Mass mortality of short-tailed shearwaters in the south-eastern Bering Sea during summer 1997

During summer 1997, hundreds of thousands of emaciated short-tailed shearwaters ( Puffinus tenuirostris ) died in the south-eastern Bering Sea. Using strip transect methodology, we documented the distribution and abundance of short-tailed shearwaters during cruises conducted prior to, during, and after the die-off, as well as the distributions and abundances of floating carcasses. The distributions and abundances of short-tailed shearwaters in 1997 were similar to those found during the 1970s and early 1980s. In August–September 1997, we observed 163 floating shearwater carcasses, most of which were between St Paul Island and Nunivak Island. We estimated ≈ 190 000 carcasses were afloat in the study area, about 11% of the surveyed population. Between spring (June) and autumn (August/September), mean net body mass of shearwaters decreased by 19%, mean pectoral muscle mass decreased by 14%, and mean percentage body lipid content decreased by 46%, from 15.6% in spring to 8.4% in autumn. Compared with spring, short-tailed shearwater diets broadened in autumn 1997, to include, in addition to adult euphausiids Thysanoessa raschii, juveniles of T. inermis, T. raschii and T. spinifera, crab megalops, fish and squid. We discuss how the ecosystem anomalies in the south-eastern Bering Sea during spring and summer 1997 relate to the mortality event and suggest possible implications of long-term climate change for populations of apex predators in the south-eastern Bering Sea.     

The conservation status of Townsend's shearwater Puffinus auricularis auricularis

Townsend's shearwater (Puffinus auricularis auricularis) is an endangered seabird endemic to the Revillagigedo Archipelago. It nested on Socorro, Clarion, and San Benedicto Islands. It was extirpated by the Barcena volcano on San Benedicto in 1952, and there are no recent indications of nesting. Introduced mammals—pigs and rabbits—preyed on them and destroyed habitat at Clarion; shearwaters were extirpated by 1988, and no breeding attempts have been reported since. Our results confirm that Socorro holds the last breeding grounds. We found breeding colonies above 800 m and a minimum population of 1100 individuals. This represents a significant reduction in distribution and population size. Intensive cat predation at Socorro could potentially kill ca. 350 females per season, and sheep progressively destroy nesting areas. Population projections suggest that demographic instability could occur in less than 100 years under severe predation and habitat degradation. Only low predation rates would allow population persistence for more than 150 years in spite of a declining population. Thus, the immediate eradication of all introduced mammals is necessary to prevent the extinction of this seabird.     

Can an introduced predator trigger an evolutionary trap in a colonial seabird?

Animals use environmental cues, social information and behavioural decision-making rules moulded by natural selection to decide where to breed. We assessed whether the presence of an alien nest predator, the Black Rat (Rattus rattus) is used by a colonial seabird, the Cory’s shearwater (Calonectris diomedea), as an environmental cue in the selection of breeding sites. We compared potential habitat preference using quality of breeders and nest fidelity as response to nest predation between two sub-colonies with different habitat characteristics, breeding success and predation pressure. Quality of individuals was better in the predated habitat and birds did not perceive the presence of predators signalling differences in predation risk and in turn of breeding success. This failure of perception could be at two levels: in the selection of habitat for first breeding and in the breeding dispersal following a reproductive failure. Preference for the sub-colony with higher predation risk suggests the presence of an evolutionary trap. In fact, the introduction of alien predators probably transformed the behaviour of shearwaters in a maladaptive response due to a mismatch between the new environmental factors and their behavioural and evolutionary algorithms. This can be a common pattern in other species with little behavioural plasticity, evolved in stable environments free of predators.     

Modelling demography and extinction risk in the endangered Balearic shearwater

Several demographic parameters of Balearic shearwater (Puffinus mauretanicus) were estimated and used to model extinction probabilities for the species, which is an endemic seabird confined to a Mediterranean archipelago. Adult survival was analyzed through capture-recapture models at two colonies free of adult predators during 1997-2002. Extinction probabilities for the world breeding population were modelled using Monte Carlo simulations of population trajectories, introducing stochasticity both demographic and environmental. Adult survival estimate (0.780, SE=0.020, 95% Confidence Intervals: 0.739-0.816) was unusually low for a Procellariiform, suggesting that sources of mortality other than predators (e.g. fishing gears) also occur. A deterministic model showed a declining trend for the world breeding population (λ=0.952), and significantly less than 1. Population viability analysis showed that in the presence of environmental and demographic stochasticities, mean extinction time for the world population was estimated at 40.4 years (SE=0.2), and mean growth rate showed a 7.4% decrease per year. Demographic stochasticity played a more important role than environmental stochasticity in population growth rate.     

Characterizing seabird bycatch in the eastern Australian tuna and billfish pelagic longline fishery in relation to temporal,spatial and biological influences

• 1. Seabirds killed incidentally in Australia's eastern tuna and billfish (ETBF) longline fishery between September 2001 and June 2006 were examined to evaluate species composition and to relate, where possible, capture events to operational and environmental factors.
• 2. During this period 2.129 million hooks on 2202 shots were observed, and 369 birds were reported killed. The majority (78%) of these were flesh‐footed shearwaters (Puffinus carniepes), 53% of which were male and 44% female. Smaller numbers of medium to large sized albatrosses (Diomedeidae, predominantly female) and other shearwaters (Puffinus spp.) and petrels (Pterodroma spp.) dominated the remainder of the bycatch.
• 3. Of the 369 birds reported taken as bycatch, 280 were available for necropsy, and species identifications performed in situ by observers were assessed. While observer identifications were generally correct for common species, performance was poor for less common ones.
• 4. The geographical location (latitude) of shots, season, time of day at which shots were set, and bait type and life status (dead or alive) influenced the seabird bycatch rate. The majority of captures (87% overall) occurred between 30 and 35°S, with bycatch being lowest in winter, and remaining at similar levels across the other seasons.
• 5. The use of live fish bait was generally associated with increased captures of both seabirds overall, and flesh‐footed shearwaters in particular. Copyright © 2010 John Wiley & Sons, Ltd.

     

Effects of colony location and nekton abundance on the at-sea distribution of four seabird species

Although seabirds are locally superabundant in the vicinity of breeding colonies, abundance farther offshore is patchy in both space and time. The present study examines the fine-scale (i.e. 1 km unit) distribution and abundance of four seabird species as a function of distance from a breeding colony (for three of the four species) and nekton density determined hydroacoustically. We found that density of the breeding species was significantly associated with nekton density, after controlling for island effects. In addition, nekton density associated with foraging aggregations of seabirds was significantly higher than that under resting aggregations. These results provide some of the clearest evidence of seabird-nekton association, albeit on an extremely close spatial scale.     

Seabird‐trawling interactions: factors affecting species‐specific to regional community utilisation of fisheries waste

Bottom trawl fishing provides substantial amounts of normally unavailable demersal prey to seabirds (e.g., discards), affecting their life‐history traits and population dynamics, as well as community structure. Within this framework, we studied seabird‐trawling interactions throughout the annual cycle in a poorly studied ecosystem in the Mediterranean, the Balearic archipelago, on a both species‐specific and a community level. Whereas the species‐specific approach showed a significant influence of season (phenology) on shaping seabird’s trawling attendance patterns, the spatio‐temporal coupling of regional community was a result of a complex interaction between fishery‐related variables. The most frequent and abundant species were the yellow‐legged gull Larus michahellis and Cory’s shearwater Calonectris diomedea, the latter attending vessels in higher numbers than expected from local population figures. Conversely, the remaining breeding species occurred in lower numbers than expected according to their local breeding populations, suggesting that discards were of relatively little importance. Discarding activity took place over the entire shelf and continental slope surrounding Mallorca, but especially in the southwest, adjacent to the breeding grounds of approximately 12% of the Balearic total seabird breeding population, including 13% the Balearic shearwater Puffinus mauretanicus world population. Overall discards corresponded to 0.74 of landings (range: 0.09–6.00) and consisted primarily of fish followed by crustaceans and molluscs (approximately 80, 15, and 5%, respectively). Seabird‐trawling interactions should be taken into account in the frame of an ecosystem‐based approach to fisheries management, and particular attention should be devoted to the critically endangered Balearic shearwater.