Intensity Of Cannibalism Research Articles

Positive temperature effects on the initiation and intensity of cannibalistic behaviour of larval pike, Esox lucius L. Is cannibalism reflected in otolith fluctuating asymmetry?

Cannibalism can be a significant factor limiting the survival of pike, Esox lucius, early life stages in both natural and aquaculture conditions. In the present research, type I cannibalism was studied in pike larvae (size range: 9–32.5 mm standard length, SL) in controlled conditions for 45 days post-hatching (dph). For this purpose, the occurrence of cannibalistic pairs, i.e. prey caught by a cannibal inside the cannibal’s mouth, was monitored for 15 min periods by two observers six times daily. Cannibalism was not observed in fish that still had yolk-sacs, but it did occur as soon as the yolk-sac was absorbed on 5 dph at a body size of 13 mm at 22 °C and 10 dph at a body size of 13.4 mm at 15 °C. The ratio of prey to predator size was on average 87%, but the smallest observed size difference was only 1.3%. The intensity of cannibalistic attacks depended on water temperature with more intense cannibalism at 22 °C than at 15 °C, and no cannibalism at 10 °C. Fluctuating asymmetry (FA) in all three sagittal otolith size parameters (area, width, and length) was higher in prey than in cannibals, the differences were not statistically significant.

Effects of resource-dependent cannibalism on population size distribution and individual life history in a case-bearing caddisfly.

Resource availability often determines the intensity of cannibalism, which has a considerable effect on population size distribution and individual life history. Larvae of the caddisfly Psilotreta kisoensis build portable cases from sedimentary sands and often display cannibalism. For this species, the availability of preferable case material is a critical factor that affects larval fitness, and material is locally variable depending on the underlying geology. In this study, we investigated how sand quality as a case material determines cannibalism frequency among larvae and, in turn, how the differential cannibalism frequency affects the body-size distribution and voltinism. Rearing experiments within a cohort revealed that a bimodal size distribution developed regardless of material quality. However, as the preferable material became abundant, the proportion of larger to smaller individuals increased. Consecutive experiments suggested that smaller larvae were more frequently cannibalized by larger ones and excluded from the population when preferable smooth material was abundant. This frequent cannibalism resulted in a bimodal size distribution with a significantly higher proportion of larger compared to smaller individuals. The size-dependent cannibalism was significantly suppressed when the larvae were raised in an environment with a scarcity of the preferable case material. This is probably because larvae cannot enjoy the benefit of rapid growth by cannibalism due to the difficulties in enlarging their case. At low cannibalism the growth of smaller individuals was stunted, and this was probably due to risk of cannibalism by larger individuals. This growth reduction in small individuals led to a bimodal size-distribution but with a lower proportion of larger to smaller individuals compared to at high cannibalism. A field study in two streams showed a similar size distribution of larvae as was found in the rearing experiment. The bimodal ratio has consequences for life history, since a size-bimodal population causes a cohort splitting: only larvae that were fully grown at 1 year had a univoltine life cycle, whereas larvae with a stunted growth continued their larval life for another year (semivoltine). This study suggests that availability of preferable case building material is an important factor that affects cannibalism, which in turn affects larval population size structure and cohort splitting.

Isogroup Selection to Optimize Biocontrol Increases Cannibalism in Omnivorous (Zoophytophagous) Bugs.

Zoophytophagous insects can substitute animals for plant resources when prey is scarce. Many arthropods feed on conspecifics to survive in these conditions. An individual’s tendency for cannibalism may depend on its genotype along with its diet specialization, in interaction with the availability of alternative food resources. We compared two isogroup lines of the zoophytophagous mullein bug, either specialized on animal or on plant diets, that were generated to improve biocontrol. We predicted that: (1) bugs from the prey-specialized line would show higher levels of cannibalism than bugs from the pollen-specialized line, and (2) both lines would decrease cannibalism levels in the presence of their preferred resource. Under laboratory conditions, large nymphal instars had 24 hours to feed on smaller instars, in the absence of additional resources, or with either spider mites or pollen present. Cannibalism was reduced by the availability of both prey and pollen, although prey had a lower effect than pollen. The intensity of cannibalism was always higher in the prey-specialized line than in the pollen-specialized line, regardless of the availability of supplemented resources. The pollen-specialized line had decreased cannibalism levels only when pollen was available. These results indicate that cannibalism is a potentially regulating force in the prey-specialized line, but not in the pollen-specialized line.

Growth, cannibalism, and survival relations in larvae of European catfish, Silurus glanis (Actinopterygii: Siluriformes: Siluridae)—attempts to mitigate sibling cannibalism

Background. Under culture conditions, intra-cohort cannibalism is one of the main factors that affects the growth and survival of fishes, especially during the early life stages of carnivorous species. Cannibalism is chiefly influenced by environmental factors, but parental effects cannot be excluded. The complete elimination of cannibalism in the larviculture of carnivorous fish species is virtually impossible, but it may be possible to mitigate its impact through a better understanding of the extrinsic and intrinsic factors that affect the intensity of cannibalism. The presently reported study had two complementary objectives: a) it examined how the growth–cannibalism–survival dynamics in cultured larvae of European catfish, Silurus glanis Linnaeus, 1758, is affected by maternal influence, and b) it evaluated the possibility of reducing cannibalism while supplementing food with tryptophan (TRP), which is a precursor of serotonin that has a becalming effect on fish. Materials and methods. Two 30-day experiments were conducted (0L : 24D, 26.5–27.0°C). In the first experiment, 3–day old larvae of European catfish originating from four female parents (f1, f2, f3, and f4) were cultured in full siblings groups. In the second experiment, larvae from all four progenies were reared together and fed commercial diets supplemented with different doses of tryptophan (T0, T1, T2). Fish mortality including cannibalism, growth, and biomass were estimated every 10 days during both experiments. Results. In both experiments, cannibalism was the main cause of mortality and losses to type II (complete) cannibalism were higher than those caused by type I (incomplete) cannibalism. No maternal influence on cannibalistic behaviour was found. Tryptophan supplementation had no significant effect on fish growth or survival. Conclusion. The results of presently reported studies confirmed that cannibalism is an important factor affecting survival in larviculture of European catfish. Controlled conditions used in initial rearing of European catfish larvae, significantly enhanced the survival of juvenile catfish in comparison to traditional pond culture.

Cannibalism among size classes of larvae may be a substantial mortality component in tuna

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 433:205-219 (2011) - DOI: https://doi.org/10.3354/meps09187 Cannibalism among size classes of larvae may be a substantial mortality component in tuna P. Reglero1,*, A. Urtizberea2, A. P. Torres1, F. Alemany1, Ø. Fiksen2, 3 1Instituto Español de Oceanografía, Centre Oceanogràfic de les Balears, Moll de Ponent s/n, 07015 Palma, Spain2Department of Biology, University of Bergen, PO Box 7803, 5020 Bergen, Norway3Uni Research, PO Box 7810, 5020 Bergen, Norway *Email: patricia.reglero@ba.ieo.es ABSTRACT: Cannibalism among size classes may reduce starvation and improve survival of larval tuna in oligotrophic ocean areas, but it may also be a substantial mortality component depending onthe availability of alternative prey. Here, we combine laboratory and field data on tuna larvae with amodel of larval foraging and bioenergetics to explore the role of cannibalism in cohort developmentat different temperatures, durations of hatching period, hatching larval densities and natural mortalityrates. Prey fields (zooplankton densities and co-occurrence of different larval stages of 3 species of tuna) were established from cruises in a main tuna spawning area around the Balearic Islands (Mediterranean Sea). Results suggest that a pure zooplankton diet is frequently insufficient to sustain larval growth. Piscivory can be a major source of larval mortality among tuna species and larvae hatched early can feed on abundant larvae of smaller size and have fewer predators themselves. We show how the intensity of cannibalism depends on the temperature dependent growth rate and the resulting relative size distribution when eggs are released continuously over a period of a few weeks. The predator-prey size distribution and the relative densities of these voracious larvae may produce overcompensation in recruitment under some environmental conditions. KEY WORDS: Cannibalism · Foraging model · Intraspecific predation · Natural mortality · Pelagic larvae · Predator-prey interactions · Size spectra · Surf-riding Full text in pdf format PreviousNextCite this article as: Reglero P, Urtizberea A, Torres AP, Alemany F, Fiksen Ø (2011) Cannibalism among size classes of larvae may be a substantial mortality component in tuna. Mar Ecol Prog Ser 433:205-219. https://doi.org/10.3354/meps09187 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 433. Online publication date: July 18, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Early development of Brycon orthotaenia (Pisces: Characidae)

Brycon orthotaenia is an important fish for commercial and sport fishing and may reach 7 kg in body weight; it is endangered in some regions of Brazil's São Francisco River Basin. Breeders were subjected to spawning induction to analyse the early development; oocytes and semen were obtained by manual extrusion and fertilization was carried out using the dry method. After fertilization, eggs were kept in incubators at 24°C. Egg samples were collected every 10 min until hatching in order to monitor embryonic development and were analysed and photographed. Larvae samples were collected daily until the seventh day to analyse the larvae development; larvae were fixed in Bouin's fluid and subjected to routine histological and histochemical techniques for glycoprotein and glyco-conjugated detection. Oocyte extrusion occurred 6 h after the second hormone dose at 26°C. The recently extruded oocytes were spherical, dark green and non-adhesive, with a diameter of 1479.67 ± 53.18 and 3094.60 ± 80.34 μm after hydration. The blastopore closure occurred within 7 h 30 min of fertilization and the fertilization rate was 50.0 ± 5.5 % at 24°C. Embryonic development was completed within 21 h 30 min of fertilization. Complete yolk sac resorption and mouth opening occurred on the third day after hatching, at which time an adhesive organ with mucosubstances was observed. On the third day, an olfactory chamber with cilia and intense cannibalism amongst the larvae was observed. The complete differentiation of the digestive system occurred on the fifth day and the nervous and sensorial systems differentiation occurred on the sixth to seventh days.

The Ecology of Atlantic Cod (<i>Gadus morhua</i>) in Canadian Arctic Lakes

The range of limnological conditions that support Atlantic cod populations in meromictic Arctic lakes is known to be relatively restricted. The degree to which differences in these features, particularly in the availability of allochthonous and autochthonous prey, affect the condition and growth of cod in these populations is unknown. We compared measures of condition among three Atlantic cod populations on Baffin Island, Nunavut, to assess their relationship to differences in potentially important habitat parameters. We also compared data spanning two decades (Ogac Lake) to five decades (Qasigialiminiq) to assess the degree to which natural and anthropogenic factors may have affected these populations. In general, growth rate and asymptotic length tend to be high under situations of intense cannibalism and when alternative prey species are relatively abundant. Biotic and abiotic habitat features in Ogac Lake appear to have been relatively stable since the 1950s, although the abundance of sea urchins appears to have decreased, which may explain the observation that the incidence of cannibalism has doubled. The mean size of angled cod in Qasigialiminiq has decreased by about 10 cm over the past 20 years.

Morphological and behavioral development of the piracanjuba larvae

The objective of this work was to study the morphologic development and the swimming and feeding behaviors of piracanjuba larvae, Brycon orbignyanus Valenciennes (1849) (Characiformes, Characidae, Bryconinae), during the period from zero to 172 hours after hatching (standard length = 3.62 - 11.94 mm). The morphological analyses were accomplished by using a trinocular stereo microscope, while the behavioral analyses were performed through periodic observations. In 28 hours after hatching, the larvae (standard length = 6.25 ± 0.13 mm) showed the following structural and behavioral characteristics that made them become active predators able to overcome a larval critical phase, the beginning of exogenous feeding: presence of pigmented eyes, terminal and wide mouth, developed oral dentition, developing digestive tube, yolk sac reduction, fins and swim bladder formation, horizontal swimming, cannibalism, and predation. Intense cannibalism among larvae was verified from 26 to 72 hours. At the end of the metamorphosis - 172 hours after hatching - the larvae measuring 11.94 + 0.80 mm in standard length presented a flexed notochord, caudal fin bifurcation, dorsal and anal fin formation, synchronized movements, and formation of shoals, characteristics that together allow enhanced perception and locomotio in exploration of the environment, determining the best moment for transfering to the fishponds. New studies can contribute to commercial fish farming by improving feeding management, performance, survival, and productivity of this species.

The Ecological Significance and Incidence of Intraguild Predation and Cannibalism among Anurans in Ephemeral Tropical Pools

Ephemeral pools are traditionally considered to be tadpole refuges, with few or no predators. While it is recognized that some tadpoles are predaceous, little attention has been given to understanding how tadpoles shape age and size structures of populations and the composition of tadpole assemblages. I examined the incidence of intraguild predation (IGP) among three species that co-occur in ephemeral pools in the Osa Peninsula, Costa Rica. I found a high incidence of IGP among the three species, with IG predators differing in their voracity for prey eggs and IG prey differing in their vulnerability to IGP. I also examined the factors that influence the intensity of cannibalism and tadpole performance in a model species, Smilisca phaeota. I manipulated predator and prey size and developmental stage, tadpole density, food quantity, and tadpole relatedness in microcosm experiments. Cannibalism in S. phaeota was dependent on tadpole predator and prey size and developmental stage, with medium and large tadpoles causing almost complete mortality of embryos, but little mortality of mobile hatchlings. In contrast, predation by small tadpoles was restricted primarily to the embryo developmental stage. Tadpole mortality was high in low plant food quantity treatments, suggesting a high incidence of cannibalism. Other measures of tadpole performance, including survival to metamorphosis, metamorph mass, and larval period, were influenced by tadpole density and plant food quantity. Additions of conspecific prey eggs and degree of tadpole relatedness did not affect tadpole performance. My results suggest that tadpoles are capable of playing a regulatory role, influencing the relative abundance and composition of species in pools through differential IGP and cannibalism on eggs and hatchlings. The intensity of IGP in ephemeral pools is likely influenced by the morphology of IG predators, reproductive mode and fecundity of IG prey, and priority effects. My study supports the view that we need to reconsider the position tadpoles occupy within the aquatic food webs, with greater appreciation for their role as predators.

Growth and morphological development of laboratory-reared larval and juvenile Pangasianodon hypophthalmus

The morphological development, including the fins, body proportions and pigmentation, of laboratory-reared larval and juvenile Pangasianodon hypophthalmus was described and their behavioral features were observed under rearing conditions. Body lengths (BL) of larvae and juveniles were 3.0 ± 0.2 (mean ± SD) mm just after hatching, and 12.9 ± 1.1 mm on day 13, reaching 23.4 ± 1.8 mm on day 25 after hatching. Aggregate fin ray numbers (for caudal fin, principal soft ray number) attained their full complements in specimens larger than 12.8 mm BL. Notochord flexion began in yolksac larvae on day 0 (10.5 h after hatching), with teeth buds and barbels appearing with jaw formation in yolksac flexion larvae on day 1. Melanophores on the body increased with growth, with a broad vertical band forming on the lateral line and an oblique band extending from above the pectoral fin base towards the forepart of the anal fin during the postflexion larval and juvenile stages. Body proportions became relatively constant in juveniles, except for maxillary barbel length (MBL), which continued to decrease. Yolksac flexion larvae started feeding on day 2 with the onset of intense cannibalism. Yolks were completely absorbed by day 3, and cannibalism ended by day 6. Subsequently, fish displayed a schooling behavior with growth, preferring relatively dark areas during the juvenile stage.

Isolation of 10 microsatellite markers in Crepidula coquimbensis (Gastropod, Calyptraeideae) for parentage analyses

AbstractMarine invertebrates show a high diversity of embryonic developmental modes and reproductive behaviour. However, little is known about the factors that are promoting the evolution of different strategies. The gastropod Crepidula coquimbensis has a direct embryonic development with encapsulated embryos showing a cannibalistic behaviour. Preliminary observations suggest that victim embryos are not randomly chosen. With intracapsular multipaternity, the intensity of cannibalism might vary according to the relatedness of the siblings. Paternity analyses based on highly polymorphic markers can provide valuable insights into this cannibalism behaviour. Ten polymorphic microsatellite loci were thus developed: the level of polymorphism is large enough to perform paternity analysis and investigate relatedness in this species.

Desenvolvimento embrionário e larval da piracanjuba, Brycon orbignyanus, Valenciennes, 1849 (Pisces, Characidae)

The knowledge of embryonic and larvae development of fishes is a fundamental key which enables a closer approach to their biology and taxonomy. The present study aims to characterize piracanjuba (Brycon orbignyanus) embryonic and larvae development. During the whole embryogenesis, 15 to 20 embryos were sampled and analyzed. Eggs of B. orbignyanus are semidense, transparent, spherical, and bear a large perivitelline space. Hatching takes place 18 hours and 30 minutes after fertilization at 25 ± 0.8ºC. Total length and weight of just hatched larvae were 4.46 ± 0.39mm and 2.56 ± 0.73mg, respectively. Larvae presented entirely developed and pigmented eyes, as well as a vertical mouth opening of 15.2 ± 1.9% of body length, 36 hours after hatching, period from which intense cannibalism was observed

Size heterogeneity prevails over kinship in shaping cannibalism among larvae of sharptooth catfish Clarias gariepinus

Because preying on close relatives may cause a loss of inclusive fitness, cannibalistic animals are generally deemed to cannibalise non-related conspecifics preferentially to kins. Whether this basic principle also applies to fish exerting intracohort cannibalism at an early developmental stage is uncertain, and more intense cannibalism among mixed progenies might just be a consequence of greater size heterogeneity. To investigate this, progenies of sharptooth catfish of equivalent initial body weights but with contrasting size heterogeneity were reared separately or in mixed groups containing equal proportions of each progeny (27 ± 1°C, 12 h light:12 h night, 2.5 L aquaria, 100 or 200 fish·L –1). Cannibalism was monitored on a daily basis until the end of the larval stage (3–15 days after hatching). Cannibalism in mixed groups was intermediate between those in pure progenies, and was positively correlated ( R 2 = 0.803, P < 0.01) with initial size heterogeneity, irrespectively of fish origin. This finding does not exclude that catfish larvae were able to discriminate between siblings and non-related fish, but this obviously had very little influence on cannibalism. The implications of this finding are discussed, as they apply to prey selection in fast growing larvae, and aquaculture of catfish.

Sibling cannibalism in dorada under experimental conditions.

Cannibalism among embryos and larvae ofBrycon moorei(Characidae) occurs during daytime and night‐time, and persists under permanent darkness. Embryos and larvae of dorada‐provisioned with formulated feed over the first week of exogenous feeding did not survive, except for those exerting cannibalism. When offered alternative fish prey [embryos ofProchilodus magdalenae(0·5–0·8 mg) andOreochromis niloticus(9–10 mg)], 1‐day‐old embryos of dorada preferred preying on these, thereby reducing early cannibalism. However, this promoted depensatory growth and more intense cannibalism later in the larval stage. Dorada provisioned withArtemianauplii in excess showed more homogeneous growth and higher survival, most cannibalistic acts being restricted to the first 24 h of exogenous feeding, just after oral teeth were fully developed (21 h after hatching). Provisioning dorada withArtemianauplii a few hours before their oral teeth were fully developed reduced early cannibalism from 41 to 15%. High proportions of deformed fish caused higher mortality, both directly and indirectly, as they promoted early cannibalism, depensatory growth and more intense cannibalism among larvae. The initial sorting of embryos, based on their occupation of the water column improved survival significantly during the first week of exogenous feeding, up to 52% in progenies containing &lt;10% of deformed fish. Size‐grading of larvae and young juveniles over the next 2 weeks reduced cannibalism to 2·6 and 1·9% day−, in the first and second weeks, respectively. These results indicate that cannibalism in dorada can be mitigated efficiently through appropriate rearing procedures, and open promising perspectives for the intensive culture of this fast‐growing tropical species.

Sibling cannibalism in dorada under experimental conditions.

Cannibalism among embryos and larvae of Brycon moorei (Characidae) occurs during daytime and night‐time, and persists under permanent darkness. Embryos and larvae of dorada provisioned with formulated feed over the first week of exogenous feeding did not survive, except for those exerting cannibalism. When oered alternative fish prey [embryos ofProchilodus magdalenae(0·5–0·8 mg) andOreochromis niloticus(9·10 mg)], 1‐day‐old embryos of dorada preferred preying on these, thereby reducing early cannibalism. However, this promoted depensatory growth and more intense cannibalism later in the larval stage. Dorada provisioned withArtemianauplii in excess showed more homogeneous growth and higher survival, most cannibalistic acts being restricted to the first 24 h of exogenous feeding, just after oral teeth were fully developed (21 h after hatching). Provisioning dorada with Artemia nauplii a few hours before their oral teeth were fully developed reduced early cannibalism from 41 to 15%. High proportions of deformed fish caused higher mortality, both directly and indirectly, as they promoted early cannibalism, depensatory growth and more intense cannibalism among larvae. The initial sorting of embryos, based on their occupation of the water column improved survival significantly during the first week of exogenous feeding, up to 52% in progenies containing &lt;10% of deformed fish. Size‐grading of larvae and young juveniles over the next 2 weeks reduced cannibalism to 2·6 and 1·9% day−1, in the first and second weeks, respectively. These results indicate that cannibalism in dorada can be mitigated eciently through appropriate rearing procedures, and open promising perspectives for the intensive culture of this fast‐growing tropical species.

Sibling cannibalism in dorada under experimental conditions. II. Effect of initial size heterogeneity, diet and light regime on early cannibalism

Cannibalism among embryos and larvae of Brycon moorei (Characidae) occurs during daytime and night-time, and persists under permanent darkness. Embryos and larvae of dorada provisioned with formulated feed over the first week of exogenous feeding did not survive, except for those exerting cannibalism. When offered alternative fish prey [embryos of Prochilodus magdalenae (0.5-0.8 mg) and Oreochromis niloticus (9-10 mg)], 1-day-old embryos of dorada preferred preying on these, thereby reducing early cannibalism. However, this promoted depensatory growth and more intense cannibalism later in the larval stage. Dorada provisioned with Artemia nauplii in excess showed more homogeneous growth and higher survival, most cannibalistic acts being restricted to the first 24 h of exogenous feeding, just after oral teeth were fully developed (21 h after hatching). Provisioning dorada with Artemia nauplii a few hours before their oral teeth were fully developed reduced early cannibalism from 41 to 15%. High proportions of deformed fish caused higher mortality, both directly and indirectly, as they promoted early cannibalism, depensatory growth and more intense cannibalism among larvae. The initial sorting of embryos, based on their occupation of the water column improved survival significantly during the first week of exogenous feeding, up to 52% in progenies containing < 10% of deformed fish, Size-grading of larvae and young juveniles over the next 2 weeks reduced cannibalism to 2.6 and 1.9% day -1 , in the first and second weeks, respectively. These results indicate that cannibalism in dorada can be mitigated efficiently through appropriate rearing procedures, and open promising perspectives for the intensive culture of this fast-growing tropical species.

Size-dependent foraging efficiency, cannibalism and zooplankton community structure.

To examine size-dependent food web interactions in systems with cannibalism, we compared the abundances of zooplankton and phytoplankton over 2 years in four lakes with cannibalistic perch (Perca fluviatilis) of which two also supported the top predator pike (Esox lucius). The abundance of perch 2 years and older was lower in lakes with pike than in lakes with only perch. In contrast, the abundance of small perch (young-of-the-year and 1-year old) was lower in lakes with only perch suggesting that intense cannibalism reduced these size classes to low levels in lakes lacking pike. Functional response experiments with differently sized perch and zooplankton showed that the attack rate of small perch susceptible to cannibalism was much higher than that of large cannibalising perch. The optimal body size of perch with respect to attack rate was also lower for small zooplankton prey than for large zooplankton. The zooplankton communities in lakes with only perch were dominated by the relatively small species Ceriodaphnia quadrangula and Bosmina spp. and total zooplankton biomass was higher in these lakes than in lakes with both pike and perch. In contrast, the mean size of cladoceran zooplankton was largest in lakes with both pike and perch owing to a dominance of the large zooplankton species Holopedium gibberum in these lakes. We relate these patterns to (1) the low foraging efficiency of large perch on small zooplankton and (2) the low abundance of small zooplanktivorous perch (due to cannibalism) in lakes with only perch. The differences in zooplankton community structure also resulted in different seasonal dynamics of phytoplankton between lakes. Cannibalism introduces a vertical heterogeneity to food webs that causes consumer-resource dynamics that are not predictable from linear food chain models.

On relationships between cannibalism, climate variability, physical transport, and recruitment success of Bering Sea walleye pollock (Theragra chalcogramma)

Walleye pollock (Theragra chalcogramma) is the single most abundant fish species in the Bering Sea and comprises the bulk of the commercial catch. Juvenile pollock are an important forage fish for older pollock, other fish, marine mammals, and birds. We examine the interaction between cannibalism, climate variability, and related patterns in physical transport. Our analysis of adult and juvenile pollock abundance and distribution time series, ocean current modelling studies, and information on climate variability indicates that cannibalism is a major determinant of interannual recruitment variability. In turn, the intensity of cannibalism appears to be dependent on the degree of spatial separation of adults and juveniles. Strong year classes occur when juvenile pollock are transported inshore and away from adults in spring - conditions typical of warm years. In cold years, transport is reduced and juveniles remain on the outer shelf in proximity to adults. Co-occurring distribution patterns of adults and juveniles resulting from these conditions lead to potentially increased cannibalism and subsequent weak year classes.

Sibling cannibalism among juvenile vundu under controlled conditions. I. Cannibalistic behaviour, prey selection and prey size selectivity

Sibling cannibalism among vundu Heterobranchus longifilis larvae started at the age of 4 days, with the prey caught tail-first then swallowed up to the head, which was eventually discarded (type I cannibalism). At 17 days old, this type of cannibalism vanished and was replaced by the ingestion of the whole prey (type II cannibalism), which could only be exerted by predators six times as heavy as their prey. Type II cannibalism consisted of a seemingly opportunistic ambush attack by a formerly passive predator towards a disorientated prey. It required no preliminary aggression or chase, or even contact with the prey, suggesting that the attack was not mediated by the tactile sense, and that cannibalism was independent of aggressive behaviour. When alternative food resources (formulated feed, live tilapia prey) were available, the intensity of cannibalism decreased but pellet-eaters or tilapia predators always achieved lower growth rates than those feeding on conspecifics, suggesting that cannibalism was the most advantageous foraging tactic. Losses to cannibalism among populations of 30-day old juvenile vundu with an initial ratio of 4% of cannibals were as high as 75·5–79·9% over 15 days. Predation peaked during the first days (up to 2·8 prey C−1 day−1), then vanished progressively as surviving prey grew faster than cannibals and escaped their predation. Cannibals preferred consuming the largest prey available with respect to the logistics of cannibalism (body weight ratio of 6·0). This preference for large prey was interpreted both as a foraging tactic aiming to maximize the energetic return, and as foraging strategy enabling the cannibals to exploit their prey as long as possible. Based on these data, comprehensive models of the impact of cannibalism on vundu populations were developed.

Sibling cannibalism among juvenile vundu under controlled conditions. I. Cannibalistic behaviour, prey selection and prey size selectivity

Sibling cannibalism among vundu Heterobranchus longifilis larvae started at the age of 4 days, with the prey caught tail‐first then swallowed up to the head, which was eventually discarded (type I cannibalism). At 17 days old, this type of cannibalism vanished and was replaced by the ingestion of the whole prey (type II cannibalism), which could only be exerted by predators six times as heavy as their prey. Type II cannibalism consisted of a seemingly opportunistic ambush attack by a formerly passive predator towards a disorientated prey. It required no preliminary aggression or chase, or even contact with the prey, suggesting that the attack was not mediated by the tactile sense, and that cannibalism was independent of aggressive behaviour. When alternative food resources (formulated feed, live tilapia prey) were available, the intensity of cannibalism decreased but pellet‐eaters or tilapia predators always achieved lower growth rates than those feeding on conspecifics, suggesting that cannibalism was the most advantageous foraging tactic. Losses to cannibalism among populations of 30‐day old juvenile vundu with an initial ratio of 4% of cannibals were as high as 75·5–79·9% over 15 days. Predation peaked during the first days (up to 2·8 prey C−1 day−1), then vanished progressively as surviving prey grew faster than cannibals and escaped their predation. Cannibals preferred consuming the largest prey available with respect to the logistics of cannibalism (body weight ratio of 6·0). This preference for large prey was interpreted both as a foraging tactic aiming to maximize the energetic return, and as foraging strategy enabling the cannibals to exploit their prey as long as possible. Based on these data, comprehensive models of the impact of cannibalism on vundu populations were developed.