Estimating the population of burrow-nesting seabirds is a challenging task, as human presence in the colony creates disturbances and can damage burrows and occupants. Here, we present a novel method using aerial photographs taken with Unmanned Aerial Vehicles (UAVs) to estimate the population size of a burrow-nesting seabird, the Black-vented Shearwater (Puffinus opisthomelas), on Natividad Island, Mexico. Our results provide a census of burrows in the colony, with very low detection error (5.6%). This is greater accuracy compared to other methods based on extrapolating results from sample plots to total colony area. We then combined this burrow census with ground truth data on occupancy to estimate population size. We obtained a population estimate of 37,858 and 46,322 breeding pairs for 2016 and 2017 respectively. The proposed method provides a cost effective and repeatable approach for monitoring numbers of burrows occupied in a colony, thereby enabling easier and faster estimates of population trends. We suggest this method can be valid for other burrow-nesting species in habitats without dense vegetation cover.

During the breeding season, seabird foraging trips are constrained by nest attendance schedule and are necessarily colony centred. Oceanographic cues play a major role in the choice of foraging areas to minimize the time spent away from the nest. Here, we analysed the foraging tracks of Black‐vented Shearwaters Puffinus opisthomelas during the incubation and chick‐rearing periods of 2016 and 2017 at Isla Natividad (Mexico). We applied expectation‐maximization binary clustering to track data to clusterize different behaviour patterns during foraging flights. We then applied binary generalized linear mixed models to characterize of foraging areas based on of environmental variables. We finally used kernel estimation techniques to describe main foraging areas. In 2016, breeding shearwaters used two core areas for foraging and resting on the water; the core area delineated by males was located northward from the colony in the Vizcaino Bay and the core area for females was located southward from the colony at the entrance of San Ignacio Lagoon. In 2017, males and females used the same areas with no evident segregation. Our study provided the first information on Black‐vented Shearwater foraging areas during the breeding season and indicated that sexual segregation within coastal waters off the central Baja California Peninsula might be a foraging strategy during years of warmer ocean, likely less productive regimes. Factors including ocean‐climate‐mediated sexual segregation at sea, leading to interannual variation in foraging areas, should be considered when evaluating management actions intended to protect critical foraging habitats for Black‐vented Shearwaters.

suMMarY: ricker's stock-recruitment equation, including the multivariate enso index (Mei) as an environmental variable, was fitted to data of the Pacific sardine (Sardinops sagax caerulea) fishery from Magdalena Bay, Baja California sur, Mexico. the equation was then incorporated into an age-structured, bioeconomic model. uncertainty was incorporated by using environmental fluctuations; seven-year projections, equivalent to one sardine generation, were computed. Five management options were considered in the projections: open access, effort at maximum sustainable economic yield (f Mse ), catch at maximum sustainable yield (C MsY ), equivalent effort level applied in the year 2004 (f 2004 ), and an arbitrary catch quota of 40000 tons (CQ 40000 ). Projection results were summarised by the indicator net Present Value (nPV) of the fishery for the modelled period. the strategies that involved some regulation in the effort level (f Mse and f 2004 ) yielded the largest nPV. on the other hand, the strategies that involved regulation of the catch predicted-in addition to a lower nPV-a substantial increase in the effort to achieve the desired catch level. this study is the first bioeconomic approach for a sardine fishery management plan in this region.Keywords: Pacific sardine, recruitment, environment, fishery management, bioeconomic model, uncertainty. resuMen: Efecto de la variabilidad ambiental en el reclutamiento y modelación bioeconómica en la pesquería de sardina del Pacífico (SardinopS Sagax caerulea) de Bahía Magdalena, Baja California Sur, México. -la ecuación stock-reclutamiento de ricker incorporándole el índice multivariado del enso (iMe) como variable ambiental fue ajustada a datos de la pesquería de sardina (Sardinops sagax caerulea) de Bahía Magdalena, Baja California sur, México. esta ecuación fue incorporada a un modelo bioeconómico estructurado por edad. la incertidumbre fue considerada al incorporar la variabilidad ambiental, y se realizaron proyecciones de siete años de duración, que equivalen a una generación de sardina. en las proyecciones se consideraron cinco estrategias de gestión: acceso abierto, esfuerzo en máximo rendimiento económico (f Mre ), captura en el máximo rendimiento sostenible (C Mrs ), esfuerzo igual al aplicado en el año 2004 (f 2004 ), y una cuota de captura de 40000 toneladas métricas (CC 40000 ). las proyecciones fueron expresadas como el valor presente neto (VPn) de la pesquería para el período modelado. las estrategias que involucraron alguna regulación en el nivel de esfuerzo pesquero (f Mre y f 2004 ) presentaron el mayor VPn. no así las estrategias que involucraron regulación en la captura, debido a que éstas predijeron un fuerte incremento en el esfuerzo para lograr el nivel de captura deseado. este estudio es la primera aproximación bioeconómica para la ordenación de la pesquería de sardina en esta área.Palabras clave: sardina del Pacífico, reclutamiento, ambiente, gestión pesquera, modelación bioeconómica, incertidumbre.Scientia Marina 74(1) March 2010, 25-35, Barcelona...

Abstract. We used the extended reconstruction of sea surface temperature (ERSST) to analyze the variation of surface temperature and the seasonal cycle along the coast of the eastern Pacific (60 • N-60 • S, 61 pixels alongshore) from 1950 to 2010 (732 months). First, we analyzed the monthly anomalies and looked for a relationship of such anomalies with total solar irradiance (TSI) and then the Regime Shift Detector (RSD) was applied to detect possible temperature regimes in the series. Afterwards, we calculated a yearly temperature range per pixel (amplitude of seasonal cycle) and through the subtraction of a latitudinal theoretical curve of temperature based on solar irradiance, the residuals of the seasonal cycle were obtained. The results showed an almost complete spatial synchrony and dominance of negative anomalies from 1950 to mid-late 1970's, with a switch to near-zero and positive anomalies that lasted up to late 1990's when a new shift to negative values was detected. Such a shift lasted until the early 2000's when positive anomalies appeared again but there was a change to negative anomalies in the late 2000's. These results were supported by the RSD. The TSI variability shows a clear relationship with that of sea surface temperature anomalies and with the regime changes. This is probably due to a difference in the amount of energy received from the sun. Comparing the "cool regime" versus the "warm regime", the second one