A. D. Nunn

Is there evidence for a shift in fish growth and recruitment success linked to climate change

This study investigated whether a putative shift in climate regime in the North Atlantic in the 1990s coincided with changes in the growth and recruitment of roach Rutilus rutilus in the north-east of England. The relationships between R. rutilus growth and recruitment and the environment were significantly different before and after the putative shift in climate regime. Water temperature, river discharge, growth, recruitment success and the Gulf Stream Index co-varied until the late 1990s, indicating a gradual progression between periods of warm-and-dry and cold-and-wet summers. Since the late 1990s, there has been an increased prevalence of warm-and-wet summers, and recruitment success has oscillated between extremes on an almost annual basis. The north wall (northern boundary) of the Gulf Stream has been undergoing a displacement south since the late 1990s, and the speed and amplitude of the change appears to support the hypothesis that there was a regime shift in the climate of the North Atlantic Ocean. It is possible that a continued displacement south of the north wall of the Gulf Stream will lead to further increases in river discharge, reductions in water temperature and reduced fish growth and recruitment success in the long term.

The diets and parasites of larval and 0+ juvenile twaite shad in the lower reaches and estuaries of the rivers Wye, Usk and Towy, UK

This study assessed the diets and parasites of larval and 0+ juvenile twaite shad Alosa fallax fallax in the lower reaches and estuaries of the rivers Wye, Usk and Towy, UK. There were significant differences between the diets of larvae and co-habiting 0+ juveniles, and of larvae and 0+ juveniles among sites, both within and among rivers. In the Wye and Usk, the diets of twaite shad larvae were dominated by chironomid larvae, whereas those in the Towy specialised upon cyclopoid copepods. The diets of 0+ juvenile twaite shad from freshwater (River Wye) were characterised by chironomid larvae, while estuarine (Towy Estuary) individuals specialised upon calanoid copepods. Parasites infecting 0+ twaite shad were Apiosoma sp. (Protozoa), Gyrodactylus sp. (Monogenea), Proleptinae (Nematoda) larvae, Pomphorhynchus laevis (Acanthocephala), Spinitectus sp. (Nematoda) larvae and Trichodina sp. (Protozoa). Over 60% of estuarine 0+ juvenile twaite shad were infected with Apiosoma sp., with maximal estimated loadings in excess of 3,000 parasites per fish. Other parasite taxa were generally present in only small numbers. There were no significant differences in the intensity of parasite infections among sites, or the condition of parasitised and non-parasitised 0+ twaite shad.

Causes and consequences of ontogenetic dietary shifts: a global synthesis using fish models: Ontogenetic dietary shifts

Ontogenetic dietary shifts (ODSs), the changes in diet utilisation occurring over the life span of an individual consumer, are widespread in the animal kingdom. Understanding ODSs provides fundamental insights into the biological and ecological processes that function at the individual, population and community levels, and is critical for the development and testing of hypotheses around key concepts in trophic theory on model organisms. Here, we synthesise historic and contemporary research on ODSs in fishes, and identify where further research is required. Numerous biotic and abiotic factors can directly or indirectly influence ODSs, but the most influential of these may vary spatially, temporally and interspecifically. Within the constraints imposed by prey availability, we identified competition and predation risk as the major drivers of ODSs in fishes. These drivers do not directly affect the trophic ontogeny of fishes, but may have an indirect effect on diet trajectories through ontogenetic changes in habitat use and concomitant changes in prey availability. The synthesis provides compelling evidence that ODSs can have profound ecological consequences for fish by, for example, enhancing individual growth and lifetime reproductive output or reducing the risk of mortality. ODSs may also influence food‐web dynamics and facilitate the coexistence of sympatric species through resource partitioning, but we currently lack a holistic understanding of the consequences of ODSs for population, community and ecosystem processes and functioning. Studies attempting to address these knowledge gaps have largely focused on theoretical approaches, but empirical research under natural conditions, including phylogenetic and evolutionary considerations, is required to test the concepts. Research focusing on inter‐individual variation in ontogenetic trajectories has also been limited, with the complex relationships between individual behaviour and environmental heterogeneity representing a particularly promising area for future research.