Recruitment Index Research Articles

Using Winter Juvenile/Adult Ratios as Indices of Recruitment in Population Models

Abstract There is an increasing interest in using winter juvenile counts as indices of recruitment in species that show delayed plumage maturation, especially for species, such as dispersed breeders, for which it is difficult to obtain good productivity estimates. To date, however, the needed mathematical work to assist in interpreting these winter juvenile/adult ratios has not been conducted. A matrix-based population model is presented that is modified to allow the fecundity component to be measured in mid- to late winter. This model is simplified to a set of equations that relate adult survival, winter juvenile/adult ratios and population growth rates, allowing an assessment of population trend with only one survival rate and age ratio data. These models have the advantage of not requiring that age of first breeding be well known. As an example, age ratios and survival rates of Harlequin Duck (Histrionicus histrionicus) populations in British Columbia and Maine are presented. Models for both population...

Assessing the freshwater distribution of yellow eel

In the global context of the decline in wild species, modeling the distribution of populations is a crucial aspect of ecological management. This can be a major challenge, especially for species, such as the European eel, that have complex life cycles, exhibit cryptic behavior, or migrate over long distances. A review of the literature suggests that eel size data could be used to assess and analyze freshwater distribution of eel. We argue that analyses based on small yellow eels (≤ 300 mm) along the longitudinal course of rivers could provide a valuable tool for population monitoring. We propose a standardized catchment recruitment index and a colonization index based on the probability of occurrence (presence/absence data) using logistic models for different size classes. The model developed here provides a convenient guide for assessing yellow eel stages in freshwater areas, and should have concrete applications for management of the species.

Biophysical modelling of larval drift, growth and survival for the prediction of anchovy (Engraulis encrasicolus) recruitment in the Bay of Biscay (NE Atlantic)

AbstractFish recruitment is the result of the integration of small‐scale processes affecting larval survival over a season and large oceanic areas. A hydrodynamic model was used to explore and model these physical–biological interaction mechanisms and then to perform the integration from individual to population scales in order to provide recruitment predictions for fisheries management. This method was applied to the case of anchovy (Engraulis encrasicolus) in the Bay of Biscay (NE Atlantic). The main data available to investigate survival mechanisms were past growth (otolith) records of larvae and juveniles sampled at sea. The drift history of these individuals was reconstructed by a backtracking procedure using hydrodynamic simulations. The relationships between (real) growth variation and variations in physical parameters (estimated by hydrodynamic simulations) were explored along the individual trajectories obtained. These relationships were then used to build and adjust individual‐based growth and survival models. Thousands of virtual buoys were released in the hydrodynamic model in order to reproduce the space–time spawning dynamics. Along the buoy trajectories (representative of sub‐cohorts), the biophysical model was run to simulate growth and survival as a function of the environment encountered. The survival rate after 3 months of drift was estimated for each sub‐cohort. The sum of all these survival rates over the season constituted an annual recruitment index. This index was validated over a series of recruitment estimations. The modelling choices, model results and the potential use of the recruitment index for fisheries management are discussed.

A strategy for developing scientific sampling tools for fishery-independent surveys of estuarine fish in New South Wales, Australia

Abstract Rotherham, D., Underwood, A. J., Chapman, M. G., and Gray, C. A. 2007. A strategy for developing scientific sampling tools for fishery-independent surveys of estuarine fish in New South Wales, Australia. – ICES Journal of Marine Science, 64: 1512–1516. The limitations of using fishery-dependent data, i.e. from commercial and recreational fisheries to assess harvested stocks of fish and invertebrates, are well known. Increasingly, fishery-independent surveys are used to validate data from fishery-dependent sources and to provide indices of recruitment and broader ecological information about species not normally retained in fishing operations. Any large-scale, long-term, fishery-independent study must develop sampling gear and designs that are standardized, representative, optimal with respect to the quantity and structure of catch, and replicated over relevant spatial and temporal scales. We present a strategy for achieving appropriate sampling designs. This involves: (i) identifying suitable sampling gears for target species; (ii) testing different configurations of gear and sampling practices to ensure that samples are optimal, representative, and cost efficient; (iii) understanding scales of spatial and temporal variability; and (iv) cost–benefit analyses to optimize replication. Examples of this strategy are illustrated, with brief considerations of the values of pilot research in developing fishery-independent sampling.

Estimating year-class strength of Icelandic summer-spawning herring on the basis of two survey methods

Abstract Gudmundsdottir, A., Oskarsson, G. J., and Sveinbjörnsson, S. 2007. Estimating year-class strength of Icelandic summer-spawning herring on the basis of two survey methods. – ICES Journal of Marine Science, 64: 1182–1190. Recruitment indices at age 1 and 2 were constructed for Icelandic summer-spawning herring using data from two inherently different survey methods on their nursery areas for the years 1988–2003. The surveys were a shrimp, bottom-trawl survey and a herring acoustic survey. Indices were compared with the year-class strength at age 2 derived from an assessment model (AMCI) used for the stock. A juvenile index at age 1 from the acoustic survey and at age 2 from the shrimp-trawl survey correlated significantly with the modelled recruitment, although only marginally with each other. One index was not considered markedly better than the other, and both have shortcomings even if the acoustic survey is believed better than the trawl survey for quantifying juvenile herring. The recruitment index at age 1 derived from the acoustic survey can be improved as an indicator of recruitment if that survey were to be extended to cover the nursery areas off western and southeastern Iceland, and the same areas covered each year.

Divergent responses of Pygoscelis penguins reveal a common environmental driver

The responses of predators to environmental variability in the Antarctic Peninsula region have exhibited divergent patterns owing to variation in the geographic settings of colonies and predator life-history strategies. Five breeding colonies of Pygoscelis penguins from King George Island and Livingston Island, South Shetland Islands, Antarctica, were examined to (1) compare the responses of sympatric congeners to recent changes in their Antarctic ecosystem and (2) assess underlying causes for such responses. We used linear regression and correlation analyses to compare indices of abundance, recruitment, and summer breeding performance of the Adélie (P. adeliae), gentoo (P. papua), and chinstrap penguins (P. antarctica). Breeding colonies of Adélie and chinstrap penguins have declined by roughly 50% since the mid-1970s, and recruitment indices of Adélie penguins have declined by roughly 80%, but no such patterns are evident for gentoo penguins. Fledging success, however, has remained stable at all breeding colonies. The different trends in abundance and recruitment indices for each species, despite generally similar indices of summer performance, suggest that winter conditions contribute to the divergent responses among the penguins. In particular, strong correlations between indices of penguin and krill recruitment suggest that penguins in the South Shetland Islands may live under an increasingly krill-limited system that has disproportionate effects on the survival of juvenile birds.

Spring oceanographic conditions and northern shrimp Pandalus borealis recruitment success in the north-western Gulf of St. Lawrence

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 339:229-241 (2007) - doi:10.3354/meps339229 Spring oceanographic conditions and northern shrimp Pandalus borealis recruitment success in the north-western Gulf of St. Lawrence Patrick Ouellet*, Louise Savard, Pierre Larouche Maurice Lamontagne Institute, Fisheries and Oceans Canada, 850 route de la mer, Mont-Joli, Quebec G5H 3Z4, Canada *Email: ouelletp@dfo-mpo.gc.ca ABSTRACT: Time series of sea-surface temperature (SST), thermally mixed layer depth, and the SST warming rate in spring at the time of larval emergence were correlated with indices of northern shrimp Pandalus borealis recruitment (cohort abundance and larval survival index) between 1994 and 2003 in the northwest Gulf of St. Lawrence, Canada. The recruitment index and larval survival index were negatively correlated to daily mean SST at the time of larval emergence. The recruitment index and larval survival index were positively correlated with the SST warming rate and with the mixed layer depth at the time of larval emergence. Overall, the analysis reveals that larval emergence during a period of weak density stratification and low SST in the spring, but followed by relatively high warming rates of the upper layer of the water column, is favourable for larval survival. We suggest that the observed relationships support the hypothesis that oceanographic conditions in the upper layer of the water column, which initiate and sustain high levels of biological production at the time of larval emergence and early development, are favourable for northern shrimp recruitment success. Thus, interannual variability in northern shrimp recruitment in the northwest Gulf of St. Lawrence may be explained by Cushing’s match/mismatch hypothesis. KEY WORDS: Northern shrimp · Sea-surface temperature · Recruitment · Match/mismatch · Gulf of St. Lawrence · Pandalus borealis Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 339. Online publication date: June 06, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Electromyographic patterns suggest changes in motor unit physiology associated with early osteoarthritis of the knee

To assess characteristics of active motor units (MUs) during volitional vastus medialis (VM) activation in adults with symptomatic knee osteoarthritis (OA) across the spectrum of radiographic severity and age-comparable healthy control volunteers. We evaluated 39 participants (age 65+/-3 years) in whom weight-bearing knee X-rays were assigned a Kellgren & Lawrence (KL) grade (18 with KL grade=0; four each with KL grades=1, 2 and 4; nine with grade 3). Electromyography (EMG) signals were simultaneously acquired using surface [surface EMG (S-EMG)] and intramuscular needle electrodes, and analyzed by decomposition-enhanced spike-triggered averaging to obtain estimates of size [surface-represented MU action potentials (S-MUAP) area], number [MU recruitment index (MURI)] and firing rates [MU firing rates (mFR)] of active MUs at 10%, 20%, 30% and 50% effort relative to maximum voluntary force [maximal voluntary isometric contraction (MVIC)] during isometric knee extension. Knee extensor MVIC was lower in OA participants, especially at higher KL grades (P=0.05). Taking the observed force differences into account, OA was also associated with activation of larger MUs (S-MUAP area/MVICx%effort; P<0.0001). In contrast, the estimated number of active units (MURI/MVICx%effort) changed differently as effort increased from 10% to 50% and was higher with advanced OA (KL=3, 4) than controls (P=0.0002). VM activation changes at the level of the MU with symptomatic knee OA, and this change is influenced by radiographic severity. Poor muscle quality may explain the pattern observed with higher KL grades, but alternative factors (e.g., nerve or joint injury, physical inactivity or muscle composition changes) should be examined in early OA.

Evaluating Walleye Length Limits in the Face of Population Variability: Case Histories from Western Minnesota

AbstractPopulation and fishery responses to the implementation of minimum length limits (356 and 381 mm total length) for walleyes Sander vitreus were evaluated for two Minnesota populations (Big Stone Lake and Lac Qui Parle) and were compared with population trends observed in a single reference lake (Lake Traverse) between 1991 and 2004. High variation in walleye recruitment (coefficient of variation (CV = 100 × SD/mean) in mean gill‐net catch per unit effort of age‐2 walleyes &gt; 98%) was observed in all study populations and also in recruitment indices from 20 populations across North America (mean CV = 112%), indicating that high variability in recruitment is common. Walleye growth rates were also variable; mean length at age 3 varied by more than 120 mm among year‐classes in all three study populations. Observed trends in population age‐ and size‐structure indices estimated from gill nets appeared to be largely related to growth and recruitment patterns both before and after the regulations were in place. No direct evidence existed to indicate that adult walleye abundance, size structure, or age structure was improved after implementation of length limits or that the regulations reduced annual variation in size structure. In light of recruitment variation, meaningful evaluation of walleye length limits will require long‐term annual sampling efforts designed to monitor the fate of multiple year‐classes of similar magnitudes during both preregulation and postregulation periods. Lastly, managers must select meaningful metrics to measure the effects of length limits. Observed improvements in fishery‐related metrics, such as size structure of harvested fish, may merely reflect changes in angler behavior rather than actual improvements in the population. Also, fishery‐based metrics may be difficult to measure given the budgetary and logistical constraints associated with creel surveys.

Oceanic changes in the Sargasso Sea and declines in recruitment of the European eel

AbstractFriedland, K. D., Miller, M. J., and Knights, B. 2007. Oceanic changes in the Sargasso Sea and declines in recruitment of the European eel. – ICES Journal of Marine Science, 64: 519–530. Anguillid eel recruitment in the North Atlantic has declined in recent decades, raising concerns that climatic changes in the Sargasso Sea may be influencing oceanic reproduction and larval survival. There is a significant negative correlation between the North Atlantic Oscillation and long-term variations in catches of glass eel stages of the European eel Anguilla anguilla recorded by the fishery independent Den Oever recruitment index (DOI) in the Netherlands, lagged by one year. Ocean-atmospheric changes in the Sargasso Sea may affect the location of spawning areas by silver eels and the survival of leptocephali during the key period when they are transported towards the Gulf Stream. A northward shift in a key isotherm (22.5°C), defining the northern boundary of the spawning area, a declining trend in winds and transport conditions in larval transport areas, and a shallowing of the mixed layer depth could affect primary productivity in areas where leptocephali feed. The relationships between these ocean parameters and the DOI suggest that these changing ocean conditions could be contributing to declining recruitment of the European eel and probably also of the American eel (A. rostrata), but anthropogenic factors during their continental life stage must also be considered.

Direct effects of current velocity on the growth, morphometry and architecture of seagrasses: a case study on Zostera noltii

Hydrodynamics affect and are affected by the presence of seagrasses. Previous studies have suggested that such effects could modify the capacity of these marine plants to cope with adverse environmental conditions. However, the direct impact of hydrodynamics on seagrass perfor- mance remains undemonstrated. In this study, the direct effects of current velocity on seagrasses were examined by cultivating single plants of Zostera noltii in 12 flume tanks with contrasting cur- rent velocities (0.01, 0.10 and 0.35 m s -1 ), while avoiding differences in other abiotic factors. Our results demonstrated that current velocity directly affects (1) dynamic plant parameters such as growth, elongation, recruitment and plastochrone index (PI), (2) the morphometry of leaves, rhizome and roots and (3) the architecture of Z. noltii plants. Growth, elongation and recruitment rates increased significantly with increasing velocities, whereas the PI was significantly reduced. The resulting morphotypes appeared to represent acclimation to hydrodynamic stresses: they had (1) an improved anchoring system and (2) a reduced risk of shoot breakage. That is, at high velocity, the root system was enlarged, the aboveground/belowground biomass ratio (AG/BG ratio) was reduced and the cross sections of leaves and rhizomes increased.

Lessons Learned in Participant Recruitment and Retention: The EXCITE Trial

Participant recruitment is considered the most difficult aspect of the research process. Despite the integral role of recruitment in randomized clinical trials, publication of data defining the recruitment effort is not routine in rehabilitation initiatives. The recruitment process for the Extremity Constraint-Induced Therapy Evaluation (EXCITE) trial illustrates obstacles to and strategies for participant accrual and retention that are inherent in rehabilitation clinical trials. The purpose of this article is to increase awareness of the multiple facets of recruitment necessary for successful clinical trials, thus supporting the continued development of evidence-based practice in physical therapy. The Recruitment Index is presented as a variable to measure recruitment efficacy. In addition, ethical aspects of recruitment are explored, including informed consent and the concept of therapeutic misconception.

Optimum expression of adult lung function based on all-cause mortality: Results from the Reykjavik study

A variety of reference curves are used to derive predicted values for adult lung function, even within ethnically similar populations. Alternatives to percentage predicted value are sometimes used to allow for height in research. Strength of association with total mortality can be used to choose the optimal expression, between forced expiratory volume in 1s (FEV(1)) divided by height(2), FEV(1)/height(3), FEV(1)% predicted and difference from predicted. Data from the Reykjavik Study cohort, 1976-2002, included 5544 men and 8062 women randomly selected from the population. Total mortality was analysed by Cox proportional hazards regression in relation to each height-adjusted measure, allowing for age group, period of recruitment and body mass index, and smoking before or at baseline. FEV(1)/height(2) and FEV(1)/height(3) had stronger associations with mortality than FEV(1)% predicted and difference from predicted in men and in women. There were similar findings for forced vital capacity (FVC) in non-smokers and in women. FEV(1)/height(2) was slightly better predictive than FEV(1)/height(3) in men, but distributions of FEV(1)/height(3) in men and women were closer than those of FEV(1)/height(2). Clinical practise and epidemiological research would benefit from agreement on how to adjust lung function for height. Replication of these analyses in other cohort studies would inform the choice between FEV(1)/height(2) and FEV(1)/height(3).

Wader recruitment indices suggest nesting success is temperature‐dependent in Dunlin Calidris alpina

Measures of annual breeding success are an important component of species monitoring programmes. It has been suggested that effective monitoring of breeding productivity for arctic breeding waders may be achieved from an analysis of annual variation in the proportion of juveniles in winter flocks. Here, we attempt to generate a recruitment index for Dunlin Calidris alpina caught during the winter in north Wales. This index revealed significant annual variation and we show that this is strongly correlated with summer temperature (but not rainfall) on the breeding grounds. Years with high recruitment were also correlated with increases in the national winter population estimate. In years of intermediate summer temperature, the recruitment index was highest and we discuss the possible implications this has for Dunlin under scenarios of future climate change. We were unable to generate a significant index for Common Redshank Tringa totanus and discuss possible reasons for this.

GROWTH, MORTALITY, RECRUITMENT AND SEX-RATIO IN WILD STOCKS OF SILVER-LIPPED PEARL OYSTER PINCTADA MAXIMA (JAMESON) (MOLLUSCA: PTERIIDAE), IN WESTERN AUSTRALIA

Abstract Growth, mortality, recruitment and sex-ratio of wild stocks of the silver-lipped pearl oyster Pinctada maxima were studied at sites spanning the geographic extent of the commercial fishery using mark-recapture experiments, recruitment cohort analysis and research surveys of stock abundance and reproductive status. Growth parameters (L∞, K) from the von Bertalanffy growth equation were estimated at 210 mm dorso-ventral measurement (DVM) (±16 mm SD) and 0.74 at the Lacepede Islands, L∞ of 199 mm DVM (±6 mm SD) and K of 0.79 on 80 Mile Beach, and L∞ of 194 mm (±6 mm SD), and K of 0.72 at Exmouth Gulf respectively. Estimates of natural mortality (M) by tagging were very low (0.02–0.03), compared with catch-curve analysis, which estimated M to be between 0.1 in deeper (30–34 m) populations and 0.18 in shallow (9–12 m) populations. Settled P. maxima spat (0 + and 1 + age classes) on adult shell were quantified (e.g., 1,317 spat found on 119,000 shell in 2003) to obtain an annual recruitment index, whic...

Do large rock lobsters inhibit smaller ones from entering traps? A field experiment

Indices of recruitment are often derived from trap surveys. If legal-sized lobsters inhibit smaller ones from entering traps, the overall catch-rate may depend on population composition and not just on overall abundance, and recruitment strength can be overestimated as average length decreases in a population. A controlled field experiment was used to examine whether trapping inhibition of Jasus edwardsii occurred during spring (November) or summer (February) in south-eastern Tasmania. Four treatments were applied. Baited traps were seeded with either: one large female, one large male or two sublegal-sized female lobsters. Baited traps with no seed were used as a control. Seeded traps always caught fewer sublegal-sized lobsters than control traps. When catches in both seasons were examined by sex of entrants, seeded traps caught fewer small lobsters than control traps in 11 of 12 comparisons. However, a strong inhibitory effect was observed only for female-seeded traps during summer. The data obtained in the present study suggest that sublegal-sized indices of recruitment are likely to be influenced in summer by the number of large females present. Spring trials suggest that corrections to a sublegal-catch index may be unnecessary during this season, but more work is required in order to better understand the complex, sex-specific and seasonal patterns of interactions of this species.

EFFECT OF AERIAL EXPOSURE ON PHYSIOLOGICAL CONDITION AND SURVIVAL OF DIPLODON CHILENSIS (BIVALVIA: HYRIIDAE) DURING TRANSLOCATION

Freshwater mussels are an important component of the aquatic biodiversity of Chile, especially in the southern part of the country, and other geographical areas of the northern and southern hemispheres. The most common species in Chile is Diplodon chilensis (Gray, 1828), which is a unique species of Hyriidae with a distribution extending from 34°58’S to 72°48’S in both lentic and lotic environments in numerous hydrographic basins (Parada & Peredo, 2002). It is also present in Argentina between parallels 32°52’ and 45°51’S (Bonetto, 1973). Diplodon chilensis populations have declined or been extirpated in lotic environments due to disturbance or habitat degradation from anthropogenic activity, mainly engineering projects. To date there have been no proposals in Chile for the protection of freshwater mussels. Relocation of unionids is being used as a conservation and management tool (Cope & Waller, 1995). They reviewed 33 projects and reported a mean survival of 50%, suggesting that relocation had been stressful to mussels. Furthermore, most relocations were monitored for < 1 year, and < 20% were monitored for five years. The success of most relocation projects has been predominately judged by mussel survival. Few studies examined measures such as growth, recruitment or condition index. Peredo et al. (2005), studying relocation of D. chilensis in Chile and its long-term evaluation, reported positive results due to recruitment and recovery of mussels 18 years after relocation. However, little is known of the effect of handling and aerial exposure on mussel survival or recommendations on the most appropriate season to conduct relocations. It is hypothesized that relocation of freshwater mussel populations is a suitable management and conservation strategy if the stress of handling is minimized and time of the year fits with MALACOLOGIA, 2006, 49(1): 217−221

Recruitment of mackerel icefish (Champsocephalus gunnari) at South Georgia indicated by predator diets and its relationship with sea surface temperature

The South Georgia population of mackerel icefish (Champsocephalus gunnari) is exploited by both a fishery and predators, including gentoo penguins (Pygoscelis papua). Because considerable uncertainty surrounds recent estimates of stock size, there is a need to consider novel approaches that may give insight into the population dynamics of this species. We derive two indices of recruitment based on the occurrence of mackerel icefish in gentoo penguin diets, one of which is scaled by a survey estimate of the density of Antarctic krill (Euphausia superba), an alternative prey species for gentoo penguins. The closure of the fishery for much of the 1990s allowed the relationship between environmental conditions and recruitment to be studied without the confounding effects of fishing mortality. The recruitment indices were positively correlated with sea surface temperature with a lag time equal to the age of the fish. These results suggest strong links between mesoscale environmental processes and the smaller scale interaction between gentoo penguins and their mackerel icefish prey.

Preliminary assessment of the Falklands Patagonian toothfish ( Dissostichus eleginoides) population: Use of recruitment indices and the estimation of unreported catches

Longline fishing for Patagonian toothfish ( Dissostichus eleginoides) has taken place in Falkland Island waters for over 10 years. This species was previously only caught as bycatch in the Loligo gahi and finfish trawl fishery. This paper presents a preliminary assessment of the Falkland Islands population of Dissostichus eleginoides using an age-structured production model (ASPM). Two models were investigated; one using a Beverton–Holt stock recruitment relationship and another using trawler CPUE based estimates of toothfish abundance to estimate yearly recruitment. A stock recruitment relationship was not included within the model that used abundance estimates, as recruitment to the population was estimated directly from the index of relative recruit abundance calculated from trawler CPUE. The model was fitted to longline standardised CPUE and to the catch-at-length data. The models produced estimates that provided similar declines in the toothfish population although the start and end biomass estimates varied slightly. The models provided estimates of between 13,000 and 26,000 tonnes of current spawning stock biomass and showed current biomass to be between 38 and 46% of virgin biomass. The fit to CPUE was poor between 1994 and 1996, which we hypothesised could have been due to unreported catches or changes in q or M. This was a time when there was considerable IUU fishing in the southwest Atlantic. When the model was allowed to estimate a level of extra catch the fit was improved and 5000 tonnes of extra catch was estimated. Two further models were briefly examined to investigate the possibility of changes in M and q but both required large changes in those parameters in order to fit. Estimates of MSY varied widely, from 912 to almost 3000 tonnes.

Population dynamics of the exploited sea cucumber Isostichopus fuscus in the western Galápagos Islands, Ecuador

AbstractLong‐term density data for the sea cucumber, Isostichopus fuscus, from Canal Bolivar (separating western Isabela and eastern Fernandina Islands), Galápagos, were compared with catch statistics and used in a stock depletion model to determine the extent of the effects of the fishery on the existing population and the potential for the population to recover after each fishing season. Recruitment indices were found to be low from 1994 until mid‐1999, when a mass recruitment event was registered and numbers of small individuals increased dramatically. The increase in density of juveniles peaked in 2001 and has declined since. Recruitment in this species of sea cucumber appears to be highly sporadic and may depend on intense climatic events such as the warm El Niño. Current levels of fishing activity are unsustainable. The management implications of pulse recruitment in this fishery are discussed.