During offshore sampling conducted between 2005 and 2007, we discovered large concentrations of the blue crab Callinectes sapidus spawning between 4 and 50 km offshore of the Louisiana coast; the greatest concentrations were found on high-relief sandy shoals. We used natural abundance carbon and nitrogen isotopes to evaluate C. sapidus migratory source locations within south-central Louisiana estuarine systems as well as residency on the shoals. There was an east-west trend of decreasing δ 13 C and increasing δ 15 N for offshore crab tissue (muscle and ovary) related to proximity to the Atchafalaya River. This indicates that crabs predominately migrate directly offshore from their home estuary rather than migrating long distances alongshore. Many δ 13 C values for offshore crab muscle and ovary were depleted relative to typical salt marsh values, indicating that some female blue crabs migrate directly offshore from low salinity regions higher in the estuary. The convergence of muscle and ovary isotope values towards a proxy for offshore residence (i.e. Callinectes similis mean isotope values) indicated that migrating C. sapidus utilize offshore prey resources and do not typically re-enter inshore estuaries during the spawning season. A correlation between crab δ 13 C values and the body size of shell-associated epibiotic acorn barnacles Chelonibia patula indicated that crabs found on shoals acquire offshore isotopic values over time. These findings have important research implications for studies involving animal migrations, as well as for management of this ecologically and economically important species. The findings provide evidence of a direct link between the inshore fishery and female blue crabs captured offshore in unique sandy shoal habitats, which likely support at least 20% of the known Louisiana blue crab spawning stock west of the Mississippi River.KEY WORDS: Callinectes sapidus · Behavior · Feeding ecology · Stable isotopes · Gulf of Mexico · Migration Resale or republication not permitted without written consent of the publisher Editorial responsibility: Romuald Lipcius,

Stomach contents and vertebrae from neonate and juvenile blacktip sharks Carcharhinus limbatus (n ¼ 334) were examined to describe their diet, feeding patterns and growth within the Timbalier-Terrebone Bay complex, LA, U.S.A. In the study area, both neonate and juvenile C. limbatus feed primarily on gulf menhaden Brevoortia patronus. However, based on the index of relative importance (I RI ), gulf menhaden constituted a larger portion of the diet of neonates (84Á05 %I RI ) than for juveniles (47Á91 %I RI ). An increase in the index of relative fullness between the afternoon and dusk time intervals and a large decrease in the percentage of empty stomachs between the night and early morning time intervals suggested that these fish exhibited a diel feeding pattern with crepuscular periods being the times of highest feeding activity. A higher percentage of empty stomachs (neonates 68% and juveniles 39%) and a significantly lower growth rate (age 0þ year C. limbatus, 0Á62 mm day À1 ; age 1þ year fish, 0Á89 mm day À1 ) could indicate that neonate C. limbatus are less efficient predators than older conspecifics. Journal compilation # 2008 The Fisheries Society of the British IslesNo claim to original US government works

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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.

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.

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 zone (15–30‰) during the spawning season (May–August), when both recruit and spawner abundances had high positive correlations with salinity (P < 0.01). After the spawning season (September–December), spawners were uniformly distributed over all estuarine zones, whereas recruits were significantly more abundant (P < 0.01) in the upper estuarine zone (0–9‰). During this time, recruit spotted seatrout abundance showed a high negative correlation with salinity (P < 0.01).

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

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. The northern Gulf of Mexico supports several of the major United States commercial fisheries, including that for the clupeid gulf menhaden, which is the largest by weight 0NMFS 1981-1984). Like many other commerically important fallwinter spawners in the Gulf, gulf menhaden spawn over the continental shelf. First eggs, then larvae, are transported to estuarine nurseries around the Gulfs perimeter by physical oceanic processes; however, little is known about these shelf circulation patterns. Appropriate currents, suitable environmental conditions, and food availability during transit are necessary if larvae are to reach nursery areas in the proper condition and in sufficient numbers to ensure adequate recruitment. Favorable drift systems can, therefore, influence larval survivorship and year-class strengths of pelagic estuarine species (Nelson et al. 1977; Miller et al. 1984; Norcross and Shaw 1984). Certainly other factors affect gulf menhaden year-class strength, such as predation, growth and survival within the estuaries, and fishing effects (Reintjes 1970). Limited information about continental shelf hydrology and the offshore distribution of larval gulf menhaden had previously led to the idea that winter recruits to northern estuaries along the U.S. Gulf coast were carried across the shelf