Richard E. Condrey

Transport of Larval Gulf Menhaden Brevoortia patronus in Continental Shelf Waters of Western Louisiana: A Hypothesis

Abstract The gulf menhaden commercial fishery in the Gulf of Mexico is the largest by weight in the United States. Spawning takes place on the continental shelf during fall and winter and the pelagic larvae are transported into estuarine nursery areas. Quantitative information on a transport mechanism had previously been lacking. Knowledge of the coupling between continental shelf and estuaries is necessary to understand the causes of high natural variability in estuarine recruitment and to develop and evaluate spawner-recruit and environment-survival relationships. Analysis of a variety of biological and physical data led to the development of a testable transport hypothesis. The hypothesis suggests that west-northwest longshore advection within the horizontally stratified coastal boundary layer is the primary mechanism transporting gulf menhaden larvae to the Calcasieu River estuary, the major estuarine system in western Louisiana.

Estimating size composition and associated variances of a fish population from gillnet selectivity, with an example for spotted seatrout (Cynoscion nebulosus)

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 present a modification to the selectivity equation used in an earlier approach which reduces heterogeneous error variance. Nonlinear least-squares parameter estimates are used to estimate the population size composition corrected for the effects of mesh selectivity and a procedure is described to estimate their variances. We applied the selectivity model and variance estimation procedure to the experimental gillnet catches of spotted seatrout from 1988 to 1990 and examined model selection parameter estimates, corrected population size compositions, and their variances. Likelihood ratio tests indicated that model selection parameters estimates were significantly different between the sexes (P < 0.01), suggesting that factors which affect the selection process may differ between the sexes. Corrected size compositions for female and male spotted seatrout population were found to differ substantially from the observed catch frequencies, indicating negative bias for smallest size classes. Variability associated with corrected size composition estimates, as expressed by 95% confidence intervals, indicated that in general, precision associated with those quantities is good.

Spotted Seatrout Distribution in Four Coastal Louisiana Estuaries

Abstract 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 a two-factor model that explained 78% of the variation in the data; factors were interpreted as recruit size (females smaller than 31 cm in total length and males smaller than 26 cm) and spawner size (females larger than 31 cm and males larger than 26 cm). Both recruit and spawner models were highly significant (P < 0.0001), and the zone-by-season interaction accounted for the greatest proportion of the variation in the models (P < 0.0001). Abundances of recruit and spawner spotted seatrout were greatest in the lower estuarine z...

The Last Naturally Active Delta Complexes of the Mississippi River (LNDM): Discovery and Implications

The most ambitious ecological restoration project yet attempted is just getting started to renaturalize the Mississippi River Deltaic Plain. All the channeling, leveeing, lumbering, damming, dredging, and polluting of this system over the past 300 + years make it difficult to envision today how a more natural ecosystem might look and function. Our hope is that an awareness of the protohistoric deltaic plain may help guide the modern restoration program. To accomplish this, we explore the historic record for a description of the last naturally active delta complexes of the Mississippi River (LNDM) as the most appropriate restoration model for Louisiana’s coast. The LNDM is our reconstruction of this system as it was encountered by the first Europeans to navigate it. To accomplish this, we focus on Alonso de Chaves’ ca. 1537 manuscript. We find Chaves’ latitude estimates accurate (R2 = 0.99), his league to equal 6.3 km, and his location of the LNDM consistent with the most authoritative first-hand accounts of the protohistoric and colonial period (Barroto, Iberville, Evia, and Dumain) . We find the LNDM was a vast seaward-advancing arc that occupied, through four distributaries, all of the five most recent delta complexes of the Mississippi River and extended across all of coastal Louisiana east of the Chenier Plain. It was characterized by plumes of freshwater that extended for more than 10 km into the Gulf of Mexico (GoM) during the spring flood of the Mississippi River and by a vast offshore oyster reef covering > 2,000 km2, impeding navigation, and functioning as an offshore harbor near the reef’s western end. Our findings support “reconnecting the river to the deltaic plain via … the reopening of old distributaries” (Day et al., Science 315:1679–1684, 2007) and the desirability of “a fully revised delta-lobe-scale chronostratigraphy” (Kulp et al., Soc Sediment Geol Special Publ, 83:279–293, 2005). Implications of our findings are discussed in light of what we view as fundamental errors in Louisiana’s coastal restoration plan and the “Berms to Barriers”/post Deepwater Horizon oil spill efforts. Here we find that many of Louisiana’s coastal restoration benchmarks —diversions restricted to the lower regions of coastal Louisiana (i.e., the Birdsfoot and the Atchafalaya delta complex); oyster reefs confined to estuarine environments; brackish-water dominated estuaries in the spring; deepwater shipping channel inlets; and artificial levees—are incompatible with a sustainable coast and that recent data are consist with a constant rate of land loss in coastal Louisiana of 69.1 km2/yr (1.47 football fields/hr) for 1932 through 2010 . We also find that the “Berms to Barriers” concept is necessarily going to fail unless the natural flows of the Mississippi through and across the LNDM are sufficiently restored so as support Louisiana’s barrier islands and coastline against the forces of the GoM. Our findings support Lamb’s (Separata du Revista da Universidale de Coimbra 24:9, 1969) argument that Chaves (ca. 1537) provides our earliest comprehensive view of the coasts of the Americas and Ovieda’s (1851) argument that De Soto’s men sailed out the mouth of Rio del Espiritu Santo (River of the Holy Spirit)—which we conclude flowed through the Atchafalaya/Vermilion Bay complex and not the Birdsfoot.

A modification of the delury method for use when natural mortality is not negligible

Abstract An alternative method for estimating population size, N0, and catchability coefficient, q, which does not involve DeLurys use of an approximation of the Taylor series, is developed. The equation is of the form C f /f=q · N 0 − (q′) K t where Ct/f is the instantaneous catch per unit effort, Kt is the cumulative catch to the start of interval t plus half of that taken during the time-interval t, and q′ is the slope of the regression of Ct/f against Kt and is related to q as q=(−1/f) [ log (1− q′ · f) + M] where M is the instantaneous rate of natural mortality.

Profile of Shark Bycatch in the U.S. Gulf of Mexico Menhaden Fishery

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...

Absorption properties of shoal-dominated waters in the Atchafalaya Shelf, Louisiana, USA

Spectral absorption coefficients of coloured dissolved organic matter (a CDOM(λ)) and particulate matter (a p(λ)) (phytoplankton (a PHY(λ)) plus non-algal particles (a NAP(λ)), measured on the shoal-dominated region off the Atchafalaya River (AR) Shelf, Louisiana, USA, are analysed, and their effect on chlorophyll-a retrievals from ocean-colour sensors examined. Compared to a CDOM(λ) and a NAP(λ), a PHY(λ) is relatively constant, with a CDOM(λ) and a NAP(λ) varying by approximately 1.2 and 1.8 times as much as a PHY(λ) at 443 nm, respectively. The specific a PHY(λ) (a*PHY(λ)) ranges from 0.006 to 0.0612 m−2(mg chla)−1 at 443 nm, which indicates a pigment-packaging effect or a variation in pigment composition. The a NAP(λ) accounts for approximately 3–93% of a p(λ) at 443 nm, with a higher contribution to a p(λ) during an October 2007 cruise (62–93%) as compared to an August 2007 cruise (31–89%). Our results indicate that a CDOM(λ) and a NAP(λ) collectively dominate light absorption, even at higher wavelengths where their effect is expected to be minimal. In situ and satellite data match-up of chlorophyll-a yield root-mean square errors of 2.17 and 2.62 for the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Medium Resolution Imaging Spectrometer (MERIS), respectively. The non-covarying a CDOM(λ) and a NAP(λ), along with variable a*PHY(λ), greatly influenced the remote retrieval of biogeochemical variables using satellite ocean-colour algorithms in this region.

Characterization and Evaluation of Bycatch Reduction Devices in the Gulf Menhaden Fishery

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.