Capelin Larvae Research Articles

How the spatio-temporal overlap of cod, haddock, and capelin larvae affects their recruitment in the Norwegian-Barents Sea system

How the spatio-temporal overlap of cod, haddock, and capelin larvae affects their recruitment in the Norwegian-Barents Sea system

Water strontium concentrations influence strontium concentrations in the pre-hatch otolith region of capelin (Mallotus villosus)

Unique otolith chemistry signatures have been useful in reconstructing environmental histories of teleost fish, including their use as a natural tag of natal habitat. The ability to use otolith chemistry as a chronological measure of life history, however, assumes that the concentrations of trace elements in the ambient environment are taken up and calcified on the otolith in proportion to their environmental availability. Capelin (Mallotus villosus) is a key forage fish species on the Newfoundland Shelf that migrates from offshore to coastal regions during the summer to spawn. Capelin eggs adhere to the sediment at spawning sites, where they remain throughout incubation. As capelin larvae disperse from spawning/rearing sites immediately upon hatch, the pre-hatch region of capelin otoliths, formed during incubation, indicates natal origin. Chemistry in the otolith pre-hatch region of capelin displays high variability, even in environmentally stable lab-rearing experiments and among individuals within the same family, potentially confounding the ability to characterize otolith chemical signatures from different regions. Here, we aimed to determine whether trace element concentrations in the pre-hatch region of capelin otoliths were influenced when naturally fertilized capelin eggs were reared to hatch under varying concentrations of Barium (Ba; 1×, 6×, 7×, 16×, 27×), Strontium (Sr; 1×, 2×, 4×, 5×, 9×), and Ba+Sr (1×, 5×/1.5×, 5×/3×, 10.5×/3.5×, 19×/5× ambient concentration). Naturally fertilized capelin eggs were collected at a beach spawning site in July 2019 and incubated in control or enriched water treatments until hatch. Sagittal otoliths were removed from larvae from each treatment (n = 20) and analysed for their trace element concentrations (e.g., Mg, Mn, Sr, Ba) using Laser Ablation Inductively Coupled Plasma-Mass Spectrometry (LA ICP-MS). Otolith Sr concentrations from 1 to 2 day old larvae increased significantly with increasing ambient Sr concentrations, and the Sr partition coefficient (0.37 ± 0.01) appeared to be concentration-dependent, decreasing non-linearly with increasing ambient water Sr concentrations. In contrast, otolith Ba concentrations remained consistently high despite environmental enrichment. We estimated high Ba partition coefficients (3.67 ± 0.52), which were calculated using the limits of detection for Ba (i.e., 0.0025 mg/L), due to low ambient Ba concentrations. These high estimated Ba partition coefficients suggested that the pre-hatch otolith Ba concentrations may be primarily maternally derived. Overall, findings suggested that regions varying in ambient water Sr concentrations during capelin egg incubation could result in distinct chemical signatures in the pre-hatch region of capelin otoliths, but variability in water Ba concentrations will not. Future studies could use this variation to investigate population connectivity and productivity, which is currently unknown for capelin.

Erratum

Erratum

Otolith Chemistry Reveals Natal Region of Larval Capelin in Coastal Newfoundland, Canada

Identifying natal origins of animals is key to determining the relative productivity of natal habitats, dispersal of individuals among local populations (i.e. connectivity), and, ultimately, metapopulation dynamics. As marine fish larvae have a high potential for dispersal, natural tags such as otolith chemistry are often used to determine natal origins. Trace elements may be incorporated into embryonic otoliths while larvae are developing in the egg, resulting in chemical signatures in the pre-hatch region of the otolith that reflect the natal habitat. Our goal was to determine whether the natal origins of 1-3 day old larval capelin (Mallotus villosus), a key forage fish in many northern marine ecosystems, could be determined using otolith chemistry. We sampled larvae from five Newfoundland regions (i.e. embayments: Placentia Bay, St. Mary’s Bay, Witless Bay, Trinity Bay, Notre Dame Bay) during July-August, 2019 to quantify regional differences in otolith chemistry. Additionally, eggs/larvae were field-reared within two regions over multiple years (Notre Dame Bay: 2014, 2015, 2018, 2019; Trinity Bay: 2018, 2019) to quantify interannual variation in region-specific otolith chemistry. Multi-elemental otolith signatures (i.e., Mg, Mn, Zn, Sr, Ba), as determined by Laser Ablation Inductively Coupled Plasma-Mass Spectrometry (LA ICP-MS), differed significantly among regions, with individuals classified into their natal region with 78% success (region-specific success: 68-100%). Classification success into natal region remained high (67-76%) despite interannual variation in otolith trace element concentrations within regions. Characterizing region-specific otolith chemical signatures that reflect natal origins of capelin larvae is the first step in determining the productivity and relative contributions of different regions of coastal Newfoundland to capelin recruitment.

Early life characteristics of capelin (Mallotus villosus) in the subarctic-arctic transition zone

Along the west coast of Greenland several fish species spawn across a wide latitudinal range encompassing significantly different environments. In an evaluation of the constraints to fish early life in high latitude ecosystems, we compared larval feeding and growth rates of an important species from the areas, the capelin (Mallotus villosus), at two latitudinal distant localities: the subarctic Kapisigdlit Fjord (64°25′N) and the arctic Disko Bay (69°15′N). In these areas, we describe oceanography by series of CTD casts and zooplankton and capelin larvae by fine-meshed nets. Zooplankton abundance and diversity were subsequently described and related to feeding and growth rates of the capelin larvae, assessed from analyses of larval gut contents and otolith ring-patterns. Early life characteristics of larvae differed markedly between the two areas. The onset of zooplankton production and the emergence of larvae took place earlier in Kapisigdlit than in the more northern Disko Bay. In Kapisiglit Fjord the dominant prey items for larvae were small calanoid and cyclopoid copepodites while large-sized calanoid nauplii dominated in the diet of Disko Bay larvae. Larval growth rates were lower in Kapisigdlit Fjord than in Disko Bay. We suggest that the later emergence of capelin larvae in Disko Bay could be compensated by enhanced feeding and thus growth rates, so that larvae from both populations would reach comparable sizes when entering the overwintering phase. However, while larval emergence and onset of plankton production are linked to different environmental cues (temperature increase vs light increase), a former match between emergence of larvae and preferred prey might be disrupted by the present temperature changes in the Arctic.

Spatial and temporal dynamics of Pacific capelin Mallotus catervarius in the Gulf of Alaska: implications for ecosystem-based fisheries management

Pacific capelin Mallotus catervarius are planktivorous small pelagic fish that serve an intermediate trophic role in marine food webs. Due to the lack of a directed fishery or monitoring of capelin in the Northeast Pacific, limited information is available on their distribution and abundance, and how spatio-temporal fluctuations in capelin density affect their availability as prey. To provide information on life history, spatial patterns, and population dynamics of capelin in the Gulf of Alaska (GOA), we modeled distributions of spawning habitat and larval dispersal, and synthesized spatially indexed data from multiple independent sources from 1996 to 2016. Potential capelin spawning areas were broadly distributed across the GOA. Models of larval drift show the GOA’s advective circulation patterns disperse capelin larvae over the continental shelf and upper slope, indicating potential connections between spawning areas and observed offshore distributions that are influenced by the location and timing of spawning. Spatial overlap in composite distributions of larval and age-1+ fish was used to identify core areas where capelin consistently occur and concentrate. Capelin primarily occupy shelf waters near the Kodiak Archipelago, and are patchily distributed across the GOA shelf and inshore waters. Interannual variations in abundance along with spatio-temporal differences in density indicate that the availability of capelin to predators and monitoring surveys is highly variable in the GOA. We demonstrate that the limitations of individual data series can be compensated for by integrating multiple data sources to monitor fluctuations in distributions and abundance trends of an ecologically important species across a large marine ecosystem.

Predation on early life stages is decisive for year-class strength in the Barents Sea capelin (Mallotus villosus) stock

Year-class strength of Barents Sea capelin has been monitored closely since the early 1970s and during this � 45 years period three short periods of almost total recruitment failure leading to three stock collapses have been observed. These events triggered much attention since there was a large commercial fishery for capelin, but also because of observed ecosystem effects attributed to the first of these collapse events. This attention motivated research to clarify mechanisms behind the recruitment failures, and many papers have been published regarding the causes of these events. Here, we review this literature and try to put the various investigations into context. Most of the research conducted gives evidence in favour of a hypothesis that was formulated after the first recruitment failure event in the mid-1980s that predation on capelin larvae was the main cause of recruitment failure. Most studies also support the hypothesis that young herring (Clupea harengus) was the main predator on capelin larvae, but other predators like young-of-the-year cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) probably also played a role. Investigations of the effect of predators such as haddock, red king crab (Paralithodes camtschaticus), diving birds, and capelin on the demersal capelin eggs have also been reviewed. Usually, these predators are found to consume capelin eggs, but most likely not to an extent that would affect the recruitment to a noticeable degree. It is concluded that the predation on capelin larvae is the main reason for the observed recruitment failures, although predation from the predators reviewed here can hardly be the only reason for almost total recruitment failures observed in some periods.

Seasonal distribution, abundance, and growth of larval capelin (Mallotus villosus) and the role of the Lower Estuary (Gulf of St. Lawrence, Canada) as a nursery area

Capelin (Mallotus villosus) spawning in the St. Lawrence Estuary is concentrated in the Upper Estuary (UE). The northwest Gulf of St. Lawrence (NW GSL) was presented as the principal nursery for capelin originating from the estuary. In 2009 and 2010, we investigated the abundance, distribution, and size structure of capelin larvae in this system, and a particle tracking model was used to simulate larval dispersion. There was evidence of retention and larval growth in the Lower Estuary (LE), and older larvae were found in the LE by the end of summer. In October 2009, it was possible to link the cohorts of large larvae to emergence events in the UE in spring. Capelin larvae were more abundant or bigger (mean length) in the LE relative to the NW GSL in fall 2006, 2008, and 2009. We conclude that the LE is the habitat of a unit of the GSL capelin population composed of individuals that are retained in this region following hatching in the UE and that there is limited mixing with larvae originating in the NW GSL.

Recruitment in the Barents Sea, Icelandic, and eastern Newfoundland/Labrador capelin (Mallotus villosus) stocks

Capelin (Mallotus villosus) is a short-lived, coldwater, pelagic species that occurs in large populations in the Barents Sea, around Iceland and in the Newfoundland–Labrador area in the North Atlantic. Most individuals spawn only once at age three or four and die shortly after spawning. The commercial fisheries for capelin in the three areas are prosecuted on the pre-spawning and spawning age groups and knowledge of recruitment to the spawning stock and factors affecting recruitment are important in the management of the fisheries. Herein, we review the state of knowledge regarding recruitment in the three areas and factors that affect recruitment.Year class strength of capelin is fixed fairly early in life; at 0-group stage in the Barents Sea, by age 1 or earlier for Icelandic capelin, and within 2weeks of hatching for the beach spawners in the Newfoundland area. No obvious single factor, common to the three stocks, has been proven to exert a significant influence on recruitment. In the Barents Sea, juvenile herring prey heavily on capelin larvae and when the estimates of the abundance of these juvenile herring were accounted for in the capelin stock–recruitment analysis, the fit in the stock–recruitment relationship improved. In Iceland, there is no reason to implicate predation as a dominant factor, although detailed studies have not been carried out. In the Newfoundland and Labrador area earlier studies suggested two factors were important for recruitment success: the frequency of onshore winds at a critical period during the residence of newly hatched larvae in the beach gravel and the presence of warm waters during the early larval phase in the pelagic environment. With further testing using more data, the temperature factor was found not to be significant but the frequency of onshore winds still explained a significant portion of the variation in year class strength. There appears to be no significant biological influence, such as predation, that has influenced recruitment in this area.

The recruitment process of the Barents Sea capelin (Mallotus villosus) stock, 2001–2003

AbstractOceanographic and predation processes are important modulators of fish larvae survival and mortality. This study addresses the hypothesis that immature Norwegian spring‐spawning herring (Clupea harengus), when abundant in the Barents Sea, determine the capelin reproduction success through consumption of Barents Sea capelin (Mallotus villosus) larvae. Combining a hydrodynamic model and particle‐tracking individual‐based model, a realistic spatio‐temporal overlap between capelin larvae and predatory immature herring was modelled for the summer seasons of 2001–2003. Capelin larvae originating from western spawning grounds became widely dispersed during the summer season, whereas those originating from eastern spawning grounds experienced a rapid drift into the southeastern Barents Sea. Herring caused a 3% mortality of the capelin larvae population in 2001 and a 16% mortality in 2003, but the effect of predation from herring on capelin larvae was negligible in 2002. Despite a strong capelin larvae cohort and a virtual absence of predatory herring, the recruitment from the capelin 2002 year class was relatively poor from a long‐term perspective. We show that the choice of capelin spawning grounds has a major impact on the subsequent capelin larvae drift patterns, constituting an important modulator of the capelin larvae survival. Variation in drift patterns during the summer season is likely to expose the capelin larvae to a wide range of hazards, including predation from young cod, sandeel and other predators. Such alternative predators might thus have contributed to the poor capelin recruitment during 2001–2003, leading to the collapse of the capelin stock in the subsequent years.

Growth and survival of Icelandic capelin Mallotus villosus larvae

Otolith increment analysis was used to reconstruct daily growth of 2 year-classes of capelin larvae, from hatch until 4 mo of age. Larvae were sampled on the continental shelf around Iceland during August 2001 and 2002. Mean hatch dates were not different between years, but hatching started earlier and lasted longer in 2002. Somatic growth was significantly faster in 2001 (0.4 mm d -1 ) than 2002 (0.3 mm d -1 ). Larvae shared a common otolith growth trajectory both within and between year-classes, described by 3 different growth phases: an initial latency period followed by a period of accelerating growth before reaching an asymptote. Daily otolith growth of the 2001 year-class was significantly faster in the age ranges 21 to 50 d and 61 to 100 d, with larvae having an average asymptotic growth of 2.1 µm d -1 in 2001 and 2.0 µm d -1 in 2002. Average daily otolith growth for calendar day increased from June to mid-July each year, decreased until early August, and then increased again. Average sea surface temperature on the capelin nursery ground increased from March to August, and was higher in 2001 than 2002. The decrease in growth during increasing ambi- ent temperature indicates that other environmental factors have significant effects on seasonal growth. Survival rate of larvae from hatch until August was 3 times higher in 2001 when larvae grew faster. Faster growth and higher survival during the first 4 mo of the 2001 year-class did not carry over to higher absolute recruitment at maturity.

Effects of predation from juvenile herring (Clupea harengus) on mortality rates of capelin (Mallotus villosus) larvae

Predation has been suggested as a cause of substantial mortality of fish larvae to the degree that it might influence recruitment. This field-based study concludes that juvenile herring ( Clupea harengus ) as small pelagic predator can significantly affect mortality rates of the planktonic larvae of capelin ( Mallotus villosus ) in the Barents Sea. Surveys were carried out in the summers of 2001 and 2003. In 2001, juvenile herring were widely distributed and overlapped with capelin larvae over a wide area, whereas in 2003, the herring were more aggregated. The study focused on predation in the areas of predator–prey overlap. Capelin larvae were observed in the herring stomachs at 11 of 24 stations and at 8 of 16 stations where herring were caught in 2001 and 2003, respectively. At those stations, an estimated 7.3% and 9.9% of the capelin larvae were eaten by herring per day in 2001 and 2003, respectively. Statistical models revealed that density of capelin larvae and copepods and occurrence of euphausiids in the stomachs affected the number of capelin larvae per predator stomach. A simplified model with only capelin larvae density as predictor was converted to a functional response relationship using an experimentally derived digestion rate estimate for capelin larvae in herring stomachs.

Integrating spatial and temporal mortality from herring on capelin larvae: a study in the Barents Sea

Abstract Pedersen, O. P., Pedersen, T., Tande, K. S., and Slagstad, D. 2009. Integrating spatial and temporal mortality from herring on capelin larvae: a study in the Barents Sea. – ICES Journal of Marine Science, 66: 2183–2194. Barents Sea herring and capelin are commercially very important fish stocks. We investigate the spatial and temporal mortality rate of capelin larvae in 2001 as a function of herring predation. Our methods are based on Lagrangian modelling, field surveys, and experimental data. The impact of juvenile herring predation on capelin recruitment is corroborated, in particular the importance of the integrated spatio-temporal overlap between the two stocks. Capelin larvae were reduced to 20–50% in two weeks in accordance with different simulation scenarios. Hamre advanced a hypothesis in 1994 that juvenile herring are important predators of capelin larvae and a main cause of poor capelin recruitment in years when herring are very abundant in the Barents Sea. This hypothesis is supported through the results of this work.

Advection and retention as life trait modulators of capelin larvae—A case study from the Norwegian coast and the Barents Sea

The Barents Sea capelin stock is, potentially, the largest capelin stock in the world, with a maximum biomass in the range of 6–8 million tonne. The main spawning grounds for this capelin stock are along the coast of northern Norway. By modeling and fieldwork, this study addresses the interaction between mesoscale physical process and newly hatched capelin larvae. The study documents a close relationship between selected spawning location, advection, retention, mortality windows and dispersal patterns.

Patterns of larval emergence of capelin (Mallotus villosus) and environmental cues at demersal spawning sites on the northeastern coast of Newfoundland

At spawning beaches in Newfoundland, Canada, capelin ( Mallotus villosus ) larval emergence is triggered by coastal water mass replacement (CWMR). CWMR causes sharp but short increases in temperature in coastal areas by the transport of warm surface water to the coast during onshore wind events. Warm water temperatures stimulate the active emergence of capelin larvae into predator-poor and prey-rich conditions favourable for larval survival. We investigated whether wind events influenced (i) the thermal properties of the water column and (ii) the larval emergence patterns at five demersal (deep-water) spawning sites on the northeastern coast of Newfoundland during the posthatch periods in 2004–2006. Winds oriented along the shore caused frequent and sharp increases in bottom temperature at all sites but did not appear to stimulate the release of larvae into the water column. Instead, peaks in larval densities corresponded to predicted peaks in hatching. Because of this and the presence of recently hatched larvae (3–5 mm) primarily in good condition, we hypothesize that larvae simply emerged from the sediment upon hatching at these demersal spawning sites. We conclude that patterns of larval emergence at demersal sites in this region are different from those reported for the beach in other regions of Newfoundland.

Effects of growth rates on the otolith increments deposition rate in capelin larvae ( Mallotus villosus)

Otolith microstructure analysis was applied to known age capelin larvae ( Mallotus villosus) in order to examine the formation of daily increments. In two validation experiments, newly hatched yolk sac larvae were stocked into eight 10 m 3 plastic bags where environmental conditions were kept as natural as possible. The bags were terminated after 35-79 days, the surviving larvae were collected and the otoliths were analysed. Survival in the bags varied between 39 - 71% with average individual length growth rates of 0.25 mm day - 1 . The ages of most larvae were underestimated and the accuracy in age estimation was generally low. Highest accuracy was found for fast growing larvae. On average, the larvae started to form increments about 12 days after hatching, and the increment width increased with age and/or length of the larvae. Larvae showing low body growth rates had fast otolith growth relative to body length.

Diet of 0-group stages of capelin (Mallotus villosus), herring (Clupea harengus) and cod (Gadus morhua) during spring and summer in the Barents Sea

Recruitment of capelin in the Barents Sea fail when juvenile herring and cod are abundant and the potential for feeding competition of wild sympatric capelin and herring larvae and small cod juveniles were investigated. The frequency of gut evacuation after capture of capelin larvae were also studied in mesocosms. Small capelin larvae ( 26 mm length). Calanus copepodites were the major food sources for contemporary herring larvae (25–35 mm length) and Calanus and euphausiids were the major prey for small juvenile herring (37–60 mm length) and cod (18–40 mm length). Capelin larvae reared in mesocosms evacuated the guts shortly after capture. Capelin larvae had a smaller mouth and fed on smaller prey than herring and cod of the same length. This implies that the small capelin larvae, in contrast to sympatric small herring and cod, are not tightly linked to the food chain involving Calanus and euphausiids. Thus, exploitative competition between capelin larvae and planktivorous fish that rely on Calanus and euphausiids in the Barents Sea may be relaxed.

Effects of predation from pelagic 0-group cod (Gadus morhua) on mortality rates of capelin (Mallotus villosus) larvae in the Barents Sea

Surveys were carried out in 2002 and 2003 to test whether predation from pelagic 0-group cod (Gadus morhua) juveniles affects mortality rates of Barents Sea capelin (Mallotus villosus) larvae. In 2002, capelin larvae were observed in 17% of the cod stomachs and predation was observed at 19 of 50 stations. In 2003, capelin larvae were observed in 8% of the cod stomachs and predation was observed at 19 of 37 stations. The stomach contents and zooplankton samples were dominated by copepods and krill. The number of capelin larvae in cod stomachs increased with increasing capelin larvae abundance and cod length and decreased with increasing stomach content of copepods and prey abundance of krill. The time when capelin larvae could be recognised after ingestion in the cod stomachs was estimated experimentally and depended on predator and prey lengths. The estimated overall predation mortality rate from juvenile cod on capelin larvae was about 1.5% per day for both years and can potentially have a significant effect on the survival of capelin larvae, depending on the overlap in the different years.

Modelling the growth, mortality, and predation interactions of cod juveniles and capelin larvae in the Barents Sea using a novel proto-moment population dynamics model

Abstract Hallfredsson, E. H., and Pope, J. G. 2007. Modelling the growth, mortality, and predation interactions of cod juveniles and capelin larvae in the Barents Sea using a novel proto-moment population dynamics model. – ICES Journal of Marine Science, 64: 1313–1323. Proto-moments of a fish population, the sums of products of powers of length with numbers at length, relate both to the traditional statistical measures, the mean, the variance, the skewness, and the kurtosis of their size distribution, and to the biologically important measures of the abundance and the biomass of the population. Population models based on this approach are constructed as matrix delay-difference equations. They model moments of the length distributions rather than the age distributions, and express population dynamic problems in an analytically tractable form. Here, a modification of this approach is explored for a case involving a predator–prey relationship among young-of-the-year fish. The modelled species are juvenile cod (the predator) and capelin larvae (the prey) in the Barents Sea. Their population dynamics are modelled by the proto-moment method, but using two different approaches for the derivation of the predation mortality term. The first approach, a published matrix-based formulation, is formed purely in terms of the proto-moments. The second approach, developed here, converts the proto-moments back to consistent size distributions to calculate the rates of predation mortality on each proto-moment. The latter model produces a realistic development in time for the predator and prey length distributions, density in numbers, and biomass for their first summer. It also provides estimates of growth for both species along with estimates of the predation mortality that cod generate on capelin in this time period. The estimates permitted the accuracy of the matrix-based approach to be investigated, better understood, and improved.

Effects of alternative prey on predation intensity from herring Clupea harengus and sandeel Ammodytes marinus on capelin Mallotus villosus larvae in the Barents Sea

Stomach contents from lesser sandeel Ammodytes marinus and herring Clupea harengus caught at one and three stations, respectively, were analysed to investigate predation intensity on capelin Mallotus villosus larvae. Most capelin larvae were found in the anterior sections of the stomachs close to the oesophagus, indicating that rapid digestion rates of larvae reduced the abundance in the posterior sections. The anterior sections of the stomachs had alternating layers of either copepods or capelin larvae and krill. This shows that the individual predators switched between feeding on either copepods or on krill and capelin larvae. A total of 549 capelin larvae was found in 440 fish stomachs. Capelin larvae were found in 20% of the sandeel stomachs, and 24, 34 and 62% of the stomachs from the three herring stations, respectively. Many of the predator stomachs contained more than five larvae, and up to 28 larvae were found in one herring stomach. The herring appeared to prey selectively on the largest capelin larvae, and the number of larvae per stomach was much higher in stomachs where krill had recently been eaten than where copepods were dominant. The predation intensity measured in this study is much higher than reported in earlier studies, and it is suggested that the predators were feeding using a searching image, and that the concentrations of alternative prey (copepods and krill) varied around a switching threshold.