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Introduction 284Importance of spawning time to survival 284Inter-annual variation in spawning time 287Spawning variability linked to the environment 287Spawning variability linked to stock demography 288Fishing-induced changes in spawning time 290Abstract Demography can have a significant effect on reproductive timing and the magnitude of such an effect can be comparable to environmentally induced variability. This effect arises because the individuals of many fish species spawn progressively earlier within a season and may produce more egg batches over a longer period as they get older, thus extending their lifetime spawning duration. Inter-annual variation in spawning time is a critical factor in reproductive success because it affects the early environmental conditions experienced by progeny and the period they have to complete phases of development. By reducing the average lifetime spawning duration within a fish stock, fishing pressure could be increasing the variability in reproductive success and reducing long-term stock reproductive potential. Empirical estimates of selection on birth date, from experiments and using otolith microstructure, demonstrate that there is considerable variation in selection on birth date both within a spawning season and between years. The few multi-year studies that have linked egg production with the survival of progeny to the juvenile stage further highlight the uncertainty that adults face in timing their spawning to optimize offspring survival. The production of many small batches of eggs over a long period of time within a season and over a lifetime is therefore likely to decrease variance and increase mean progeny survival. Quantifying this effect of demography on variability in survival requires a focus on lifetime reproductive success rather than year specific relationships between recruitment and stock reproductive potential. Modelling approaches are suggested that can better quantify the likely impact of changing spawning times on year-class strength and lifetime reproductive potential. The evidence presented strengthens the need to avoid fishing severely age truncated fish stocks.

In order to evaluate if marine protected areas (MPAs) can be expected to confer conservation benefits to large, mobile marine species it is important to assess their site fidelity and habitat ranging patterns. The flapper skate (Dipterus cf. intermedia) is a large, threatened elasmobranch for which MPAs are being considered on the west coast of Scotland. To inform MPA establishment, a multiannual mark–recapture programme, a year‐long static array acoustic study and an archival tagging study of flapper skate were undertaken. Capture–mark–recapture (CMR) modelling of 280 individuals indicated significant heterogeneity in the recapture rate suggesting the region contained a mixture of site‐attached (resident) and vagrant (transient) individuals. The analysis estimated that 100–400 resident individuals were present in the study area. The number of transient individuals was estimated at around 25% of all those tagged. The average annual survival probability of resident individuals was estimated to be 0.64. The acoustic study of 20 individuals demonstrated that over half were resident on a day‐by‐day basis for months at a time. Three individuals were detected over the entire year. Two individuals moved away immediately after tagging and over half moved out of the study area in the springtime. Three data storage tags revealed that resident individuals utilized most of the available depth habitat (6–205 m) in the area and occasionally visited deeper areas outside the immediate study area. The results indicate that the establishment of a MPA would confer conservation benefits to flapper skate in the area. Management should consider all depths in the study area, areas beyond the study site, and alternative conservation measures such as technical gear measures for fisheries. This study has implications for the conservation and management of similar long‐lived, mobile marine species.© 2014 Crown copyright. Aquatic Conservation: Marine and Freshwater Ecosystems © 2014 John Wiley & Sons, Ltd.

The recent decline in many fish stocks has been accompanied by marked changes in age at maturity. However, there is little information on whether other components of reproductive investment have changed and the relative roles of phenotypic plasticity or genetic selection in such change. This study explored how reproductive investment in cod Gadus morhua from different regions around Scotland has changed between a period of high (1969, 1970) and low (2002, 2003) spawning-stock size. Maturity ogives indicated that inshore North Sea cod now mature at a smaller size and younger age than they did around 1970. The relationship between potential fecundity and size indicated that cod in the inshore region are now more fecund than 30 yr ago. Cod from the inshore region of the North Sea now have a higher fecundity at a given size and age than cod from the offshore region and the west of Scotland. There was no such spatial trend around 1970. Similarly, whilst the relative fecundity of cod in recent times is positively correlated with age, no such relationship was evident in 1969 and 1970. Nutritional influences on maturity and fecundity, particularly liver condition, were also evident from the recent study. However, the temporal and spatial differences in fecundity-size relationships were not consistent with a change in growth conditions, as there has been a significant decrease in body condition in recent times. Our findings regarding the temporal change in reproductive investment in the inshore North Sea region appear consistent with genotypic changes in life-history traits predicted to arise from intense periods of size-selective mortality.

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