Now showing items 410-429 of 468

• #### Temperature and food effects on larval Pacific herring (Clupea pallasi) in Prince William Sound, Alaska

The effects of food availability and water temperature on larval Pacific herring growth rates and survival were studied using a coupled biophysical model for 1993 through 1997. The herring growth model included feeding gains, metabolic costs, mortality losses and vertical migration of the herring larvae. In years when springtime oceanographic processes resulted in a high concentration of zooplankton, food availability did not limit larval herring growth rates; water temperature determined survival. However, in other years, food availability did limit survival, either due to insufficient food concentrations or to inaccessibility of the food. Vertical migration occasionally was restricted by strong water column stratification, which prevented the larvae from reaching food concentrations sufficient for growth. Thus the amount of food, the temperature, and the vertical distribution of the food and the larvae were found to affect growth. The study of vertical properties of factors affecting larval fish must be included in larval fish research.
• #### Temporal and spatial distribution of grazers and kelp phlorotannins in Kachemak Bay, Alaska

The potential influence of grazers on the density and distribution of kelp thalli is substantial and may be mediated by kelp phlorotannins serving in a defensive role. The purpose of this study was to determine how temporal and spatial phlorotannin patterns in four kelp species in Kachemak Bay, Alaska, are influenced by density and distribution of the gastropod grazer Lacuna vincta and environmental variables. Temporal phlorotannin patterns from June 2004 through December 2005 were mainly explained by the life history of particular kelp species as well as strong correlations with light attenuation and nitrate concentration. The Optimal Defense Theory of resource allocation to differentiated tissues was supported by observations of higher proportional allocation to attachment structures and meristematic tissue in all kelp species. Lacuna vincta distribution was not clearly related to phlorotannin content and therefore, grazer habitat and food choices may be influenced by the combination of high phlorotannin content, tissue toughness and/or nutritional content. Strong physical disturbances such as currents and wave action may supersede these factors and drive grazer distribution. An understanding of the biological and physical factors affecting phlorotannin content and distribution in kelp thalli may suggest reasons for temporal and spatial kelp bed variability.
• #### Temporal and spatial variability of sinking particles in the southeast Bering Sea

The factors affecting the timing, quantity and fate of southeastern Bering Sea primary production, including coupling to higher trophic levels, were investigated via sinking particles collected using sediment traps. Stable carbon and nitrogen isotopic composition and lipid composition of zooplankton and sinking particles were measured for middle (M2) and outer (M3) shelf samples collected during 1997-2000. The quantity collected by the M2 sediment trap was high in late summer and fall, as well as during spring blooms, and was much greater than that collected at M3. M2 zooplankton and trap samples were enriched in ¹⁵N and ¹³C over those from M3. This could be explained by greater primary productivity over the middle shelf, associated with consumption of more of the available inorganic nitrogen. M2 sediment trap samples contained more fatty acids typical of diatoms, while M3 samples contained more fatty acids typical of zooplankton. Diatoms were much more numerous in the M2 than the M3 trap. Cholesterol was the dominant sterol, indicating that much of the material in the traps was fecal matter. During two of the years sampled, 1997 and 1999, ice edge blooms occurred from late April to early May. Ice receded earlier in 1998 and 2000, so phytoplankton bloomed in open water in late May. Lipids indicating greater phytoplankton input were high in the M2 trap during the ice-edge bloom years. Conversely, in 1998 and 2000, there was greater coupling between phytoplankton and zooplankton, much of the material collected was fecal pellets rather than intact diatoms and lipids were more characteristic of zooplankton sources. In zooplankton some monounsaturated fatty acids decreased sharply between February and April, reflecting mobilization of lipids for egg production. A polyunsaturated fatty acid characteristic of prymnesiophytes was elevated in winter and spring 1998 zooplankton, resulting from grazing of the 1997 coccolithophorid bloom. Overall, the results indicate that primary productivity is greater at M2 than at M3. Much of the annual primary production occurs outside of the April-May spring bloom period. Grazing of primary production is greater at M3 than M2, and at M2 more primary production is grazed in warm than cold years.
• #### A Temporal comparison of the eelgrass (Zostera marina L.) food web and community structure at Izembek Lagoon, Alaska from the mid-1970's to 2008

This thesis investigates food web and community structure in Izembek Lagoon, Alaska, an ecologically important sub-arctic seagrass system. Unprecedented environmental changes in high latitudes, such as increased sea-surface temperatures and a shorter duration of shore-fast sea ice, may now favor seagrass over phytoplankton production as compared to forty years ago. Any resulting shifts in food web and community dynamics could have substantial consequences given the importance of seagrass habitat for Alaskan fisheries, global migratory bird populations and benthic energy transformation. Recent (2008) stable isotope (C and N) values and benthic community metrics were gathered and compared to results from a similar study from the mid-1970’s to gauge temporal food web and community structure differences. An increase in reliance on seagrass carbon was detected in organisms involved in detrital and sediment processing. An increase in abundance of certain benthic organisms and a decrease in overall community evenness were also seen. These findings suggest an escalation in delivery of seagrass carbon to the food web, possibly induced by changing seagrass morphology or bed density at this location.
• #### Temporal variation and habitat use of nearshore crab populations in Kachemak Bay, Alaska

Larval, juvenile, and adult crab distribution was surveyed in three different habitats in Kachemak Bay, Alaska from June 2005 to September 2006 to determine temporal and spatial variability. Crab distribution varied temporally and spatially in all life stages. Nine sites of varying habitat complexity were surveyed monthly using scuba, light traps, and shrimp pots to measure habitat variables, quantify larval, juvenile, and adult crabs, and survey potential crab predators. No single bay-wide variable determined the appearance of all crab larvae. Spatial differences in larval abundance probably resulted from large scale physical transport mechanisms. Overall juvenile and adult crab abundance increased with habitat complexity; however species richness was not positively correlated with complexity. This study suggested that the canopy structure provided by Nereocystis luetkeana had minimal effects on spatial crab distribution in all life stages. Canopy structure may not influence the spatial distribution of larval crabs and is thought to have little importance for juvenile and adult crabs. Understory kelp density may more directly affect juvenile and adult crabs by providing more microhabitats for refuge. Habitat use and the importance of structural complexity vary by life history stage and species depending on survival strategy.
• #### A test of local adaptation in seasonally separate subpopulations of pink salmon (Oncorhynchus gorbuscha)

Differences in fitness related traits were observed between first generation (F₁) hybrid and control lines of temporally distinct subpopulations of pink salmon (Oncorhynchus gorbuscha). The lines were cultured in a common freshwater environment, released to sea together, and collected at their natal stream as adults. Early-and late-run pink salmon, which are partially genetically isolated by the time at which they return to Auke Creek in Southeast Alaska to spawn, were crossed to create F₁ and F₂ hybrid groups in the even- and odd-year brood lines. Marine survival of controls exceeded that of F₁ hybrids of the even-year brood line, whereas no difference in marine survival between those experimental groups was detected in the odd-year brood line. First generation hybrids expressed intermediate time of return relative to controls in both brood lines. Second generation hybrids exhibited similar embryonic development rates to controls in both brood lines. These results demonstrate that removal of a genetic barrier as fine as that which occurs within a brood line and location can disrupt local adaptation in a population of pink salmon, which may cause outbreeding depression in hybrids and may potentially reduce the overall biodiversity and productivity of the population.
• #### The carbon cycle in an anoxic marine sediment: Concentrations, rates, isotope ratios, and diagenetic models

The carbon cycle in the anoxic sediments of Skan Bay, Alaska, was investigated in order to better understand the processes that control biogeochemical transformations in an organic-rich sediment environment. Depth distributions of concentration and $\delta\sp{13}$C were determined for five major carbon reservoirs: methane (CH$\sb4$), dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), particulate inorganic carbon (PIC), and particulate organic carbon (POC). In addition, methane oxidation and sulfate reduction rates were measured under quasi-in situ conditions using radio-tracer techniques. Diagenetic models were applied to concentration, reaction rate, and isotope ratio depth distributions and the results were integrated into a comprehensive, depth-dependent model of the Skan Bay carbon cycle that considered advective, diffusive, and biological and chemical reactive fluxes for the five major carbon reservoirs. The Skan Bay carbon cycle is fuelled by POC, which is deposited at the sediment surface at a rate of 2290 $\pm$ 480 umol $\cdot$ cm$\sp{-2}$ $\cdot$ yr$\sp{-1}$. Isotope mass-balance calculations indicate that about 60% of this material is derived from kelp while the remainder originates as phytoplankton. About 60% of the organic matter is consumed in the upper 40 cm of the sediment column. The $\delta\sp{13}$C-POC and $\delta\sp{13}$C-DOC depth distributions suggest that the material derived from kelp is more labile, accounting for greater than 60% of the total POC consumption. The products of anaerobic metabolism of POC accumulate in the DOC reservoir creating a large DOC concentration gradient at the sediment-water interface. Flux and stable carbon isotope mass-balance calculations suggest that a sizable portion (30 to 80%) of the DOC produced by degradation of POC diffuses from the sediment prior to oxidation to dissolved inorganic carbon. Methane production appears to occur primarily at depths greater than 40 cm. The CH$\sb4$ diffuses upward and is almost quantitatively oxidized to DIC in a narrow subsurface zone. Methane oxidation accounts for only 20% of the DIC production, but exerts a profound influence on the $\delta\sp{13}$C-DIC profile, contributing to the distinct mid-depth minimum. Pore waters are supersaturated with respect to calcite at depths greater than 10 cm, but isotope mass-balance considerations indicate that carbonate mineral formation is not occurring in these sediments.
• #### The Colonization Mechanism Of Pink Salmon Populations In Glacier Bay, Alaska, Based On Genetic Data

Following retreat of the last glacial advance in the early 1700s, pink salmon Oncorhynchus gorbuscha colonized many watersheds in Glacier Bay, Alaska. Streams in the lower Bay were populated first, and colonization proceeded up the Bay during the last 200 years. The objective of this study was to use analyses of genetic data---microsatellite and allozyme loci, and mitochondrial DNA haplotypes---to elucidate the colonization mechanism. The even- and odd-year broodlines served as replicate experiments; the mechanisms of colonization for the two broodlines were similar in most respects. The population genetic structure, based on allele/haplotype frequencies and genetic diversity (FST), suggested that in general, deglaciated streams were populated by colonists from nearby locations. The populations in lower Glacier Bay were likely established by colonists from populations outside Glacier Bay. In turn, the lower Bay populations contributed colonists to populations farther up the Bay, which subsequently provided colonists to the most recently deglaciated locations in the upper Bay, although in the even-year there appeared to be some contribution to the youngest populations from older populations, outside of or in lower Glacier Bay. Few genetically divergent donor sources contributed colonists based on the limited linkage disequilibrium, higher relatedness, and lower allelic diversity within Glacier Bay populations. The number of fish involved in initial colonization was not large, based on slightly reduced genetic diversity within Glacier Bay, but minimal founder effect signals precluded very small numbers of fish as well. Most of the genetic variation appeared early in the formation of populations and effective population size estimates were >100 fish in every population. Some gene flow after initial colonization is supported by the increased allelic diversity and decline in relatedness with population age, but heterogeneity within Glacier Bay suggested that gene flow must be limited among some populations. Colonization of the youngest streams coincided with the historically high abundance of pink salmon in Southeast Alaska during the 1990s; I speculate that the rapid expansion in the size of these populations subsequent to this study was the result of high survival rather than extensive gene flow.
• #### The Concept Of Microbial Affinity For Limiting Nutrients In Steady State And Rhythmic Systems

To evaluate the role of biological rhythms in competition for survival, rhythms in cell division and limiting nutrient transport ability induced by light/dark (LD) cycles were investigated for three species of pelagic, freshwater algae growing in phosphoruslimited continuous and serially diluted batch (SDB) cultures. Nutrient transport ability of nutrient-starved microbial populations was measured as the initial slope (affinity) of a plot of limiting nutrient transport rate (V) versus extracellular limiting nutrient concentration (S). A method was devised for the determination of the affinity in continuous culture (a(,T)) by monitoring S with time. Cell division was asynchronous for the green alga, Selenastrum capricornutum, grown in LD continuous cultures and a rhythm in a(,T) for soluble reactive phosphate (Pi) was greatly affected by choice of biomass parameter. Division was strongly phased in LD SDB culture and weakly phased in continuous light (LL) SDB culture, indicating that nutrient perturbations have a greater effect on phasing of division than LD cycles for S. capricornutum. A rhythm in Pi transport rate in LD SDB culture was similar to the rhythm in continuous culture a(,T) when expressed per cell volume or cell dry weight but not when expressed per cell number. Cell division was phased for the green alga, Scenedesmus quadricauda, grown in LD continuous culture. A rhythm in a(,T) for Pi was not greatly affected by choice of biomass parameter. Cell division was also rhythmic in LD for the blue-green alga, Synechococcus Nageli. Synechococcus was an extremely efficient Pi transporter at low Pi concentrations in LD continuous culture, indicating that it should be widespread in oligotrophic systems and has probably been overlooked in past floristic studies.
• #### The ecology of a high-latitude rocky intertidal community: Processes driving population dynamics in Kachemak Bay, Alaska

The population dynamics and interactions of selected key species relative to community structure were investigated in the rocky intertidal of Kachemak Bay, southcentral Alaska (59$\sp\circ$35$\sp\prime$N, 151$\sp\circ$30$\sp\prime$W). The roles of recruitment processes and predation in regulating intertidal populations were emphasized in this investigation. Species cover was distinctly seasonal. Total cover typically exceeded 80% during the summer, especially in lower intertidal. Winter cover averaged 40-60%, with macroalgal cover varying up to six-fold between summer and winter. Barnacle recruitment varied both inter-annually and with respect to species. From 1991-1993, mean recruitment densities varied from 0.85-8.71 cm$\sp{-2}$ (range = 0-71 cm$\sp{-2}).$ In the upper intertidal, time-integrated summer recruit density of Semibalanus balanoides and Balanus glandula was 0.13 cm$\sp{-2}.$ Recruit density of S. cariosus in the low intertidal was 4.32 cm$\sp{-2}.$ In the low intertidal, recruits often saturated the surface, resulting in density-dependent mortality in two out of three years, a phenomenon which did not occur in the upper intertidal where space was never limiting. Predation was a significant source of mortality for barnacle recruits only in 1991, a poor recruitment year. However, predation by Nucella lima limited mussel (Mytilus trossulus) populations at some sites. Where N. lima density exceeded 100 m$\sp{-2},$ mussel cover was less than half that where Nucella was rare (31% vs. 72%). High densities of N. lima were estimated to remove 60-90% of mussels per season. Recruitment of the macroalga Fucus gardneri was almost 50 times greater in the presence of live barnacles than on bare rock surfaces or barnacle shells killed by heating. Recruitment in quadrats with tests of mechanically killed barnacles was intermediate. The results indicate that F. gardneri propagules are stimulated to attach by a chemical cue, probably a polypeptide, produced by barnacles. Based on population dynamics and species interactions investigated in Kachemak Bay, the mid- to low intertidal community appears to function similarly to the classical paradigm of regulation by competition and predation. The major exception is high inter-annual variability in predation relative to recruitment and competition.
• #### The effects of ocean acidification on walleye pollock (Theragra chalcogramma) early life history stages

Since the Industrial Revolution of the late 1700's, atmospheric and marine carbon dioxide levels have drastically increased. Ocean acidification is the result of the shift in the marine carbon cycle caused by the increase in marine and atmospheric carbon dioxide. Changing environmental conditions caused by ocean acidification have been shown to have adverse effects on different marine species as well as life history stages. As a result, ecologically and economically important teleost fish species such as walleye Pollock (Theragra chalcogramma) could be adversely affected by ocean acidification conditions. This study explores the responses of walleye pollock eggs and larvae incubated under different projected levels of ocean acidification, looking at hatch timing and growth parameters to examine potential adverse responses to more acidic conditions. Older walleye pollock juveniles (age 1+) were used to uncover potential physiological responses to ocean acidification pertaining specifically to stress, overall body condition indices, and blood chemistry. I found that while the two early life history stages of walleye pollock could survive under ambient, high, medium, and low pH conditions (pH 8.1, 7.9, 7.6, and 7.2, respectively), there were some physiological responses to projected levels of ocean acidification. Hatch timing was not delayed in the lowest pH treatment as expected. In addition, size at hatch, yolk area, and eye diameter did not differ among pH treatments. Walleye pollock juveniles reared under projected levels of ocean acidification demonstrated shifts in blood gas levels and blood pH. However, exposure to a lower pH environment of pH 7.9, 7.6, or 7.2 did not induce a response for either the stress indicators or body condition indices that were measured. To uncover the mechanism for their resilience, more testing is needed to gain further insight into underlying compensatory mechanisms of various life history stages and populations.
• #### The evolutionary history of reproductive strategies in sculpins of the subfamily oligocottinae

The sculpin subfamily Oligocottinae is a group of 17 nearshore species and is noteworthy for the fact that it contains both intertidal and subtidal species, copulating and noncopulating species, and many species with very broad geographic ranges. These factors, as well as the consistency with which the constituent genera have been grouped together historically, make the Oligocottinae an ideal group for the study of the evolution of a reproductive mode known as internal gamete association (IGA), which is unique to sculpins. I conducted a phylogenetic study of the oligocottine sculpins based on an extensive molecular dataset consisting of DNA sequences from eight genomic regions. From the variability present in those sequences, I inferred phylogenetic relationships using parsimony, maximum likelihood, and Bayesian inference. Results of these phylogenetic analyses show that some historical taxonomy and classifications require revision to align taxonomy with evolutionary relatedness. Specifically, the monotypic genus Leiocottus should be synonymized with Clinocottus; membership in the tribe Oligocottini should be reduced to include only the genera Oligocottus, Clinocottus, and Orthonopias; and the genus Sigmistes should be removed from the subfamily Oligocottinae. Using this new phylogenetic framework, I conducted an analysis of the evolution of reproductive behaviors and associated morphological characters in members of Oligocottinae. These traits were obtained through a critical review of the relevant literature and mapped on the phylogeny. Ancestral state reconstruction was used to explore their evolution. The results show that copulation and the presence of an enlarged male genital papilla are likely the ancestral states of Oligocottinae and that these characters were secondarily lost in the lineage composed of Artedius corallinus, A. fenestralis, A. lateralis, and A. notospilotus. The results also show that parental care in the group is split between the Artedius lineage, where males guard egg clutches, and the rest of the group, where egg guarding behavior is not present. I speculate that the differing ecology of these two groups has affected the evolution of reproduction and parental care in the subfamily, where subtidal lineages (i.e., Artedius) engage in parental care but have transitioned away from copulation, while the intertidal lineages maintained copulation but hide their eggs rather than guard them.
• #### The Geochemistry Of Manganese, Iron And Phosphorus In An Arctic Lake

Sediment redox processes were investigated in an oligotrophic, arctic lake containing metal oxide crusts in oxidizing surficial sediments (up to 22% Mn and 26% Fe). Toolik Lake, Alaska, a 12,000 year old kettle lake, has the lowest Pb-210 derived sedimentation rates reported for any lake (27 g m('-2) yr('-1)). Three independent methods for estimation of Mn, Fe and P retention within the lake (stream budgets, sediment traps and sediment burial rates) provide similar rates. Of the amounts entering the lake, 28% of P, 50% of Mn and 55% of Fe are retained. Common water column removal mechanisms for these elements and organic C are suggested by sediment trap data. A steady state diagenetic model with terms for diffusion, reduction and oxidation shows that Mn and Fe crusts migrate within surficial sediments. Metal oxide burial rates are equivalent to oxide dissolution rates (reduction), rates of upward diffusion of soluble divalent metals and metal precipitation rates (oxidation). High inputs of labile Mn and Fe from streams, plus low sedimentation and organic matter oxidation rates are important for crust formation. Approximately 12% of Mn and 2% of acid reducible Fe retained by the lake since its formation exist as diagenetic oxides; the rest is buried within reducing sediment. Sediment inorganic P migrates with Fe to form P enriched sediment zones with pore water PO(,4) concentrations beneath these zones regulated by vivianite (Fe(,3)(PO(,4))(,2) 8H(,2)O) formation. The migration of Mn and Fe within sediments results in the enrichment of Ba, Co, Ca, Ni, Ra-226 and carbonate in metal oxide enriched sediments. Barium is enriched in Mn crusts because of diagenetic migration.
• #### The Influence Of Estuarine Habitats On Expression On Life History Characteristics Of Coho Salmon Smolts In South-Central Alaska

Expression of traits that lead to life history diversity in salmonids may provide population-level resilience and stability in dynamic environments. I examined habitat use and variability in life history trait expression in juvenile coho salmon Oncorhynchus kisutch occupying two contrasting estuary environments in south-central Alaska. My goal was two-fold: first, to determine if salmon were using estuaries as rearing environments and were therefore potentially vulnerable to selection pressures within; and second, to compare traits of salmon that reared in contrasting estuary environments to explore the potential for differential trait expression related to estuary size and habitat complexity differences. Juvenile coho salmon reared in estuaries for extended periods of time and patterns of use corresponded to environmental conditions within the estuaries. Populations using adjacent but contrasting estuary environments exhibited differential trait expression and were genetically distinct. My work highlights how pristine, functioning estuary habitats contribute to resilience of salmon populations to environmental changes in two ways: first, by providing habitats for individuals to increase in size and condition prior to ocean entry; and second, by providing for alternative life history tactics (providing quality habitat to delay marine entry times and increase body size). Management approaches for resilient salmon runs must therefore maintain both watershed and estuary function.
• #### The Influence Of Habitat Complexity, Prey Quality, And Predator Avoidance On Sea Otter Resource Selection In Alaska

The differential selection of habitat by animals is one of the fundamental relationships that enable species to coexist. Habitat selection may be among various discrete categories (e.g., mudflat, boulder field, or meadow) or among a continuous array of characteristics such as vegetation percent cover, benthic substrate size, substrate rugosity, distance to prey resources, or distance to suitable escape terrain from predation. Sea otters are particularly suitable for resource selection studies because they are capable of selecting a wide variety habitat types in response to prey availability, competition, and predation. In Alaska, sea otters associate with a range of habitats types including continuous bedrock reefs in the western Aleutians to heterogeneous fjord systems in Kackemak Bay, Lower Cook Inlet. Sea otters inhabiting the western Aleutians exhibit highly restricted habitat selection patterns characteristic of declining populations. In contrast, sea otters inhabiting Kachemak Bay exhibit selective use of a broad range of habitat types. Many factors contribute to the selective use of habitats by animals, including habitat suitability, prey quality, and predation risk. This thesis was designed to test factors contributing to sea otter resource selection in an area undergoing population increase versus an area experiencing high predation pressure. The contribution of prey size, abundance, biomass, potential energy density are considered in addition to physical habitat characteristics such as grain size, rugosity, depth, structural habitat complexity, and exposure to prevailing weather. Findings suggest that foraging sea otters differentially select habitat and prey resources based on prey accessibility and not on prey abundance or potential prey energy density. Findings further suggest that sea otter foraging site selection is based on habitat complexity in areas with increasing populations, but in areas with high predation pressure, proximity to suitable escape terrain appears to be more important than prey quality or benthic habitat complexity.

• #### To pup or not to pup? Using physiology and dive behavior to answer the Weddell Seal's overwinter question

Female Weddell seals (Leptonychotes weddellii) haul-out on the fast-ice surrounding the Antarctic continent in October and November each year to give birth to and nurse their pups. Breeding follows directly after weaning (December) and the annual molt begins in January-February. Animals reduce foraging efforts during the lactation and molting periods, but very little is known regarding the influence of this reduced activity on physiological condition. After a period of embryonic diapause, the annual molt coincides with embryo attachment and the start of active gestation. Consequently, female physiological condition at this time may influence reproductive success the following year. Overall female health and the ability to forage successfully throughout the gestation period (austral winter) may impact the likelihood that a pregnancy is brought to term. Therefore, this study tested whether overwinter changes in Weddell seal physiology and foraging efforts are reflected in reproductive outcomes the following year (i.e., to answer the over winter question of "to pup or not to pup?"). From 2010-2012, 100 (January-February: n = 53; October-November: n = 47) adult female Weddell seals were captured in Erebus Bay, Antarctica to assess overwinter changes in physiological condition and/or dive behavior that may be associated with reproductive success. Morphometric measurements and isotopic dilution procedures revealed that female Weddell seals gain ~10-15% of their body mass across the winter period, primarily in the form of blubber and lipid mass. The proportion of mass and lipid gain was similar regardless of whether females returned the following year and successfully gave birth, or did not produce a pup. Further, the amount of mass and energy acquired across gestation in the Weddell seal was markedly less than previously reported for other phocid species. Despite changes in activity patterns and body composition, Weddell seals maintained blood hemoglobin and muscle myoglobin concentrations across the winter. Therefore, Weddell seal total body oxygen stores and calculated aerobic dive limit (cADL) were conserved. This ensures that females have the physiological capabilities to effectively forage directly following the annual molt when they are at their leanest and must regain body mass and lipid stores. Although aerobic capacities did not change, dive effort varied considerably throughout the austral winter. Proxies of dive effort (duration, depth, %dives > cADL) were highest just after the molt (January-February) and just prior to the subsequent pupping season (August-September). Additionally, the proportion of each day spent diving increased mid-winter. Females that were observed the following year with a pup significantly increased all indices of foraging effort during the austral winter as compared to females that returned without a pup. This study is the first to identify and measure differences in dive efforts due to reproductive status, and indicates that successful reproduction is associated with greater foraging effort.