Pre-recruit Survival Research Articles

Lifting the Vendace, Coregonus albula, on the Life Table: Survival, Growth and Reproduction in Different Life-Stages during Very High and Low Abundance Regimes

We analyzed the variability in vendace population parameters in the context of a life table. Parameters related to growth, fecundity and survival were estimated for post-recruitment (age > 1 growing season) life stages of Lake Southern Konnevesi vendace in both very high and low population abundance regimes. Pre-recruitment survival producing population stability was then determined. We found a very strong compensatory density dependence in growth, fecundity and survival: during low abundance, a lifetime reproductive output of a female was almost 20 times that of the abundant regime. To maintain the low abundance regime, pre-recruitment survival must counterbalance it by decreasing to a very low level. Potential drivers of high variability in pre-recruit survival and potential for depensation, Allee effect, are discussed, as well as the implications of the results on fisheries management and risk of extinction due to anthropogenic stressors such as global warming or extensive predator stocking.

Could ecological release buffer suppression efforts for non-native lake trout (Salvelinus namaycush) in Yellowstone Lake, Yellowstone National Park?

Yellowstone Lake in Yellowstone National Park, USA, has the longest ongoing suppression program for non-native lake trout (Salvelinus namaycush) in the western USA. Harvest data from the suppression program, along with data from an assessment program initiated in 2011, was used to estimate lake trout abundance and mortality rates. Abundance and biomass estimates were used to estimate stock–recruitment dynamics, which were inputs to a simulation model forecasting responses to continued suppression. Abundance increased during 1998–2012 when total annual mortality exceeded 0.59 and declined thereafter. The fishing mortality rate required to reduce abundance was 67% greater than predicted by models that used prerecruit survival estimates from the lake trout’s native range. Prerecruit survival in Yellowstone Lake was estimated at four to six times greater than native range survival rates. Simulated abundance continued to decline if recent suppression efforts were maintained. High prerecruit survival in Yellowstone Lake likely illustrates ecological release for an invasive species in an ecosystem containing few predators or competitors and demonstrates the potential pitfalls of assuming equal demographic rates for native and non-native populations.

Unraveling the recruitment problem: A review of environmentally-informed forecasting and management strategy evaluation

Studies describing and hypothesizing the impact of climate change and environmental processes on vital rates of fish stocks are increasing in frequency, and concomitant with that is interest in incorporating these processes in fish stock assessments and forecasting models. Previous research suggests that including environmental drivers of fish recruitment in forecasting is of limited value, concluding that forecasting improvements are minimal while potential spurious relationships were sufficient to advise against inclusion. This review evaluates progress in implementing environmental factors in stock-recruitment projections and Management Strategy Evaluations (MSEs), from the year 2000 through 2017, by reviewing studies that incorporate environmental processes into recruitment forecasting, full-cycle MSEs, or simulations investigating harvest control rules. The only successes identified were for species with a short pre-recruit survival window (e.g., opportunistic life-history strategy), where the abbreviated life-span made it easier to identify one or a limited set of key drivers that directly impact dynamics. Autoregressive methods appeared to perform as well, if not better, for species with a longer pre-recruit survival window (e.g., seasonal, inter-annual) during which the environment could potentially exert influence. This review suggests that the inclusion of environmental drivers into assessments and forecasting is most likely to be successful for species with short pre-recruit survival windows (e.g., squid, sardine) and for those that have bottlenecks in their life history during which the environment can exert a well-defined pressure (e.g., anadromous fishes, those reliant on nursery areas). The effects of environment may be more complicated and variable for species with a longer pre-recruit survival window, reducing the ability to quantify environment-recruitment relationships. Species with more complex early life histories and longer pre-recruit survival windows would benefit from future research that focuses on relevant species-specific spatio-temporal scales to improve mechanistic understanding of abiotic-biotic interactions.

Stock-recruitment relationships in elasmobranchs: Application to the North Pacific blue shark

Stock-recruitment relationships in elasmobranchs are uncertain due to a lack of data, especially regarding pre-recruit survivorship. A pre-recruit survival model for the early life history of elasmobranchs was developed and parameterized using biological data. Then, an existing age-structured model for the reproductive ecology of teleost fishes was modified for elasmobranchs and combined with the pre-recruit model. The combined model was then applied to the North Pacific blue shark (Prionace glauca). The stock-recruitment relationships of this species were clarified using the biological data collected from wide areas of the western North Pacific. The model provides a point estimate for steepness, which represents a fraction of the unfished recruitment when spawning stock biomass is 20% of the unfished spawning stock biomass. Numerical simulations were conducted to incorporate uncertainties in the biological parameters and produce the variance of steepness. The mean value and its standard deviation for steepness with the Beverton-Holt model were 0.584 (standard deviation=0.099). The results suggest that the stock-recruitment relationship in North Pacific blue shark remains highly density-dependent and that its productivity is higher than that of other viviparous elasmobranchs.

Evaluating the impact of ocean acidification on fishery yields and profits: The example of red king crab in Bristol Bay

A stage-structured pre-recruit model was developed to capture hypotheses regarding the impact of ocean acidification on the survival of pre-recruit crab. The model was parameterized using life history and survival data for red king crab (Paralithodes camtschaticus) derived from experiments conducted at the National Marine Fisheries Service Kodiak laboratory. A parameterized pre-recruit model was linked to a post-recruit population dynamics model for adult male red king crab in Bristol Bay, Alaska that included commercial fishery harvest. This coupled population dynamics model was integrated with a bioeconomic model of commercial fishing sector profits to forecast how the impacts of ocean acidification on the survival of pre-recruit red king crab will affect yields and profits for the Bristol Bay red king crab fishery for a scenario that includes future ocean pH levels predictions. Expected yields and profits were projected to decline over the next 50–100 years in this scenario given reductions in pre-recruit survival due to decreasing ocean pH levels over time. The target fishing mortality used to provide management advice based on the current harvest policy for Bristol Bay red king crab also declined over time in response to declining survival rates. However, the impacts of ocean acidification due to reduced pre-recruit survival on yield and profits are likely to be limited for the next 10–20 years, and its effects will likely be masked by natural variation in pre-recruit survival. This analysis is an initial step toward a fully integrated understanding of the impact of ocean acidification on fishery yields and profits, and could be used to focus future research efforts.

A stock–recruitment relationship based on pre-recruit survival, illustrated with application to spiny dogfish shark

Understanding the relationship between abundance of spawners and subsequent recruitment is one of the central issues in fisheries stock assessment. We developed a new, pre-recruit survival based stock–recruitment model that enables explicit modeling of survival between embryos and age 0 recruits, and allows the description of a wide range of pre-recruit survival curves. The model is especially useful for low fecundity species that produce relatively few offspring per litter and exhibit a more direct connection between spawning output and recruitment than species generating millions of eggs. The proposed model provides additional flexibility in the stock–recruitment options that may be explored in any fishery stock assessment, and it is now available within the Stock Synthesis assessment platform. In this paper, we describe the mathematical formulation of the new stock–recruitment model, explain how this model can be specified within Stock Synthesis, and use it to model the stock–recruitment relationship of the spiny dogfish shark in the Northeast Pacific Ocean. We compare the results of the application of our new stock–recruitment model, with those from traditional Beverton–Holt relationship, and illustrate why the new approach is more appropriate for this species.

A whole-lake density reduction to assess compensatory responses of gizzard shad Dorosoma cepedianum

We used a fishery-induced density reduction of gizzard shad Dorosoma cepedianum at a previously unharvested lake to evaluate compensatory density dependence in recruitment processes. We also studied gizzard shad populations at two nearby unharvested lakes to provide contrast with the harvested population. Gizzard shad spawner biomass was reduced by 72% at the harvested lake after 2 years of gill-net removals, although variation in total shad biomass was more modest. We evaluated responses by gizzard shad to the range of biomasses present among the three lakes and 5 years of the study. Annual growth increments varied little over 5 years and were not related to population density across the three lakes. Length-at-maturity differed among lakes and years, but was not related to population density. Despite the range in spawner biomass among the lakes during the study, annual recruitment estimates showed little relationship to the size of the spawner population, suggesting density-dependent prerecruit survival. A spawner–recruit analysis on pooled data from the three lakes indicated that prerecruit survival was negatively related to spawner biomass. Our study provides a rare glimpse of fish compensatory responses following exploitation of a previously unharvested population and has implications for population dynamics theory and fisheries management.

Prerecruit survival and recruitment of northern Gulf of St Lawrence Atlantic cod

Abstract Duplisea, D. E., and Robert, D. 2008. Prerecruit survival and recruitment of northern Gulf of St Lawrence Atlantic cod. – ICES Journal of Marine Science, 65: 946–952. Recruitment (R) of exploited marine fish populations is usually modelled exclusively as a function of spawning-stock biomass (SSB). A problem arising when modelling over long time-series is that the nature of the R–SSB relationship is unlikely to be stationary. Changes are often interpreted as productivity regime shifts and are linked to alterations in prerecruit survival rate. We examine the role of environment and predation by fish and harp seals as factors affecting the R–SSB relationship in the northern Gulf of St Lawrence cod, by fitting linear models using combinations of covariates to explain cod prerecruit survival. The most parsimonious model (based on a Bayesian Information Criterion, BIC) included cod, mackerel, and temperature, whereas redfish and seals did not appear in any of the best-fit models. Recruitment models derived from this analysis could be used in operating models for management strategy evaluation simulations for northern Gulf cod, so one could develop harvest control rules that are robust to changes in recruitment productivity regimes.

Pelagic fishes and the cod recruitment dilemma in the Northwest Atlantic

Like most other stocks of Atlantic cod (Gadus morhua) in the Northwest Atlantic, cod in the southern Gulf of St. Lawrence declined to low abundance in the early 1990s. Recovery has been slow in contrast with the rapid recovery from similar levels of abundance in the mid-1970s. This difference reflects remarkably high prerecruit survival of cod in the earlier period of low abundance rather than unusually poor survival in the 1990s. The period of high prerecruit survival of cod coincided with the collapse of herring (Clupea harengus) and mackerel (Scomber scombrus) stocks resulting from overfishing. These pelagic fishes are potential predators or competitors of the early life history stages of cod. We report a strong negative relationship between the biomass of these pelagic fishes and recruitment rate of southern Gulf cod. This is consistent with the recent suggestion that the success of large predatory fishes may depend on "cultivation" effects in which the adults crop down forage fishes that are predators or competitors of their young. Our results also point to the possibility of a triangular food web involving cod, seals, and pelagic fishes, making it difficult to predict the effect of a proposed cull of seals on the recovery of cod.

Evaluation of an environment–recruitment model for capelin (Mallotus villosus)

An earlier study reported that recruitment of the 1966-1978 year classes of beach-spawning capelin (Mallotus villosus) in NAFO Div. 2J3K was significantly correlated with onshore winds that facilitate larval emergence from the spawning beaches (WIND) and post-emergent sea surface temperatures during the first 6 months of pelagic life (TEMPSUM). We used this relationship to predict recruitment for the 1979-1990 year classes and found that these estimates were not significantly correlated with observed year-class abundance. However, there was a significant correlation when two outlying year classes were omitted. A new relationship was developed between survival (ln fraction recruitment/spawning stock biomass) and the original independent variables for the period 1974-1990. The new model was not significant (p=0.06) but for the individual independent variables, WIND was significant (p=0.04) and TEMPSUM was not (p=0.24). With WIND as the sole predictor, 25% of the variation in survival was explained (r=−0.50, p=0.04). The continued influence of WIND on pre-recruit survival of capelin is not an unexpected result considering that the mechanism linking wind effects to larval survival was established during intensive field studies. In contrast, TEMPSUM was derived through correlation analysis supported by a biologically plausible, but unproven, explanation of its effect on larval survival. We suggest that the retention of WIND in this re-evaluation is significant because it demonstrates that models based on realistic biological mechanisms are more likely to be retained when re-evaluated than are those models derived through exploratory analysis.

A comparative analysis of recruitment variability in North Atlantic flatfishes — testing the species range hypothesis

The hypothesis that recruitment variation in flatfishes should be most variable at the northern edge of the species range, least near the centre of the range, and intermediate near the southern limit was tested using stock and recruitment data generated from sequential population analysis for several different flatfish stocks involving four species (plaice Pleuronectes platessa, sole Solea vulgaris from the eastern Atlantic, American plaice Hippoglossoides platessoides, and yellowtail flounder Limanda ferruginae from the western Atlantic). Several groundfish species have been found to conform to this so-called species range hypothesis with the suggestion that density-independent processes predominate at the edges of the distributional range and density-dependent processes dominate in the centre of the range. Our results were generally inconsistent with the hypothesis: the coefficient of variation (CV) of recruitment for plaice in the eastern Atlantic was independent of latitude, the CV of recruitment for sole exhibited a dome-shaped relationship with latitude with the highest CVs occurring at the mid-point of the range, and the CV of recruitment for the western Atlantic stocks exhibited a monotonic decrease with latitude. We extended our latitudinal analyses by assessing both the degree of dependency of recruitment on spawning stock biomass and the spatial and temporal scales of variability in recruitment and pre-recruit survival for the eastern Atlantic stocks. In general our analysis revealed no evidence of a strong stock and recruitment relationship for any of the stocks examined, and previously published analyses revealed no such patterns with latitude. Analysis of both de-trended recruitment and pre-recruit survival time series over the species ranges of sole and plaice revealed strong positive correlations among adjacent stocks and inverse correlations among stocks at the extremes of the range. Recruitment variation in the flatfish stocks examined appears to be dominated by density-independent factors, operating at a local scale, on the egg and larval stages.

Growth, Movement, Recapture Rate and Survival of Hatchery-Reared Lobsters (Homarus Gammarus (Linnaeus, 1758)) Released Into the Wild On the English East Coast

From 1983 to 1988 over 49,000 three-month-old hatchery-reared lobsters were tagged with a microwire tag and released into the wild in Bridlington Bay on the east coast of England. The area supports a substantial fishery based on a large stock of naturally settled lobsters. Since 1988 approximately 57,000 lobsters have been tested at sea and at the landing place in order to recapture microtagged lobsters and assess their growth, movement, recapture rate and survival. Results to date show that microtagged lobsters have survived in the wild for up to eight years and have been caught in traps (or pots) by commercial fishermen. Lobsters began to reach the minimum legal size of 85 mm carapace length four to five years after release, but showed substantial individual variation in size at age. Most recaptures were recorded within six kilometres of known release sites, and showed strong site fidelity. Some recaptured females carried eggs. Data from additional T-bar tag-recapture experiments are used to estimate the exploitation rate generated by standard pots assuming either zero or a high rate of T-bar tag mortality and tag shedding. The exploitation rate is used to convert spot estimates of the catch rate of microtagged lobsters into estimates of their abundance for comparison with the number of lobsters released at individual sites. Corresponding estimates of survival from release to recapture average 84% and 50% for the two assumptions made about tag mortality and tag shedding in the T-bar tag-recapture experiment. It appears that juvenile hatchery-reared lobsters have survived well to recruitment and we offer this as a first quantitative assessment of pre-recruit survival for Homarus gammarus. The significance of this result for lobster stock enhancement and ecology is discussed.