Papers by Richard Condrey
Northeast gulf science, Jul 1, 1990
Saltwater intrusion is believed to be one of the greatest threats to Louisiana's fishery and wild... more Saltwater intrusion is believed to be one of the greatest threats to Louisiana's fishery and wildlife resources. The Louisiana Department of Wildlife and Fisheries has main• tained salinity recording stations throughout the state's coastal marshes since the 1960's. We applied several different analytical approaches to the salinity data from 17 stations to determine whether this data base could be used to detect and quantity long•term salinity trends in coastal Louisiana. We did not detect a large•scale, consistent trend over time in coastal salinities across the state. Problems that hindered the detection of long-term trends included short periods of record and the placement of the recording stations in salt an,d brackish marsh areas, where we would not expect to find great changes in salinity. For the data to be useful in monitoring salinity trends in coastal marshes, especially with respect to saltwater intrusion, stations should be added in fresh and intermediate marshes. In addition, the relationships our study revealed between short• and long-term data indicate that records covering less than a decade are insufficient to denote long-term salinity changes, barring some major modification of the hydrologic regime.
North American Journal of Fisheries Management, Feb 1, 1999
Abstract Bycatch reduction is a major issue in many U.S. fisheries, and workers in the U.S. Gulf ... more Abstract Bycatch reduction is a major issue in many U.S. fisheries, and workers in the U.S. Gulf of Mexico menhaden industry have used bycatch reduction devices since the 1950s. Currently industry workers employ a hose cage and a large fish excluder, usually in combination, to reduce the retention of large bycatch species (defined here as any vertebrate species 1.0 m or greater in total length). In this paper, we examine the effectiveness of these devices to reduce large bycatch and recommend possible modifications of the devices to further reduce the bycatch. A principal component analysis was conducted to assess possible groupings of bycatch reduction devices. The analysis suggested that a hose cage with a larger area and smaller openings would be effective at mitigating the retention of large bycatch.
Bulletin of Marine Science, 2009
ABSTRACT Recent studies have highlighted the biomass and ecological roles of benthic microalgae (... more ABSTRACT Recent studies have highlighted the biomass and ecological roles of benthic microalgae (BMA) on the continental shelf. However, few studies have specifically examined BMA in the north-central Gulf of Mexico. We examined the origin and biomass of sediment associated algae on Ship Shoal, a submerged sandbank with depth and sediment characteristics favorable to benthic primary production. Light levels at the sediment surface ranged from < 1% to 30% of surface PAR, and were judged sufficient for benthic photosynthesis throughout the year. Sediment algal biomass, as chlorophyll a, was highest in the spring and summer and was not consistently correlated with any of the physical parameters recorded including sediment light levels and water depth. Photosynthetic pigment analysis indicated sedimentary algae across Ship Shoal were predominately diatoms on all sampling dates. Microscopic analysis suggested the diatoms were primarily BMA with only a minor fraction of settled phytoplankton. Our results differ from studies of muddy sediments which have typically found that sediment algae on the Louisiana shelf were derived from phytoplankton. Comparison of pigments from the sediment and bottom water suggested weak exchange of benthic and pelagic algae between the two compartments. Algal biomass in the sediment exceeded that of the overlying water column over much of Ship Shoal during the spring and summer. The high benthic algal biomass (equivalent to typical estuarine values) suggests benthic primary product (BPP) may contribute to the Ship Shoal food web and that BPP may be an important ecosystem component on the other large shoals found on Louisiana's inner shelf.
There are 25 species of sharks in the Gulf of Mexico. This analysis focuses on two of those speci... more There are 25 species of sharks in the Gulf of Mexico. This analysis focuses on two of those species indigenous to the Louisiana Coast: the Blacktip shark and the Bull shark. The steps involved in preparing the data for analysis involved much manipulation through SAS ® , as did the statistical analysis. Using a mixed model, the factors involved in shark abundance at three sampling sites along the Louisiana coast will be assessed (especially for the Blacktip shark) and using these factors, a model to predict the probability of encountering each of these species will be analyzed using a logistic regression model. Factors assessed are month, location (station), and time of day.
Provenance, Journal of the Society of Georgia Archivists, 1992
Fisheries Research, Jun 1, 1999
We outline a procedure by which conservative management (de®ned as management which errs on the s... more We outline a procedure by which conservative management (de®ned as management which errs on the side of the resources in the face of uncertainty) can use a series of stepwise analyses to explore for possible over®shing in multispecies ®sheries for which there is only aggregated data on effort. The procedure provides a multivariate framework for analyzing these data and has two statistical aspects. The ®rst aspect develops a formula for the 95% con®dence intervals around the predicted MSY estimate. The second aspect ®ts a seemingly unrelated regression (SUR) model which takes into consideration the possibility of correlation among the individual species' catch data. We apply this procedure to the multispecies pelagic ®sheries from West Africa. Our philosophy is not to advocate the use of these models to manage a ®shery, but to advocate a conservative approach to those ®sheries for which only such minimal data exist. Our analyses denote the comparative broad 95% con®dence intervals about MSY estimates and that the SUR is applicable for this multispecies ®shery. Our surplus production ®ts suggest over®shing in one of the six single species ®ts and in both of the two single genius aggregations. While the ®t of the aggregate total catch doesn't suggest over®shing, it does suggest that the ®shery is almost at F MSY. We conclude that these ®ts provide management with a more realistic approach to the status of the stocks than a previously published equilibrium ®t, which suggested a tremendous potential for increasing catch by increasing effort outside of the historic range.
Biotechnology and Bioengineering, Jul 1, 1982
International Journal of Remote Sensing, Aug 10, 2011
... DOI: 10.1080/01431161.2010.486807 Puneeta Naik a , Eurico J. D'Sa a * , Mark... more ... DOI: 10.1080/01431161.2010.486807 Puneeta Naik a , Eurico J. D'Sa a * , Mark Grippo b , Richard Condrey c & John Fleeger b pages 4383-4406. Available online: 17 Aug 2011. ...
North American Journal of Fisheries Management, Feb 1, 2001
Abstract We describe the 1994 and 1995 releasable bycatch (bycatch) of sharks (Carcharhinidae and... more Abstract We describe the 1994 and 1995 releasable bycatch (bycatch) of sharks (Carcharhinidae and Sphyrnidae) in the U.S. Gulf of Mexico fishery for gulf menhaden Brevoortia patronus. “Releasable bycatch” is defined as catch of nontarget species observed in the purse seine from the time it is brought alongside the carrier ship until all the catch is pumped into the hold and the net is cleaned. Shark bycatch in the gulf menhaden fishery was positively skewed, 726 sharks being observed in 30% of the fishing sets sampled. Ten species of sharks were identified, blacktip sharks Carcharhinus limbatus being the most common. Approximately 20% of sharks were not identified to species. At the time of release, 75% of the sharks in the bycatch were dead, 12% were disoriented, and 8% were healthy. An annual bycatch of approximately 30,000 sharks for the fishery was estimated for the 1994 and 1995 fishing seasons. By means of a logit model, the likelihood of observing shark bycatch was explained by spatial and temporal...
Fisheries Research, Feb 1, 1994
We present a method of estimating the corrected size composition and associated variances of a fi... more We present a method of estimating the corrected size composition and associated variances of a fish population as a companion paper to a recently developed method of estimating gillnet selectivity which uses a non-linear iterative least-squares approach. In this paper, we ...
Limnology and Oceanography, Mar 31, 2011
We used stable isotopes to examine the relative importance of phytodetritus and microphytobenthos... more We used stable isotopes to examine the relative importance of phytodetritus and microphytobenthos (MPB) in supporting benthic food webs on the Louisiana continental shelf. Primary producers and macroinfauna were collected from Ship Shoal (SS), a submerged, sandy, barrier island where sediment-associated algae are primarily MPB and from silty, off-shoal areas where sediment-associated algae are primarily phytodetritus or a mixture of the two resources. Macroinfauna, as individual taxa and trophic guilds, were significantly more enriched in 13 C on SS indicating greater dependence on MPB, which is enriched in 13 C compared to phytoplankton. Using d 13 C in a two-source mixing model, the estimated MPB dietary contribution for SS macroinfauna averaged across trophic guilds, ranged from 53.4% to 83.0%, depending on the mixing-model end-members used, and 5 of 14 taxa had lower 95% confidence intervals (CI). 20%, indicating that MPB was a primary resource for most SS macroinfauna. Off-shoal, the dietary contribution of MPB ranged from14.5% to 47.7% and most taxa had a lower CI near 0%. Settled phytoplankton are the primary microalgal food source in muddy sediments, but the importance of MPB increases in more sandy sediments where MPB are the predominant microalgal resource. Sandy shoals play a unique food-web role in deltaic shelf systems and support benthic food webs on the continental shelf.
Continental Shelf Research, Mar 1, 2010
Marine sediment may contain both settled phytoplankton and benthic microalgae (BMA). In riverdomi... more Marine sediment may contain both settled phytoplankton and benthic microalgae (BMA). In riverdominated, shallow continental shelf systems, spatial, and temporal heterogeneity in sediment type and water-column characteristics (e.g., turbidity and primary productivity) may promote spatial variation in the relative contribution of these two sources to the sediment organic matter pool available to benthic consumers. Here we use photosynthetic pigment analysis and microscopic examination of sediment microalgae to investigate how the biomass, composition, and degradation state of sedimentassociated microalgae vary along the Louisiana (USA) inner shelf, a region strongly influenced by the Mississippi River. Three sandy shoals and surrounding muddy sediments with depths ranging from 4 to 20 m were sampled in April, August, and October 2007. Pigment composition suggested that sediment microalgae were primarily diatoms at all locations. We found no significant differences in sediment chlorophyll a concentrations (8-77 mg m À 2) at the shoal and off-shoal stations. Epipelic pennate diatoms (considered indicative of BMA) made up a significantly greater proportion of sediment diatoms at sandy (50-98%) compared to more silty off-shoal stations (16-56%). The percentage of centric diatoms (indicators of settled phytoplankton) in the sediment was highest in August. Sediment total pheopigment concentrations on sandy stations (o 20 mg m À 2) were significantly lower than concentrations at nearby muddy stations (4 40 mg m À 2), suggesting differences in sediment microalgal degradation state. These observations suggest that BMA predominate in shallow sandy sediments and that phytodetritus predominates at muddy stations. Our results also suggest that the relative proportion of phytodetritus in the benthos was highest where phytoplankton biomass in the overlying water was greatest, independent of sediment type. The high biomass of BMA found on shoals suggests that benthic primary production on sandy sediments represents a potentially significant local source of sediment microalgal carbon that may be utilized by benthic consumers in continental shelf food webs.
Asian fisheries science, Dec 1, 1987
Simulations of a mark-recapture experiment are used to demonstrate the bias associated with use o... more Simulations of a mark-recapture experiment are used to demonstrate the bias associated with use of a widely accepted equation for-estimating growth rates from data where absolute age is unknown. The bias results in an overestimation of K, the growth rate constant, and an underestimation of 1-, the theoretical maximum size. The bias appears to be associated with a failure to account for the redistribution of the error term when the basic growth equation is transformed to eliminate the necessity of estimating age.
Transactions of The American Fisheries Society, 1993
We analyzed experimental gill-net catches of spotted seatrout Cynoscion nebulosus at 28 stations ... more We analyzed experimental gill-net catches of spotted seatrout Cynoscion nebulosus at 28 stations in various estuarine habitats over 3 years (1988–1990). Cluster analysis indicated that the 28 stations reduced to three “natural” groupings representing salinity zones that correspond to upper (oligohaline, 0–9‰), intermediate (mesohaline, 10–14‰), and lower (polyhaline, 15–30‰) estuarine zones. Principal components analysis applied to log-transformed gill-net catches yielded
Canadian Journal of Fisheries and Aquatic Sciences, Dec 1, 1982
The published data on ingestion-limited growth in aquatic animals is shown to be consistent with ... more The published data on ingestion-limited growth in aquatic animals is shown to be consistent with Blackman kinetics. As such, if ingestion limits growth rate there is a linear relationship between growth and ingestion from starvation to satiation. If, however, growth is limited by some factor other than ingestion rate, there is no increase in growth rate with increasing ingestion rate.Key words: ingestion, growth, growth efficiency, Blackman kinetics
Canadian Journal of Fisheries and Aquatic Sciences, Mar 1, 1991
This study proposes a new method of estimating the selectivity of gill nets. Using data on the di... more This study proposes a new method of estimating the selectivity of gill nets. Using data on the distribution of fish lengths from the catches of various meshes in an experimental gill net, a system of m equations and n unknown coefficients is simultaneously solved describing the functional relationship of the moments from an assumed mathematical model across mesh size and size-class of fish. The solution to the model is a response surface describing the probability of capture of fish of size-class j in mesh i. This new method is applied to spotted seatrout (Cynocion nehulosus) in coastal Louisiana and used to estimate the relative abundance of the various size-classes of fish in the population. We suggest that this approach for estimating gillnet selectivity has several advantages over other methods: it is very flexible in terms of choosing a mathematical model which would best represent the data; it takes full advantage of the empirical data allowing catch information, nij, to contribute to the final solution both as a function of mesh size and size-class; and it offers simplicity and elegance in its overall iterative least squares approach and is tractable in terms of assessing the reliability of the parameters and model used.
College & Research Libraries News, Sep 1, 1993
Gulf of Mexico science, 1996
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Papers by Richard Condrey