Shawn R Noren

• Ph.D. Biology, UC Santa Cruz
• Research Associate at University of California, Santa Cruz

Over the past several decades, scientists have constructed bioenergetic models for marine mammals to assess potential population-level consequences following exposure to a disturbance, stressor, or environmental change, such as under the Population Consequences of Disturbance (pCOD) framework. The animal's metabolic rate (rate of energy expenditure...

Growth of structural mass and energy reserves influences individual survival, reproductive success, population and species life history. Metrics of structural growth and energy storage of individuals are often used to assess population health and reproductive potential, which can inform conservation. However, the energetic costs of tissue depositio...

The demands on the locomotor muscles at birth are different for cetaceans than terrestrial mammals. Cetacean muscles do not need to support postural costs as the neonate transitions from the womb because water's buoyant force supports body weight. Rather, neonatal cetacean muscles must sustain locomotion under hypoxic conditions as the neonate acco...

Bioenergetic approaches are increasingly used to understand how marine mammal populations could be affected by a changing and disturbed aquatic environment. There remain considerable gaps in our knowledge of marine mammal bioenergetics, which hinder the application of bioenergetic studies to inform policy decisions. We conducted a priority-setting...

Fat-level measurements used to indicate individual body condition and fitness are useful only when taken at a region along the body where fat responds to variations in caloric intake. Investigations to identify appropriate species-specific regions are limited, especially for cetaceans that have a specialized fat (blubber) that serves as an energy r...

Marine mammals endure extended breath-holds while performing active behaviors, which has fascinated scientists for over a century. It is now known that these animals have large onboard oxygen stores and utilize oxygen-conserving mechanisms to prolong aerobically supported dives to great depths, while typically avoiding (or tolerating) hypoxia, hype...

Muscle biochemistry of aquatic birds and mammals varies in accordance with swimming and diving performance, as well as with ontogeny. Similar to other odontocetes, the locomotor muscles (longissimus dorsi) of neonatal melon-headed whales (Peponocephala electra) have low myoglobin content (Mb; 1.06 ± 0.20 g Mb/100 g wet muscle mass; mean ± SE;...

An animal's physiology limits the environmental conditions where it can persist; quantifying the physiology of the walrus is timely since they are being impacted by alterations in sea ice. We examined postnatal changes in hematology, an important attribute that supports diving, by analyzing a longitudinal data set from aquaria walruses (five males...

Body size and oxygen stores in the blood and muscle set breath-hold limits in marine mammals, yet these characteristics are understudied in immature cetaceans. We examined body mass and hematology from birth through adulthood in beluga whales (Delphinapterus leucas). At birth, body mass was 8% and 6% of the maximum mass recorded for adult females a...

The accelerating rate of anthropogenic alteration and disturbance of environments has increased the need for forecasting effects of environmental change on fish and wildlife populations. Models linking projections of environmental change with behavioral responses and bioenergetic effects can provide a basis for these forecasts. There is particular...

The length of time required for postnatal maturation of the locomotor muscle (longissimus dorsi) biochemistry [myoglobin (Mb) content and buffering capacity] in marine mammals typically varies with nursing duration, but it can be accelerated by species-specific behavioral demands, such as deep-diving and sub-ice transit.We examined how the swimming...

Little is known about the postnatal development of the physiological characteristics that support breath-hold in cetaceans, despite their need to swim and dive at birth. Arctic species have the additional demand of avoiding entrapment while navigating under sea ice, where breathing holes are patchily distributed and ephemeral. This is the first inv...

Habitat use and activity patterns of Pacific walruses (Odobenus rosmarus divergens) have changed with climate-induced reductions in sea ice. Increases in the time active in water could result in negative energy balance, precluding females from sustaining lactation, which could impact population demographics. Little is known about lactation costs in...

Physiological constraints dictate animals' abilities to exploit habitats. For marine mammals, it is important to quantify physiological limits that influence diving and their ability to alter foraging behaviors. We characterized age-specific dive limits of walruses by measuring anaerobic (acid buffering capacity) and aerobic (myoglobin content) cap...

Unlike their terrestrial ancestors, marine mammals routinely confront extreme physiological and physical challenges while breath-holding and pursuing prey at depth. To determine how cetaceans and pinnipeds accomplish deep-sea chases, we deployed animal-borne instruments that recorded high-resolution electrocardiograms, behaviour and flipper acceler...

Pacific walruses may be unable to meet caloric requirements in the changing Arctic ecosystem, which could affect body condition and have population-level consequences. Body condition has historically been monitored by measuring blubber thickness over the xiphoid process (sternum). This may be an unreliable condition index because blubber at other s...

Abstract Decreases in sea ice have altered habitat use and activity patterns of female Pacific walruses Odobenus rosmarus divergens and could affect their energetic demands, reproductive success, and population status. However, a lack of physiological data from walruses has hampered efforts to develop the bioenergetics models required for fully und...

Cetaceans (dolphins and whales) are born into the aquatic environment and are immediately challenged by the demands of hypoxia and exercise. This should promote rapid development of the muscle biochemistry that supports diving, but previous research on two odontocete (toothed whales and dolphins) species showed protracted postnatal development for...

Physical constraints while carrying an infant represent one of many reproductive costs. For bottlenose dolphins Tursiops truncatus, near-term pregnancy and 'carrying' a calf in echelon position (calf alongside mother's mid-lateral flank) alter maternal swimming gait and performance. As calves mature an alternate form of 'carrying', infant position...

Muscle samples were collected from pup, juvenile and adult Weddell seals (Leptonychotes weddellii) near McMurdo Sound, Antarctica during the austral summer of 2006. Blubber samples were collected from juvenile and adult seals. Samples were analyzed for emerging and legacy persistent organic pollutants (POPs) including current and historic-use organ...

A hallmark of the dive response, bradycardia, promotes the conservation of onboard oxygen stores and enables marine mammals to submerge for prolonged periods. A paradox exists when marine mammals are foraging underwater because activity should promote an elevation in heart rate (f(H)) to support increased metabolic demands. To assess the effect of...

Pacific walruses Odobenus rosmarus divergens use sea ice as a platform for resting, nursing, and accessing extensive benthic foraging grounds. The extent of summer sea ice in the Chukchi Sea has decreased substantially in recent decades, causing walruses to alter habitat use and activity patterns which could affect their energy requirements. We dev...

Constraints on locomotion could be an important component of the cost of reproduction as carrying an increased load associated with eggs or developing fetuses may contribute to decreased locomotor performance for females across taxa and environments. Diminished performance could increase susceptibility to predation, yet the mechanism(s) by which gr...

Odontocetes have an exceptional range in body mass spanning 10 3 kg across species. Because, size influences oxygen utilization and carbon dioxide production rates in mammals, this lineage likely displays an extraordinary variation in oxygen store management compared to other marine mammal groups. To examine this, we measured changes in the partial...

Cetacean mother-calf dyads demonstrate formation locomotion that may provide hydrodynamic and/or social benefits. For example, echelon position (calf in close proximity of its mother's mid-lateral flank) enables calves to increase swim performance at reduced locomotor effort compared to periods of solitary swimming. Yet cetacean mother-calf dyads a...

Rapid changes in sea ice cover associated with global warming are poised to have marked impacts on polar marine mammals. Here we examine skeletal muscle characteristics supporting swimming and diving in one polar species, the narwhal, and use these attributes to further document this cetacean's vulnerability to unpredictable sea ice conditions and...

Our objective was to elucidate age-related changes in lipids associated with skeletal muscle of Weddell seals and to suggest possible physiological implications. Muscle biopsies were collected from pups, juveniles and adults in McMurdo Sound, Antarctica and analyzed for intramuscular lipid (IML) and triacylglyceride (IMTG) amounts, fatty acid group...

Blubber is a critical component of thermoregulation for marine mammals, particularly for cetaceans. However, the cost of overcoming blubber's buoyant force during descent could constrain blubber deposition. One- to 12-year-old healthy, free-ranging common bottlenose dolphins (Tursiops truncatus) were studied in Sarasota Bay, Florida, during summer...

Water conducts heat 25 times faster than air creating an extreme environment for mammalian thermoregulation. Blubber is a key component of dolphin thermoregulation but the cost of descent (COD) to overcome blubber's buoyant force while diving could constrain its deposition. This conflict was examined in 1‐12 year‐old bottlenose dolphins in Sarasota...

Mammals balance heat dissipation with heat production to maintain core body temperatures independent of their environment. Thermal balance is undoubtedly most challenging for mammals born in polar regions because small body size theoretically results in high surface-area-to-volume ratios (SA:V), which facilitate heat loss (HL). Thus, we examined th...

Gray seals (Halichoerus grypus) undergo a terrestrial postweaning fast (PWF) that depletes energy reserves acquired during the suckling interval. Plasticity in PWF duration may ensure that pups of variable body condition depart for sea with adequate energy reserves. To test this hypothesis, we examined body condition of 30 gray seal pups at weaning...

Pinniped muscle development tracks life history such that species with short maternal dependency periods attain greater proportions of adult myoglobin levels earlier in life than species with protracted dependency periods. To determine if a similar pattern exists for mammals that develop at sea, the development of muscle myoglobin and acid bufferin...

Summary 1. Formation locomotion theoretically provides energy savings and it is evident across diverse taxa. Echelon position, described in cetacean (dolphin and whale) mother-infant dyads as calf in very close proximity of its mother's mid-lateral flank, may be a type of formation locomotion that provides hydrodynamic benefits for the calf. Until...

Summary • Infant carrying behaviour occurs across diverse taxa inhabiting arboreal, volant and aquatic environments. For mammals, it is considered to be the most expensive form of parental care after lactation, yet the effect of infant carrying on the energetics and performance of the carrier is virtually unknown. • Echelon swimming in cetacean (do...

Morphological and physiological development impacts swimming performance throughout ontogeny. Our investigation of the ontogeny of swim performance (mean and maximum swim speed) and swim effort (stroke amplitude and tailbeat frequency) of independently swimming bottlenose dolphins (Tursiops truncatus) demonstrated that swimming capabilities are ext...

Tuna purse-seiners in the eastern tropical Pacific (ETP) capture yellowfin tuna by chasing and encircling herds of associated dolphins. This fishery has caused mortality in 14 dolphin species (20 stocks) and has led to significant depletions of at least three stocks. Although observed dolphin mortality is currently low, set frequency remains high a...

To successfully transition from nursing to foraging, phocid seal pups must develop adequate diving physiology within the limited time between birth and their first independent foraging trip to sea. We studied the postpartum development of oxygen stores in gray seals (Halichoerus grypus, n=40) to better understand the ontogeny of diving capacity in...

A bstract Skeletal muscles of marine mammals must support the metabolic demands of exercise during periods of reduced blood flow associated with the dive response. Enhanced muscle buffering could support anaerobic metabolic processes during apnea, yet this has not been fully investigated in cetaceans. To assess the importance of this adaptation in...

Bradycardia is an important component of the dive response, yet little is known about this response in immature marine mammals. To determine if diving bradycardia improves with age, cardiac patterns from trained immature and mature bottlenose dolphins ( Tursiops truncatus) were recorded during three conditions (stationary respiration, voluntary bre...

Semi-aquatic mammals move between two very different media (air and water), and are subject to a greater range of physical forces (gravity, buoyancy, drag) than obligate swimmers or runners. This versatility is associated with morphological compromises that often lead to elevated locomotor energetic costs when compared to fully aquatic or terrestri...

Enhanced oxygen reserves in the blood facilitate diving in marine mammals. For pinnipeds (seals and sea lions), a developmental period of 4 to 24 months is required for blood oxygen stores to reach adult capacities. We investigated whether a similar developmental period for the blood occurs in cetaceans (dolphins and whales), a group of mammals tha...

Myoglobin is an important oxygen store for supporting aerobic diving in endotherms, yet little is known about its role during postnatal development. Therefore, we compared the postnatal development of myoglobin in marine endotherms that develop at sea (cetaceans) to those that develop on land (penguins and pinnipeds). We measured myoglobin concentr...

Cetaceans exhibit an exceptionally wide range of body mass that influence both the capacities for oxygen storage and utilization; the balance of these factors is important for defining dive limits. Furthermore, myoglobin content is a key oxygen store in the muscle as it is many times higher in marine mammals than terrestrial mammals. Yet little con...