Northeast Coast Of Newfoundland Research Articles

Variable forage fish biomass and phenology influence marine predator diet, foraging behavior, and species interactions in coastal Newfoundland, Canada

Abstract Forage fish species provide essential linkages for energy transfer within pelagic marine food webs. Capelin (Mallotus villosus), the focal forage fish in coastal Newfoundland, Canada, suffered a stock collapse in 1991 and has not recovered. Despite this collapse, capelin continue to provide locally abundant prey aggregations. Here, I synthesize the lessons learned from a long-term capelin-predator research program (2004–2022) on the northeast Newfoundland coast during the postcollapse period. I highlight the importance of simultaneously estimating forage fish biomass and predator responses in a multispecies and multiyear context. High interannual variation in capelin spawning timing and biomass was observed. Lower capelin biomass consistently resulted in predator species- and assemblage-level dietary shifts toward a higher diversity of lower trophic level, alternative prey. Energetic foraging costs of seabirds also increased under lower capelin biomass, but responses differed among species. Summer capelin consumption by dominant seabirds (9389 tonnes) and whales (778 tonnes) indicated predator energetic requirements and revealed higher natural mortality relative to fishery-based (1289 tonnes) mortality. Overall, this case study illustrated that, despite high observed behavioural plasticity, varying species-specific predator responses to changing capelin biomass integrated to increase potential competitive interactions under low capelin biomass, providing a basis for ecosystem-level change.

All roads lead to Rome: inter-origin variation in metabolomics reprogramming of the northern shrimp exposed to global changes leads to a comparable physiological status

Impacts of global ocean changes on species have historically been investigated at the whole-organism level. However, acquiring an in-depth understanding of the organisms’ cellular metabolic responses is paramount to better define their sensitivity to environmental challenges. This is particularly relevant for species that experience highly different environmental conditions across their distribution range as local acclimatization or adaptation can influence their responses to rapid global ocean changes. We aimed at shedding light on the cellular mechanisms underpinning the sensitivity to combined ocean warming (OW) and acidification (OA) in the northern shrimp Pandalus borealis, from four different geographic origins defined by distinctive environmental regimes in the northwest Atlantic: i.e. St. Lawrence Estuary (SLE), Eastern Scotian Shelf (ESS), Esquiman Channel (EC) and Northeast Newfoundland Coast (NNC). We characterized targeted metabolomics profiles of the muscle of shrimp exposed to three temperatures (2, 6 or 10°C) and two pH levels (7.75 or 7.40). Overall, shrimp metabolomics profiles were modulated by a significant interaction between temperature, pH and origin. Temperature drove most of the metabolomics reprogramming, confirming that P. borealis is more sensitive to OW than OA. Inter-origin differences in metabolomics profiles were also observed, with temperature*pH interactions impacting only shrimp from SLE and ESS, pH affecting only shrimp from SLE and temperature impacting shrimp from all origins. Temperature influenced metabolomics pathways related to the tricarboxylic acid cycle (TCA) and amino acid metabolism, resulting mainly in an accumulation of TCA intermediates and tyrosine. Temperature*pH and pH in isolation only affected amino acid metabolism, leading to amino acids accumulation under low pH. However, the ratio of ATP : ADP remained constant across conditions in shrimp from all origins suggesting that their energetic status is not affected by OW and OA. Still, the accumulation of TCA intermediates and tyrosine suggests the possible enhancement of immune responses under future OW and OA conditions. Our findings suggest that shrimp from SLE are more sensitive at the molecular level, compared to others, to future complex environmental conditions. This underlines the importance of investigating intraspecific variation in mechanisms of responses to combined drivers when trying to define species’ sensitivity to global ocean changes.

RNA-seq analysis of the mantle transcriptome from Mytilus edulis during a seasonal spawning event in deep and shallow water culture sites on the northeast coast of Newfoundland, Canada.

The blue mussel (Mytilus edulis) has global commercial and ecological importance both in wild and cultured conditions. However there is a qualitative and quantitative lack of knowledge of the molecular mechanisms associated with its reproductive physiology, especially with reference to environmental interactions. Here we initiated a transcriptomic analysis (RNA-sequencing (RNA-seq)) of the mantle from both sexes sampled during a seasonal spawning event and from two culture depths (shallow-5m; deep- 15m). Mantle libraries were produced from 3 males and 3 females sampled from each of two shallow sites and two deep sites for a total of 12 replicate male and 12 replicate female libraries (24 total libraries). Overall a total of 2.3 billion raw 100 base reads with an average of 96.5 million reads/library were obtained and assembled into 296,118 transcripts with an average length of 568bp. Overall, 315 transcripts from male libraries and 25 from female libraries were found to be upregulated in deep water as compared to shallow (edgeR adjusted p value≤0.05). Conversely, 126 transcripts from male libraries and 135 from female libraries were found to be significantly downregulated at the same depth. Thirteen transcripts were selected for qPCR validation based on importance in reproduction, antimicrobial defense and metabolism. Of these, 9 RNA-seq identified transcripts were shown by qPCR to be differentially expressed between groups: 2 were upregulated in deep compared with shallow water (dhx38, mt-co1), 2 were upregulated for female compared with male mantle (pias2, mapkap1) and 6 genes (fndc3a, acbd3, klhl10, ccnb3, armc4, mt-co1) showed to be upregulated in males compared to females. The majority of qPCR studied transcripts were identified as involved in gamete development based on the UniProt database. This study further characterizes the importance of the mantle transcriptome during reproductive activities of M. edulis.

Stable isotope analysis reveals that humpback whales (Megaptera novaeangliae) primarily consume capelin (Mallotus villosus) in coastal Newfoundland, Canada

On the Newfoundland (Canada) foraging ground, humpback whales (Megaptera novaeangliae (Borowski, 1781)) are found associated with a dominant forage fish species, capelin (Mallotus villosus (Müller, 1776)), that experienced a population collapse in the early 1990s and has not recovered. Our primary goal was to reconstruct dietary proportions of humpback whales on their summer foraging grounds off the northeast coast of Newfoundland during July–August 2016 and 2017 using a Bayesian stable isotope mixing model (MixSiar). Modelled dietary proportions were similar in both years, with capelin comprising ∼90% of the diet. However, both δ13C and δ15N in humpback whale skin differed significantly between years, resulting in minimal isotopic niche overlap (9%). Lipid-extracted and nonlipid-extracted skin samples were used to develop a lipid normalization equation: Δ13C = –3.184 + 1.011(C:N). Overall, findings suggest that capelin is the primary prey type of humpback whales in coastal Newfoundland, despite the continued collapsed state of the capelin population. Findings also reiterate that dietary reconstruction from stable isotope analysis of cetacean skin can be misinterpreted without concurrently sampled isotopic ratios of potential prey types.

Capelin (Mallotus villosus) availability influences the inshore summer diet of Atlantic cod (Gadus morhua) in coastal Newfoundland

In the early 1990s, the Atlantic cod (Gadusmorhua) population on the Newfoundland and Labrador shelf declined dramatically, leading to a fishing moratorium in 1992. The Northern cod population has not fully recovered, possibly due to the simultaneous population collapse of an important prey type, capelin (Mallotus villosus), which migrates from the continental shelf into coastal Newfoundland to spawn every summer. Our objective was to test whether capelin availability influenced short-term dietary shifts of cod while inshore on the northeast Newfoundland coast. We quantify the dietary composition and relative abundance and biomass of prey types in cod stomachs sampled weekly or bi-weekly throughout July-August 2017 and 2018. Survey-based acoustic estimates of capelin biomass and the timing of spawning in the study area revealed that peak capelin biomass was five times higher (0.239 g/m²) and two weeks earlier (July 28) during 2018 relative to 2017 (0.048 g/m², August 9). Cod stomachs were ~ 10 times more likely to contain capelin during 2018 relative to 2017. As capelin availability increased throughout each summer, cod shifted from a high diversity diet of lower-quality invertebrate prey (e.g., shrimp, crab) to a low diversity, capelin-dominated diet, whereby capelin presence, abundance and biomass increased. These findings indicate that capelin remains a primary prey type of cod in inshore waters during their summer growing season, but dietary proportions of capelin vary with their availability. As low dietary proportions of capelin are associated with reduced body condition and reproductive potential in cod, findings support the need for an integrated capelin-cod management approach.

Seabirds vary responses to supplemental food under dynamic natural prey availability and feeding aggregation composition

Abstract While foraging, a predator can feed solitarily or in a group. The net energy gain of joining a group is predicted to vary with prey patch quality, species-specific prey capture behavior, and the size and species composition of the predator group. In coastal Newfoundland, Canada, capelin (Mallotus villosus), a key forage fish, migrates inshore to spawn during the summer, resulting in a dramatic shift in prey availability. During July–August 2015–2017, we examined the numerical and behavioral responses of procellarid (Great Shearwater [Ardenna gravis], Sooty Shearwater [A. grisea], Northern Fulmar [Fulmarus glacialis]), and gull species (Herring Gull [Larus argentatus], Great Black-backed Gull [L. marinus]) to fish offal under varying capelin availability as well as flock size and composition using an at-sea experiment on the northeast Newfoundland coast. The experiment consisted of providing offal every 30 s (10-min experimental period), along with 10-min control periods before and after. We recorded the species-specific number of birds on the water, the number of birds simultaneously attempting to capture offal, and the number of successful attempts (“foraging success”). The number of birds on the water was lower during high capelin availability for all species, except for Northern Fulmar. The number of conspecifics simultaneously attempting to capture offal increased with the number of conspecifics on the water, but plateaued at different numbers (4–17) for most species. The species-specific proportion of successful attempts (i.e. foraging success) varied with flock size and composition (i.e. number of conspecifics, heterospecifics, species). Foraging success of Herring Gulls and fulmars were moderately affected by flock size and composition, suggesting that they may be dominant competitors. Findings suggest that seabirds rely more heavily on supplemental food sources, such as fisheries discards and offal, when natural prey availability declines, potentially resulting in a higher risk of by-catch during fisheries activities as forage fish stocks decline.

High individual flexibility in the foraging behavior of a marine predator, the common murre

The foraging ecology of breeding seabirds is largely influenced by prey availability and energy demands related to reproduction which, in combination with other factors, can affect resource specialization in space and time. In this study, we combined GPS tracking, dive behavior, and stable isotope ratios of carbon and nitrogen to examine behavioral and dietary flexibility within individuals in a breeding pursuit-diving seabird, the common murre (Uria aalge), on the northeast Newfoundland coast. We examined individual flexibility over 2 years (2016, 2017) during which the timing of arrival and availability of their primary prey, capelin (Mallotus villosus), varied. In both years, we found high within-individual variation in foraging trip and dive characteristics, coupled with low spatial overlap of foraging trips both within and among individuals, indicative of flexible behavior. Concurrently, the isotopic niche of breeding common murres showed a higher degree of dietary consistency, evidenced by similar amounts of variation within and among individuals in stable isotope ratios (δ13C, δ15N). Dietary reconstruction revealed that the proportion of different prey types in the diet varied across individuals, suggesting a degree of dietary flexibility. When capelin (prey) availability was low (in 2017), foraging trips were longer and farther from the colony, maximum dive duration decreased, and the proportion of capelin in the diet decreased. Behavioral flexibility, however, remained similar across both years, regardless of prey availability. Our results suggest that common murres can tolerate and respond to fluctuations in prey availability through flexible foraging strategies. Increased foraging distances during low capelin availability suggest increased energetic costs, and thus, an energetic threshold may be reached above which lower prey availability cannot be tolerated.

Egg cannibalism in capelin Mallotus villosus at beach and deep-water spawning habitats in the north-west Atlantic Ocean.

We investigated egg cannibalism in spawning capelin Mallotus villosus on the north-east Newfoundland coast during July 2012-2014, specifically whether sex, spawning condition (i.e., spawning or spent) and spawning habitat influenced egg cannibalism. Capelin spawning in deep-water were 4.5-14 times more likely to be cannibals than those at the beach, probably due to the higher spatial overlap of spawners and conspecific eggs within this habitat relative to beaches. Males were 2.1-3.7 times more likely to be cannibals than females, but female cannibals had more eggs per stomach. Spawning fish were 1.6-1.9 times more likely to be cannibals than spent fish, but spent female cannibals had more eggs per stomach relative to spawning males and females in either habitat. Findings suggest that cannibalism may be an important foraging strategy, especially at deep-water spawning habitat, possibly extending the spawning season for males or increasing the probability of post-spawning survival for females. Although 44% of sampled females and 50% of males were cannibals, the estimated mortality due to egg cannibalism was low (0.49-2.97% of eggs produced annually), suggesting that egg cannibalism does not influence recruitment to a great extent in Newfoundland capelin.

Investigation of the context of humpback whale non-song calls in the North Atlantic

Humpback whales display behavioural plasticity in their foraging behaviours and non-song calling behaviours. Prey type appears to be associated with some of the variation in foraging behaviours and, thus, may also be related to variation in use of non-song calls related to foraging. Our goal was to compare non-song calls from two regions and identify any call types that occur in only one of the regions. We used recordings from stationary hydrophones within two foraging grounds: from the northeast Newfoundland coast, where capelin is the main prey; and the Gulf of Maine, where herring and sand lance dominate the diet. These areas are sympatric and foraging groups are thought to be from the same breeding aggregation, suggesting that call type differences would not have a genetic-basis. Most of the call types were the same across both areas, as has been found across many foraging grounds, but a small number of call types and call sequences were heard in only one of the two regions. We hope to use multi-sensor tag data and video recordings to help identify the contexts of these calls to further determine whether non-song call variation can be linked to prey type. Humpback whales display behavioural plasticity in their foraging behaviours and non-song calling behaviours. Prey type appears to be associated with some of the variation in foraging behaviours and, thus, may also be related to variation in use of non-song calls related to foraging. Our goal was to compare non-song calls from two regions and identify any call types that occur in only one of the regions. We used recordings from stationary hydrophones within two foraging grounds: from the northeast Newfoundland coast, where capelin is the main prey; and the Gulf of Maine, where herring and sand lance dominate the diet. These areas are sympatric and foraging groups are thought to be from the same breeding aggregation, suggesting that call type differences would not have a genetic-basis. Most of the call types were the same across both areas, as has been found across many foraging grounds, but a small number of call types and call sequences were heard in only one of the two regions. We hope to use multi-senso...

Temperature and salinity influence the chemistry in the pre-hatch otolith region of capelin, Mallotus villosus, during lab and field egg incubation experiments

Identifying the natal origin of marine fish is important to understand connectivity and productivity among populations residing in different habitats. Capelin, Mallotus villosus, is a key marine forage fish species that spawns at both beach (warmer, less saline) and deep-water (15–40 m; cooler, more saline) habitats along the northeast Newfoundland coast. Currently, the contribution from each habitat to the spawning population is unknown. Previous research, where capelin eggs from known families were lab-reared, identified family-based otolith chemical signatures in the pre-hatch (embryonic) region of larvae. In this study, we investigated whether temperature and salinity influenced embryonic otolith chemistry to determine whether variation in environmental conditions would result in habitat-specific signatures, thereby overwhelming family-based signatures and allowing the identification of natal origin. Capelin eggs from many families were incubated together under controlled temperature (4, 8, 10 °C) and salinity (10, 20, 30 psu) treatments in the lab and uncontrolled conditions within each habitat in the field. Elemental concentrations (i.e., Sr, Ba, Mg, Mn) in the pre-hatch region of 1-day old larvae were quantified via LA ICP-MS. Elemental concentrations varied among individuals reared under identical conditions, likely due to family-based chemical signatures. Despite this variation, mean elemental concentrations differed when mean temperatures varied by ≥4 °C between treatments (lab) and rearing habitats (field), resulting in high treatment- and habitat-specific classification success (~73–88%) of individuals. In contrast, embryonic otolith chemistry did not vary consistently with salinity. Temperature differs consistently between rearing habitats and, thus, these findings suggest that when capelin rearing habitats differ by ≥4 °C within a year, chemical signatures in the embryonic otolith may be used to determine the natal origin of individuals.

Life history variation across latitudes: observations between capelin (Mallotus villosus) from Newfoundland and the eastern Canadian Arctic

Life history trait variation within a species promotes regional-specific strategies that optimize fitness in a particular environment. Capelin (Mallotus villosus) is an important forage fish species with a circumpolar, temperate distribution, but has increased in relative abundance in Arctic regions recently. To examine for region-specific life history strategies, we compared life history characteristics (length, body condition, age of sexual maturity and growth) of spawning male capelin collected from the eastern Canadian Arctic, in Pangnirtung Fjord, Nunavut (66°N; July 2014 and June–July 2015) with a sub-Arctic location on the northeast coast of Newfoundland (49°N; July 2014 and 2015). First year growth was higher for sub-Arctic relative to Arctic capelin. In contrast, body condition (regression of total length versus mass) was lower for capelin in the Arctic compared to the sub-Arctic population. The age structure of spawning males suggested that Newfoundland capelin reached sexual maturity earlier, as the youngest spawners in Newfoundland were age 2+ (median age: 3+) relative to Pangnirtung where the median spawning age was 4+ (maximum age 5+). Overall, Arctic capelin were generally characterized by lower growth, especially in the first year, later age of reproduction, and lower body condition, relative to the sub-Arctic population. These differences may be the result of limited gene flow on the northern margins of this species’ geographical distribution. They also support previously reported genetic distinction among the sub-Arctic and Arctic clades in the North Atlantic.

Dietary Niche Shifts of Multiple Marine Predators under Varying Prey Availability on the Northeast Newfoundland Coast

Understanding species interactions among top marine predators and interactions with their prey can provide important insight into community-level responses to changing prey availability and the role of apex predators as indicators of ecosystem change. On the northeast Newfoundland coast, marine predators rely on capelin (Mallotus villosus), a dominant forage fish, as a food source. Capelin migrate into coastal regions to spawn during July, essentially transforming food supply from low during early summer (i.e. pre-spawning) to high later in the summer (i.e. spawning). During July-August, 2016, we used stable isotopic ratios of nitrogen (δ15N) and carbon (δ13C) to investigate shifts in dietary niche metrics at the predator group-level (trophic position, dietary niche breadth) and community-level (niche overlap, trophic diversity) for multiple marine predators under varying capelin availability. Predator groups included non-breeding shearwaters (great shearwater Ardenna gravis, sooty shearwater A. grisea), humpback whales (Megaptera novaeangliae), and gull chicks (herring gull Larus argentatus, great black-backed gull L. marinus). We also tested the sensitivity of community-level dietary metrics to a variety of published trophic discrimination factors. Tissue samples from shearwaters (blood cellular component), gull chicks (whole blood), and whales (skin), representing average diets over 2-3 weeks, were collected during three periods (early, mid, late) corresponding to increasing capelin availability. Isotopic niche breadth (Standard Ellipse Area, SEAb) narrowed and trophic position shifted toward higher δ15N for all predator groups as capelin availability increased, suggesting a higher reliance on capelin. Trophic diversity (distance to centroid) decreased with increased capelin availability, while pairwise niche overlap between predator groups was highly variable and sensitive to varying trophic discrimination factors. Findings suggest that although capelin is the dominant forage fish during the summer, predators rely on capelin as prey to varying degrees. Combining species- and community-level metrics of dietary niche and trophic diversity may provide a more complete picture of predator responses to prey availability and, thus, may be important monitoring tools to indicate changes in the food supply of marine predators.

Intrinsic factors influence the timing of arrival of capelin (Mallotus villosus) to spawning grounds in coastal Newfoundland

Capelin (Mallotus villosus) is an important forage fish species in many northern marine ecosystems and, thus, is the primary prey species of many top predators. On the Newfoundland shelf, capelin undergo extensive inshore migrations (>350km) from offshore areas to coastal spawning grounds in the spring, where the timing of inshore arrival is highly variable. We investigated the influence of intrinsic factors (i.e., length, age, spawning experience) and proxies for extrinsic factors (i.e., environmental conditions via otolith chemistry; diet via stable carbon and nitrogen isotope ratios) on the individual-level timing of arrival of capelin at spawning sites on the northeast coast of Newfoundland during July 2012 and 2013. Despite high inter-annual and sex-based variation in almost all factors examined, intrinsic factors varied with timing of arrival at spawning sites, with larger, older male and female capelin arriving first at coastal spawning sites followed by smaller, younger capelin. Alternately, proxies of extrinsic factors did not vary with timing of arrival. Our findings suggest that selectively exploiting early-arriving fish may impact the age/size structure of the population, potentially leading to increased variability in the timing of spawning at the population level and possibly recruitment.

Spawning delays of northern capelin (Mallotus villosus) and recovery dynamics: A mismatch with ice-mediated spring bloom?

The capelin stock off the northeast coast of Newfoundland and southern Labrador collapsed in the early 1990s along with most of the finfish community. Among a host of concomitant physical and behavioral changes was the onset of delayed spawning, a phenomenon that has persisted for over two decades. From the mid-1990s onward, the Newfoundland and Labrador shelf has been warming with ice levels reduced in most years, generally leading to earlier spring plankton blooms. The delayed spawns and earlier blooms have resulted in an increased mismatch between plankton production and larval emergence, which we hypothesized could result in reduced early-life survival and prolonged stock recovery. Among indices associated with the mismatch, including time between blooms and spawning, composition and abundance of zooplankton during early ontogeny, and sea surface temperature and ice coverage, potential linkages were found with first year capelin survival. Increased capelin productivity in recent years has been associated with an increase in preferable and total zooplankton abundance and a decreasing trend in the mismatch with the spring bloom. A generalized linear model incorporating a match–mismatch index and stage I–IV calanus copepods explained 82% of the variance associated with annual age 0 capelin abundance estimates since stock collapse. A central mechanism underlying improvements in capelin productivity appears to be a general reduction in ice coverage associated with a recent warm oceanographic regime that reached record high levels in 2011.

Relative importance of local enhancement as a search strategy for breeding seabirds: an experimental approach

During the breeding season, seabirds may use many behavioural strategies to reduce the time and energy spent searching for patchily distributed prey. Seabirds breeding at a large colony on the northeast Newfoundland coast (Funk Island), primarily common murres, Uria aalge, and northern gannets, Morus bassanus, predominantly feed on capelin, Mallotus villosus. Within foraging ranges, high-abundance capelin aggregations can be predictably located at deep-water (<40 m) spawning sites during the spawning period in mid- to late July, before which capelin are distributed in small, ephemeral schools. To investigate the 'local enhancement' hypothesis, we conducted a field-based experiment by deploying seabird-mimicking plastic models, or 'decoys', during JulyeAugust in 2009 and 2013, to determine whether breeding murres, gannets and Atlantic puffins, Fratercula arctica, respond to seabird aggregations. We used three decoy treatments: ‘Murre’, ‘Gannet’ and ‘Hotspot’ (both murre and gannet decoys). Pursuit-diving and plunge-diving birds were 4e7 and 17 times, respectively more likely to respond to decoy treatment relative to control periods. All species responded more to conspecifics, or to species within the same foraging guild, during single-species treatments (i.e. Murre, Gannet), but responded similarly (i.e. murres, puffins) or more (i.e. gannets) to the Hotspot treatment, suggesting that predator density in general is an important cue. Fewer murres responded to decoys during capelin spawning relative to pre-spawning, suggesting that murres use local enhancement to a lesser degree when prey can be predictably located nearby. This study provides experimental evidence that seabirds use local enhancement as a search strategy, but to varying degrees under changing prey conditions.

Underwater behaviour of common murres foraging on capelin: influences of prey density and antipredator behaviour

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 501:279-290 (2014) - DOI: https://doi.org/10.3354/meps10696 Underwater behaviour of common murres foraging on capelin: influences of prey density and antipredator behaviour Kevin A. Crook, Gail K. Davoren* Department of Biological Sciences, University of Manitoba, Room 212B Biological Sciences Building, 50 Sifton Rd, Winnipeg, Manitoba R3T 2N2, Canada *Corresponding author: gail.davoren@ad.umanitoba.ca ABSTRACT: Diving behaviour of seabirds has been studied using data logging devices, but little is known about underwater predator–prey interactions during dives. We used stationary video cameras to investigate how the underwater foraging behaviour of common murres Uria aalge was influenced by the density and behaviour of their main prey fish, capelin Mallotus villosus, at spawning sites on the northeast Newfoundland coast during July, 2009-2012. From ~720 h of video, we analyzed 99 events where capelin and murres were observed together, ranging from 1-20 s, and 952 events where murres were observed alone, ranging from 1-14 s. Although 91% of all video footage of capelin was in high density schools, 69% of active foraging behaviour of murres (i.e. attempted contacts, approaches) was exhibited on individual capelin, compared to 24% on low density shoals and 7% on high density schools. Similarly, more murres were observed turning, a proxy of area-restricted search behaviour, when solitary and low density capelin shoals persisted for longer durations relative to when schools persisted for longer. When murres made contact with capelin (n = 16), ~70% (n = 11) were deemed successful (i.e. resulted in ingestion or ascent with fish in bill). Unsuccessful contacts resulted from fish escaping during beak manipulations to orient the fish head-first. Capelin were 7-11 times more likely to accelerate when murres displayed active versus passive (i.e. search, travel) foraging behaviours and 5-6 times more likely to accelerate in response to murre presence when in schools relative to low density shoals or solitary individuals. Overall, these results suggest that murres may increase their foraging success within areas of high prey density by preferentially searching for and targeting solitary fish that are less responsive to predators. KEY WORDS: Seabird · Common murre · Capelin · Foraging behaviour · Schooling · Antipredator · Predator–prey Full text in pdf format PreviousNextCite this article as: Crook KA, Davoren GK (2014) Underwater behaviour of common murres foraging on capelin: influences of prey density and antipredator behaviour. Mar Ecol Prog Ser 501:279-290. https://doi.org/10.3354/meps10696 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 501. Online publication date: March 31, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Distribution of marine predator hotspots explained by persistent areas of prey

Investigations of distributional and density patterns of marine predators often reveal areas where high abundances of one or many species overlap in space and time (‘biological hotspots’); however, mechanisms underlying hotspot formation are often unclear, leading to difficulties determining spatial and temporal boundaries of protected areas. On the northeast Newfoundland coast, I previously described annually persistent aggregations of a key forage fish species, capelin (Mallotus villosus): (1) two pre- and post-spawning staging areas in deep (>150 m) bathymetric channels, (2) a cluster of four persistently used demersal spawning sites (17–40 m), and (3) a coastal migratory route (<50 m). Through at-sea surveys repeated over 8 years (2000–2003, 2007, and 2009–2011), I show that the majority of predator hotspots identified were spatially associated with (i.e., within 10 km) these persistent capelin areas for breeding seabirds (common murre: 85.2 ± 4.6 %; northern gannet: 66.9 ± 6.6 %), overwintering seabirds (great and sooty shearwaters: 88.0 ± 6.9 %), and baleen whales (humpback, minke, and fin whales: 86.8 ± 8.6 %). Most predator hotspots were closer to the spawning (3.8–14.0 km) relative to the staging areas (13.1–27.6 km), especially for murres and shearwaters. Interspecific differences were attributed to variation in maximum dive depths and dietary preferences. Predators only aggregated within the spawning area, while capelin were spawning, suggesting that interannual variation in association with predator and capelin hotspots was attributed to variation in survey timing relative to capelin spawning. As these areas of persistent capelin are bound by static bathymetric and large-scale oceanographic features and can be delimited in time based on the capelin spawning period, they may be important candidate areas for protection.

Physical characteristics of persistent deep-water spawning sites of capelin: Importance for delimiting critical marine habitats

In coastal Newfoundland, high abundances of top predators aggregate (biological hotspots) over deep-water (demersal) spawning sites of capelin (Mallotus villosus), the focal forage fish on which most top predators rely for prey. We explore the mechanisms underlying the spatial persistence of hotspot formation by investigating physical characteristics associated with the persistent use of demersal spawning sites of capelin on the northeast Newfoundland coast from 2003 to 2010. The continued presence of suitable spawning sediment (0.5–16 mm) in permanent bathymetric depressions was a key determinant of site use persistence, whereas minimum temperature (~2°C) influenced the use of sites with suitable sediments. We suggest that biological hotspots associated with demersal spawning sites with similar physical characteristics could be used to delineate critical marine habitats for protection throughout the circumpolar distribution of this key forage fish species.

Beach and demersal spawning in capelin (Mallotus villosus) on the northeast Newfoundland coast: egg developmental rates and mortality

Timing of spawning and site selection in fish are important fitness-related traits that ultimately influence reproductive success. Capelin ( Mallotus villosus (Müller, 1776)), a key forage fish in the north Atlantic, spawn eggs that adhere to sediments on beaches and in demersal (deep-water) habitats throughout their geographic range, resulting in divergent thermal regimes for the incubating eggs. We compare the timing and duration of spawning of capelin and its influence on the developmental and survival rates of eggs between a beach and a demersal spawning site on the northeast Newfoundland coast in 2004 and 2005. Spawning events at the beach were at least 10 days earlier and shorter (2–3 days) relative to the demersal site (8–12 days). Hourly and mean daily incubation temperatures at the beach were higher and more variable relative to the demersal site, resulting in two distinct developmental strategies: low to high mortality and rapid development (beach) versus low mortality and slow development (demersal). Higher egg mortality at beach sites was explained by higher and more variable temperatures and potentially limited oxygen replenishment relative to demersal sites. The divergent biology of beach and demersally spawned eggs suggest that each will respond differently to environmental change and, thus, require different approaches for successful management.

Northern Range Extension of the Gladiatior Box Crab, Acanthocarpus alexandri Stimpson, 1871 (Decapoda: Brachyura: Calappidae) in the Northwest Atlantic

Abstract A specimen of a gladiator box crab, Acanthocarpus alexandri Stimpson, 1871, was captured off the northeast coast of Newfoundland during June 2009. This is the first report of the species in Canadian Atlantic waters, and represents a major northern expansion in the distributional range by approximately 800-900 kilometres. The known distribution of this western Atlantic species now extends from Newfoundland to Brazil, encompassing tropical, temperate, and sub-arctic marine ecosystems.