Content uploaded by William Don Bowen
Author content
All content in this area was uploaded by William Don Bowen on Feb 26, 2015
Content may be subject to copyright.
A preview of the PDF is not available
Duration of lactation and postweaning changes in mass and body-composition of harbor seal, Phoca-Vitulina, pups
Canadian Journal of Zoology
Abstract and Figures
We studied changes in body mass and body composition of harbour seal pups from weaning to 5 – 6 weeks postweaning in June – August 1988 and 1989 on Sable Island, Canada. Known-age pups (n = 52) were captured at 3-day intervals from late lactation through about 40 days postweaning. Pups were weaned, on average, at 24.1 ± 0.44 days (mean ± SE) postpartum at a body mass of 24.9 ± 0.45 kg. There were no significant differences between years or sexes in the age and mass at weaning or in the rate of mass loss during the postweaning period. The duration of the postweaning fast averaged from 15 – 17 days as assessed by stomach lavage. The rate of mass loss was independent of weaning mass. At weaning, pups contained an average of 47.7% water and 32.8% fat, based on deuterium oxide dilution. During the first 14 days postweaning, the estimated body composition of pups did not change, despite the loss of body mass. Over the next 26 days, the estimated percent body water increased to about 63% and body fat declined to about 12%. The average energy density of harbour seal pups at weaning was low (16.3 kJ/g) compared with that of other phocids (17.7 – 22.2 kJ/g). This low energy density at weaning may reflect the highly aquatic and precocial development of harbour seal pups.
Figures - uploaded by William Don Bowen
Author content
All figure content in this area was uploaded by William Don Bowen
Content may be subject to copyright.
... Since most phocids have a short lactation period, growth is extremely rapid during this initial developmental stage (Bowen 1991). Once individuals are weaned, they have limited foraging experience (Bowen 1991), which means that they will not grow and can even lose weight during the post-weaning period, allocating more energy towards foraging effort (Condit & Ortiz 1987, Muelbert & Bowen 1993, Muelbert et al. 2003. ...
... Nutritionally related deficiencies at birth or throughout lactation -for example, because of mother-pup separation -are important sources of mortality for neonate seals (Huggins et al. 2013, Ashley et al. 2020, Wilson & Jones 2021. Hence, larger individuals have an advantage over smaller individuals in terms of stored resources (Iverson et al. 1993, Muelbert & Bowen 1993. However, relatively small individuals at birth may be able to express compensatory growth if maternal milk is sufficient. ...
... Due to their smaller size compared to larger phocids that are capital breeders (e.g. grey seals Halichoerus grypus), it has been hypothesized that harbour seal females likely use a combination of stored energy ('capital breeding' as defined by Jönsson 1997) and daily resource acquisition ('income breeding') to cover the energetic costs of lactation (Smith et al. 1991, Muelbert & Bowen 1993, Boness et al. 1994, Boness & Bowen 1996, Cottrell et al. 2002. In the St. Lawrence Estuary, females give birth to one pup between mid-May and mid-June (Dubé et al. 2003). ...
Juvenile survival, a fundamental parameter in the population dynamics of long-lived species, is often tightly linked to early-life body growth. Here, based on repeated mass measurements on 555 harbour seal Phoca vitulina pups marked between 1998 and 2023 in the St. Lawrence Estuary, we first characterized the shape of neonatal growth patterns of the pups using Bayesian hierarchical nonlinear models. Second, we evaluated the effect of sex on neonatal growth to better understand the development of sexual dimorphism in this species and tested for compensatory growth. Finally, we assessed the influence of local variables (wind speed, sea surface temperature, pup abundance and breeding site) during the neonatal stage on pup weaning mass. Our results showed that neonatal growth follows a Gompertz curve, characterized by minimal growth the first few days after birth, followed by a significant increase in mass until a stabilization near weaning (~30 d of age). We found no sex difference in the growth pattern, but males were slightly heavier at birth than females. Larger pups accumulated more mass than smaller pups, suggesting increasing returns for greater body mass at birth but no compensatory growth. Finally, wind speed, sea surface temperature, pup abundance and breeding site did not affect weaning mass. This study provides insight into the characterization of nonlinear growth in harbour seal pups. Monitoring neonatal growth provides a tool to assess potential patterns of juvenile survival, which are important in studies of population dynamics.
... Unfortunately, analysis of the pelage can only differentiate individuals between animals younger or older than 1 year (Corpe et al. 1998) due to the different qualities of the hairs. Body mass in pups varies based on the quality and quantity of nursing received, the timing of weaning, and how long it takes them to learn how to hunt (Muelbert and Bowen 1993). The condition of the umbilical cord can be used to age pups to some extent, but as the cord drops off between Day 6 and 10 (Dierauf et al. 1986), its usefulness for older than 10 days of age estimation is nonexistent. ...
... The condition of the umbilical cord can be used to age pups to some extent, but as the cord drops off between Day 6 and 10 (Dierauf et al. 1986), its usefulness for older than 10 days of age estimation is nonexistent. Weaning happens quite abruptly, around 21 to 24 days old (Muelbert and Bowen 1993;Cordes and Thompson 2013), but can sometimes take up to 4 weeks. During the first 5 weeks following weaning, weaners lose about 21% of their body mass while they learn how to hunt (Muelbert and Bowen 1993). ...
... Weaning happens quite abruptly, around 21 to 24 days old (Muelbert and Bowen 1993;Cordes and Thompson 2013), but can sometimes take up to 4 weeks. During the first 5 weeks following weaning, weaners lose about 21% of their body mass while they learn how to hunt (Muelbert and Bowen 1993). Thus, body mass alone cannot be used as a measure to age young weaners. ...
To study patterns in behavior, fitness, and population dynamics, estimating the age of the individuals is often a necessity. Specifically, age estimation of young animals is very important for animal rehabilitation centers because it may determine if the animal should be taken in and, if so, what care is optimal for its rehabilitation. Accurate age estimation is also important to determine the growth pattern of an individual, and it is needed to correctly interpret the influence of early body condition on its growth trajectories. The purpose of our study was to find body measurements that function as good age estimators in young (up to 3 months old) harbor seals (Phoca vitulina vitulina), placing emphasis on noninvasive techniques that can be used in the field. To meet this goal, body mass (BM), dorsal standard length (DSL), upper canine length (CL), body condition (BC), and sex were determined from 45 Harbor Seal pups of known age. Generalized additive mixed models were fitted to find how well these morphometric measures predicted age, and the results from the selected model were used to compute growth curves and to create a practical table to determine the age of young animals in the field. We found that both DSL and CL—and to some extent sex—were useful predictors for estimating age in young harbor seals and that the growth rate of pups raised in captivity is significantly lower than for those raised in the wild. In addition, we found no evidence for compensatory growth, given that animals that arrived at the center with a poor BM or BC continued to show lower BM or BC throughout almost the entire rehabilitation period.
... However, the increase of chitin degradation, a characteristic compound of the invertebrate exoskeleton, is consistent with pups feeding at a lower trophic level than adults 37 . Some studies reported that initially newlyweaned harbor seals feed on small crustaceans and fishes 28,36 . Crustaceans play a major role in the pups diet, suggesting that pups are inefficient in capturing fish at this age 28 . ...
... Some studies reported that initially newlyweaned harbor seals feed on small crustaceans and fishes 28,36 . Crustaceans play a major role in the pups diet, suggesting that pups are inefficient in capturing fish at this age 28 . As their foraging and diving skills improve, pups switch to an adult diet, but ingestion of solid food may occur while the pup is still nursing 40 . ...
... In comparison to other phocid species, harbor seal pups are particularly precocial at entering the sea shortly after birth and swimming with their mother throughout the lactation period 20,26,27 . Swimming requires higher energy expenditure, so the post-weaning fast is shorter than other species due to less energy storage during lactation 28 . Harbor seal pups lost 21% of weaning mass over the first 5 weeks of the post-weaning stage and fasted an average of 15-17 days. ...
Dietary changes are the major variation cause in the composition of the gut microbiota. The short lactation phase in phocids provides an exceptional opportunity to explore the microbiota's response to a quick transition from a milk-based to a solid diet. We investigated the effects of age and sex on the gut microbiota of harbor seals in Mexico using rectal and fecal samples from pups and adults. 16S gene sequencing revealed age explains most of the observed variations in microbial composition. Individuals with frequent contact (pups—female adults) have major microbial similarities than those with little or no contact (pups—male adults). Overall, adults and females (regardless of sex and age, respectively) have a greater microbial richness; as seals grow, the core microbiome shrinks, and microbial diversity increases. We found pathways related to milk and chitin digestion in pups' microbiomes, indicating pups were transitioning to a solid diet. An enrichment of routes related to dramatic weight loss and body mass indicated higher metabolic stress in pups in late breeding season, when they are weaned and start intermittent fasting. Our findings highlight the host-microbiome interaction in harbor seals during late breeding season in response to food shifts and metabolic stress.
... Insufficient body reserves because of low foraging success directly impacts the reproductive expenditure of pinniped females, resulting in a low weaning weight for pups, in turn, affecting their survival (Muelbert and Bowen 1993;Le Boeuf and Crocker 2005). At Punta Banda Estuary, Baja California, a reduction in harbor seal pup numbers, from 40 to 12, from 2013 to 2016, coincided with a period of ocean warming from 2014 to 2016, with various pups abandoned by their mothers (Fernández-Martín 2018), who were forced to end lactation earlier than they should (Fedak et al. 1996;Bowen et al. 2001). ...
At the edge of their distribution, populations are more susceptible to habitat changes and have higher risk of abundance decline. In the northeast Pacific Ocean, the harbor seal’s southernmost distribution occurs in the southern California Current Large Marine Ecosystem, off the Baja California Peninsula, which includes nine islands and archipelagos, and some sites on the coast. A decrease in abundance in 2016 at coastal colonies has been associated to an increase in pebble extraction activities at some beaches. The present study analyzed seal counts spanning 2016–2022 and evaluated them as a function of sea surface temperature 50 km around each colony, and of pebble extraction occurrence. We found a consistent decrease in the number of the species during the study period for all colonies off the Baja California Peninsula, coinciding with an increase in SST that could indicate lower habitat suitability. However, the decline of seal numbers on the islands of Todos Santos, San Jeronimo, San Benito, Natividad, and San Roque was slower, possibly because they are surrounded by more productive waters. Additionally, the loss of several seal colonies on the coast seemed associated to disturbances caused by pebble extraction activities nearby. The present study provides evidence of the effect of ocean warming and disturbance on harbor seal relative to distribution and abundance. Since it is a protected species under Mexican law, future conservation policies should account for climate change effects, and include pebble extraction management along the western coast of the Baja California Peninsula.
... Ce résultat est néanmoins fortement lié à la masse corporelle des deux phoques adultes S11 et S12, 112 et 118 kg respectivement, capturés fin mai juste avant la saison de reproduction : il est ainsi fortement probable que ces domaines vitaux de surface plus restreinte soient liés à la saison du suivi télémétrique, certaines études ayant déjà montré que les phoques vaux-marins réduisent leur alimentation et la distance de leurs voyages de chasse pendant la saison de reproduction (Thompson 1993, Thompson et al. 1994, Boness et al. 2006. Les adultes capturés en octobre 2019 étaient tous largement plus légers (70 à 83 kg), bien que de taille similaire, et il est effectivement attendu que les phoques veauxmarins adultes perdent de la masse corporelle pendant les saisons de reproduction et mue, en été (Muelbert & Bowen 1993, Coltman et al. 1997. ...
... After weaning, pups undergo a post-weaning fast (PWF), mainly on land, for several weeks prior to their first departure to sea [28,29,30,31]. The PWF, common to many phocid species [31], is very energy-intensive, with pups losing up to 50 % of their lipid reserves and 10 % of the protein reserves acquired during the lactation period [28,[32][33][34][35]. Although the function of the PWF period is not clearly understood, it is a critical time for the development of coordination and mobility, particularly in the aquatic environment [30,[36][37][38][39]. ...
Weaned southern elephant seals (SES) quickly transition from terrestrial to aquatic life after a 5- to 6-week post-weaning period. At sea, juveniles and adult elephant seals present extreme, continuous diving behaviour. Previous studies have highlighted the importance of the post-weaning period for weanlings to prepare for the physiological challenges of their future sea life. However, very little is known about how their body condition during this period may influence the development of their behaviour and brain activities. To characterise changes in the behavioural and brain activity of weanlings prior to ocean departure, we implemented a multi-logger approach combining measurements of movements (related to behaviour), pressure (related to diving), and brain electrical activity. As pups age, the amount of time allocated to resting decreases in favour of physical activity. Most resting (9.6 ± 1.2 h/day) takes place during daytime, with periods of slow-wave sleep representing 4.9 ± 0.9 h/day during the first 2 weeks. Furthermore, an increasing proportion of physical activity transitions from land to shore. Additionally, pups in poorer condition (lean group) are more active earlier than those in better condition (corpulent group). Finally, at weaning, clear circadian activity with two peaks at dawn and dusk is observed, and this pattern remains unchanged during the 4 weeks on land. This circadian pattern matches the one observed in adults at sea, with more prey catches at dawn and dusk, raising the question of whether it is endogenous or triggered by the mother during lactation.
... To improve the chances of offspring survival, parents in capital breeding species transfer large quantities of stored energy (i.e., blubber or other fat deposits) to dependent offspring [4,5]. Although this stored energy provides offspring with energetic reserves to support the transition to independent foraging, offspring nonetheless only have a limited amount of time to develop the skills needed to acquire food and avoid predation (e.g., [6,7]). Size-and age-specific physiological constraints together with inexperience make the transition to independent foraging in juveniles a crucial period with important consequences for survival, dispersal, and recruitment to the breeding population [8]. ...
Most vertebrate offspring must transition from the relative security of parental care (nutrition and protection) to independent foraging. Offspring face many challenges during this critical period, particularly in species where parental care ends at weaning, such as the grey seal (Halichoerus grypus). We studied the development of movement behaviour in naïve grey seal pups from their first trips to sea to about five months of age. Twenty-five (12 males and 13 females) newly-weaned pups were fitted with satellite-linked GPS tags on Sable Island, Nova Scotia, Canada in January 2016. The influence of fixed effects (pup size, sex, week) and the random effect of pup identity on trip characteristics were examined. Movement behaviour was analyzed using a move persistence mixed-effects model. Habitat use was highly variable among individuals and covered much of the geographic distribution of the population. Unlike older juveniles, subadults, and adults in this population, most naïve pups used multiple haulout sites to begin and end trips. There was little evidence of area-restricted search behaviour during trips, suggesting that naïve pups were using an opportunistic foraging tactic that may result in more variable foraging success than that of older, experienced animals. Naïve pups made longer trips with longer haulout durations between them than observed for older greys seals. Males and females differed in some trip characteristics, but sex effects were small over the first few months of life. Offspring size at weaning was not a useful predictor of trip characteristics. Move persistence of grey seal pups was initially high and then decreased over time as individuals gained experience. Both intrinsic and extrinsic factors were influential on the movements of grey seal pups. Greater body length at weaning, longer duration spent on shore after weaning, shallower water column depth, and farther distance from shore were all associated with lower move persistence. Female grey seal pups had lower move persistence than males. Overall, the movements of naïve grey seal pups during the first few months of life were characterized by extensive exploration, but move persistence decreased over time suggesting they may be using an exploration-refinement foraging tactic.
... The harbour seal Phoca vitulina is the most widely distributed pinniped, occupying a wide variety of habitats and climatic zones across the Northern Hemisphere (Liu et al. 2022). Harbour seals, with a relatively small body size, have developed a hybrid tactic of resource use for reproduction, which includes at-sea foraging behaviour, similar to Otariids, and a longer lactation duration than other phocids (Oftedal et al. 1987;Muelbert and Bowen 1993;Boness et al. 1994;Cottrell et al. 2002). Weaned harbour seal pups rely on their stored energy reserves during their transition period to independent feeding following weaning . ...
Marine mammal populations worldwide greatly benefitted from conservation measures put in place since the 1970s following overexploitation, and many pinniped populations have recovered. However, threats due to bycatch, interspecific interactions or climate change remain, and detailed knowledge on vital rates, population dynamics, and their responses to environmental changes is essential for efficient management and conservation of wild populations. In this study, we quantified pup abundance and survival of individually marked harbour seal (Phoca vitulina Linnaeus, 1758) pups during the preweaning period at Bic Island and Métis sites in the St. Lawrence Estuary from 1998 to 2019. We used mark-recapture models to evaluate competing hypotheses regarding variation in daily preweaning survival rates and capture probability during the pups’ first 30 days of life. Pup abundance increased from 76 [95% CI: 59, 101] to 323 [95% CI: 233, 338] in the past two decades at Bic Island and from 66 [95% CI: 47, 91] to 285 [95% CI: 204, 318] at Métis. Preweaning survival was generally higher at Bic (0.73 [95% CI: 0.58, 0.82]) than at Métis (0.68 [95% CI: 0.52, 0.79]). We hypothesize that differences between habitats and human disturbance contribute to lower preweaning survival at Métis, but behavioural studies are needed to understand the impacts of disturbance on mother–pup interactions during the nursing period.
La croissance en début de vie est souvent associée à la survie juvénile, un paramètre démographique clé en dynamique de population. Selon la théorie des traits d’histoire de vie, puisque les ressources sont limitées, les individus doivent faire des compromis entre différentes fonctions coûteuses, dont la croissance. Ainsi, plusieurs facteurs peuvent avoir un impact sur la croissance, surtout sur la croissance en bas âge (aussi nommée néonatale), notamment le sexe, l’identité individuelle ou encore l’environnement. Il est donc intéressant d’étudier la croissance et les facteurs qui l’affectent à différents stades de développement, étant donné ses effets possibles sur les autres traits vitaux. Or, les études sur les patrons de croissance requièrent une mesure d’âge des individus, qui est souvent peu accessible pour les populations sauvages. Ainsi, mon projet de maîtrise se divisait en deux principaux objectifs. D’abord, le premier objectif (Chapitre 2) visait à valider une méthode d’estimation de l’âge chez les chiots du phoque commun (Phoca vitulina) de l’estuaire du Saint-Laurent. Cette méthode se base sur les scores de dégénération du cordon ombilical. Pour ce faire, j’ai utilisé les données du suivi de la population de phoque commun de l’estuaire depuis 1998 afin d’évaluer l’exactitude et la précision de la méthode ainsi que de mesurer sa capacité à estimer des dates de naissance. La conclusion de ce premier chapitre est que la méthode était répétable et précise et estimait de manière fiable les dates de naissance des individus. Le second objectif (Chapitre 3) de mon projet de maîtrise était d’évaluer la croissance néonatale des chiots du phoque commun. D’abord, j’ai caractérisé le patron de croissance néonatale en comparant différentes courbes de croissance linéaires et non linéaires. Ensuite, j’ai évalué les différences entre les femelles et les mâles pour détecter des signes de dimorphisme sexuel précoces. Puis, j’ai étudié la présence du phénomène de croissance compensatoire et finalement, j’ai analysé l’effet de différents facteurs environnementaux sur la masse au sevrage. Mes résultats montrent que les chiots du phoque commun suivaient un patron de croissance non linéaire de type Gompertz. Je n’ai pas détecté de différence entre les femelles et les mâles dans leur patron de croissance, mais j’ai détecté une petite différence de ~4% en masse où les mâles sont légèrement plus lourds que les femelles à la naissance. Mes résultats ne permettent pas de distinguer un phénomène de croissance compensatoire chez le phoque commun pendant la période néonatale, toutefois j’ai détecté un effet de rendement de croissance. Les jeunes nés avec une masse supérieure à la moyenne retirent plus d’avantages en termes de gain de masse que les plus petits. La masse à la naissance est donc un trait important qui détermine la masse au sevrage chez cette espèce. Finalement, je n’ai pas détecté de corrélation entre la température de surface de la mer, la vitesse du vent, l’abondance de chiots ou le site de naissance avec la masse au sevrage des individus. En somme, mon projet de maîtrise a permis de valider une méthode empirique pour estimer l’âge des chiots et la date de naissance, deux paramètres importants pour les études en écologie animale et la gestion. Il montre aussi l’importance des études sur les patrons de croissance à différents stades de développement et de considérer des facteurs individuels comme le sexe et la masse à la naissance dans ces études. La condition des nouveau-nés, notamment leur masse à la naissance, semble être un bon indicateur de leur masse au sevrage, qui est un facteur déterminant pour la survie lors de la première année de vie chez cette espèce. De plus, nos résultats mettent en évidence que la variabilité de la croissance néonatale des chiots du phoque commun de cette population ne semble pas associée à la variabilité de certains facteurs environnementaux externes, notamment la température de surface de la mer, la vitesse du vent, l’abondance de chiot qui est un proxy de la densité de la population et le site de naissance. Ainsi, cela suggère que les femelles pourraient tamponner les effets de l’environnement sur leur jeune ou encore que les conditions environnementales soient généralement bonnes pour le phoque commun. Comme la croissance néonatale influence plusieurs traits vitaux des jeunes, son suivi est non seulement un outil indirect pour faire le suivi de l’état de la population, mais également un indice sur l’état écologique du Saint-Laurent.
The glucocorticoid (GC) hormone cortisol is often measured in seals to indicate their stress levels, although other endogenous GCs are usually overlooked. We investigated concentrations of four endogenous GCs in the urine of "orphan" harbour seal pups in rehabilitation. We hypothesised that the GC levels would be elevated if pups were socially isolated, without water access, and with low body mass. Ninety-six samples were collected from 32 pups at four different rehabilitation centres and were analysed by Ultra Performance Liquid Chromatography and Tandem Mass Spectrometry. Median urinary creatinine (Cr) concentrations of endogenous prednisolone (31.6 ng/mg/Cr) and prednisone (31.1 ng/mg/Cr) occurred in similar magnitude to cortisol (37.0 ng/mg/Cr), while median cortisone concentrations were higher (390 ng/mg/Cr). Prednisolone and prednisone concentrations were more strongly inversely related to pup growth rate and pup mass than cortisol and cortisone. Concentrations of all four GCs decreased with mass gain for pups with water access but did not decrease for pups without water; linear mixed models indicated the interaction between these trends was significant for cortisol and cortisone, but not for prednisolone or prednisone. These results indicate the potential value of measuring all four of these endogenous GC hormones in phocid seal pups.
Although the social organization and behaviour of pinnipeds has received considerable attention, the focus of much of this work has been on adults (e.g. Bartholomew, 1970; Stirling, 1975a, 1983; Le Boeuf, 1978; Jouventin and Cornet, 1980; Gentry and Kooyman, 1986). Generally, the problems faced by the pup and the behavioural adaptations which have evolved to cope with them are given cursory treatment if mentioned at all. In this chapter, I review what is known about the early development of seals with the objective of gaining an insight into the factors which have shaped their life history patterns and to point out the current deficiencies in our understanding of pinniped neonatal behaviour. Because of gaps in information on many critical points, many of the conclusions drawn in this chapter must be considered tentative. Wherever possible, I have tried to identify unanswered questions in the hope of stimulating research in these areas.
Mass loss and energy requirements of harp (Phoca groenlandica) and gray seal (Halichoerus grypus) pups were examined in individuals that spent the postweaning fast either on land or in water. Water-fasted and land-fasted harp seals lost body mass at the same rate (day⁻¹) during an 8-wk fast. Approximately 50% of the mass loss (80% of energy utilized) was from blubber. The remainder was from the core (carcass and viscera). Specific metabolic rates did not differ between treatments. Gray seals fasting on land or in water lost mass at the same relative rate () as harp seals. They differed from harp seals in that more of the mass loss (>70%), and hence energy utilized (>90%), was from blubber. As in harp seals, there was no significant difference in rate of total mass loss between treatments. However, water-fasted gray seal pups lost significantly more blubber and exhibited higher specific metabolic rates than those fasting on land. Differences in the relative amounts of blubber and core used by harp and gray seals during the postweaning fast are correlated with differences in breeding habitats. Phocid seals that normally fast on land deplete their blubber layer to a greater extent than do species that usually fast in water. Selection presumably favors preservation of the blubber layer for insulation in species that may be forced to cope with the higher thermal conductivity of water.
Postnatal harp seals, collected during the 1979 and 1980 whelping seasons in the Gulf of St. Lawrence, were examined with respect to proximate composition and energy content of psoas muscle, blubber, viscera, and carcass (eviscerated lean body mass). During nursing, blubber stores of pups increased qualitatively as well as quantitatively, with caloric density increasing from 3.7 kcal/g to 8.9 kcal/g by age 9 days. Over the same time period, caloric density of carcass doubled to 2.5 kcal/g, with neutral lipid stores accounting for 12.5% of carcass wet weight. Neutral lipid levels in viscera approached 9% at weaning. These lipid stores in the carcass and viscera represent important energy sources during the subsequent post weaning fast.
This chapter focuses on ecosystem structure. Ecosystem can be viewed as how the sun's energy is captured and passed from plants to animals and then from animals to animals and the strategies that animals have evolved to capture a share of that energy, use it, and flourish in the Gulf of Alaska. Marine animals thrive in the Gulf of Alaska (GOA) for two basic reasons: (1) the ecosystem is productive, and a lot of food is available to animals living there, and (2) a small number of successful species in the Gulf made the most of the available energy by organizing themselves, as revolving body forms, physiology, and behaviors that allow them to successfully withstand the rigors of the subarctic ocean, capture food, grow, and reproduce faster than they themselves are eaten, harvested, or fall victims to contaminants or disease. The chapter explores the changing structure of the ecosystem during a typical year. The survival strategies of the key species of fish, birds, and mammals that tie them to their habitats are also discussed.
We develop an efficient and effective implementation of the Newton-Raphson (NR) algorithm for estimating the parameters in mixed-effects models for repeated-measures data. We formulate the derivatives for both maximum likelihood and restricted maximum likelihood estimation and propose improvements to the algorithm discussed by Jennrich and Schluchter (1986) to speed convergence and ensure a positive-definite covariance matrix for the random effects at each iteration. We use matrix decompositions to develop efficient and computationally stable implementations of both the NR algorithm and an EM algorithm (Laird and Ware 1982) for this model. We compare the two methods (EM vs. NR) in terms of computational order and performance on two sample data sets and conclude that in most situations a well-implemented NR algorithm is preferable to the EM algorithm or EM algorithm with Aitken's acceleration. The term repeated measures refers to experimental designs where there are several individuals and several measurements taken on each individual. In the mixed-effects model each individual's vector of responses is modeled as a parametric function, where some of the parameters or "effects" are random variables with a multivariate normal distribution. This model has been successful because it can handle unbalanced data (different designs for different individuals), missing data (observations on all individuals are taken at the same design points, but some individuals have missing data), and jointly dependent random effects. The price for this flexibility is that the parameter estimates may be difficult to compute. We propose some new methods for implementing the EM and NR algorithms and draw conclusions about their performance. We also discuss extensions of the mixed-effects model to incorporate nonindependent conditional error structure and nested-type designs.
1. This paper describes the factors affecting local recruitment of juvenile red squirrels, Sciurus vulgaris L., in a coniferous and a deciduous woodland. It also investigates which factors affect body mass at weaning (10-12 weeks old). 2. In a 4-year study, of 85 weaned juveniles from 53 different nests, heavy young were more likely to be recruited in the study areas than lighter young. More young born early in a breeding season were recruited than young from later nests, but there was no difference in recruitment rate between juveniles from spring and summer litters. 3. Differential local recruitment by body mass at weaning occurred from weaning to 6 months after birth (when the period of natal dispersal and heavy early mortality is finished). However, body mass at weaning was not correlated with body mass at 18 months old, and no differences in body mass were found between recruits that survived and those that disappeared before this age. 4. In both spring and summer litters, significantly more early nests recruited young than did late nests, although no significant differences in mean body mass existed between young from early and late nests. 5. Mean body mass of siblings was positively affected by the body mass of the mother while lactating (both areas) and negatively by litter size (coniferous area only). Hence, heavier mothers produced heavier offspring than mothers of lower body mass. 6. Body mass at weaning of local recruits affected home range quality, suggesting that juvenile recruits of higher body mass settled in plots with a higher food abundance than lighter recruits.