scholarly journals Practical Application of a Bioenergetic Model to Inform Management of a Declining Fur Seal Population and Their Commercially Important Prey

2020 ◽  
Vol 7 ◽  
Author(s):  
Elizabeth A. McHuron ◽  
Katie Luxa ◽  
Noel A. Pelland ◽  
Kirstin Holsman ◽  
Rolf Ream ◽  
...  
Keyword(s):  
Energy Intake ◽  
Growth Rates ◽  
Juvenile Fish ◽  
Food Limitation ◽  
Population Decline ◽  
Prey Consumption ◽  
Foraging Efficiency ◽  
Fur Seals ◽  
Fur Seal ◽  
Pup Growth

Food availability is a key concern for the conservation of marine top predators, particularly during a time when they face a rapidly changing environment and continued pressure from commercial fishing activities. Northern fur seals (Callorhinus ursinus) breeding on the Pribilof Islands in the eastern Bering Sea have experienced an unexplained population decline since the late-1990s. Dietary overlap with a large U.S. fishery for walleye pollock (Gadus chalcogrammus) in combination with changes in maternal foraging behavior and pup growth has led to the hypothesis that food limitation may be contributing to the population decline. We developed age- and sex-specific bioenergetic models to estimate fur seal energy intake from May–December in six target years, which were combined with diet data to quantify prey consumption. There was considerable sex- and age-specific variation in energy intake because of differences in body size, energetic costs, and behavior; net energy intake was lowest for juveniles (18.9 MJ sea-day–1, 1,409.4 MJ season–1) and highest for adult males (66.0 MJ sea-day–1, 7,651.7 MJ season–1). Population-level prey consumption ranged from 255,232 t (222,159 – 350,755 t, 95% CI) in 2006 to 500,039 t (453,720 – 555,205 t) in 1996, with pollock comprising between 41.4 and 76.5% of this biomass. Interannual variation in size-specific pollock consumption appeared largely driven by the availability of juvenile fish, with up to 81.6% of pollock biomass coming from mature pollock in years of poor age-1 recruitment. Relationships among metabolic rates, trip durations, pup growth rates, and energy intake of lactating females suggest the most feasible mechanism to increase pup growth rates is by increasing foraging efficiency through reductions in maternal foraging effort, which is unlikely to occur without increases in localized prey density. By quantifying year-specific fur seal consumption of pollock, our study provides a pathway to incorporate fur seals into multispecies pollock stock assessment models, which is critical for fur seal and fishery management given they were a significant source of mortality for both juvenile and mature pollock.

scholarly journals The Behavioral Ecology of Maternal Effort in Fur Seals and Sea Lions

Behaviour ◽  
1990 ◽  
Vol 114 (1-4) ◽  
pp. 3-20 ◽  
Author(s):  
Fritz Trillmich
Keyword(s):  
Energy Transfer ◽  
Food Availability ◽  
Growth Rates ◽  
High Energy ◽  
Food Abundance ◽  
Foraging Efficiency ◽  
Intake Rate ◽  
Sea Lions ◽  
Fur Seals ◽  
Pup Growth

AbstractOtariid seals form a group of similar species distributed from subpolar to tropical seas. Many species were recently studied under conditions of low and high food abundance during major oceanographic disturbances. Evidence for the phenotypic flexibility of and constraints on the rearing strategy of these species derives from inter- and intra-specific comparisons and experimental measurements. I review how changes in food abundance influence foraging behavior and energetics of mothers, pup growth rates, milk composition, weaning age, and the fertility cost of pup rearing. Eared seal females rear young by alternating between lactation ashore and foraging at sea. Subpolar fur seals always wean pups at four month of age, a trait which seems to be genetically fixed and adaptive in their highly seasonal environment. Temperate and tropical fur seals and sea lions can respond to changes in food abundnace by increasing or decreasing time to weaning. During pup rearing, mothers regulate body mass to different absolute values when abundance of food resources changes. This seems to be a constraint caused by reduced foraging efficiency at low food availability. Most species feed exclusively during the night, but sea lions (Zalophus californianus) and Northern fur seals (Callorhinus ursinus) also forage during the day by diving deeper. Females of some species increase the rate of at-sea energy expenditure at low food abundance while keeping the duration of foraging trips constant. Females of other species stay at sea longer working at the same rate. The latter species may be food specialist with a narrower time window for efficient foraging. Pups grow slower when mothers increase time at sea, and at very low food abundance pups may starve. Pups have little influence on the duration of maternal foraging trips, but may diminish the mothers' time ashore by increasing the rate of milk extraction and prolonged non-nutritive sucking. The impact of long maternal at-sea times is reduced by increasing milk fat content as time at sea increases. This mechanism does not fully compensate pup energy intake rate for longer trip durations. Non-migratory species can partly compensate for reduced pup growth rates by lengthening the lactation period. In the Galapagos fur seal (A. galapagoensis), this entails a considerable cost to the mother by reducing her future fertility. Lactation reduces the probability of a successful simultaneous pregnancy and, if pregnancy succeeds, sibling competition for maternal milk ensues. Competition is usually won by the older sibling leading in many cases to the death of the newborn. The rate of energy transfer to pups is high in food-rich years and low in scarce ones. Because pups are more likely to be weaned as yearlings when juvenile growth rate is high than when it is low, high energy transfer to the pup in year "a" reduces the cost of reproduction incurred in year "a+1". The flexibility of the rearing strategy of temperate and tropical species permits mothers to adjust phenotypically to variance in food availability thus partly masking the theoretically expected trade-offs in the life history of these species.

Pup Growth and Maternal Care in New Zealand Fur Seals, Arctocephalus forsteri, at Maatsuyker Island, Tasmania

1997 ◽  
Vol 24 (3) ◽  
pp. 307 ◽  
Author(s):  
Mary-Anne Lea ◽  
Mark. A. Hindell
Keyword(s):  
New Zealand ◽  
Interannual Variability ◽  
Body Mass ◽  
Growth Rates ◽  
Maternal Care ◽  
Early Growth ◽  
Fur Seals ◽  
Fur Seal ◽  
New Zealand Fur Seal ◽  
Pup Growth

The growth, maternal attendance and sucking behaviour of 11 New Zealand fur seal pups, Arctocephalus forsteri, on Maatsuyker Island, Tasmania, were studied during the first six months of lactation. Early growth rates (0–50 days) ranged from 78 to 138 g day-1 and were amongst the highest recorded for any fur seal. Male pups from Maatsuyker Island in 1993 grew at double the rate reported from Kangaroo Island in 1989 and 1990. Growth of pups was influenced by the attendance behaviour of mothers. Mothers that spent relatively long periods at sea had pups that grew more slowly. The proportion of time spent sucking by pups decreased during the attendance period of mothers. Distinct interannual variability was also determined for body masses of pups weighed in March in five successive years, 1990–94, with mean body mass differing by up to 20% between years.

Interannual variation in birth mass and postnatal growth rate of Juan Fernández fur seals

1998 ◽  
Vol 76 (5) ◽  
pp. 978-983 ◽  
Author(s):  
Hugo Ochoa-Acuña ◽  
John M Francis ◽  
Daryl J Boness
Keyword(s):  
Growth Rate ◽  
Body Mass ◽  
Growth Rates ◽  
Interannual Variation ◽  
Postnatal Growth ◽  
Male And Female ◽  
Fur Seals ◽  
Fur Seal ◽  
Attendance Pattern

The objectives of this study were to establish body mass at birth, postnatal growth rate, and the factors that influence these parameters for the Juan Fernández fur seal, Arctocephalus philippii. Females of this species have an unusual attendance pattern in which foraging trips and shore visits last, on average, 12.3 and 5.3 days, respectively. Pup mass was obtained from cohorts born during the reproductive seasons in 1988 through 1992. Birth masses of male and female pups were significantly different, averaging 6.1 and 5.5 kg, respectively (F = 13.2, P < 0.0003, n = 238). Birth masses also differed among cohorts, being lowest in 1992 and highest in 1990. During the first 2 months of life, male and female pups grew at the same rate (79 ± 61.5 g · day-1 (mean ± SD); F[1] = 0.03, P = 0.8562). Interannual differences in growth rate during the first month were significant (F[4] = 8.14, P < 0.0001), as was the interaction between month and year effects (F[2] = 6.81, P = 0.0012). Growth rates for the 1990 cohort were lower than those in all other years except 1992. Birth masses and postnatal growth rates of Juan Fernández fur seal pups are comparable to those of other otariid species.

scholarly journals Factors affecting energy expenditure in a declining fur seal population

2019 ◽  
Vol 7 (1) ◽  
Author(s):  
Elizabeth A McHuron ◽  
Jeremy T Sterling ◽  
Daniel P Costa ◽  
Michael E Goebel
Keyword(s):  
Environmental Changes ◽  
Food Limitation ◽  
Population Decline ◽  
Indirect Evidence ◽  
Diving Behaviour ◽  
Trip Duration ◽  
Metabolic Rates ◽  
Fur Seals ◽  
Northern Fur Seals ◽  
Pribilof Islands

Abstract Quantifying metabolic rates and the factors that influence them is key to wildlife conservation efforts because anthropogenic activities and habitat alteration can disrupt energy balance, which is critical for reproduction and survival. We investigated the effect of diving behaviour, diet and season on field metabolic rates (FMR) and foraging success of lactating northern fur seals (Callorhinus ursinus) from the Pribilof Islands during a period of population decline. Variation in at-sea FMR was in part explained by season and trip duration, with values that ranged from 5.18 to 9.68 W kg−1 (n = 48). Fur seals experienced a 7.2% increase in at-sea FMR from summer to fall and a 1.9% decrease in at-sea FMR for each additional day spent at sea. There was no effect of foraging effort, dive depth or diet on at-sea FMR. Mass gains increased with trip duration and were greater in the fall compared with summer, but were unrelated to at-sea FMR, diving behaviour and diet. Seasonal increases in at-sea FMR may have been due to costs associated with the annual molt but did not appear to adversely impact the ability of females to gain mass on foraging trips. The overall high metabolic rates in conjunction with the lack of any diet-related effects on at-sea FMR suggests that northern fur seals may have reached a metabolic ceiling early in the population decline. This provides indirect evidence that food limitation may be contributing to the low pup growth rates observed in the Pribilof Islands, as a high metabolic overhead likely results in less available energy for lactation. The limited ability of female fur seals to cope with changes in prey availability through physiological mechanisms is particularly concerning given the recent and unprecedented environmental changes in the Bering Sea that are predicted to have ecosystem-level impacts.

Rearing two New Zealand fur seal (Arctocephalus forsteri) pups to weaning

2008 ◽  
Vol 56 (1) ◽  
pp. 33 ◽  
Author(s):  
Sacha A. Dowell ◽  
Laura J. Boren ◽  
Sandra S. Negro ◽  
Chris G. Muller ◽  
Abigail K. Caudron ◽  
...  
Keyword(s):  
New Zealand ◽  
Growth Rates ◽  
Recognition System ◽  
The Other ◽  
Energy Costs ◽  
Rare Occurrence ◽  
Lower Mass ◽  
Fur Seals ◽  
Fur Seal ◽  
New Zealand Fur Seal

The rearing of two pups to weaning is a rare occurrence in pinnipeds and in many cases it remains unknown whether it is a result of twinning or fostering. This study followed two cases where female New Zealand fur seals (Arctocephalus forsteri) raised two pups, at a colony in Kaikoura, New Zealand. Maternal attendance behaviour was observed, mass and condition of the pups were measured and genetic samples were collected to assess relatedness. In one case, the female gave birth to twins, while the other case was found to be fostering of a second pup. In both cases, the filial pups of each female exhibited significantly lower mass, condition and growth rates than the colony average. The twins’ mother reared both pups to weaning and did not appear to spend a different amount of time ashore compared with single-pup mothers. The current study confirms both fostering and twinning in New Zealand fur seals, with the potential for successfully raising the pups to weaning, despite their well developed recognition system and the energy costs involved.

scholarly journals Data from fur seal scats reveal when Namibian Merluccius capensis are hatched and how fast they grow

2013 ◽  
Vol 70 (7) ◽  
pp. 1429-1438 ◽  
Author(s):  
Margit R. Wilhelm ◽  
Jean-Paul Roux ◽  
Coleen L. Moloney ◽  
Astrid Jarre
Keyword(s):  
Growth Rates ◽  
Stock Assessment ◽  
Growth Function ◽  
Hatch Date ◽  
Linear Mixed Effects Model ◽  
Linear Mixed Effects ◽  
Fur Seals ◽  
Fur Seal ◽  
Date Estimate ◽  
The Mean

Abstract Wilhelm, M. R., Roux, J-P., Moloney, C. L., and Jarre, A. 2013. Data from fur seal scats reveal when Namibian Merluccius capensis are hatched and how fast they grow. – ICES Journal of Marine Science, 70: . Scat samples were collected regularly at several breeding colonies of Cape fur seals along the Namibian coast. Merluccius capensis otoliths were obtained from these samples, identified, and measured. Cohorts were easily distinguishable using otolith length measurements converted to fish total length. Growth rates of 2- to 21-month-old hake and hatch dates for each of 15 cohorts were estimated from September 1994 to October 2009 (1994–2008 cohorts) using a Schnute growth function and a non-linear mixed-effects model. The function describing growth of these young hake was length Lt (cm) at age t (years) Lt = 3.17 + (25.0 − 3.17) × [1 − e−0.665 × (t − 0.140)]/[1 − e−0.665 × (1.74–0.140)]. Cohort-specific random effects showed a population hatch date estimate of 31 July (austral winter), varying by 94 days among cohorts, from 31 May (1996 cohort) to 1 September (2004 cohort). The mean growth rate from ages 6 to 12 months was 1.26 cm month−1 for the population, ranging between 0.97 cm month−1 (1996 cohort) and 1.38 cm month−1 (2004 cohort). As this rate is almost double the previously estimated value, which is currently used in the stock assessment models, this result may have major implications for the current stock assessment results and the management of the stock. Re-examination of growth rates needs to be extended to older fish.

scholarly journals Ontogeny of body size and shape of Antarctic and subantarctic fur seals

2007 ◽  
Vol 85 (12) ◽  
pp. 1275-1285 ◽  
Author(s):  
Sebastián P. Luque ◽  
Edward H. Miller ◽  
John P.Y. Arnould ◽  
Magaly Chambellant ◽  
Christophe Guinet
Keyword(s):  
Body Size ◽  
Body Mass ◽  
Morphological Traits ◽  
Body Shape ◽  
Size And Shape ◽  
Fur Seals ◽  
Fur Seal ◽  
Adult Body ◽  
Weaning Age ◽  
Lactation Duration

Pre- and post-weaning functional demands on body size and shape of mammals are often in conflict, especially in species where weaning involves a change of habitat. Compared with long lactations, brief lactations are expected to be associated with fast rates of development and attainment of adult traits. We describe allometry and growth for several morphological traits in two closely related fur seal species with large differences in lactation duration at a sympatric site. Longitudinal data were collected from Antarctic ( Arctocephalus gazella (Peters, 1875); 120 d lactation) and subantarctic ( Arctocephalus tropicalis (Gray, 1872); 300 d lactation) fur seals. Body mass was similar in neonates of both species, but A. gazella neonates were longer, less voluminous, and had larger foreflippers. The species were similar in rate of preweaning growth in body mass, but growth rates of linear variables were faster for A. gazella pups. Consequently, neonatal differences in body shape increased over lactation, and A. gazella pups approached adult body shape faster than did A. tropicalis pups. Our results indicate that preweaning growth is associated with significant changes in body shape, involving the acquisition of a longer, more slender body with larger foreflippers in A. gazella. These differences suggest that A. gazella pups are physically more mature at approximately 100 d of age (close to weaning age) than A. tropicalis pups of the same age.

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