Resolving climate impacts on fish stocks

Evidence is accumulating that the increase in CO2 is affecting the global climate, with far‐reaching implications for biological processes and ecosystem services. Recent studies suggest that there is evidence for a northward shift in the distributional range of fish species, but the mechanisms underlying these changes remain uncertain. Hence, it is largely unknown whether the observed distributional shifts are caused by a relocation of the spawning and feeding grounds, a change in the local survival of fish, or immigration into new habitats

A feeding guild indicator to assess environmental change impacts on marine ecosystem structure and functioning.

Integrating food web indicators into ecological status assessments is central to developing effective management measures that can improve degraded ecosystems. This is because they can reveal how ecosystems respond to environmental change that cannot be inferred from studying habitat, species or assemblages alone. However, the substantial investment required to monitor food webs (e.g. via stomach contents analysis) and the lack of internationally agreed approaches to assessing them has hampered their development. Inventories of trophic interactions have been collated world-wide and across biomes, and can be applied to infer food web structure and energy flow. Here, we compile a new marine dataset containing 8,092 unique predator–prey interactions from 415,294 fish stomachs. We demonstrate how feeding guilds (i.e. groupings based on diet and life stage) could be defined systematically and in a way that is conducive to their application internationally across ecosystems; and apply them to the North Sea fish assemblage to demonstrate their responsiveness to anthropogenic pressures. We found evidence for seven distinct feeding guilds. Differences between guilds were related to predator size, which positively correlated with piscivory, phylogeny, with multiple size classes of a species often in the same guild, and habitat, as pelagic, benthic and shallow-coastal foraging was apparent. Guild biomasses were largely consistent through time at the North Sea-level and spatially aggregated at the regional level with change relating to changes in resource availability, temperature, fishing and the biomass of other guilds. This suggests that fish biomass was partitioned across broad feeding and environmental niches, and changes over time were governed partly by guild carrying capacities, but also by a combination of covariates with contrasting patterns of change. Management of the North Sea ecosystem could therefore be adaptive and focused towards specific guilds and pressures in a given area. Synthesis and applications. We propose a food web indicator which has been explicitly called for to inform policy via food web status assessment as part of the European Union's Marine Strategy Framework Directive and the indicator toolkit supporting The Convention for the Protection of the Marine Environment of the North-East Atlantic (the ‘OSPAR Convention’)

Quantifying heterogeneous responses of fish community size structure using novel combined statistical techniques

To understand changes in ecosystems, the appropriate scale at which to study them must be determined. Large marine ecosystems (LMEs) cover thousands of square kilometres and are a useful classification scheme for ecosystem monitoring and assessment. However, averaging across LMEs may obscure intricate dynamics within. The purpose of this study is to mathematically determine local and regional patterns of ecological change within an LME using empirical orthogonal functions (EOFs). After using EOFs to define regions with distinct patterns of change, a statistical model originating from control theory is applied (Nonlinear AutoRegressive Moving Average with eXogenous input – NARMAX) to assess potential drivers of change within these regions. We have selected spatial data sets (0.5° latitude × 1°longitude) of fish abundance from North Sea fisheries research surveys (spanning 1980–2008) as well as of temperature, oxygen, net primary production and a fishing pressure proxy, to which we apply the EOF and NARMAX methods. Two regions showed significant changes since 1980: the central North Sea displayed a decrease in community size structure which the NARMAX model suggested was linked to changes in fishing; and the Norwegian trench region displayed an increase in community size structure which, as indicated by NARMAX results, was primarily linked to changes in sea-bottom temperature. These regions were compared to an area of no change along the eastern Scottish coast where the model determined the community size structure was most strongly associated to net primary production. This study highlights the multifaceted effects of environmental change and fishing pressures in different regions of the North Sea. Furthermore, by highlighting this spatial heterogeneity in community size structure change, important local spatial dynamics are often overlooked when the North Sea is considered as a broad-scale, homogeneous ecosystem (as normally is the case within the political Marine Strategy Framework Directive)

Planktivorous fishes Links between the Mediterranean littoral and pelagic

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Fish

In the following chapter we consider changes that have been observed in the distribution of fish species over the past century, we look at how fish growth rate and larval survival has been influenced by changing climate and we consider the role played by fish in wider marine food-webs (as prey or predators). We then consider what might happen to marine fish in the future, in the face of predicted temperature rises, extreme weather events and ocean acidification. We examine gaps in the current knowledge base and consider some of the socio-economic consequences that might arise as a result of climate impacts on marine fish

Fisheries

‘What is already happening’ There is evidence that location where high catches of cod, haddock, plaice and sole occur, as reported by UK commercial fishing vessels, seems to have shifted over the past 80-90 years. Climate change may be a factor but fishing and habitat modification have also had an important effect. Shifting distributions of fish, partly as a result of climate change are having an impact on the effectiveness of some fishery closure areas and on the apportionment of fishery resources between neighbouring countries (e.g. mackerel in the north-east Atlantic). New fisheries have developed for a number of warmer-water species including seabass, red mullet, anchovy and squid. The stock biomass of seabass in the Western Channel has quadrupled since 1985 from 500t, to over 2000t in 2004/5. ‘What could happen in the future’. As a result of climate change, the UK as a whole is expected to benefit from slightly (i.e. +1-2% compared to present) higher fishery yields by 2050, although regions such as the Irish Sea and English Channel may see a reduction. Models suggest that cod stocks in the Celtic and Irish Seas may to disappear completely by 2100, while those in the North Sea are expected to decline. Climate change has been ‗eroding‘ the maximum sustainable yield of cod in the North Sea by around 32,000t per decade. Very little work has been carried out on the social and economic implications of climate change for the UK fishing industry, however calculations suggest that consequences will be significant only for fishery-dependent communities in the North of Scotland and in the southwest England. Ocean acidification may pose a significant threat to the UK shellfish industry, but more research is required

Cod

Reviews the literature on the impact of climate change and variability on fish and shellfish populations ICES Cooperative Research Report No. 301 “Resolving climate impacts on fish stocks” has arrived in all its 385‐page splendour. As with all ICES publications, it is freely available online here or can be ordered from ICES in a hard‐copy version. The report states, “Climate change will affect fishery resources and challenge managers to develop sustainable exploitation strategies. Knowledge of the effects of climate on fishery resources is still fragmentary”. The report presents an overview of the literature on the impact of climate change and variability on fish and shellfish populations in the Northeast Atlantic and the Mediterranean and Black seas, focusing on the processes that govern the response of fish and shellfish to climate change. Results have appeared in the reports of various ICES working and study groups and are collected for the first time in this CRR. One of the report’s editors, Adriaan Rijnsdorp, explains its significance: “For me, the most important aspect is that we brought together a large group of scientists, covering a broad range of expertise: physical oceanography, biophysical modelling, marine ecosystem dynamics, ecophysiology, zooplankton ecology, fish ecology, and fishery science. “We took a bottom–up approach, trying to review the main processes that determine how climate will impact fish populations, formulate a number of a priori working hypotheses, and analyse critically the possible effect of climate on the observed dynamics of a selection of well studied fish and shellfish species”. The work was part of a research project carried out by nine European research institutes and funded by theSixth Framework Programme (FP6) of the European Union (RECLAIM, Contract 044133) and the national programmes

Fish and fisheries

Abundances of warm-water fish species (e.g. red mullet, john dory, triggerfish) have increased in UK waters during recent decades, while many coldwater species have experienced declines. There has been a massive influx of snake pipefish to UK waters since 2004, but unusual fish occurrences or sudden proliferations of species cannot definitively be attributed to climate change. A number of commercial and non-commercial fish species are suggested to have exhibited shifts in mean latitude over the past 25 years. Poor ‘recruitment’ in traditional fishery target species such as cod, plaice and herring may be related to a shift in the composition of zooplankton, which are a key prey for developing larvae. In some parts of the southern North Sea, cold-water species, such as cod and eelpout, have been shown to experience metabolic stress during warm years, as evidenced by slower growth rates and difficulties in supplying oxygen to body tissues. Climate change will have far-reaching impacts on the dynamics of fish populations, however knowledge of underlying mechanisms is rather limited, especially in non-commercial species. Excessive fishing pressure has caused fish populations to become more vulnerable to short-term natural climate variability by removing the oldest individuals, and making such populations less able to ‘buffer’ against occasional poor year classes. In the short term, climate change will have little influence on fish stock recovery, which depends instead upon reducing fishing effort to allow existing year classes to survive to maturity. Climate-related shifts in species distribution, behavior and depth preference may affect the ‘catchability’ of certain stocks to fishing fleets. Long-term climate change may affect the overall productivity of fish stocks in a given area. Some species may be adversely affected leading to reductions in sustainable yield whilst others, for example seabass, red mullet and John Dory, may be positively affected leading to enhanced fishing opportunities

Use of morphological characteristics to define functional groups of predatory fishes in the celtic sea

An ecomorphological method was developed, with a focus on predation functions, to define functional groups in the Celtic Sea fish community. Eleven functional traits, measured for 930 individuals from 33 species, led to 11 functional groups. Membership of functional groups was linked to body size and taxonomy. For seven species, there were ontogenetic changes in group membership. When diet composition, expressed as the proportions of different prey types recorded in stomachs, was compared among functional groups, morphology-based predictions accounted for 28-56% of the interindividual variance in prey type. This was larger than the 12-24% of variance that could be explained solely on the basis of body size