No abstract

Oil spills are extreme environmental perturbations (i.e. ecological catastrophes) affecting marine food webs and especially top predators, in which effects are likely amplified. As such, seabirds suffer from direct mortality and food depletion, with potentially important consequences for the population growth rate and probability of extinction. However, little is known about the effects of sex-skewed mortality (due to sex spatio-temporal differences in at-sea distribution) in seabird population dynamics. We analyzed the mortality of European shags Phalacrocorax aristotelis after the Prestige oil spill and its effects on breeding colonies in Galicia (southwest North Atlantic). Most adults found dead were females (85%). The year after the spill, Monte Carlo simulations of population trajectories predicted a reduction of 11% in the number of breeding pairs when skewed mortality was considered, and a lower rate (8%) when assuming random sex distribution of adult mortality. The further reduction predicted with the sex-biased mortality was probably the result of unmated adults unable to reproduce. This difference, although slight, is a concern for conservation owing that the colonies studied were already showing a 5% annual decline due to other factors also related to human activities.

The study is an attempt to evaluate the feasibility of intensive tench culture using non-specific diets as a preliminary step to check the acclimatization of the species under intensive rearing systems. Five-month-old juvenile tench were reared in recirculating systems at mean water temperatures of 22°C for 75 days. Fish fed with four different commercial diets (trout starter, trout first feeding, sea-bass and eel), showed significantly higher final weights than the fish fed either eel or sea-bass diets. Initial weight for all treatments was 2.3 ± 0.53 g. Final weight for the commercial diet groups was 3.56 ± 0.4 g, compared with the remaining groups that reached 2.09 ± 0.47 g (P < 0.05). Significantly higher survival rates were observed in the eel and sea-bass groups (84.7 and 51.5%, respectively) than in either of the trout diet groups (38%). Specific growth rates (1.26 vs -0.18) and condition factor (1.26 vs 0.93) were also higher than those fed with salmonid diets (P < 0.05). Results obtained in this study indicate that regardless of the speciesÕ slow growth, when compared with other cyprinids, final growth rates and survival of tench fed exclusively on sea-bass or eel diets can be considered satisfactory. It must be pointed out that these promising results were obtained at lower temperatures than previous studies of tench in culture systems. The use of belt feeders did not show improvement in growth compared with manually fed fish when trout diets were used.

:  Reintroduction of captive‐reared animals has become increasingly popular in recent decades as a conservation technique, but little is known of how demographic factors affect the success of reintroductions. We believe whether the increase in population persistence associated with reintroduction is sufficient to warrant the cost of rearing and relocating individuals should be considered as well. We examined the trade‐off between population persistence and financial cost of a reintroduction program for Crested Coots (Fulica cristata). This species was nearly extirpated from southern Europe due to unsustainable levels of hunting and reduction in amount and quality of habitat. We used a stochastic, stage‐based, single‐sex, metapopulation model with site‐specific parameters to examine the demographic effects of releasing juveniles or adults in each population for a range of durations. We parameterized the model with data from an unsuccessful reintroduction program in which juvenile captive‐bred Crested Coots were released between 2000 and 2009. Using economic data from the captive‐breeding program, we also determined whether the strategy that maximized abundance coincided with the least expensive strategy. Releasing adults resulted in slightly larger final abundance than the release of nonreproductive juveniles. Both strategies were equally poor in achieving a viable metapopulation, but releasing adults was 2–4 times more expensive than releasing juveniles. To obtain a metapopulation that would be viable for 30 years, fecundity in the wild would need to increase to the values observed in captivity and juvenile survival would need to increase to almost unity. We suggest that the most likely way to increase these vital rates is by increasing habitat quality at release sites.

Ecological traps, in combination with other factors, can reduce population sizes and even lead to local extinction. Here, we present the first evidence that hunting sites can act as ecological traps for waterfowl: wintering common coots Fulica atra were preferentially attracted to hunting sites in southern European wetlands, and showed decreasing population trends in these sites, compared to non-hunting sites. We demonstrate that the supply of energy-rich supplementary food (grain) triggered the trap. We also show that a behavioural mechanism, acting as an evolutionary load (the tendency to form mixed coot flocks during the winter), decreased population size of a threatened waterfowl species, the crested coot F. cristata. Our results suggest the use of precautionary policies regarding supplementary food in coot and associated diving-duck species, if negative conservation impacts are to be avoided.