Environmental factors and fisheries influence the foraging patterns of a subtropical seabird, the Westland Petrel (Procellaria westlandica), in the Tasman Sea

Abstract

Environmental and anthropogenic influences in the marine environment are primary drivers of behavior and demographic outcomes for marine birds. We examined factors influencing the foraging patterns of the Westland Petrel (Procellaria westlandica), a highly threatened, endemic petrel that inhabits subtropical water masses primarily in the Tasman Sea, with a poorly known at-sea distribution. Risk assessments place the species at moderate risk of population impacts from fisheries-related mortality. Studies in the 1990s indicated that trawl fisheries would have an important influence on the Westland Petrel's foraging behavior. We investigated the influence of climatic conditions, marine productivity, bathymetry, the core fishery zone, concurrent fishing activity, light conditions, sex, and breeding stage on Westland Petrel foraging patterns. We analyzed the stable isotopes of carbon and nitrogen from blood sampled during the incubation period and examined changes in isotopic niche width over a 6-yr period. We found that the Westland Petrel's foraging zone varied only slightly between years and that the location of intensively used areas was strongly influenced by bathymetric slope and latitude, and negatively influenced by chlorophyll-a. The core fishery zone had a secondary influence, suggesting that these petrels co-occur with fisheries, but are not dependent on waste for food. Trophic niche width was significantly wider during strong El Niño conditions, indicating that food type, rather than location, was most affected by climatic variation. Consistent use of one marine area across varying times and conditions increases the risk of adverse effects of climate or human-induced impacts on the species. However, marine spatial management tools become viable in these conditions. Further, with rapid increases in sea surface temperatures and extreme values recorded in the region in recent periods, changes to fisheries zones and distributions of natural prey of the species are likely to occur and may change the population's sustainability. Direct all requests to reproduce journal content to the AOS Publications Office at pubs@americanornithology.org que les pétrels cohabitent avec les activités de pêche mais ne sont pas dépendants des rejets de pêche pour s'alimenter. Les niches trophiquesétaient significativement plus larges lorsque fortes dans des conditions El Niño, ce qui indique que le type de nourriture, plutôt que la localisation,était le plus affecté par la variation du climat. Une utilisation continue d'une zone marineà différents moments et dans diverses conditions augmente le risque d'impacts climatiques ou anthropiques négatifs sur l'espèce. Cependant, les outils de gestion spatiale du milieu marin deviennent viables dans ces conditions. De plus, avec de rapides augmentations de la SST et des valeurs extrêmes enregistrées dans la région récemment, des changements aux zones de pêches et dans la répartition naturelle des proies de l'espèce sont susceptibles de se produire et peuvent affecter la pérennité de la po...

Foraging niche overlap during chick-rearing in the sexually dimorphic Westland petrel

“…The present study confirmed and refined the chick-rearing movements of Westland petrels previously reported by at-sea observations [ 84 ] and tracking studies [ 45 , 48 ]. The species displayed restricted breeding movements (432 ± 20 km d –1 ) during the present study compared to the non-breeding movements (1351 km d –1 , [ 44 ]).…”

“…Data from 2016 and 2017 were gathered during the present study, data from 2012 and 2015 are from Waugh et al . [ 45 ]. …”

“…The investigation of the time spent foraging by individuals in the present study in relation to oceanographic variables revealed a significant influence of depth, slope, sea surface temperature and current. Slope was also reported to increase the foraging intensity estimated by kernel density estimate [ 45 ]. These findings are consistent with the slope and current involved in horizontal advection, uplifting and mixing of subsurface waters in the area [ 121 ].…”

“…Foraging trip metrics (duration, maximum distance from the colony, total horizontal distance travelled, average speed) were calculated using the adehabitatHR package [ 60 ]. Additional trip duration data were obtained during the chick-rearing period, from, respectively, 29 trips in 2012 and six trips in 2015 [ 45 ]. Trip duration distribution of these pooled trips was assessed for bimodality with calculation of the bimodality coefficient [ 61 ] and mode(s) estimation(s) by mixture distribution implemented in the modes package [ 62 ].…”

“…Preliminary studies showed that despite a wingspan of 140 cm conferring this flap-glider species with a high flight capability [ 40 ], this species has a reduced foraging range and performs shorter trips than other smaller Procellariiforms [ 41 , 42 ]. In addition, although males are larger than females (SSD of 6% in body mass, [ 43 , 44 ]), both sexes appear to forage in the same areas throughout the whole breeding cycle [ 45 ]. Furthermore, in contrast to its congenerics [ 46 , 47 ], Westland petrels sustain the increased nutritional requirements of chick-provisioning with no indication of bimodality in foraging trip duration [ 45 , 48 ].…”