Larval Capelin Research Articles

Evidence for adaptive strategies in larval capelin on the northeastern coast of Newfoundland, Canada

Abstract Fish species with high mortality during early life may maximize fitness using adaptive strategies to time hatching to match favorable environmental conditions (match/mismatch) or extending spawning/hatching to disperse risk (bet-hedging). We examined support for these strategies in a collapsed forage fish, capelin (Mallotus villosus), in coastal Newfoundland (2018–2021). Capelin shift from spawning at warm, intertidal to cool, subtidal (15–40 m) habitats in warmer years, with unknown recruitment consequences. We hypothesized that match/mismatch (specifically, Coastal Water Mass Replacement Hypothesis) would be supported if densities of recently hatched larvae showed pulses that overlapped with high prey and low predator densities. Generalized additive models revealed that larval densities increased with zooplankton prey biomass, but were not influenced by predator biomass or temperature, contrasting with pre-collapse studies and providing equivocal support for match/mismatch. Protracted larval emergence and previously documented high variability in larval traits supported a bet-hedging strategy. Larval condition (i.e. length, yolk-sac diameter) did not differ between habitats but varied among years, where the highest proportion of larvae in poor condition was from the intertidal site in the warmest year (2018). Findings suggest that spawning habitat shifts may have limited impact on stock recovery relative to year-specific environmental conditions that influence larval condition.

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.

Spatiotemporal variability in Newfoundland capelin (Mallotus villosus) larval abundance and growth: Implications for recruitment

We examined larval capelin density and growth dynamics in two relatively unstudied northern coastal embayments of Newfoundland (White Bay and Notre Dame Bay), comparing these larval characteristics to those measured in the annually-surveyed Trinity Bay in order to assess the spatiotemporal variability in larval dynamics and its potential implications on subsequent recruitment. We conducted ichthyoplankton surveys in August of 2015 and 2016, assessing larval density and using otolith microstructure analyses to estimate larval age and growth rates. Size of larvae captured over the two years ranged between 4 and 17 mm, corresponding to an estimated age of 1–33 d. Our results indicated substantial spatial and interannual variability in both density and growth. Larval density was similar between bays in 2015 but drastically different in 2016, where the northern bays were characterized by an order of magnitude less larvae than Trinity Bay. Larval growth was significantly higher in the northern bays in 2015, but lower in 2016, relative to Trinity Bay. This spatiotemporal variability in growth, abundance, and survival potential of larval capelin indicates that the proportion of recruits originating from these key spawning areas fluctuates interannually, with potential implications for the assessment and management of the stock.

Re-visiting the drivers of capelin recruitment in Newfoundland since 1991

Capelin is a small forage fish that plays a key role in the transfer of energy from secondary producers to vertebrate predators in Arcto-boreal food webs. Profound changes in abundance and distribution of capelin occurred in 1991 in Newfoundland, which corresponded with the collapse of the groundfish stocks. There has been minimal recovery of capelin biomass since 1991. We re-assessed the relationships between larval survival, recruitment, and onshore winds post-1991. We also investigated the link between larval capelin vital rates (growth) and recruitment for three current years of data: 2002, a collapsed population state; 2006, a transitioning state; and 2013, a recovering state. Like research pre-1991, we found a positive relationship between the age-2 recruitment index and larval abundance of the same cohort. However, the relationship between onshore winds and recruitment failed post-1991. Capelin are spawning persistently later since 1991 when there are fewer onshore wind events, which is likely a factor hindering the recovery of the capelin stock. Instead, the age-2 recruitment index was related to Pseudocalanus spp. density during the larval stage. Increased availability of preferred prey in autumn, due to a shift in zooplankton phenology seen around 2006, may have improved larval survival in recent years. We found faster growth in the recovering population state (2013) which suggests better larval growth conditions in recent years. Low larval survival from beach spawning may be inhibiting the recovery of the capelin stock, but enhanced productivity of small copepods in autumn can potentially compensate for the negative effect of later spawning.

Does otolith chemistry indicate the natal habitat of Newfoundland capelin Mallotus villosus?

Identifying natal origins is important for understanding population structure (e.g. connectivity), but is often difficult to determine for fish with high dispersal potential. Natural tags, such as otolith microchemistry, however, provide the potential to tackle this challenge. Capelin Mallotus villosus is a key marine forage fish that spawns in two distinct habitats in coastal Newfoundland, beach (intertidal, or above low tide zone) and deep-water (15–40m) habitat, where eggs remain throughout incubation. Capelin are predicted to occupy deep-water habitat as temperatures increase at beaches; however, the contribution of deep-water spawning habitat to recruitment is unclear. Here we test whether otolith chemistry differs between field-reared capelin eggs/larvae at beach relative to deep-water habitat on the northeastern Newfoundland coast during July–August 2011–2013. Throughout experimental rearing, we monitored temperature, salinity and trace metals in ambient water. Ambient trace metal concentrations were homogenous across rearing habitats, but beach-reared larval otoliths had significantly lower Ba/Ca, Sr/Ca, Mn/Ca, and Mg/Ca relative to those reared in deep-water. Temperature was consistently higher at beach relative to deep-water rearing habitat (~3–7°C) throughout the experiment, and the partition coefficients of Sr/Ca in larval capelin otoliths (DSr) were negatively related to temperature (log DSr=−0.026 T (°C)+0.907). As salinity and ambient trace metal concentrations did not vary consistently between habitats, these findings suggest that rearing temperature primarily influenced otolith chemistry. Overall, this study reveals the potential to use otolith chemistry in adult capelin to determine the natal (egg) rearing habitat and, thus, the relative contribution of each spawning/rearing habitat to recruitment in future investigations.

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.

Distribution and spawning dynamics of capelin (Mallotus villosus) in Glacier Bay, Alaska: a cold water refugium

AbstractPacific capelin (Mallotus villosus) populations declined dramatically in the Northeastern Pacific following ocean warming after the regime shift of 1977, but little is known about the cause of the decline or the functional relationships between capelin and their environment. We assessed the distribution and abundance of spawning, non‐spawning adult and larval capelin in Glacier Bay, an estuarine fjord system in southeastern Alaska. We used principal components analysis to analyze midwater trawl and beach seine data collected between 1999 and 2004 with respect to oceanographic data and other measures of physical habitat including proximity to tidewater glaciers and potential spawning habitat. Both spawning and non‐spawning adult Pacific capelin were more likely to occur in areas closest to tidewater glaciers, and those areas were distinguished by lower temperature, higher turbidity, higher dissolved oxygen and lower chlorophyll a levels when compared with other areas of the bay. The distribution of larval Pacific capelin was not sensitive to glacial influence. Pre‐spawning females collected farther from tidewater glaciers were at a lower maturity state than those sampled closer to tidewater glaciers, and the geographic variation in the onset of spawning is likely the result of differences in the marine habitat among sub‐areas of Glacier Bay. Proximity to cold water in Glacier Bay may have provided a refuge for capelin during the recent warm years in the Gulf of Alaska.

Life history, distribution, and size structure of Pacific capelin in Prince William Sound and the northern Gulf of Alaska

Seasonal distribution and size structure of larval, juvenile, and adult Pacific capelin, Mallotus villosus (Muller), were determined using data collected opportunistically during studies of larval fish and adult salmon and herring in Prince William Sound and the Gulf of Alaska. Larval and mainly juvenile capelin were widely distributed inside and west of Prince William Sound. Schools of adults were observed at the Prince William Sound-Gulf of Alaska interface in June, July, and August. Spawning was in June and July. Abundance of larval capelin offshore (>1 km) peaked in July, declining thereafter. Larvae appeared to move inshore, because nearshore (<1 km) abundance increased steadily from July to October. For part of the year, nursery areas are nearshore as capelin aged 0 and 1 dominated catches; most were caught within 400 m of the shore at bottom depths less than 100 m. Capelin catches were highest during May-June in three of the four years, and seasonal variability probably resulted from distributional changes inside bays and fjords, and/or variable growth and maturation rates. Recruiting events appeared to be annual, but annual catch rates declined from 1994 to 1997 as a consequence of changes in survival or distribution.

Juvenile herring prey on Barents Sea capelin larvae

Abstract Due to a negative correlation between juvenile herring abundance and Barents Sea capelin recruitment, it has been hypothesised that predation by herring (Clupea harengus, L.) causes poor recruitment in the capelin stock (Mallotus villosus, Muller). In order to investigate whether herring are important predators of larval capelin, stomachs of herring were collected in the Barents Sea during the summers of 1992 and 1993. Capelin larvae were found in 5.6 and 3.0 % of the herring stomachs collected in the two years respectively. Herring showed preference for the larger capelin larvae. The observed predation rates correspond to estimated encounter rates between individual herring and larval capelin. The study confirms that predation takes place, but the observed rates are too low to explain the poor capelin recruitment in the two years. Increased swimming speed and selective feeding by herring in areas with high densities of capelin larvae is proposed as a mechanism that can explain the recruitment fa...

Larval condition and vulnerability to predation: reply to comment by Suthers

Discussion 1538 Scientists recognize that observations and experiments at a variety of spatial and temporal scales and in a variety of different systems are required to obtain a complete understanding of a particular phenomenon. However, scientists also recognize that an individual study can usually only focus on one particular system at a certain time and place and that many different studies are required to achieve a general conclusion. The objective of our study on larval capelin (Mallotus villosus) (Elliott and Leggett 1998) was to provide an experimental test of whether larvae in poor condition had lower relative survival rates than larvae in good condition when exposed to a predator. We employed an experimental design that had been successfully used by a variety of other researchers (Litvak and Leggett 1992; Pepin et al. 1992; Pepin and Shears 1995; Elliott and Leggett 1996) to test selective mortality hypotheses under laboratory conditions in small aquaria. In our abstract, we explicitly stated that the results of our study “suggest that RNA/DNA ratios are not useful indicators of vulnerability to predation for larval capelin.” Clearly, we did not intend to have this conclusion be considered a broad statement that applied to all other systems. As in all scientific disciplines, we presented our data with the intention that other researchers would conduct further studies using a variety of experimental systems and protocols to provide further tests that would either support or refute our results. After a variety of studies on this topic had been conducted, we would hope that a metanalysis would provide a more complete understanding of the effects of larval condition on vulnerability to predation. Ultimately, the results of this research could lead to the incorporation of lar val condition indices into assessments of the future survival probabilities of larvae into fisheries models. Unfortunately, in the comment by Suthers, our conclusions have been overstated and interpreted as a definitive re jection of the utility of RNA/DNA ratios and larval dry weight in the study of larval condition. As stated above, our conclusions pertained to larval capelin and only in the context of the experimental conditions employed. Furthermore, in the second to last paragraph of Elliott and Leggett (1998), we explicitly stated that our conclusions are based on our results, some of which are in contrast with previous studies of larval capelin in small enclosures: “This difference in out come may result from the use of different experimental conditions and predator species or from the possibility that different measures of larval size (length versus dry weight) may not be equivalent in their influence on the vulnerability of larvae to predation.” In other words, variation in the spe cies used or experimental protocol could have caused a different result (as has been reported in many other studies of selective mortality). A general conclusion on the influence

Larval condition and vulnerability to predation: an analysis based on mixed-prey experiments

Many recent studies in larval fish ecology measure larval nutritional condition (e.g., RNA/DNA ratios), with the ultimate goal of assessing future survival probabilities. Larvae of intermediate or poor condition are generally considered to be more vulnerable to predators than larvae in good condition. The objective of our study was to experimentally test whether larvae in poor condition have lower relative survival rates when exposed to a predator. We conducted mixed-prey experiments with larval capelin (Mallotus villosus) on days 6, 8, and 10 posthatching by putting 75 fed and 75 starved larvae in 38-L containers with (treatments) and without (controls) predators (juvenile lumpfish, Cyclopterus lumpus). There were no significant differences in the mean condition (RNA/DNA ratios) or dry weights of larvae recovered from controls and treatments. These results suggest that RNA/DNA ratios are not useful indicators of vulnerability to predation for larval capelin.

Influence of temperature on size-dependent predation by a fish (Gasterosteus aculeatus) and a jellyfish (Aurelia aurita) on larval capelin (Mallotus villosus)

We compared the size-dependent mortality patterns of newly emerged larval capelin (Mallotus villosus) at three different temperatures (3, 9, and 15°C) when exposed to predation by threespine stickleback (Gasterosteus aculeatus) and moon jellyfish (Aurelia aurita). Controlled experiments were conducted in both microcosms (38 L) and mesocosms (3100 L). Some temperature-related trends were evident in experiments with sticklebacks, but not with jellyfish. Sticklebacks fed selectively on smaller capelin larvae at 15°C, were nonselective at 9°C, and fed on larger larvae at 3°C. There was no prey size selection by A. aurita at any of the temperatures examined. Our findings support the view that the direction and magnitude of size-selective predation vary depending on the predator-prey assemblage and environmental conditions examined.

Influence of temperature on size-dependent predation by a fish (Gasterosteus aculeatus) and a jellyfish (Aurelia aurita) on larval capelin (Mallotus villosus)

Influence of temperature on size-dependent predation by a fish (Gasterosteus aculeatus) and a jellyfish (Aurelia aurita) on larval capelin (Mallotus villosus)

A comparison of the length distributions of larval capelin (Mallotus villosus) taken by Gulf III, MIK and MOCNESS samplers

Abundance of Barents Sea capelin larvae (6–25 mm) is estimated every summer using samples from a Gulf III sampler. It has been suggested that a MIK net would be more efficient in sampling larvae exceeding 18–20 mm in length. On this basis the length distributions of larval capelin captured by Gulf III, MIK, and MOCNESS in six consecutive hauls were compared. The catches taken by Gulf III and MIK nets had similar length distributions whereas the MOCNESS captured smaller larvae than the other samplers. There would thus be no gain in replacing the Gulf III with the MIK for estimating abundance of larval capelin smaller than 25 mm.

The effect of temperature on predation rates of a fish (Gasterosteus aculeatus) and a jellyfish (Aurelia aurita) on larval capelin (Mallotus villosus)

Des etudes sur le terrain ont montre que la temperature exerce un effet sur la mortalite des larves de poisson. Des experiences en laboratoire, a l'echelle de microcosmes (38 L) et de mesocosmes (3100 L), ont permis de tester l'effet de trois temperatures (3, 9 et 15°C) sur le taux de mortalite de larves de capelan (Mallotus villosus) nouvellement emergees en la presence et en l'absence de predateurs, soit l'epinoche (Gasterosteus aculeatus) et la meduse (Aurelia aurita). Il existe une correlation positive entre le taux de predation exercee par l'epinoche et la temperature dans les essais en microcosme, mais pas dans les essais en mesocosme; cette difference a ete reliee a la duree de l'experience et au degre de satiete des epinoches. A 3°C, les taux de predation exercee par la meduse etaient significativement inferieurs a ce qu'ils etaient a 9 et a 15°C dans les essais en microcosme et un nombre significativement plus eleve de larves ont ete trouvees mortes, mais non consommees a 3°C. En consequence, il n'y avait pas de difference, relativement au taux de mortalite totale, selon la temperature dans le cas de la predation exercee par la meduse en microcosme. Les essais avec la meduse en mesocosme n'ont pas fait ressortir, non plus, de difference significative entre les taux de mortalite des larves selon la temperature. Sur le terrain, l'emergence en masse des larves de capelan doit deborder la capacite de predation des petits predateurs comme l'epinoche qui ont un taux de capture eleve et un petit volume intestinal, mais pas celle de la meduse, qui a un taux de capture assez faible, mais un grand volume intestinal.

Sampling methods for assessing the diets of Atlantic puffin chicks

Three methods for sampling the diets of Atlantic puffin Fratercula arctjca chicks were compared and evaluated. Prey-carrying puffins were captured in mist-nets, or observed with a telescope or with unaided eyes. Prey samples collected in mist-nets yielded higher proportions of gravid capelin Mallotus villosus than did samples obtained visually. Telescopic samples produced higher estimates of the numbers of larval fish landed by puffins (larval fishes are often lost when food-laden birds are caught in mist-nets), and yielded underestimates of the lengths of male capelin Slight correction factors made the 3 prey sampling methods comparable Visual sampling procedures had the advantages of creating less disturbance and allowing puffins to deliver food to chicks. Use of telescopic sampling is, however, dependent on colony topography. Forage fishes, heavlly dominated by 2-yr-old capelin, made up 88% and 98% of the frequency and mass, respectively, of the prey delivered to puffin chicks. Small prey (larval capelin and sandlance Ammodytes spp., hake Urophycis tenuis, crustaceans) were most commonly fed to young chicks. Gravid and male capelin tended to be more commonly fed to chicks midway through the nestling period, a time of rapid growth. Spent female and immature capelin were fed more commonly to older chicks The lengths of gravid capelin tended to increase through the nestling penod. Gravid and spent female and male capelin and sandlance fed to puffin chicks were shorter in 1992 than in 1993 or 1994. Successful puffin chlcks on Great Island, Newfoundland, Canada, were fed an average of 1105 (SD = 435) prey items weighlng 2812 g (SD = 579) equivalent to 12506 kJ (SD = 2391). Extrapolation of these findings suggests that the population of Atlantic puffins in Newfoundland consumes about 8000+ t of forage fishes, mostly 2-yr-old female capelin during a breeding season. Data on age-class and gender status of prey harvests by marine birds will provide needed input in energetics and trophic models.

Early development of shoaling behaviour in larval capelin(mallotus villosus)

The ontogeny of shoaling behaviour in early‐stage larval capelin was examined for larvae raised under different conditions of prey concentration and disturbance. Shoals were evident from the first day of observation (day 2 post‐hatch) and time spent shoaling increased as the larvae got older. Both the number of follows and avoids decreased with age as the larvae spent more time in shoals. Disturbance appreared to have little affect on the development of shoaling. As they got older, larvae in high prey concentrations had some tendency to spend more time in shoals than fish in low prey concentrations.

Causes of spatio‐temporal variation in the patchiness of larval fish distributions: differential mortality or behaviour?

ABSTRACTWe studied age‐ and size‐related patterns in the patchiness of distributions of larval capelin (4–21 mm TL) on the Newfoundland Grand Bank. The distribution of yolk‐sac larvae was highly contagious, and was consistent with the distribution of spawning capelin. Lloyd's patchiness index declined fivefold from the yolk‐sac (4–6 mm) to the small post‐yolk‐sac (9–11 mm) stage. The patchiness index then increased steadily and by 2.5‐fold through the medium (14–16 mm) and large (19–21 mm) post‐yolk‐sac stages. This increase in patchiness was accompanied by a steady increase in the strength of the correlation between the abundance of larvae and of the edible zooplankton, and between the centre of mass of the larval and zooplankton vertical distributions through these length classes. In an attempt to distinguish between the alternative hypotheses of differential mortality or behavioural aggregation as the cause of the changes in larval capelin patchiness observed, we compared these changes with changes in the patterns of vertical migration, patchiness, and correlation with food abundances in a co‐occurring, non‐schooling zooplanktivore, Sagitta ekgans. Sagitta vertical migration and correlations between predatodprey abundance were similar to those observed in capelin. However, patchiness indices calculated for Sagitta were similar to the lowest values observed for capelin larvae. We conclude that the initial decline in patchiness observed in small larvae was due primarily to advection and diffusion away from the spawning site. The subsequent increase in larval patchiness, which did not occur in the non‐schooling Sagitta, was attributed to active behaviours of the larvae in response to the vertical and horizontal distributions of their prey. The implications of these findings for the interpretation of larval early life history are discussed.

Predation by Jellyfish on Larval Fish: An Experimental Evaluation Employing in situ Enclosures

Large in situ enclosures were used to investigate the mortality of yolk-sac larval capelin (Mallotus villosus) by four species of jellyfish predators. Daily instantaneous larval mortality increased linearly with predator density but was independent of initial larval density, indicating a linear functional response of the four jellyfish species. The addition of alternative prey did not modify the linearity of the functional response and did not significantly reduce or increase larval mortality imposed by two jellyfish species. The evidence of a linear response in large enclosures contrasts with the curvilinear (Type II) response previously reported in studies conducted in small laboratory containers. Larval mortality was strongly dependent on predator size within jellyfish species and increased with initial larval size. Larval capelin appeared more susceptible to predation at the time of transition from endogenous to exogenous feeding. Daily larval mortality rates due to predation varied between 0.015 and 1.58 depending on jellyfish species and appeared more strongly determined by body mass than differences in feeding appendages of jellyfish. Our results indicate that reduced larval mortality to jellyfish predation is achievable only by timing larval release in water mass where jellyfish numbers are naturally reduced. We estimated that macro invertebrate predation has the potential of being the primary regulator of larval survival and we hypothesized that large intra- and interannual variation in larval survival may be due to the variability in the emergence timing of capelin larvae relative to the growth trajectory of jellyfish.

Patterns of Larval Emergence and Their Potential Impact on Stock Differentiation in Beach Spawning Capelin (Mallotus villosus)

The environmental cues triggering larval capelin (Mallotus villosus) emergence in the St. Lawrence estuary and in coastal Newfoundland are different. In the estuary, emergence from the intertidal and subtidal spawning grounds starts with dusk and ends with dawn, indicating an active response to low light intensity. In the laboratory, emergence from undisturbed sediments collected in the field is perfectly synchronized with the dark phase of the illumination cycle. Nocturnal emergence would represent an adaptation reducing vulnerability to visual predators. Previous work has shown that in Newfoundland, capelin emergence from intertidal beaches is triggered by abrupt changes in water temperature following the sporadic advection to the coast of surface water masses characterized by low predator and high prey abundances. We argue that regional differences in the emergence pattern of the species represent different strategies to avoid predation at the onset of the planktonic drift when the vulnerable yolk sac larvae are densely aggregated. Selection acting on the behaviour of the early larval stages could contribute to stock differentiation in capelin.