Biology of the red abalone, Haliotis rufescens, in Northern California

The red abalone, Haliotis rufescens Swainson 1822, supports the only recreational free-dive abalone fishery in the United States. I examined annual survivorship of three size classes ( 178 mm) of red abalone from five sites in northern California and one site in southern California using capture-mark-recapture data. Survival was variable spatially and among size classes. Survivorship values were incorporated into a size based projection matrix model. Elasticity values were found to be greatest for the sub-legal red abalone 150 mm to 178 mm (maximum shell length) indicating that changes in the vital rates of this size class are most important to population growth. Current methods to describe the age-at-length relationship of red abalone are insufficient because shell lengths exceed those predicted by growth models. I evaluated the utility of analyzing atomic bomb generated radioisotope 14C in shell to validate this relationship

Temporal Dynamics of Lipid and Fatty Acid Characteristics of Gulf Menhaden, \u3ci\u3eBrevoortia patronus\u3c/i\u3e in the Northern Gulf of Mexico

Gulf Menhaden, Brevoortia patronus, in the northern Gulf of Mexico support a large commercial fishery and are thought to play an important trophic role in the coastal ecosystem. The temporal dynamics of both fatty acid and oil content have a direct impact on the value of Gulf Menhaden to predators and to the fishery. In this work, we describe how oil content of Gulf Menhaden varies with season, sex, age, condition, and tissue and investigate how fatty acid composition of mature (137.5 mm FL) female tissues varies with season, month, and tissue type. We found pronounced temporal (January to October) variation in mean oil content ranging from 0.062 to 0.579 mg g−1 that exhibited a significant (p \u3c 0.001) seasonal pattern. We observed significant differences in oil content between tissue (muscle vs. ovary) of mature females and these exhibited a significant seasonal contrast, indicating that females were provisioning eggs in the fall. PERMANOVA analysis indicated the existence of significant differences (p \u3c 0.001) in the composition of fatty acids of muscle tissue collected in different months. Mean eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and long chain polyunsaturated fatty acid (LC-PUFA) levels exhibited significant seasonal differences (p \u3c 0.05), and in the case of DHA and LC-PUFA, both exhibited mean tissue-specific differences (p \u3c 0.05). This work indicates that the value of Gulf Menhaden as prey and a fishery resource in the region varies during the year and we propose that trophic models of the Gulf of Mexico ecosystem should account for this variation

Reproductive Dynamics of Gulf Menhaden (\u3ci\u3eBrevoortia patronus\u3c/i\u3e) in the Northern Gulf of Mexico: Effects On Stock Assessments

Gulf menhaden (Brevoortia patronus) produce one of the largest U.S. fisheries, yet information on reproductive dynamics of the stock is sparse. Males and females reach 50% maturity at 140.8 and 137.2 mm fork length, respectively and recruit into the commercial fishery at this size. Analysis of fishery-dependent data from 1964 through 2014 indicated that somatic condition was lower during the late 1980s and late 2000s and that reproductively active fish from 2014 were significantly larger and had greater gonadosomatic index values than those from 1964 through 1970. Histological analysis performed on fish from 2014 through 2016 revealed spawning-capable and actively spawning fish of both sexes from early October through midMarch. Females have indeterminate fecundity, are batch spawners, and spawn every 2.1-4.3 days, although oocyte recruitment shows some characteristics of determinate fecundity. Mean relative batch fecundity was 107.8 eggs/g ovary-free body weight (standard error 17.1). Estimates from age-structured assessment models based on updated fecundity and maturity measures resulted in a 100-1000x greater production of eggs than previous estimates. Model output, including the number-at-age, age-specific fishing-induced mortality, and spawners-per-recruit are sensitive to alterations in age-specific annual fecundity. Therefore, updated estimates of Gulf menhaden reproductive dynamics can affect assessments of the stock

Management Strategy Evaluation for the Atlantic Surfclam (Spisula solidissima) Using a Spatially Explicit, Vessel-Based Fisheries Model

The commercially valuable Atlantic surfclam (Spisula solidissima) is harvested along the northeastern continental shelf of the United States. Its range has contracted and shifted north, driven by warmer bottom water temperatures. Declining landings per unit of effort (LPUE) in the Mid-Atlantic Bight (MAB) is one result. Declining stock abundance and LPUE suggest that overfishing may be occurring off New Jersey. A management strategy evaluation (MSE) for the Atlantic surfclam is implemented to evaluate rotating closures to enhance Atlantic surfclam productivity and increase fishery viability in the MAB. Active agents of the MSE model are individual fishing vessels with performance and quota constraints influenced by captains\u27 behavior over a spatially varying population. Management alternatives include 2 rules regarding closure locations and 3 rules regarding closure durations. Simulations showed that stock biomass increased, up to 17%, under most alternative strategies in relation to estimated stock biomass under present- day management, and LPUE increased under most alternative strategies, by up to 21%. When incidental mortality caused by the fishery increased, the benefits seen under the alternative management were enhanced. These outcomes suggest that area management involving rotating closures could be valuable in insulating the stock and the commercial fishery from further declines as a northerly shift in range proceeds

Evaluation of SAMSON for use in a South Platte decision support system

December 1996.Includes bibliographical references (pages 28-29).The South Platte River basin is a tributary of the Missouri River. Three states share the basin (Colorado, Nebraska, and Wyoming), with most of the basin in Colorado (79 percent). Colorado's population has been growing rapidly, especially in Front-Range cities, increasing the demand on water resources in the basin. Highly productive plains agriculture is also a substantial user of water resources and new uses also can be expected for wildlife and recreation. A decision support system (DSS) is being planned by the State of Colorado for water management in South Platte River Basin. Anticipated needs of the system include data development and some model development specific to the South Platte. Due to the unique characteristics of the South Platte River Basin, the implementation of this framework is expected to be slightly different from other basins in Colorado. The SAMSON (Stream-Aquifer Model for Management by SimulatiON) Model, developed in the 1980s specifically for the South Platte River Basin, has been recommended by past studies for use in a South Platte DSS. This report provides and analysis of the current SAMSON model. The conclusions of this report recommend that SAMSON in its present form not be used as part of a DSS, largely due to recent developments in modeling philosophy, application, and use. SAMSON proved the entire South Platte River Basin system could be effectively modeled, and pointed to the priorities for data collection and development. Components of SAMSON could be part of future DSS systems, but they should be separated into individual modules and evaluated individually against existing models. In summary, the analysis of SAMSON clearly show the need for a modular and data-centered approach for a South Platte DSS.Grant no. 14-08-0001-G2008/5 Project no. 09; financed in part by the Department of the Interior, U.S. Geological Survey, through the Colorado Water Resources Research Institute

Spring bloom dynamics and zooplankton biomass response on the US Northeast Continental Shelf

This paper is not subject to U.S. copyright. The definitive version was published in Continental Shelf Research 102 (2015): 47-61, doi:10.1016/j.csr.2015.04.005.The spring phytoplankton bloom on the US Northeast Continental Shelf is a feature of the ecosystem production cycle that varies annually in timing, spatial extent, and magnitude. To quantify this variability, we analyzed remotely-sensed ocean color data at two spatial scales, one based on ecologically defined sub-units of the ecosystem (production units) and the other on a regular grid (0.5°). Five units were defined: Gulf of Maine East and West, Georges Bank, and Middle Atlantic Bight North and South. The units averaged 47×103 km2 in size. The initiation and termination of the spring bloom were determined using change-point analysis with constraints on what was identified as a bloom based on climatological bloom patterns. A discrete spring bloom was detected in most years over much of the western Gulf of Maine production unit. However, bloom frequency declined in the eastern Gulf of Maine and transitioned to frequencies as low as 50% along the southern flank of the Georges Bank production unit. Detectable spring blooms were episodic in the Middle Atlantic Bight production units. In the western Gulf of Maine, bloom duration was inversely related to bloom start day; thus, early blooms tended to be longer lasting and larger magnitude blooms. We view this as a phenological mismatch between bloom timing and the “top-down” grazing pressure that terminates a bloom. Estimates of secondary production were available from plankton surveys that provided spring indices of zooplankton biovolume. Winter chlorophyll biomass had little effect on spring zooplankton biovolume, whereas spring chlorophyll biomass had mixed effects on biovolume. There was evidence of a “bottom up” response seen on Georges Bank where spring zooplankton biovolume was positively correlated with the concentration of chlorophyll. However, in the western Gulf of Maine, biovolume was uncorrelated with chlorophyll concentration, but was positively correlated with bloom start and negatively correlated with magnitude. This observation is consistent with both a “top-down” mechanism of control of the bloom and a “bottom-up” effect of bloom timing on zooplankton grazing. Our inability to form a consistent model of these relationships across adjacent systems underscores the need for further research

Seasonal Phytoplankton Blooms in the North Atlantic Linked to the Overwintering Strategies of Copepods

The North Atlantic Ocean contains diverse patterns of seasonal phytoplankton blooms with distinct internal dynamics. We analyzed blooms using remotely-sensed chlorophyll a concentration data and change point statistics. The first bloom of the year began during spring at low latitudes and later in summer at higher latitudes. In regions where spring blooms occurred at high frequency (i. e., proportion of years that a bloom was detected), there was a negative correlation between bloom timing and duration, indicating that early blooms last longer. In much of the Northeast Atlantic, bloom development extended over multiple seasons resulting in peak chlorophyll concentrations in summer. Spring bloom start day was found to be positively correlated with a spring phenology index and showed both positive and negative correlations to sea surface temperature and the North Atlantic Oscillation in different regions. Based on the characteristics of spring and summer blooms, the North Atlantic can be classified into two regions: a seasonal bloom region, with a well-defined bloom limited to a single season; and a multi-seasonal bloom region, with blooms extending over multiple seasons. These regions differed in the correlation between bloom start and duration with only the seasonal bloom region showing a significant, negative correlation. We tested the hypothesis that the near-surface springtime distribution of copepods that undergo diapause (Calanus finmarchicus, C. helgolandicus, C. glacialis, and C. hyperboreus) may contribute to the contrast in bloom development between the two regions. Peak near-surface spring abundance of the late stages of these Calanoid copepods was generally associated with areas having a well-defined seasonal bloom, implying a link between bloom shape and their abundance. We suggest that either grazing is a factor in shaping the seasonal bloom or bloom shape determines whether a habitat is conducive to diapause, while recognizing that both factors can re-enforce each other