Temperature Depth Recorders Research Articles

Increased foraging effort and reduced chick condition of razorbills under lower prey biomass in coastal Newfoundland, Canada

When resources are finite, individuals optimize energy allocation between survival and reproduction to maximize fitness. As food becomes more limited within foraging ranges of breeding colonies, long-lived seabirds are predicted to increase time spent foraging, and chick growth, breeding success and ultimately adult survival, will be reduced. Across 3 years (2017, 2019, 2020), we investigated responses of breeding razorbills Alca torda in coastal Newfoundland, Canada, to inter- and intra-annual variation in biomass of the primary forage fish, capelin Mallotus villosus, which migrate from offshore into coastal regions during the summer to spawn. We combined capelin biomass (hydroacoustic surveys) with chick-rearing razorbill foraging effort (GPS, temperature-depth recorders), dietary proportions (blood δ15N and δ13C) and adult/chick body condition. Peak capelin biomass was near the long-term average for the study area in 2017 (0.109 g m-2) and 2019 (0.098 g m-2) and the lowest on record in 2020 (0.002 g m-2). In 2017 and 2019, razorbill foraging effort decreased after spawning capelin arrived inshore, but this decrease was not observed in 2020 (mean ± SE trip distance: 12.8 ± 2.8 km in 2017, 14.3 ± 1.7 km in 2019, 150.4 ± 25.2 km in 2020; number of dives per trip: 48.4 ± 11.8 in 2017, 385.8 ± 67.4 in 2020). Increased foraging effort during 2020 was associated with lower chick and adult body condition, likely due to parental birds flying farther and diving more to capture capelin. Findings suggest that lower capelin biomass observed in recent years may have long-term population-level consequences for razorbills and other seabirds in this region.

What’s the catch? Examining optimal longline fishing gear configurations to minimize negative impacts on non-target species

Changes to fishing gear configurations have great potential to decrease fishing interactions, minimize injury and reduce mortality for non-target species in commercial fisheries. In this two-part study, we investigate potential options to optimize fishing gear configurations for United States Pacific pelagic longline vessels to maintain target catch rates whilst reducing bycatch mortality, injury, and harm. In part one, a paired-gear trial was conducted on a deep-set tuna longline vessel to compare catch rates and catch condition of target and non-target species between wire and monofilament leader materials. Temperature-depth recorders were also deployed on hooks to determine sinking rates and fishing depth between the two leader materials. In part two, hooks of different configurations (size, diameter, shape, metal type, and leader material) were soaked in a seawater flume for 360 days to obtain quantitative estimates of breaking strength, as well as the time taken for gear to break apart. We found that switching from wire to monofilament leaders reduced the catch rate of sharks by approximately 41 %, whilst maintaining catch rates of target species (Bigeye tuna, Thunnus obesus). However, trailing gear composed of monofilament did not break apart even after 360 days. In contrast, branchlines with wire leaders began to break at the crimps after approximately 60 days. Additionally, the breaking strength of soaked fishing hooks was greater for larger, forged hooks composed of stainless steel typically used in United States Pacific longline fisheries. These results have direct implications for fisheries management and the operational effectiveness of bycatch mitigation strategies for longline fisheries worldwide.

Effects of competitive pressure and habitat heterogeneity on niche partitioning between Arctic and boreal congeners

The rapidly changing climate in the Arctic is expected to have a major impact on the foraging ecology of seabirds, owing to changes in the distribution and abundance of their prey but also that of competitors (e.g. southerly species expanding their range into the Arctic). Species can respond to interspecific competition by segregating along different niche axes. Here, we studied spatial, temporal and habitat segregation between two closely related seabird species: common guillemot Uria aalge (a temperate species) and Brünnich’s guillemot Uria lomvia (a true Arctic species), at two sympatric sites in Iceland that differ in their total population sizes and the availability of marine habitats. We deployed GPS and temperature-depth recorders to describe foraging locations and behaviour of incubating and chick-rearing adults. We found similar evidence of spatial segregation at the two sites (i.e. independent of population sizes), although segregation in environmental space was only evident at the site with a strong habitat gradient. Unexpectedly, temporal (and, to a limited extent, vertical) segregation appeared only at the least populated site. Overall, our results show complex relationships between the levels of inferred competition and that of segregation.

Foraging conditions for breeding penguins improve with distance from colony and progression of the breeding season at the South Orkney Islands

BackgroundAccording to central place foraging theory, animals will only increase the distance of their foraging trips if more distant prey patches offer better foraging opportunities. Thus, theory predicts that breeding seabirds in large colonies could create a zone of food depletion around the colony, known as “Ashmole’s halo”. However, seabirds’ decisions to forage at a particular distance are likely also complicated by their breeding stage. After chicks hatch, parents must return frequently to feed their offspring, so may be less likely to visit distant foraging patches, even if their quality is higher. However, the interaction between prey availability, intra-specific competition, and breeding stage on the foraging decisions of seabirds is not well understood. The aim of this study was to address this question in chinstrap penguins Pygoscelis antarcticus breeding at a large colony. In particular, we aimed to investigate how breeding stage affects foraging strategy; whether birds foraging far from the colony visit higher quality patches than available locally; and whether there is evidence for intraspecific competition, indicated by prey depletions near the colony increasing over time, and longer foraging trips.MethodsWe used GPS and temperature-depth recorders to track the foraging movements of 221 chinstrap penguins from 4 sites at the South Orkney Islands during incubation and brood. We identified foraging dives and calculated the index of patch quality based on time allocation during the dive to assess the quality of the foraging patch.ResultsWe found that chinstrap penguin foraging distance varied between stages, and that trips became shorter as incubation progressed. Although patch quality was lower near the colony than at more distant foraging patches, patch quality near the colony improved over the breeding season.ConclusionsThese results suggest chinstrap penguin foraging strategies are influenced by both breeding stage and prey distribution, and the low patch quality near the colony may be due to a combination of depletion by intraspecific competition but compensated by natural variation in prey. Reduced trip durations towards the end of the incubation period may be due to an increase in food availability, as seabirds time their reproduction so that the period of maximum energy demand in late chick-rearing coincides with maximum resource availability in the environment. This may also explain why patch quality around the colony improved over the breeding season. Overall, our study sheds light on drivers of foraging decisions in colonial seabirds, an important question in foraging ecology.

Less Soak Time Saves Those upon the Line: Capture Times and Hooking Mortality of Sharks Caught on Bottom Longlines

AbstractThe National Marine Fisheries Service is mandated by the Magnuson–Stevens Fishery Conservation and Management Act to implement effective annual catch limits and accountability measures to prevent overfishing. These requirements compel further research into alternative fishing practices that could reduce mortality of sharks (class Chondrichthyes) and allow fishers to release unwanted sharks to the water alive, while still effectively catching targeted species. We used hook timers and temperature–depth recorders aboard contracted vessels and participants in the National Marine Fisheries Service’s Shark Research Fishery to collect hooking time and time‐on‐the‐line data for 10 species of sharks that were commonly encountered in the fishery. A subset of standardized fishing sets compared the most popular circle hook and J‐hook models. Over 60% of sharks were hooked within 4 h of hook soak time. The fastest to bite the hook was the Atlantic Sharpnose Shark Rhizoprionodon terraenovae and the slowest was the Dusky Shark Carcharhinus obscurus. Shark resilience to time on the longline varied among species, with Sandbar Shark C. plumbeus exhibiting the most resilience and Atlantic Sharpnose Shark the least. Shorter set soak times, approximately 2 h, would still maximize catch, while minimizing at‐vessel mortality. The most frequently used circle hook model did not significantly reduce at‐vessel mortality over large J‐style hooks. The recent circle hook requirement will have little effect for fishers that previously used 12/0 J‐hooks, but it may be beneficial by preventing the use of smaller J‐hooks that are more likely to cause at‐vessel mortality.

Diving behaviour of Grey Petrels and its relevance for mitigating long-line by-catch

The Grey Petrel (Procellaria cinerea) is listed as Near Threatened globally owing to incidental mortality on long-line fishing gear and reduced breeding success on islands caused by the introduction of alien predators. However, there are few studies of its foraging ecology and none of its diving behaviour. We obtained data from temperature-depth recorders (n = 7 birds) and global positioning satellite trackers (n = 15) deployed on Grey Petrels breeding on Gough Island, South Atlantic Ocean. Most birds foraged in the productive oceanic waters west or north-west of South Georgia. Average maximum dive-depth was 3.2 ± 2.2 m with most dives <5 m (85%) and 95% of dives <7 m deep. The maximum dive-depth (22 m) was deeper than previous measurements of dive-depth in Procellaria petrels, and maximum dive-duration also was longer than previously recorded in Procellaria petrels (at least 39 s). Individuals varied greatly in the mean number of dives per day (range 0.4-24.5). Sex did not influence depth or duration of dives but sample sizes were small. The time of day influenced dive-depth, and dives during daylight were, on average, deeper than dives at night, but the effect was weak; the maximum dive-depth at night was 17 m. By providing insights into the diving behaviour of Grey Petrels our findings help to explain their high mortality on fishing long-lines. We suggest that fisheries adopt bird-scaring lines that protect long-lines from scavenging seabirds during the setting process to a depth of at least 10 m, which could be achieved by increasing line-weighting or modifying bird-scaring lines, or both. An understanding of the foraging ecology of commonly recorded by-catch species, such as Grey Petrels, is essential in the design of future devices to mitigate seabird by-catch in long-line fisheries.

Telomere length and environmental conditions predict stress levels but not parental investment in a long-lived seabird

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 556:251-259 (2016) - DOI: https://doi.org/10.3354/meps11864 Telomere length and environmental conditions predict stress levels but not parental investment in a long-lived seabird Rebecca C. Young1,4,*, Chris P. Barger1,5, Ine Dorresteijn2,6, Mark F. Haussmann3, Alexander S. Kitaysky1 1University of Alaska Fairbanks, Institute of Arctic Biology; Department of Biology and Wildlife, Fairbanks, AK 99775, USA 2University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK 99775, USA 3Dept. of Biology, Bucknell University, Lewisburg, PA 17837, USA 4Present address: 3447 Valley Branch Road, Nashville, IN 47448, USA 5Present address: Alaska Department of Fish & Game, 1300 College Road, Fairbanks, AK 99701, USA 6Present address: Leuphana University Lüneburg, Faculty of Sustainability, Scharnhorststr. 1, C11.018, 21335 Lüneburg, Germany *Corresponding author: rebeccacyoung721@gmail.com ABSTRACT: Telomeres are increasingly regarded as viable biomarkers of individual quality, and thus may be associated with other proximate markers of quality. We compared telomere length to such quality markers in a long-lived seabird, the thick-billed murre Uria lomvia, breeding under varying environmental conditions on 3 colonies in the Bering Sea. Individual quality was assessed using behaviors associated with parental investment (trip rate and nest attendance, determined by bird-borne data loggers), body condition, and physiological stress (baseline corticosterone). Telomere length was related to physiological stress and body condition, while parental investment in reproduction was not. This implies that maintenance of consistent levels of parental care was prioritized and that individual quality changes were expressed physiologically (changes in telomere length) rather than behaviorally. Under poor environmental conditions, short telomeres were associated with lower levels of physiological stress. However, under good environmental conditions, they were associated with higher levels of stress. These findings confirm that telomere length variation is related to patterns in stress hormones and support previous findings that environmental conditions are an important mediator of telomere dynamics. KEY WORDS: Individual quality · Brünnich’s guillemot · Corticosterone · Parental investment · Temperature-depth recorder · Telomeres · Thick-billed murre · Uria lomvia Full text in pdf format PreviousNextCite this article as: Young RC, Barger CP, Dorresteijn I, Haussmann MF, Kitaysky AS (2016) Telomere length and environmental conditions predict stress levels but not parental investment in a long-lived seabird. Mar Ecol Prog Ser 556:251-259. https://doi.org/10.3354/meps11864 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 556. Online publication date: September 08, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

The seasonal evolution of shelf water masses around Bouvetøya, a sub-Antarctic island in the mid-Atlantic sector of the Southern Ocean, determined from an instrumented southern elephant seal

Our study makes use of a fortuitous oceanographic data set collected around the remote sub-Antarctic island of Bouvetoya by a conductivity–temperature–depth recorder (CTD) integrated with a satellite-relayed data logger deployed on an adult female southern elephant seal ( Mirounga leonina ) to describe the seasonal evolution of the western shelf waters. The instrumented seal remained in waters over the shelf for 259 days, collecting an average of 2.6 (±0.06) CTD profiles per day, providing hydrographic data encompassing the late austral summer and the entire winter. These data document the thermal stratification of the upper water layer due to summer surface heating of the previous year’s Antarctic Surface Water, giving way to a cold subsurface layer at about 100 m as the austral winter progressed, with a concomitant increase in salinity of the upper layer. Upper Circumpolar Deep Water was detected at a depth of approximately 200 m along the western shelf of Bouvetoya throughout the year. These oceanographic data represent the only seasonal time series for this region and the second such animal–instrument oceanographic time series in the sub-Antarctic domain of the Southern Ocean. Keywords: Biotelemetry; diving; elephant seal; oceanography; marine predators; CTD-SRDL. (Published: 27 October 2016) To access the supplementary material for this article, please see supplementary files in the column to the right (under Article Tools). Citation: Polar Research 2016, 35 , 28278, http://dx.doi.org/10.3402/polar.v35.28278

Bubble momentum plume as a possible mechanism for an early breakdown of the seasonal stratification in the northern North Sea

The presence of a seasonal thermocline likely plays a key role in restraining methane released from a seabed source in the deeper water column, thereby inhibiting exchange to the atmosphere. The bubble plume itself, however, generates an upward motion of fluid, e.g. upwelling and may thereby be partially responsible for an early breakdown of the seasonal thermocline. Measurements at site 22/4b, located at (57°55′N, 1°38′E) in the UK Central North Sea, 200 km east of the Scottish mainland, where gas is still being released since a blow out in 1990, have been used to identify the generation of the seasonal thermocline, and thus, the depth of the upper mixed layer and its breakdown in autumn. Data derived from two landers, containing an Acoustic Doppler Current Profiler and a Conductivity Temperature Depth recorder, were used to determine the mixed layer depth and the breakdown of the thermocline. Mixing of upper layer fluid into the lower layer has been inferred from large amplitude variations in the near-bottom temperature.The ADCPs estimate velocity profiles in four beam directions using Doppler shifted frequency from acoustic pings sent out and received by four different transducers in a specific configuration. Besides that, the intensity of the backscattered sound per transducer is also recorded. Bubbles from the nearby plume contaminate the signal during part of the tidal cycle, but in bubble free periods, the mixed layer depth can be estimated using the acoustic backscatter signal as local maxima. Results show that the thermocline broke down between mid-October and early November, several weeks earlier than the breakdown of the thermocline in nearby/comparable areas, likely caused by bubble-induced downwelling at the site. The early breakdown of the thermocline was accompanied by multiple occurrence of a strong jet-like structure, associated with the seasonal tidal mixing front.

Hooking mortality of scalloped hammerhead Sphyrna lewini and great hammerhead Sphyrna mokarran sharks caught on bottom longlines

The scalloped hammerhead Sphyrna lewini and the great hammerhead S. mokarran are typically caught as bycatch in a variety of fisheries and are listed as globally Endangered by the International Union for the Conservation of Nature. Due to very high at-vessel mortality for these species, research is needed on fishing methods to reduce mortality for longline-captured sharks. A series of fishing experiments were conducted employing hook timers and temperature–depth recorders on contracted commercial vessels fishing with bottom-longline gear to assess factors related to mortality. A total of 273 sets were deployed with 54 485 hook timers. Scalloped and great hammerheads had at-vessel mortality rates of 62.9% and 56.0%, respectively. Median hooking times for scalloped and great hammerheads were 3.5 h and 3.4 h, respectively, and 50% mortality was predicted at 3.5 h and 3.8 h. When these data are considered for potential management strategies to reduce the mortality of hammerhead sharks, a limitation on gear soak time would probably improve hammerhead shark survivorship. However, it may prove to be difficult for a fishery to remain economically viable if the soak time is limited to less than the median hooking time for the target species. Additional management options, such as time/area closures, may need to be explored to reduce bycatch mortality of scalloped and great hammerheads.

The dynamic simulation of the pelagic longline deployment

It is important to understand the deployment of pelagic longline gear for reducing non-target species interactions, and increasing fishing efficiency. In the present study hook depth data, simultaneous settlement data, and three-dimensional (3D) ocean current data were collected aboard the fishing vessel “Huananyu 716” while operating near the Cook Islands (10°50'S–15°05'S, 156°14'W–168°01'W) from September 2012 to November 2012. Taking into account the hydrodynamic force of longline fishing gear floats, dynamic equations of pelagic longline gear deployment were built using the lumped mass method and solved by the Euler–Trapezoidal method. The space shape and tension distribution of the longline gear were analyzed, a model was derived, and then verified. Results indicate that: (1) there were no significant differences (P>0.05) between the hook depth measured by Temperature Depth Recorders (TDRs) during settlement and the simulated hook depth, except for the first hook (P<0.001); (2) during the settlement, the tension of the nodes of the main line increased greatly; and (3) the fluctuations of gear space shape, tensile, and hydrodynamic forces of the main line nodes were closely associated with current velocities of the water column where the gear was located. The stronger the current, the larger the fluctuation in spatial location of the fishing gear. These results suggest that the dynamic model of longline fishing gear developed in the present study could be used: (1) to calculate the tension of nodes and floats in a variety of ocean current conditions; (2) to present the dynamic process of the deployment and settlement of each node and the 3D shape of the longline in a variety of ocean currents

Irreplaceable area extends marine conservation hotspot off Tunisia: insights from GPS-tracking Scopoli’s shearwaters from the largest seabird colony in the Mediterranean

Recent meta-analyses identified conservation hotpots at the scale of the Mediterranean, yet those may be crude by lack of detailed information about the spatial ecology of the species involved. Here, we identify an irreplaceable marine area for >95 % of the world population of the Scopoli’s shearwater (Calonectris diomedea), which is endemic to the Mediterranean and breeds on the island of Zembra off Tunis. To this end, we studied the three-dimensional at-sea movements of 50 breeding adults (over a total of 94 foraging trips) in 2012 and 2013, using GPS and temperature–depth recorders. Feathers were also collected on all birds to investigate their trophic status. Despite Zembra being the largest seabird colony in the Mediterranean (141,000 pairs), the per capita home-range of Scopoli’s shearwaters foraging from this colony was not larger than that of birds from much smaller colonies, indicating highly beneficial feeding grounds in the Gulf of Tunis and off Cap Bon. Considering depleted Mediterranean small pelagic fish stocks, supposed to be Scopoli’s shearwater prey base, we therefore speculate that birds may now also largely feed on zooplankton, something which is supported by our stable isotopic analyses. Crucially, shearwater at-sea feeding and resting areas showed very little overlap with a conservation hotspot recently defined on the western side of the Gulf of Tunis using meta-analyses of species distributions relative to anthropogenic threats. We therefore propose a major extension to this conservation hotspot. Our study stresses the importance of detailed biotelemetry studies of marine megafauna movement ecology for refining large-scale conservation schemes such as marine protected area networks.

Studying the Impacts of Local Oceanographic Processes on Adélie Penguin Foraging Ecology

AbstractWe are conducting a multi-platform field study to investigate the impact of local physical processes on Adélie penguin foraging ecology in the vicinity of Palmer Deep off Anvers Island, Western Antarctic Peninsula (WAP). Guided by real-time remotely sensed surface current measurements of convergence derived from a network of high-frequency radars (HFRs), we adaptively sample the distribution and biomass of phytoplankton and Antarctic krill, which influence Adélie penguin foraging ecology, to understand how local oceanographic processes structure the ecosystem. The recent application of ocean observing and animal telemetry technology over Palmer Deep has led to new understanding and many new questions related to polar ecosystem processes. The HFR coastal surface current mapping network is uniquely equipped to resolve local circulation patterns over Palmer Deep. The surface current measurements enable identification of regions of convergence and divergence in real time. Guided by these maps, our field study adaptively samples the measured convergence and divergence zones within the context of semi-diurnal and diurnal mixed tidal regimes. The in situ sampling includes (a) a mooring deployment, (b) multiple underwater glider deployments, (c) small boat acoustic surveys of Antarctic krill, and (d) penguin ARGOS-linked satellite telemetry and temperature-depth recorders (TDRs). The combination of real-time surface convergence maps with adaptive in situ sampling introduces HFR to the Antarctic in a way that allows us to rigorously and efficiently test the influence of local tidal processes on top predator foraging ecology.

Diving behaviour of white-chinned petrels and its relevance for mitigating longline bycatch

The white-chinned petrel (Procellaria aequinoctialis) is the seabird species most commonly killed by Southern Hemisphere longline fisheries. Despite the importance of diving ability for mitigating longline bycatch, little is known of this species’ diving behaviour. We obtained data from temperature–depth recorders from nine white-chinned petrels breeding on Marion Island, southwestern Indian Ocean, during the late incubation and chick-rearing period. Maximum dive depth (16 m) was slightly deeper than the previous estimate (13 m), but varied considerably among individuals (range 2–16 m). Males dived deeper than females, and birds feeding chicks dived deeper than incubating birds, but dive rate did not differ between the sexes. Time of day had no significant effect on dive depth or rate. Our findings will help to improve the design and performance of mitigation measures aimed at reducing seabird bycatch in longline fisheries, such as the calculation of minimum line sink rates and optimum aerial coverage of bird-scaring lines.

Fine-scale catch data reveal clusters of large predators in the pelagic realm

The management and conservation of large pelagic fish commonly rely on fisheries data and thus crucially depend on our understanding of the fish response to the fishing gear. Stock assessment of both tropical and temperate tuna strongly leans on the catch statistics derived from pelagic longline fisheries. However, the role of the spatial distribution of catches of tuna and bycatch species over the gear, which can affect the estimated tuna abundance, is still neglected. In this study, we analyzed data obtained from 147 instrumented pelagic longline sets equipped with hook timers and temperature depth recorders to characterize the distribution of hooking contacts and success at a fine temporal and spatial scale. Scientific surveys were carried out in the Central–South Pacific Ocean (French Polynesia), targeting tropical (Thunnus albacares, Thunnus obesus) and temperate (Thunnus alalunga) tuna. Data analysis based on spatial point processes and stochastic modeling demonstrate the presence of spatio-temporal clusters for both hooking contacts and hooking success. The comparative analysis of the observed spatio-temporal patterns for different oceanographic zones revealed the persistent structure of the clusters, suggesting that they are neither related to local environmental conditions nor to the spatial distribution of prey species.

Numeric modeling of a pelagic longline based on minimum potential energy principle

Fishing parameters(such as the shooting speed of mainline,vessel speed,time interval between two hooks,numbers of hooks between two floats) can be adjusted to deploy the hooks to water layers that are preferred by target species,such as tuna.As a result,the catch rate of the target species can be increased and the catch of bycatch species(e.g.,loggerhead turtles,Caretta caretta;blue sharks,Prionace glauca;silky sharks,Car-charhinus falciformis) can be reduced.Together,these actions improve fishing efficiency and help maintain bio-logical diversity.To better understand the relationship between these factors and the fishing depth of longline gear,we developed a numeric model of the behavior of a pelagic longline.We conducted surveys on board Chinese large scale tuna longliners in the Indian Ocean between September 2008 and January 2009.During the surveys,the vessels targeted bigeye tuna(Thunnus obesus)but also caught yellowfin tuna(Thunnus albacares),swordfish(Xiphias gladius),albacore(Thunnus alalunga) and billfishes(Istiophoridae).The hook depths(188 hooks) were measured using temperature depth recorders(TDRs) and the three dimensional current was measured at a range of depths at 24 sites using an acoustic doppler current profiler(ADCP).We developed a three-dimensional numerical longline model(3DNLM) using finite element analysis and the minimum potential energy principle method.We used Matrix Laboratory(MATLAB) software to program and conduct the numerical calculations.The three di-mensional current data were assigned to seven,50 m depth intervals(e.g.,0–50,50–100,or 300–350 m).The co-ordinates of all the nodes of the longline(including the float lines,mainline,and branch lines) were calculated by inputting three-dimensional current profile data,fishing gear parameters(the diameter of the mainline and branch line,the total weight of the branch line and the bait in the water,the density of the mainline and branch line,the elastic modulus of the mainline,the length of the branch line,and the length of the float rope),operating parame-ters(vessel speed,line shooter speed,and the time interval between two hooks) into the numerical model.The model then outputs the shape of the longline under water and the depth of each hook.We verified the model output using experimental data.The model was able to accurately depict the three-dimensional shape and hook depths of the pelagic longline.There was no significant difference between the hook depth measured by TDR and the model estimate of hook depth(P=0.220.05).The average difference between two methods was 12.03 m(range: 0.02–40.36 m,S2=100.30,S=10.01,n=188).The underwater shape of the main line was represented by a wave-shaped curve.The shape was related to the force of the branch line.This load was concentrated at the re-spective node of the main line and made the depth of this node deeper.The main line between two nodes may have floated somewhat because of lift generated by sea currents,especially upwelling currents.The model estimates of the three-dimensional shape and the hook depths were influenced by the value of the drag coefficient(CN90).CN90 was defined as the drag coefficient associated with water flow plumb to the cylinder.The value of the drag coeffi-cient(CN90) was determined based on the Reynolds number(Re) of the study object.

Must marine predators always follow scaling laws? Memory guides the foraging decisions of a pursuit-diving seabird

Foraging animals are expected to adapt their movement patterns to their environment in a way that maximizes efficiency. The search strategies they rely on to achieve this is an enduring question in ecology. Scale-free Levy and Brownian search strategies have received particular attention as both strategies are considered effective when prey are abundant and Levy search is thought to optimize success when prey are patchy. Environmental context has been shown to explain Levy and Brownian movement patterns for various marine predators, but potential effects of habitat structure and cognitive skills are often overlooked. We used bird-borne global positioning sensors (GPS) and temperature depth recorders (TDR) to assess flight paths and dive profiles of foraging parental common murres, Uria aalge. Movement patterns while flying and diving were best approximated by Brownian motion even though their primary prey, capelin, Mallotus villosus, are patchily distributed. Contrary to expectations, there was virtually no support for Levy flights. Further analyses revealed that murre foraging activities are not random, but are rather more deterministic. Murres repeatedly returned to previously visited sites (within ∼2 km), indicating a role of memory, and they focused foraging activities using small-scale area restricted search (ARS;

How age and sex drive the foraging behaviour in the king penguin

As predicted by life history theory, once recruited into the breeding population and with increasing age, long-lived animals should be able to manage more efficiently the conflict between self-maintenance and reproduction. Consequently, breeding performances should improve with age before stabilizing at a certain level. Using temperature–depth recorders and isotopic analysis, we tested how age affects the foraging behaviour of king penguin Aptenodytes patagonicus during one trip in the chick-rearing phase. Depending on sex and age, king penguins expressed two different foraging strategies. Older birds gained more daily mass per unit body mass than younger ones. Older females conducted shorter trips, dived deeper and performed more prey pursuits. They also had higher blood levels of δ15N than younger individuals and males indicating sex- and age-specific dietary regimes. However, we found no differences in carbon isotopic signature, suggesting that individuals exploited the same foraging areas independently of sex and age. Our results suggest that king penguins are able to increase the quantity of energy extracted with increasing age and that such a strategy is sex-related. Our study is the first to reveal of an interaction between age and sex in determining foraging efficiency in king penguins.

A hard-knock life: the foraging ecology of Cape cormorants amidst shifting prey resources and industrial fishing pressure

Once one of the most numerous seabirds of the Benguela upwelling system, the population of Cape cormorants Phalacrocorax capensis has decreased by 60% in the past three decades and the species is listed as Near Threatened. Declines in prey availability and/or abundance brought about by recent changes in the distribution of pelagic fish stocks and industrial purse-seine fishing are hypothesised to be a key driver of seabird population decreases in the southern Benguela. We investigated the foraging behaviour of breeding Cape cormorants by deploying GPS and temperature–depth recorders on 24 breeding adults from three islands off the coast of South Africa, two of them to the north of Cape Point and a third farther south on the western Agulhas Bank. This provided the first measures of foraging dispersal by a cormorant in the Benguela system, and enabled a comparison of foraging behaviour between birds from these islands. Foraging trips of Cape cormorants lasted between 17 min and >7 h, at a maximum distance of between 2 and 58 km away from their colony. Foraging effort was significantly greater for birds from farther north off the West Coast in terms of trip duration, distance travelled, number of dives and time spent flying compared to those from the southernmost island (Dyer), which is probably a response to low prey availability in the north. Coastal reserves that exclude pelagic fishing from inshore feeding grounds around Cape cormorant breeding colonies may result in increased local prey availability, which would benefit Cape cormorant populations.

Foraging trip time-activity budgets and reproductive success in the black-legged kittiwake

Seabirds are central place foragers during the breeding season and, as marine food resources are often patchily distributed, flexibility in foraging behaviour may be important in maintaining prey delivery rates to chicks. We developed a methodological approach using a com- bination of GPS data loggers and temperature-depth recorders that allowed us to describe the behaviour of surface-feeding seabirds. Specifically, we tested whether differences in foraging behaviour of black-legged kittiwakes Rissa tridactyla could be linked with reproductive success by comparing 2 consecutive years at 2 sites. At Rathlin Island (Northern Ireland) during 2010, for- aging differed markedly from that during 2009 and from that at Lambay Island (Republic of Ire- land) during both years. Birds exhibited foraging trips of greater duration, travelled a greater total distance, spent more time in transit and spent longer recuperating on the surface of the water. This notable shift was associated with a decline in breeding success, with greater loss of eggs to preda- tion and lower prey delivery rates, resulting in the starvation of 15% of chicks. We suggest that food resources were reduced or geographically less accessible during 2010, with suitable foraging areas located further from the colony. Birds did not invest greater amounts of time attempting to catch prey. Thus, our results indicate that kittiwakes at Rathlin modulated their foraging behav- iour not by increasing foraging effort through feeding more intensively within prey patches but by extending their range to increase the probability of encountering more profitable prey patches.