Temporal and spatial variation in adult and juvenile mobile fauna associated with natural and artificial coastal habitats

Coastal habitats are important for commercially exploited and protected species of fish and larger mobile invertebrates. The addition of artificial structures within the marine environment has the potential to alter the connectivity between habitats and to affect metapopulations of a region. Baited remote underwater videos (BRUV) were used to investigate the spatial and seasonal variation in abundance of adult and juvenile mobile species associated with subtidal natural and artificial habitats within Poole Bay on the south coast of England in 2019. Metrics included the relative maximum abundance (MaxN), number of species seen (S), assemblage structure and size range of fish. Higher values of MaxN and S were recorded on artificial structures in the spring and early summer; however, this pattern was reversed by mid-summer and early autumn when more fish were recorded on the natural reefs. Yet overall differences in MaxN and S between habitats were not significant. Differences in assemblage composition between habitats varied monthly, but this was mostly driven by particular sites. Although most fish observed were juveniles, there were some seasonal differences in the size of fish using natural and artificial sites, especially bib (Trisopterus luscus), black bream (Spondyliosoma cantharus), bass (Dicentrarchus labrax) and pollack (Pollachius pollachius). The artificial habitats in this region appeared to be important in certain months, so temporal studies of this type need to be incorporated within surveys, particularly those in proximity to protected areas.

Spatio-temporal resolution of spawning and larval nursery habitats using otolith microchemistry is element dependent

Otolith chemistry is frequently employed in the reconstruction of fish environmental histories. While some elements have been strongly correlated with environmental factors (e.g. salinity, temperature, water chemistry), others may not indicate exogenous factors and simply add endogenous variability to a data set. Several commonly assessed elements were previously identified as being only present in the proteinaceous fraction of endolymph from black bream Acanthopagrus butcheri, suggesting that the choice of elements in otolith multi-elemental fingerprinting could influence their utility as natural environmental markers. To test this hypothesis, we performed several cluster analyses based on different sets of trace element data extracted from both the core and larval region of otoliths of juvenile black bream. We clustered in 3 different ways: (1) all elements analysed; (2) elements identified as being primarily in the salt fraction of the endolymph (i.e. inorganic); and (3) elements identified as being associated with the protein fraction of the endolymph. We subsequently assessed the power of the resulting clusters to resolve cohort identity and/or collection location based on differences in otolith chemistry using multinomial logistic regression. Our results indicate that clustering based solely on salt-fraction elements is best for resolving spatio-temporal variability in spawning sources and larval nursery habitats of black bream.

Consequences of catch-and-release angling for black bream Spondyliosoma cantharus, during the parental care period: implications for management

Black sea bream Spondyliosoma cantharus is highly valued for its sporting and eating qualities. Due to its inshore spawning aggregations and male nest guarding behaviors, it is considered vulnerable to over-exploitation via recreational angling. Accordingly, greater uptake of the practice of catch-and-release (C&R) may provide some potential to limit the effects of angling on populations. Thus, the consequences of C&R for 40 S. cantharus (mean length 306 ± 10 mm) were assessed. Fish were sampled following their capture from charter boats by recreational anglers with varying levels of skill and experience. Of these fish, 17% were deeply hooked (e.g. in esophagus) and considered at high risk of post-release mortality (PRM). Blood lactate levels ranged between 0.40 and 2.60 mmol l − 1 (mean ± SE: 1.25 ± 0.09) and were significantly and positively correlated with fight time. Reflex impairments were observed in 32% of the catch, also suggesting an elevated probability of PRM. Hook damage was the only significant predictor of reflex impairment. The dominance of males (89%) across the catches highlighted the potential for additional indirect impacts of angling via the predation of eggs by conspecifics in the vacated nests of captured males. These results are discussed within the context of post-release performance of individual S. cantharus, the potential for C&R to limit impact at the population level and a need to consider future regulation of the fishery to ensure sustainability of stocks.