Juvenile recruitment is an important determinant of change within marine protected areas (MPAs). Understanding spatio‐temporal variability in recruitment rates will help managers set realistic ...expectations for rates of population and community level change within individual MPAs. Here we ask whether seabird foraging rates can be used as a proxy for juvenile fish recruitment at spatial scales relevant to MPA management. We investigated the foraging rates of six piscivorous seabirds inside and outside of three island and four mainland MPAs in Southern California and compared these rates to estimates of juvenile fish density from kelp forest surveys conducted at the same sites during the same 2 years (2012 and 2013). Juvenile fish communities at island and mainland sites were dominated by three families, Embiotocidae, Labridae and Pomacentridae, in both years. Additionally, there was an influx of young‐of‐the‐year rockfishes (family Sebastidae) at most sites in 2013. Seabird and fish distributions were similar at the regional (approximately 15–30 km) scale, but less similar at the site‐specific scale. Site‐specific differences reflected differences in the diet and foraging habits of individual seabird species. While fish surveys were specific to the kelp forest habitat, seabirds were sampling multiple habitats (i.e. multiple water depths over multiple bottom substrates) within a given site. Our results suggest that integrating seabird data with data on juvenile fish abundance can produce a more holistic index to proxy spatio‐temporal variability in juvenile fish recruitment. In other words, seabird studies can provide additional information not captured by fish surveys and help resource managers better understand local patterns of fish recruitment at the community level. This will help resource managers establish realistic expectations for how quickly fish populations should change within individual MPAs.
The imperial cormorant (Phalacrocorax atriceps) is one of the most abundant cormorant species in the Chilean channels and fjords. Although its reproductive and non-reproductive distributions have ...been studied, works on its diet are inexistent. This paper describes the diet and determines the dominance and diversity of the prey consumed during the winter periods of 2011 and 2014 in Caulín Bay, Chiloé, southern Chile. A total of 73 pellets were collected (30 in 2011 and 43 in 2014). Prey were identified and classified into three categories: fishes (53.57%), cephalopods (39.29%) and crustaceans (7.14%). When prey consumption was analyzed according to their distribution in the water column, we observed statistically significant differences in a preference of benthic demersal over pelagic prey.
The predation by the Grey Heron Ardea cinerea and the Cormorant Phalacrocorax carbo has been studied in a dyked area intended for extensive brackishwater aquaculture on the French Atlantic coast. A ...pond was divided in two parts, one of which (0.9 ha) wa protected with nets and threads, the other one (0.3 ha) left without protection. Fish (Mugilidae) were stocked in November, during the wintering period of the birds. Three weeks later, remaining fish in both parts of the ponds were counted. During experimentation, number, presence and predation behaviour of birds were observed. A spectacular but temporary gathering of birds occurred during the first days following the fish stocking. Cormorants and Grey Herons respectively used deeper and shallower areas of the pond. Intensity of predation (number of attacks/minute) was higher among cormorants. Dominant features of predation exerted by these birds are: the rapid exhaustion of the fish population; and the higher predation level by cormorants than by herons, although the latter obtains a very high success ratio (number of catch/number of attacks).
Ecological theory predicts that co-existing, morphologically similar species will partition prey resources when faced with resource limitations. We investigated local movements, foraging dive ...behavior, and foraging habitat selection by breeding adults of 2 closely related cormorant species, double-crested cormorants Phalacrocorax auritus and Brandt’s cormorants P. penicillatus. These species nest sympatrically at East Sand Island in the Columbia River estuary at the border of Oregon and Washington states, USA. Breeding individuals of each species were tracked using GPS tags with integrated temperature and depth data-loggers. The overall foraging areas and core foraging areas (defined as the 95% and 50% kernel density estimates of dive locations, respectively) of double-crested cormorants were much larger and covered a broader range of riverine, mixed-estuarine, and nearshore marine habitats. Brandt’s cormorant foraging areas were less expansive, were exclusively marine, and mostly overlapped with double-crested cormorant foraging areas. Within these areas of overlap, Brandt’s cormorants tended to dive deeper (median depth = 6.48 m) than double-crested cormorants (median depth = 2.67 m), and selected dive locations where the water was deeper. Brandt’s cormorants also utilized a deeper, more benthic portion of the water column than did double-crested cormorants. Nevertheless, the substantial overlap in foraging habitat between the 2 cormorant species in the Columbia River estuary, particularly for Brandt’s cormorants, suggests that superabundant prey resources allow these 2 large and productive cormorant colonies to coexist on a single island near the mouth of the Columbia River.
Numerous factors such as predation, disease, injury, and environmental conditions (e.g., river flows, hydropower operations) can influence survival rates of fish. Although mortality due to predation ...is commonly assumed to be additive and result in a directly proportional reduction on survival rates, compensatory processes may work to counteract or negate the effects of predation mortality on survival rates. We applied a random effects model to a long-term, mark-recapture-recovery data set on anadromous steelhead (Oncorhynchus mykiss) from the Snake River Basin in the northwestern United States to assess whether avian predation mortality constitutes an additive or compensatory source of mortality. Specifically, our assessment focused on predation mortality due to double-crested cormorants (Phalacrocorax auritus) and Caspian terns (Hydroprogne caspia) on colonies in the Columbia River estuary. In addition, we evaluated several candidate environmental indices to examine potential interactions between the effects of predation versus environmental conditions on steelhead survival rates. Average predation rates were 3.3% for the double-crested cormorant colony and 17.0% for the Caspian tern colony. For both colonies, the estimated correlation between the predation rate and survival rate of steelhead was near zero, indicating that mortality due to avian predation is compensatory. Models that included variables for river flow, juvenile migration timing, and an index of forage biomass in the ocean accounted for 56–59% of the variation in steelhead survival, whereas avian predation rates accounted for <1% of the variation. Management efforts to reduce the abundance of the bird colonies are unlikely to improve the survival or conservation status of steelhead; however, results indicate that steelhead survival could be improved by hydropower management decisions that increase river flows and reduce juvenile migration delays.
The aim of the present study was to determine the concentrations of nonylphenols (NPs) and 4-t-octylphenol (4tOP) in the muscles, liver, and kidneys of selected waterbird species. Three species with ...different feeding habits were selected, i.e., greater scaup (Aythya marila), great crested grebe (Podiceps cristatus), and great cormorant (Phalacrocorax carbo) to investigate the potential effects of diet on the level of contaminants tested. The determination and quantification of analytes were performed using gas chromatography with mass spectrometric detection (GC-MS).
The highest NP concentrations were noted in the kidneys of greater scaups and great crested grebes (208.3 and 160.8 μg kg−1 ww, resp.), which were six to fourteen-fold higher than those in the muscles (15.0 and 25.6 μg kg−1 ww, resp.) and livers (22.9 and 13.8 μg kg−1 ww, resp.) of these species. In greater scaups, the mean concentration of NPs in the livers was lower than in the muscles, while in great crested grebes, it was the opposite and higher concentrations were noted in the muscles. The mean concentrations of NPs in the muscles and livers of great cormorants were at similarly low levels (12.5 and 9.7 μg kg−1 ww, resp.). The concentrations of 4tOP in all samples were low, ranging from <LOQ to 0.29 μg kg−1 ww. The results of our study indicated that sex and diet did not affect the NP tissue concentrations in different waterbird species, but the phenological period (migration vs breeding) might influence the contamination levels in the kidneys.
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•NPs are good indicators of exposure to APs in waterbirds.•Highest NP concentrations were noted in kidneys.•Sex did not affect the inter-tissue distribution of NPs.•Diet had no significant effect on the interspecific differences in the distribution of NPs.•Long-distance migratory flights might have had an impact on pollution levels in birds.
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