Patterns of seasonal occurrence,distribution, and site fidelity of coastal bottlenose dolphins (Tursiops truncatus) in southern New Jersey,U.S.A.

Coastal bottlenose dolphins (Tursiops truncatus) form a mosaic of resident and seasonal migratory populations along the United States Atlantic seaboard. Seasonal, poorly known migrants (identified as a separate stock) move as far north as New Jersey. During 2003–2005, 73 boat‐based photo‐identification surveys were conducted in southern New Jersey to discern seasonal occurrence, distribution, and patterns of movement and site fidelity. Neonates, young‐of‐year, and adults occurred in the study area from late May through late September, corresponding to water temperatures of 14.0–16.3°C. Of 205 individuals identified, 44% (n= 90) were sighted multiple times within or among years, including 10% (n= 20) of individuals identified in all 3 yr. Almost half (47%) of the multiple sightings were observed along a core area encompassed by the southern part of the Jacques Cousteau National Estuarine Research Reserve. In contrast to stocks studied in southern coastal areas of the U.S. Atlantic and Gulf of Mexico, estuaries were used significantly less than open‐beach habitat, which is consistent with the relative prey abundance in these habitats. Research at additional sites will help confirm whether bottlenose dolphins at the northern end of their migratory range exhibit local site fidelity and habitat preferences similar to those found in this study.     

Fishery and Ontogenetic Driven Changes in the Diet of the Spiny Dogfish, Squalus acanthias, in Patagonian Waters, Argentina

The diet of the spiny dogfish in northern and central Patagonian waters was studied from the by-catch of the bottom trawling fisheries directed to Argentine hake Merluccius hubbsi and Argentine red shrimp Pleoticus muelleri between 1996 and 1998. Food habits were analyzed in relation to sex and maturity of sharks. Also, the relationship between diet and abundance of the main prey was explored. Intraspecific diet comparisons were performed. Differences in diet were found between immature individuals, mature males, and mature females. The Argentine shortfin squid Illex argentinus, the Argentine hake and ctenophores Pleurobrachia pileus were the most important prey for the spiny dogfish. Immature and small individuals were pelagic predators. After sexual maturity, the spiny dogfish shifted its diet. Mature and large individuals tended to reduce the consumption of ctenophores, and increase the consumption of demersal and benthic species. Previous diet studies on the spiny dogfish in 1984–1985 and 1994 indicated that the Argentine hake was the most important prey. In the present study, carried out in 1998, squid was the most important prey, followed by the hake. This diet change was related to the major decrease of hake due to overfishing and the increase of squid abundance between 1994 and 1999.     

Understanding the migration ecology of European red admirals Vanessa atalanta using stable hydrogen isotopes

Tracking migratory movement of small animals with variable migration patterns is difficult with standard mark–recapture methods or genetic analysis. We used stable hydrogen isotope (δD) measurements of wings from European red admirals Vanessa atalanta to study several aspects of this species’ migration. In the central part of southern Europe we found large differences in δD values between red admirals sampled in autumn and spring supporting the hypothesis that reproduction takes place in the Mediterranean region during winter. There was also an apparent influx to southern Europe in the spring of individuals with a more southerly origin, since many samples had higher δD values and similar to those expected from coastal areas of North Africa. We found a clear seasonal difference in the δD values of red admirals sampled in northern Europe. Spring migrants arriving in northern Europe generally had high δD values that indicated a southerly origin. In autumn, δD values suggested that red admirals were mostly from regions close to the sampling sites, but throughout the sampling period there were always individuals with δD values suggesting non‐local origins. The migration pattern of this species is supposedly highly variable and plastic. δD differences between individuals in the western part of Europe were generally small making migratory patterns difficult to interpret. However, butterflies from western Europe were apparently isolated from those from north‐eastern Europe, since δD values in the western region rarely corresponded to those of autumn migrants from the north‐east. Use of δD data for inferring butterfly migration in Europe is complex, but our study showed that this technique can be used to help uncover previously unknown aspects of red admiral migration.     

Mapping Global Diversity Patterns for Migratory Birds

Nearly one in five bird species has separate breeding and overwintering distributions, and the regular migrations of these species cause a substantial seasonal redistribution of avian diversity across the world. However, despite its ecological importance, bird migration has been largely ignored in studies of global avian biodiversity, with few studies having addressed it from a macroecological perspective. Here, we analyse a dataset on the global distribution of the world’s birds in order to examine global spatial patterns in the diversity of migratory species, including: the seasonal variation in overall species diversity due to migration; the contribution of migratory birds to local bird diversity; and the distribution of narrow-range and threatened migratory birds. Our analyses reveal a striking asymmetry between the Northern and Southern hemispheres, evident in all of the patterns investigated. The highest migratory bird diversity was found in the Northern Hemisphere, with high inter-continental turnover in species composition between breeding and non-breeding seasons, and extensive regions (at high latitudes) where migratory birds constitute the majority of the local avifauna. Threatened migratory birds are concentrated mainly in Central and Southern Asia, whereas narrow-range migratory species are mainly found in Central America, the Himalayas and Patagonia. Overall, global patterns in the diversity of migratory birds indicate that bird migration is mainly a Northern Hemisphere phenomenon. The asymmetry between the Northern and Southern hemispheres could not have easily been predicted from the combined results of regional scale studies, highlighting the importance of a global perspective.     

Altitudinal distribution and seasonal life cycle of drosophilid flies (Diptera: Drosophilidae) in central Japan,with reference to their biogeographic features

Altitudinal distribution and seasonal life cycle of drosophilid flies (Diptera) were studied on the southwestern slope of Mt. Higashi-Kagonoto in Tomi and at Ishi-no-yu in Shiga Heights, Nagano, central Japan. Collections of flies were carried out from early spring to late autumn using traps baited with fermenting banana. Based on the present results and previous faunal reports from central Japan, major native drosophilid species collected in this study were classified into migratory (5 species), high-altitude (6), mid-altitude (14) and low-altitude (14) species. The migratory species are assumed to perform extensive seasonal migration between low- and high-altitude areas. Among these native species, Drosophila alpina (a high-altitude species) and D. moriwakii (a mid-altitude species) are assumed to pass only one generation in a year, while the others pass two or more generations. Five of the six high-altitude species are assigned as the Palearctic elements, while four of the five migratory species and 12 of the 14 low-altitude species are assigned as the Sino-Japanese elements. The mid-altitude species consist of approximately equal numbers of the Palearctic and Sino-Japanese elements. Among the high-altitude species, D. alpina and Hirtodrosophila makinoi are also distributed in high-altitude areas in Hokkaido, northern Japan. The other high-altitude species and most of the mid-altitude species generally occur in low-altitude areas in Hokkaido or the further north. The Sino-Japanese elements occurring at high and mid altitudes in central Japan are also distributed at high altitudes in southern and southwestern China.     

Spatial overlap of shark nursery areas and the salmon farming industry influences the trophic ecology of Squalus acanthias on the southern coast of Chile

Potential interactions between marine predators and humans arise in the southern coast of Chile where predator feeding and reproduction sites overlap with fisheries and aquaculture. Here, we assess the potential effects of intensive salmon aquaculture on food habits, growth, and reproduction of a common predator, the spiny dogfish—identified as Squalus acanthias via genetic barcoding. A total of 102 (89 females and 13 males) individuals were collected during winter and summer of 2013–2014 from the Chiloé Sea where salmon aquaculture activities are concentrated. The low frequency of males in our study suggests spatial segregation of sex, while immature and mature females spatially overlapped in both seasons. Female spiny dogfish showed a functional specialist behavior as indicated by the small number of prey items and the relative high importance of the austral hake and salmon pellets in the diet. Immature sharks fed more on pellets and anchovies than the larger hake‐preferring mature females. Our results also indicate that spiny dogfish switch prey (anchovy to hake) to take advantage of seasonal changes in prey availability. Despite differences in the trophic patterns of S. acanthias due to the spatial association with intensive salmon farming, in this region, there appears to be no difference in fecundity or size at maturity compared to other populations. Although no demographic effects were detected, we suggest that a range of additional factors should be considered before concluding that intensive aquaculture does not have any impact on these marine predators.     

Range-wide migration corridors and non-breeding areas of a northward expanding Afro-Palaearctic migrant,the European Bee-eater Merops apiaster

Across their ranges, different populations of migratory species often use separate routes to migrate between breeding and non-breeding grounds. Recent changes in climate and land-use have led to breeding range expansions in many species but it is unclear whether these populations also establish new migratory routes, non-breeding sites and migration phenology. Thus, we compared the migration patterns of European Bee-eaters Merops apiaster from two established western (n = 5) and eastern (n = 6) breeding populations in Europe, with those from a newly founded northern population (n = 19). We aimed to relate the breeding populations to the two known non-breeding clusters in Africa, and to test for similarities of migration routes and timing between the old and new populations. Western Bee-eaters used the western flyway to destinations in West Africa; the eastern birds uniformly headed south to southern African non-breeding sites, confirming a complete separation in time and space between these long-established populations. The recently founded northern population, however, also used a western corridor, but crossed the Mediterranean further east than the western population and overwintered mainly in a new non-breeding area in southern Congo/northern Angola. The migration routes and the new non-breeding range overlapped only slightly with the western, but not with the eastern, population. In contrast, migration phenology appeared to differ between the western and both the northern and the eastern populations, with tracked birds from the western population migrating 2–4 weeks earlier. The northern population thus shares some spatial traits with western Bee-eaters, but similar phenology only with eastern population. This divergence highlights the adjustments in the timing of migration to local environmental conditions in newly founded populations, and a parallel establishment of new breeding and non-breeding sites.     

Season-specific directional movement in migratory Australian butterflies

Large numbers of adults of certain species of butterfly flying in an apparently 'purposeful' manner are often noted by entomologists and the general public. Occasionally, these are recorded in the literature. Using these records we summarise information regarding the direction of movement in Australian butterflies and test whether there are consistent patterns that could account for known seasonal shifts in geographical range. The data were analysed using contingency tables and directionality statistics. Vanessa itea, Vanessa kershawi, Danaus plexippus , Danaus chrysippus and Badamia exclamationis flew predominately south in the spring–summer and north in the autumn–winter. Tirumala hamata has a strong southern component to its flight in spring but, as in Euploea core, appears non-directional in the autumn. For many supposedly known migratory species, the number of literature records are few, particularly in one season (mainly autumn). Thus, for Appias paulina , four of seven records were south in the spring–summer, as were six of nine records for Catopsilia pomona, and three of five for Zizina labradus. For Belenois java , flight records were only available for the spring and these showed geographical differences; predominantly north-west in northern Australia (Queensland) and south-west in southern Australia (Victoria, New South Wales). There were too few records for Papilio demoleus in the literature (four only) to draw any conclusions. Major exceptions to the seasonal trend of south in the spring and north in the autumn were Junonia villida , which showed a predominant north-westward direction in both seasons, and Eurema smilax, with a predominant southern or western flight in both seasons. We discuss these species specific trends in migration direction in relation to seasonal shifts in suitable habitat conditions, possible cues used in orientation and in timing changes in direction.     

Compensatory frugivory in migratory Sylvia warblers: geographical responses to season length

Seasonal shifts in the diets of Garden Warblers Sylvia borin , Blackcaps S. atricapilla and Lesser Whitethroats S. curruca at a North German site were studied from samples obtained by flushing the digestive tract of the birds. The significance of seven species of berries and pulpy fruits in the diet of these species while feeding in riparian vegetation during the premigratory and migratory seasons was assessed and compared with the pattern of frugivory shown by the same species in southern Germany. Because of the short time span between hatching and onset of migration, first-year long- and medium-distance migratory Sylvia warblers from northern Europe are forced to accelerate their juvenile development. Presumably to meet the higher nutritional demands of an accelerated development, juvenile Garden Warblers and Blackcaps in northern Germany ate relatively more fruit during premigration than Blackcaps in southern Germany. Fruit occurred in about 90% of their diet samples during both premigration and migration. However, this might not hold true for experienced adult birds. Garden Warblers accelerated the rate of fattening and reduced the time needed to prepare for migration when feeding on a mixed fruit diet. There were indications that Blackcaps directly influenced the fruit choice of Garden Warblers when fruits preferred by both species were scarce. Blackcaps and Garden Warblers showed subtle differences in their seasonal preferences for black elder Sambucus nigra and woody nightshade Solanum dulcamara .     

Genetic Structure and Demographic History Reveal Migration of the Diamondback Moth Plutella xylostella (Lepidoptera: Plutellidae) from the Southern to Northern Regions of China

The diamondback moth Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) is one of the most destructive insect pests of cruciferous plants worldwide. Biological, ecological and genetic studies have indicated that this moth is migratory in many regions around the world. Although outbreaks of this pest occur annually in China and cause heavy damage, little is known concerning its migration. To better understand its migration pattern, we investigated the population genetic structure and demographic history of the diamondback moth by analyzing 27 geographical populations across China using four mitochondrial genes and nine microsatellite loci. The results showed that high haplotype diversity and low nucleotide diversity occurred in the diamondback moth populations, a finding that is typical for migratory species. No genetic differentiation among all populations and no correlation between genetic and geographical distance were found. However, pairwise analysis of the mitochondrial genes has indicated that populations from the southern region were more differentiated than those from the northern region. Gene flow analysis revealed that the effective number of migrants per generation into populations of the northern region is very high, whereas that into populations of the southern region is quite low. Neutrality testing, mismatch distribution and Bayesian Skyline Plot analyses based on mitochondrial genes all revealed that deviation from Hardy-Weinberg equilibrium and sudden expansion of the effective population size were present in populations from the northern region but not in those from the southern region. In conclusion, all our analyses strongly demonstrated that the diamondback moth migrates within China from the southern to northern regions with rare effective migration in the reverse direction. Our research provides a successful example of using population genetic approaches to resolve the seasonal migration of insects.     

A model-driven approach to quantify migration patterns: individual, regional and yearly differences

1.?Animal migration has long intrigued scientists and wildlife managers alike, yet migratory species face increasing challenges because of habitat fragmentation, climate change and over-exploitation. Central to the understanding migratory species is the objective discrimination between migratory and nonmigratory individuals in a given population, quantifying the timing, duration and distance of migration and the ability to predict migratory movements. 2.?Here, we propose a uniform statistical framework to (i) separate migration from other movement behaviours, (ii) quantify migration parameters without the need for arbitrary cut-off criteria and (iii) test predictability across individuals, time and space. 3.?We first validated our novel approach by simulating data based on established theoretical movement patterns. We then formulated the expected shapes of squared displacement patterns as nonlinear models for a suite of movement behaviours to test the ability of our method to distinguish between migratory movement and other movement types. 4.?We then tested our approached empirically using 108 wild Global Positioning System (GPS)-collared moose Alces alces in Scandinavia as a study system because they exhibit a wide range of movement behaviours, including resident, migrating and dispersing individuals, within the same population. Applying our approach showed that 87% and 67% of our Swedish and Norwegian subpopulations, respectively, can be classified as migratory. 5.?Using nonlinear mixed effects models for all migratory individuals we showed that the distance, timing and duration of migration differed between the sexes and between years, with additional individual differences accounting for a large part of the variation in the distance of migration but not in the timing or duration. Overall, the model explained most of the variation (92%) and also had high predictive power for the same individuals over time (69%) as well as between study populations (74%). 6.?The high predictive ability of the approach suggests that it can help increase our understanding of the drivers of migration and could provide key quantitative information for understanding and managing a broad range of migratory species.     

Geographical differences in seasonal clutch size variation in multi-brooded bird species

The seasonal pattern of clutch size variation in birds varies among species. In single-brooded bird species clutch sizes decline continuously with date from an early season maximum. In resident multi-brooded species, clutch sizes first increase to a mid-season maximum and then decrease again. Limited data for multi-brooded migratory birds suggest that clutches in these species also show a continuous decline throughout the season, but it remains to be resolved whether this applies generally and whether migration adds a constraint to the system. We here report on a study of the Eastern Bluebird Sialia sialis conducted using data collected by volunteers across most of its range. In the southern part of its range, where Eastern Bluebirds are largely year-round residents, clutches initially increase, reach a mid-season maximum and gradually decline later in the season. In the northern part of the range, where the majority of Eastern Bluebirds are migratory, clutch sizes decline continuously throughout the season. To determine whether seasonal changes in the clutch size of multi-brooded species are determined by migratory behaviour of the population we compared our results with published data on the Dunnock Prunella modularis and conclude that in multi-brooded species migratory behaviour is not a sufficient condition for a continuous seasonal decline in clutch size, but it could be a necessary one. We propose two mechanisms for the pattern observed among multi-brooded migrants: (i) a time or energy cost of migration, and (ii) a more abrupt increase in seasonal resources in spring at more northerly latitudes.     

Evolution of bird migration in a biogeographical context

We infer from the literature that migratory habits of birds evolved in various phylogenetic lineages and biogeographical contexts, either after gradual range expansion into seasonal habitats, or due to environmental changes within established breeding ranges. Shifts of breeding ranges are the results of interactions between colonization due to dispersal and extinction due to deteriorating conditions. Range expansions provide a platform for the evolution of migration from the newly colonized areas towards seasonally favourable non‐breeding areas. A comparison of palaeoclimatic changes with concurrent evolution and distribution of passerine birds suggests that at least some of the basic genera of the Passerida radiated on the northern continents when quasi‐tropical or subtropical climates prevailed. The Passerida may be a special case, but they suggest that ‘tropical origin’ does not necessarily imply a ‘southern origin’ of migratory species. Climate deterioration required adaptations either towards on‐site survival under harsh conditions or towards escape movements allowing improved non‐breeding survival in less seasonal climates or with reversed seasonality. Taxon‐specific life‐history traits and environmental conditions favoured either sedentary or migratory lines of adaptation. Repeated climate variation induced range shifts and concurrent increases or decreases in the expression of migratory behaviour. Two examples of waders suggest that the principle of range shift, followed by the development of migratory habits, is also applicable for other taxonomic groups.     

Continental efforts: migration speed in spring and autumn in an inner-Asian migrant

Migration speed in passerines is generally assumed to be higher in spring than in autumn. So far this has been only shown for the western Palaearctic-Afrotropic migration system. I compiled published records of the movements of Siberian stonechats Saxicola torquata maura in Central and northern Asia to reconstruct their spatiotemporal movement patterns in this region and to estimate migration speed in spring and autumn. My estimate of spring migration speed in the Siberian stonechats does not differ from that in autumn and is lower than the reported spring migration speeds in European passerines. Northward progression of Siberian stonechats seems to be constrained by the prevailing environmental conditions, as indicated by low temperatures and vegetation indices. Low food availability at stopover and the obstruction of the migration route by steep environmental gradients may apply also to other migratory species in the area.     

The behaviour of sharks

Summary Despite the recent upsurge of interest in shark research, the current status of knowledge of the behavioural repertoire of most species is alarmingly incomplete. Clearly, from the steadily decreasing numbers of sharks caught by commercial and sport fishermen, sharks are highly vulnerable to human exploitation. Although education is making inroads, there is still steady opposition to the enforcement of catch limits and management strategies for most species. Accurate life history and behavioural information is required to enforce management policies. Wetherbee et al. (1990) cited a case in which commercial fishermen accused the spiny dogfish of stripping the commerical and recreational fisheries of their herring and salmon catch. A detailed study of the spiny dogfish diet disproved their claims.Sharks are clearly not mindless eating machines, as they have been labelled in the past. They are intelligent and have complex patterns of movement, space utilization, and social organization. Using a combination of remote and direct observational techniques, the scientific community is beginning to have a more complete understanding of these important apex predators in coral reef and oceanic ecosystems. More importantly, researchers who are interested in pursuing the fascinating field of shark behaviour still have a wide choice of direction.     

Interspecific exchange of avian influenza virus genes in Alaska: the influence of trans-hemispheric migratory tendency and breeding ground sympatry

The movement and transmission of avian influenza viral strains via wild migratory birds may vary by host species as a result of migratory tendency and sympatry with other infected individuals. To examine the roles of host migratory tendency and species sympatry on the movement of Eurasian low-pathogenic avian influenza (LPAI) genes into North America, we characterized migratory patterns and LPAI viral genomic variation in mallards (Anas platyrhynchos) of Alaska in comparison with LPAI diversity of northern pintails (Anas acuta). A 50-year band-recovery data set suggests that unlike northern pintails, mallards rarely make trans-hemispheric migrations between Alaska and Eurasia. Concordantly, fewer (14.5%) of 62 LPAI isolates from mallards contained Eurasian gene segments compared to those from 97 northern pintails (35%), a species with greater inter-continental migratory tendency. Aerial survey and banding data suggest that mallards and northern pintails are largely sympatric throughout Alaska during the breeding season, promoting opportunities for interspecific transmission. Comparisons of full-genome isolates confirmed near-complete genetic homology (>99.5%) of seven viruses between mallards and northern pintails. This study found viral segments of Eurasian lineage at a higher frequency in mallards than previous studies, suggesting transmission from other avian species migrating inter-hemispherically or the common occurrence of endemic Alaskan viruses containing segments of Eurasian origin. We conclude that mallards are unlikely to transfer Asian-origin viruses directly to North America via Alaska but that they are likely infected with Asian-origin viruses via interspecific transfer from species with regular migrations to the Eastern Hemisphere.     

The influence of seasonal migration on range size in temperate North American passerines

Seasonal migration has been alternately proposed to promote geographic range size in some contexts and to constrain it in others, but it remains unclear if migratory behavior has a general effect on range size. Because migration involves movement, most hypotheses about the relationship between migration and range size invoke an influence of migration on the process of dispersal-mediated range expansion. Intuitively, a positive relationship between migratory behavior and dispersal ability could bolster range expansion among migratory species, yet some biogeographic patterns suggest that long-distance migration may instead impede range expansion, especially in the temperate zone. We conducted a comparative analysis of the relationship between migratory behavior and range size by testing the effect of migratory status, migration distance and morphological dispersal ability on breeding range size among all temperate North American passerines. Further, we assessed whether these traits affect range expansion into suitable habitat by analyzing their relationship with range filling (the proportion of climatically-suitable area occupied, or ‘filled’ by a species). Contrary to previous studies, we found migration and dispersal ability to be poor predictors of range size and range filling in North America. Rather, most variation in range size is explained by latitude. Our results suggest that migratory behavior does not affect range size within the scale of a continent, and furthermore, that temperate North American passerines’ breeding ranges are not influenced by their dispersal abilities. To better understand why migratory behavior appears to promote range size in some contexts and constrain it in others, future studies should investigate how migratory behavior affects dispersal at the individual level, as well as the relationship between the evolution of migratory behavior and the breadth of species’ climatic niches.     

Zugunruhe of migratory and non-migratory birds in a circannual context

Recent findings in non-migratory birds have reopened questions about the interpretation and seasonal organization of Zugunruhe . I address the relationship between Zugunruhe and migration by comparing underlying circannual patterns in captive populations of migratory and non-migratory stonechats. Zugunruhe was highly variable and lacked clear periodicity, indicating its sensitivity to external cues. Patterns of Zugunruhe were similar in African residents, European short-distance migrants, and Siberian long-distance migrants, revealing no major difference in circannual organization. Moult was regulated independently of Zugunruhe and timed more rigidly, particularly in stonechats from equatorial Africa. The persistent and variable circannual patterns of Zugunruhe suggest that non-migratory and migratory stonechats have similar underlying programs but have modified the expression of actual migration. The findings, together with published observations from other species, emphasize the importance of considering programs for migration in a wide range of species, without losing sight of its environmental context.     

Reply to Hussey et al.: The requirement for accurate diet-tissue discrimination factors for interpreting stable isotopes in sharks

Carbon and nitrogen stable isotope analyses have improved our understanding of food webs and movement patterns of aquatic organisms. These techniques have recently been applied to diet studies of elasmobranch fishes, but isotope turnover rates and isotope diet–tissue discrimination are still poorly understood for this group. We performed a diet switch experiment on captive sandbar sharks (Carcharhinus plumbeus) as a model shark species to determine tissue turnover rates for liver, whole blood, and white muscle. In a second experiment, we subjected captive coastal skates (Leucoraja spp.) to serial salinity reductions to measure possible impacts of tissue urea content on nitrogen stable isotope values. We extracted urea from spiny dogfish (Squalus acanthias) white muscle to test for effects on nitrogen stable isotopes. Isotope turnover was slow for shark tissues and similar to previously published estimates for stingrays and teleost fishes with low growth rates. Muscle isotope data would likely fail to capture seasonal migrations or diet switches in sharks, while liver and whole blood would more closely reflect shorter term movement or shifts in diet. Nitrogen stable isotope values of skate blood and skate and dogfish white muscle were not affected by tissue urea content, suggesting that available diet–tissue discrimination estimates for teleost fishes with similar physiologies would provide accurate estimates for elasmobranchs.     

Do abiotic and ontogenetic factors influence the diet of a generalist predator? Feeding ecology of the Pacific spiny dogfish (<Emphasis Type="Italic">Squalus suckleyi</Emphasis>) in the northeast Pacific Ocean

Stomach contents from 1221 Pacific spiny dogfish (Squalus suckleyi) were collected from the Gulf of Alaska over 2004–2006 and analyzed to determine predominant prey species. Pacific spiny dogfish in the Gulf of Alaska have a variable diet suggesting that they are generalist feeders. Of the 68.30% of stomachs with prey contents, the most important prey groups based on the percent prey-specific index of relative importance (%PSIRI) were shrimp (27.06%), cephalopods (17.16%), and forage fish (17.11%). Remaining components of the diet were inconsistent. Commercially valuable species, such as salmon, Oncorhynchus spp., and rockfish, Sebastes spp. constituted only 2.37% and 1.51% of the diet of Pacific spiny dogfish, respectively. Diet diversity was not significantly influenced by spatial, temporal or ontogenetic factors; however, trophic level of prey and average prey item weight varied both interannually and with ontogeny. With increasing size, Pacific spiny dogfish incorporate larger prey items into their diet, and diet composition may be driven more by seasonal availability and prey size than any other factors.