were not discernible in these juveniles, and fin-ray counts were used to differentiate between the species. The dorsal, anal and caudal rays of 325 plaice and 116 flounder were counted and plotted, resulting in a clear separation between the two species. Thus, fin-ray counts may be used to reliably separate these two species on the west coast of Ireland. The ranges observed for both species lie within those previously reported. Analysis of fin-ray counts for both plaice and flounder showed no significant difference between the two regions studied. However, for plaice, a significant difference in dorsal fin-ray numbers was observed between the Galway beaches. No evidence of plaice/flounder hybrids, as identified by intermediate ray counts, was observed. There was no relationship between the numbers of dorsal and anal fin rays for plaice. However, a positive relationship was found between the numbers of dorsal and anal rays for flounder.

The role of wind-forcing in the distribution of larval fish in Galway Bay, Ireland

The ichthyoplankton of Galway Bay was sampled over the spring and summer of 2007 and 2008 to determine what environmental factors influenced the distribution of larval and early juvenile fish. A total of 549 fish representing 27 taxa were caught. Catches decreased throughout each sampling season, and were generally poor in 2007. Catches were numerically dominated by sprat ( Sprattus sprattus ), dab ( Limanda limanda ), sand eel ( Hyperoplus immaculatus ) and whiting ( Merlangius merlangus ). Environmental factors driving distribution of fish were modelled using a binomial generalized linear model. The strength and direction of wind in the five days preceding sampling was the only significant environmental factor. Sustained onshore winds increased the probability of encountering larval fish in the areas sampled. The rainfall, tidal state, tow depth and wind conditions during sampling were not significant. Among the parameters measured it appears that onshore winds sufficiently strong to overcome the residual circulation are the main physical driver for the distribution of larval fish in Galway Bay.

Gbm.auto: A software tool to simplify spatial modelling and Marine Protected Area planning

Boosted Regression Trees. Excellent for data-poor spatial management but hard to use Marine resource managers and scientists often advocate spatial approaches to manage data-poor species. Existing spatial prediction and management techniques are either insufficiently robust, struggle with sparse input data, or make suboptimal use of multiple explanatory variables. Boosted Regression Trees feature excellent performance and are well suited to modelling the distribution of data-limited species, but are extremely complicated and time-consuming to learn and use, hindering access for a wide potential user base and therefore limiting uptake and usage. BRTs automated and simplified for accessible general use with rich feature set We have built a software suite in R which integrates pre-existing functions with new tailor-made functions to automate the processing and predictive mapping of species abundance data: by automating and greatly simplifying Boosted Regression Tree spatial modelling, the gbm.auto R package suite makes this powerful statistical modelling technique more accessible to potential users in the ecological and modelling communities. The package and its documentation allow the user to generate maps of predicted abundance, visualise the representativeness of those abundance maps and to plot the relative influence of explanatory variables and their relationship to the response variables. Databases of the processed model objects and a report explaining all the steps taken within the model are also generated. The package includes a previously unavailable Decision Support Tool which combines estimated escapement biomass (the percentage of an exploited population which must be retained each year to conserve it) with the predicted abundance maps to generate maps showing the location and size of habitat that should be protected to conserve the target stocks (candidate MPAs), based on stakeholder priorities, such as the minimisation of fishing effort displacement. Gbm.auto for management in various settings By bridging the gap between advanced statistical methods for species distribution modelling and conservation science, management and policy, these tools can allow improved spatial abundance predictions, and therefore better management, decision-making, and conservation. Although this package was built to support spatial management of a data-limited marine elasmobranch fishery, it should be equally applicable to spatial abundance modelling, area protection, and stakeholder engagement in various scenarios.

Towards a flexible Decision Support Tool for MSY-based Marine Protected Area design for skates and rays

Original Article Towards a flexible Decision Support Tool for MSY-based Marine Protected Area design for skates and rays Simon Dedman,* Rick Officer, Deirdre Brophy, Maurice Clarke, and David G. Reid Marine and Freshwater Research Centre, Galway-Mayo Institute of Technology, Galway, Ireland Marine Institute, Rinville, Oranmore, Co, Galway, Ireland *Corresponding author: tel: þ1 415 944 7258; email: simon.dedman@research.gmit.ie

The timing of early life events and growth rate estimates of age-0 year group brill Scophthalmus rhombus along the west coast of Ireland.

The timing of spawning and hatching, larval durations and growth exhibited by juvenile brill Scophthalmus rhombus captured along the Irish west coast were estimated using otolith microstructure analysis. Scophthalmus rhombus were estimated to have hatched between February and May, with fish settling onto nursery grounds between March and June. Fish collected later on in the season exhibited higher otolith growth rates in comparison to earlier collected fish. This is the first study to describe the early life history of a commercially valuable but understudied flatfish species.