Ocean Associates Inc.

Abingdon, VA, United States

Ocean Associates Inc.

Abingdon, VA, United States
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Moser M.L.,National Oceanic and Atmospheric Administration | Patten K.,Washington State University | Corbett S.C.,Ocean Associates Inc. | Feist B.E.,National Oceanic and Atmospheric Administration | Lindley S.T.,National Oceanic and Atmospheric Administration
Environmental Biology of Fishes | Year: 2017

Sturgeon diet and feeding habitats are notoriously difficult to document. We mapped the locations of feeding pits in Willapa Bay, Washington, to characterize estuarine habitats used by sub-adult and adult sturgeon for infaunal feeding. Monthly summer surveys of intertidal plots revealed that feeding pit density was highest in July and August, when sturgeon occupy Willapa Bay. The ephemeral nature of feeding pits and high daily densities (> 1000 pits/ha) indicated intensive sturgeon feeding over unvegetated littoral mud flats during high tide. Feeding pit density was lowest in subtidal areas, over sand (grain sizes primarily >63 μ), and at sites with dense stands of non-indigenous seagrass, Zostera japonica. Sub-adult and adult sturgeon apparently used these habitats significantly less than would be predicted based on their availability. Feeding pit formation was negatively correlated with Z. japonica shoot dry weight and positively correlated with the abundance of thalassinid shrimp burrows. Experimental removal of Z. japonica resulted in increased sturgeon feeding, but experimental removal of burrowing shrimp did not significantly affect feeding pit formation. Aquaculture activities that harden substrate and proliferation of invasive seagrass both appear to produce estuarine substrates that are unsuitable for benthic feeding by sturgeon. © 2017 Springer Science+Business Media Dordrecht (outside the USA)

Marks L.M.,University of California at Santa Barbara | Reed D.C.,University of California at Santa Barbara | Obaza A.K.,Ocean Associates Inc.
Management of Biological Invasions | Year: 2017

Determining the feasibility of controlling marine invasive algae through removal is critical to developing a strategy to manage their spread and impact. To inform control strategies, we investigated the efficacy and efficiency of removing an invasive seaweed, Sargassum horneri, from rocky reefs in southern California, USA. We tested the efficacy of removal as a means of reducing colonization and survivorship by clearing S. horneri from 60 m2 circular plots. We also examined whether S. horneri is able to regenerate from remnant holdfasts with severed stipes to determine whether efforts to control S. horneri require the complete removal of entire individuals. The experimental removal of S. horneri in early winter, just prior to the onset of reproduction, reduced recruitment in the next generation by an average of 54% and reduced survivorship to adulthood by an average of 25%. However, adult densities one year after clearing averaged 83% higher in removal plots and 115% higher in control plots. We attribute these higher densities to anomalously warm water associated with the 2015–16 El Niño that reduced native canopy-forming algae and enhanced the recruitment and survival of S. horneri. We did not find any evidence to suggest that S. horneri has the capacity to regenerate, indicating that its control via removal does not require the tedious task of ensuring the removal of all living tissue. We developed efficiency metrics for manual removal with and without the aid of an underwater suction device and found the method with maximum efficiency (biomass removed worker-1 hr-1) varied based on the number of divers and surface support workers. Our findings suggest that controlling S. horneri via removal will be most effective if done over areas much larger than 60 m2 and during cool-water years that favor native algae. Such efforts should be targeted in places such as novel introduction sites or recently invaded areas of special biological or cultural significance where S. horneri has not yet become widely established. © 2017 The Author(s). Journal compilation & REABIC.

Beaulieu-McCoy N.E.,Ocean Associates Inc. | Sherman K.K.,Ocean Associates Inc. | Trego M.L.,Ocean Associates Inc. | Crocker D.E.,Sonoma State University | Kellar N.M.,National Oceanic and Atmospheric Administration
General and Comparative Endocrinology | Year: 2017

Chronic stress can have detrimental effects on an individual's health and reproductive success. The use of cortisol quantification as an indicator of stress in free-ranging cetaceans and phocids is increasing but no studies have applied this technique on blubber in otariids. We measured cortisol concentrations in blubber samples obtained from California sea lions, Zalophus californianus, stranded in San Diego County and those incidentally killed in the California drift gillnet fishery. We also measured progesterone concentrations to assess female reproductive status and, in males, as a potential secondary measure of adrenal steroid production. Blubber cortisol and progesterone values were compared across demographic groups (sex and maturity), season, and proportion blubber lipid extracted. Stranded animals (247.3 ± 70.767SE ng/g blubber) had significantly higher cortisol concentrations compared to fishery bycaught (8.1 ± 2.108SE ng/g blubber) animals. These findings are likely driven by inherent differences in the cause of death and associated nutritional state coupled with the mean duration of expiration for these two groups of animals (i.e., the duration from an animal's initial perception of the threat-to-self until death). The duration of transition from healthy state to death in stranded animals is on the order of many hours to weeks while in fishery bycaught animals, this transition occurs much more rapidly (i.e., seconds to tens of minutes). The presumed longer duration of the mortality event in stranded animals gives sufficient time for elevated cortisol to diffuse into the blubber. No significant differences between demographic groups, or season were found. However, blubber cortisol declined inversely with proportion blubber lipid extracted, suggesting utility in assessing long-term nutritional status. Blubber progesterone was significantly higher in mature females than immature females (153.8 ± 54.546SE ng/g blubber and 9.7 ± 3.60SE ng/g blubber respectively), containing on average 15 times more progesterone, irrespective of pregnancy state. Additionally, a significant relationship between mean cortisol and progesterone was found in males with >35% blubber lipid (p < 0.0001). This study is an initial step in validating blubber cortisol and progesterone concentrations as a potential marker of stress response and reproductive state, respectively, in otariids. Especially when paired with dart biopsying, this approach could represent a relatively rapid way to assess baseline stress, nutritional status and reproductive states in otariids while minimizing the effects of sampling. © 2017

Obaza A.,Ocean Associates Inc. | Obaza A.,National Oceanic and Atmospheric Administration | Hoffman R.,National Oceanic and Atmospheric Administration | Clausing R.,University of California at Los Angeles
Fisheries Management and Ecology | Year: 2015

Changes in fish assemblages were tracked in representative eelgrass (Zostera marina L.) beds within two estuaries on the urbanised coast of southern California, USA, San Diego Bay and Mission Bay, from 1987 to 2010. Assemblages were sampled twice yearly (spring and summer) at day and night using beach seines. Assemblage stability was examined over time along with changes in assemblage structure across time of day and season, including the influence of temporally variable abiotic variables. Only the occasionally occurring fish, those present in <70% of samples, in Mission Bay appeared to be shifting to a new assemblage. Although season and sampling time significantly affected assemblages, correlations with abiotic factors were low. Given the long history of urban development of these estuaries, community shifts may have occurred prior to the onset of sampling, giving the appearance of stability. Alternatively, eelgrass habitat may be providing a refuge from long-term disturbances. © 2015 John Wiley & Sons Ltd.

PubMed | California State University, Long Beach, San Diego State University, National Oceanic and Atmospheric Administration, Ocean Associates Incorporated and 3 more.
Type: Journal Article | Journal: Journal of fish biology | Year: 2015

In June 2013, a record-breaking female Isurus oxyrinchus (total length 373 cm, mass 600 kg) was captured by rod and reel off Huntington Beach, California, where it was subsequently donated to research and provided a rare opportunity to collect the first data for a female I. oxyrinchus of this size. Counts of vertebral band pairs estimate the shark to have been c. 22 years old, depending upon assumptions of band-pair deposition rates, and the distended uteri and spent ovaries indicated that this shark had recently given birth. The stomach contained a c. 4 year-old female California sea lion Zalophus californianus that confirmed the high trophic position of this large I. oxyrinchus, which was corroborated with the high levels of measured contaminants and tissue isotope analyses.

Kellar N.M.,National Oceanic and Atmospheric Administration | Trego M.L.,National Oceanic and Atmospheric Administration | Trego M.L.,Ocean Associates Inc. | Chivers S.J.,National Oceanic and Atmospheric Administration | Archer F.I.,National Oceanic and Atmospheric Administration
Marine Biology | Year: 2013

The northeastern offshore population of the pantropical spotted dolphin (Stenella attenuata) in the eastern tropical Pacific remains listed as depleted under the Marine Mammal Protection Act, and recent estimates of abundance show that recovery has been slow. One hypothesis for the slow recovery is that continued chase and encirclement by the tuna fishery negatively affects reproduction. Insufficient life-history sampling in this region over the last two decades makes traditional estimates of reproductive rates impossible. Here, we examine the current reproductive patterns of these dolphins by measuring blubber progesterone (BP) concentrations in biopsy samples to assess pregnancy state. BP was quantified in 212 biopsies from female offshore spotted dolphins sampled between 1998 and 2003 in the northeastern tropical Pacific, and we found that 11.5 % of the biopsied females (mature and immature) were pregnant. The relationship between pregnancy and fishery exposure was analyzed, and we found that pregnant females were exposed to significantly less fishery activity than non-pregnant ones (p = 0.022), suggesting that the fishery may have an inhibitive effect on pregnancy. Spatial analysis indicated that pregnancy was more aggregated than random (p < 0.05) at a scale up to 180-nmi, with the highest proportion pregnant in the mouth of the Gulf of California, an area with relatively low reported fishery activity. © 2013 Springer-Verlag Berlin Heidelberg (outside the USA).

Fiedler P.C.,National Oceanic and Atmospheric Administration | Redfern J.V.,National Oceanic and Atmospheric Administration | Van Noord J.,National Oceanic and Atmospheric Administration | Hall C.,National Oceanic and Atmospheric Administration | And 3 more authors.
Marine Ecology Progress Series | Year: 2013

Tropical cyclones are environmental disturbances that may have important effects on open-ocean ecosystem structure and function, but their overall impact has rarely been assessed. The Stenella Abundance Research Line Transect and Ecosystem (STARLITE) survey, in August-November 2007, investigated spatial and temporal ecosystem variability in the eastern tropical Pacific Ocean off southwestern Mexico. Oceanographic, plankton, flyingfish, seabird, and cetacean sampling was conducted along eight 170 km transect lines, each of which were surveyed on 2 consecutive days at ∼3 wk intervals. Tropical storm Kiko passed though the study area on 15-17 October and forced changes in the physical environment and in the ecosystem, from plankton to top predators. Kiko mixed water from beneath the strong, shallow thermocline to the surface. As a result, surface temperature decreased by 0.6°C, the thermocline and chlorophyll maximum layer shoaled by 10-20 m, stratification decreased by 27%, and chlorophyll increased by 33% at the surface and 35% over the euphotic zone. These changes persisted for at least 4 wk. Zooplankton biomass increased by 59% about 3 wk after the phyto - plankton increase. Changes in the stomach fullness and diet composition of planktivorous flyingfish were consistent with the increase in zooplankton biomass. Among top predators, the sighting rate of dolphins declined, while the response of seabirds varied by species and was confounded by seasonal migration patterns. Tropical cyclones are a recurrent disturbance in this region. They initiate a bottom-up forcing of the ecosystem, creating persistent patches of higher primary and secondary production, and may be regarded as a disturbance regime.

Becker E.A.,National Oceanic and Atmospheric Administration | Becker E.A.,Ocean Associates Inc. | Forney K.A.,National Oceanic and Atmospheric Administration | Foley D.G.,University of California at Santa Cruz | And 4 more authors.
Endangered Species Research | Year: 2014

Temporal variability in species distribution remains a major source of uncertainty in managing protected marine species, particularly in ecosystems with significant seasonal or interannual variation, such as the California Current Ecosystem (CCE). Spatially explicit species- habitat models have become valuable tools for decision makers assisting in the development and implementation of measures to reduce adverse impacts (e.g. from fishery bycatch, ship strikes, anthropogenic sound), but such models are often not available for all seasons of interest. Broadscale migratory patterns of many of the large whale species are well known, while seasonal distribution shifts of small cetaceans are typically less well understood. Within the CCE, species- habitat models have been developed based on 6 summer-fall surveys conducted during 1991 to 2008. We evaluated whether the between-year oceanographic variability can inform species predictions during winter-spring periods. Generalized additive models were developed to predict abundance of 4 cetacean species/genera known to have year-round occurrence in the CCE: common dolphins Delphinus spp., Pacific white-sided dolphin Lagenorhynchus obliquidens, northern right whale dolphin Lissodelphis borealis, and Dall's porpoise Phocoenoides dalli. Predictor variables included a combination of temporally dynamic, remotely sensed environmental variables and geographically fixed variables. Across-season predictive ability was evaluated relative to aerial surveys conducted in winter-spring 1991 to 1992, using observed:predicted density ratios, nonparametric Spearman rank correlation tests, and visual inspection of predicted and observed distributions by species. Seasonal geographic patterns of species density were captured effectively for most species, although some model limitations were evident, particularly when the original summer-fall data did not adequately capture winter-spring habitat conditions. © Inter-Research 2014.

Javor B.,Ocean Associates Inc. | Dorval E.,Southwest Fisheries Science Center
Fisheries Research | Year: 2014

Pacific sardine (Sardinops sagax), a commercially valuable species, have a broad distribution along the North American coast that spans Canada, the United States, and Mexico. The goal of this research was to evaluate water temperature history of the fish inferred from stable oxygen isotopes in otoliths in order to differentiate and connect stocks across regions, and between juveniles and adults. Local seawater composition in the Pacific Northwest affected major north-south trends in δ18O composition of juvenile otoliths. Inferred temperature correlated inversely with the age (otolith weight) of juveniles within a region, possibly resulting from changes in depth preferences as the fish grew. The correlations between δ13C and δ18O in juvenile otoliths were relatively weak in the northernmost and southernmost samples, but comparisons of the sample means indicated significant differences between some regions. Otoliths from adult sardine captured between California and Canada recorded δ18O values reflecting cooler temperatures than otoliths from juveniles, and without regional differentiation. These results are consistent with a northern stock that mixes during annual migrations. © 2014 Elsevier B.V.

Demer D.A.,Southwest Fisheries Science Center | Zwolinski J.P.,Ocean Associates Inc. | Cutter G.R.,Southwest Fisheries Science Center | Byers K.A.,Southwest Fisheries Science Center | And 2 more authors.
ICES Journal of Marine Science | Year: 2013

To annually assess the northern stock of Pacific sardine (Sardinops sagax) in the California Current and set harvest quotas for the US fishery, managers have used an age-structured stock synthesis model fitted with results from acoustic-trawl (ATM), daily-egg-production, and aerial-photogrammetric survey methods, fishery landing and individual-length data, and many assumed or empirically derived parameters. In these assessments, sardine landed at ports spanning from Ensenada, México to Vancouver Island, Canada were assumed to be solely from the northern stock. It was also assumed that the ATM estimates of sardine biomass were negligibly biased for the sizes of fish sampled by the survey trawls (i.e., catchability q = 1 for sardine standard length (SL) values greater than ∼17 cm). Due to these catchability and length-selectivity assumptions, the ATM- and assessment-estimated abundances are mostly similar for larger sardine. However, the assessment estimates include large abundances of small sardine (SL values less than ∼15 cm) that are not represented in either the ATM-survey results or the fishery landings, and generally did not recruit to the migrating northern stock sampled by the ATM surveys. We considered four explanations for this disparity: (i) the ATM length-selectivity assumption is correct; (ii) the non-recruiting small fish may comprise a smaller portion of the stock than indicated by the assessments; (iii) during years of low recruitment success, those size classes may be virtually completely fished by the Ensenada and San Pedro fisheries; or (iv) they may belong to the southern sardine stock. This investigation emphasizes the previously identified importance of differentiating samples from the northern and southern stocks and surveying their entire domains. © 2013 Published by Oxford University Press on behalf of International Council for the Exploration of the Sea 2013.

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