Although frequently suggested as a goal for ecosystem-based fisheries management, incorporating ecosystem information into fisheries stock assessments has proven challenging. The uncertainty of input data, coupled with the structural uncertainty of complex multi-species models, currently makes the use of absolute values from such models contentious for short-term single-species fisheries management advice. Here, we propose a different approach where the standard assessment methodologies can be enhanced using ecosystem model derived information. Using a case study of the Irish Sea, we illustrate how stock-specific ecosystem indicators can be used to set an ecosystem-based fishing mortality reference point (F ECO ) within the “Pretty Good Yield” ranges for fishing mortality which form the present precautionary approach adopted in Europe by the International Council for the Exploration of the Sea (ICES). We propose that this new target, F ECO , can be used to scale fishing mortality down when the ecosystem conditions for the stock are poor and up when conditions are good. This approach provides a streamlined quantitative way of incorporating ecosystem information into catch advice and provides an opportunity to operationalize ecosystem models and empirical indicators, while retaining the integrity of current assessment models and the F MSY -based advice process.

Aim: Invasive species are of increasing global concern. Nevertheless, the mechanisms driving further distribution after the initial establishment of non‐native species remain largely unresolved, especially in marine systems. Ocean currents can be a major driver governing range occupancy, but this has not been accounted for in most invasion ecology studies so far. We investigate how well initial establishment areas are interconnected to later occupancy regions to test for the potential role of ocean currents driving secondary spread dynamics in order to infer invasion corridors and the source–sink dynamics of a non‐native holoplanktonic biological probe species on a continental scale. Location: Western Eurasia. Time period: 1980s–2016. Major taxa studied: ‘Comb jelly’ Mnemiopsis leidyi. Methods: Based on 12,400 geo‐referenced occurrence data, we reconstruct the invasion history of M. leidyi in western Eurasia. We model ocean currents and calculate their stability to match the temporal and spatial spread dynamics with large‐scale connectivity patterns via ocean currents. Additionally, genetic markers are used to test the predicted connectivity between subpopulations. Results: Ocean currents can explain secondary spread dynamics, matching observed range expansions and the timing of first occurrence of our holoplanktonic non‐native biological probe species, leading to invasion corridors in western Eurasia. In northern Europe, regional extinctions after cold winters were followed by rapid recolonizations at a speed of up to 2,000 km per season. Source areas hosting year‐round populations in highly interconnected regions can re‐seed genotypes over large distances after local extinctions. Main conclusions: Although the release of ballast water from container ships may contribute to the dispersal of non‐native species, our results highlight the importance of ocean currents driving secondary spread dynamics. Highly interconnected areas hosting invasive species are crucial for secondary spread dynamics on a continental scale. Invasion risk assessments should consider large‐scale connectivity patterns and the potential source regions of non‐native marine species.

How climatic variability and anthropogenic pressures interact to influence recruitment is a key factor in achieving sustainable resource management. However, the combined effects of these pressures can make it difficult to detect non-stationary interactions or shifts in the relationships with recruitment. Here we examine the links between climate and Irish Sea cod recruitment during a period of declining spawning stock biomass (SSB). Specifically, we test for a shift in the relationship between recruitment, SSB and climate by comparing an additive (generalized additive model, GAM) and non-additive threshold model (TGAM). The relationship between recruitment success, SSB and the climatic driver, sea surface temperature, was best described by the TGAM, with a threshold identified between recruitment and SSB at approximately 7900 t. The analysis suggests a threshold shift in the relationship between recruitment and SSB in Irish Sea cod, with cod recruitment being more sensitive to climatic variability during the recent low SSB regime.

Monitoring the abundance and distribution of taxa is essential to assess their contribution to ecosystem processes. For marine taxa that are difficult to study or have long been perceived of little ecological importance, quantitative information is often lacking. This is the case for jellyfish (medusae and other gelatinous plankton). In the present work, 4 years of scyphomedusae by-catch data from the 2007-2010 Irish Sea juvenile gadoid fish survey were analysed with three main objectives: (1) to provide quantitative and spatially-explicit species-specific biomass data, for a region known to have an increasing trend in jellyfish abundance; (2) to investigate whether year-to-year changes in catch-biomass are due to changes in the numbers or in the size of medusa (assessed as the mean mass per individual), and (3) to determine whether inter-annual variation patterns are consistent between species and water masses. Scyphomedusae were present in 97% of samples (N = 306). Their overall annual median catch-biomass ranged from 0.19 to 0.92 g m(-3) (or 8.6 to 42.4 g m(-2)). Aurelia aurita and Cyanea spp. (Cyanea lamarckii and Cyanea capillata) made up 77.7% and 21.5% of the total catch-biomass respectively, but species contributions varied greatly between sub-regions and years. No consistent pattern was detected between the distribution and inter-annual variations of the two genera, and contrasting inter-annual patterns emerged when considering abundance either as biomass or as density. Significantly, A. aurita medusae were heavier in stratified than in mixed waters, which we hypothesize may be linked to differences in timing and yield of primary and secondary productions between water masses. These results show the vulnerability of time-series from bycatch datasets to phenological changes and highlight the importance of taking species- and population-specific distribution patterns into account when integrating jellyfish into ecosystem models. (C) 2014 Elsevier Ltd. All rights reserved.

The annual egg production (AEP) of cod (Gadus morhua), plaice (Pleuronectes platessa) and haddock (Melanogrammus aeglefinus) in the Irish Sea during the 2008 spawning season was estimated using generalized additive models (GAMS that further developed previous applications of the annual egg production method to Irish Sea stocks by including 2-D spatial smoothing, automatic selection of the degree of smoothing and precision estimates. The estimates of AEP from the GAMs were compared to those from a stratified mean method and the sensitivity of the estimates to different model specifications, outliers, boundary effects and prediction period was assessed. The influence of outlying large observations was notable but overall the estimates of AEP were robust to the factors studied, with effect sizes comparable to the estimates' coefficients of variation. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Climate change and overfishing may lead to ecosystem instability and may benefit nonexploited organisms such as jellyfish. In the Irish Sea, an increase in jellyfish abundance was evident (r2=0.29, P=0.03) in a 16-year time-series (1994-2009) collected during juvenile fish surveys. Jellyfish abundance correlated positively with sea surface temperature (SST) over the preceding 18 months (r=0.65, p(ACF)< 0.001) and copepod biomass in the previous year (r=0.56, p(ACF)=0.03) and negatively with spring (February-May) precipitation (r=-0.57, p(ACF)=0.02). Principal components regression indicated that climatic indices explained 68% of the interannual variability in jellyfish abundance (P=0.003), where the components were based on the North Atlantic Oscillation Index, SST and precipitation. The frequency of cnidarian material present in Continuous Plankton Recorder (CPR) samples has also increased since 1970, with a period of frequent outbreaks between 1982 and 1991. Before this period, the herring stock in the northern Irish Sea declined rapidly to a low level, potentially stimulating structural change in the ecosystem. In 1985, there was a step decrease in CPR copepod biomass and in 1989, a step increase in the phytoplankton colour index, suggesting a cascading regime shift during the 1980s. Subsequent overexploitation of gadids, coupled with warm temperatures and the poor recruitment of cod, led to the rapid decline in cod biomass from 1990. While the biomass of sprat has decreased in the last decade, the herring stock has recovered partially. Reductions in demersal fishing pressure since 2000, intended to stimulate cod recovery, appear to have facilitated further rises in haddock biomass. Since the 1980s regime shift, sea temperatures have increased, the fish community has altered and jellyfish abundance has risen such that jellyfish and haddock may now play an increasingly important role in the ecosystem.

There is concern that overfishing may lead to a proliferation of jellyfish through a process known as fishing down the food web. However, there has been no global synthesis of patterns of gelatinous zooplankton biomass (GZB), an important first step in determining any future trends. A meta-analysis of epipelagic-GZB patterns was undertaken, encompassing 58 locations on a global scale, and spanning the years 1967–2009. Epipelagic-GZB decreased strongly with increasing total water column depth (r2 = 0.543, p < 0.001, n = 58): in shallow (<50 m) coastal waters, epipelagic-GZB was typically 742× the levels in deep ocean (>2,000 m) sites. However, the ratio of GZB to primary productivity showed high values across a range of depths, i.e. this measure of the relative abundance of gelatinous zooplankton did not co-vary with depth.

An assessment of Irish Sea (ICES Division VIIa, North) herring using a two-stage biomass model was undertaken given lack of internal consistency in the survey age-disaggregated index. The model constrains recruitment variability and reduces the number of catchability parameters to address concerns of overparameterization. An extra parameter was incorporated to estimate the component of the variance resulting from the mixing of Celtic Sea and Irish Sea juvenile herring in the survey area. This additional variance, although imprecise, represented a large part of the total variance associated with the recruit survey data. More information on the variability of Irish Sea herring recruitment is required to estimate additional variance in the context of the two-stage biomass model presented. Limitations in the age-composition data and potential interannual variation in the selection pattern of the fishery favour an assessment method, such as the two-stage biomass method, which is based on a simplified age structure and does not require separability assumptions.

Inter-annual variability in settlement and recruitment of O-group dab Limanda limanda L. was investigated between 1996 and 2003 on Port Erin Bay, Isle of Man. The annual settlement index of post larvae dab (ind <= 20 mm) varied considerably between years with a corresponding coefficient of variation of 97%. The timing of the settlement of dab was associated with metamorphosis and varied significantly with temporal variation in estimated spawning activity. Inter-annual variation in the numbers of settling post larvae was strongly associated with stage one larvae abundance indices from adjacent offshore waters. O-group abundance indices were significantly correlated with the index of settlement abundance, but not however, with larvae indices. These relationships suggest that the strength of the recruiting year-class of O-group dab in Port Erin Bay is established early in life, during or before the pelagic phase, in the waters west of the Isle of Man. Inter-annual variability in O-group mortality rates suggests a possible density-dependent process operating during the nursery ground phase. (c) 2007 Elsevier B.V. All rights reserved.