Descriptions of larval, prejuvenile, and juvenile finescale menhaden (Brevoortia gunteri) (family Clupeidae), and comparisons to gulf menhaden (B. patronus)

Larval and juvenile development of finescale menhaden (Brevoortia gunteri) is described for the first time by using wild-caught individuals from Nueces Bay, Texas, and is compared with larval and juvenile development of co-occurring gulf menhaden (B. patronus). Meristics, morphometrics, and pigmentation patterns were examined as development proceeded. An illustrated series of finescale menhaden is presented to show changes that occurred during development. For finescale menhaden, transformation to the juvenile stage was completed by 17−19 mm standard length (SL). By contrast, transformation to the juvenile stage for gulf menhaden was not complete until 23−25 mm SL. Characteristics useful for separating larval and juvenile finescale menhaden from gulf menhaden included 1) the presence or absence of pigment at the base of the insertion of the pelvic fins; 2) the standard length at which medial predorsal pigment occurs; 3) differences in the number of dorsal fin ray elements; and, 4) the number of vertebrae.

Effect of Cattail (Typha domingensis) Extracts, Leachates, and Selected Phenolic Compounds on Rates of Oxygen Production by Salvinia (Salvinia minima)

Salvinia (Salvinia minima Willd.) is a water fern found in Florida waters, usually associated with Lemna and other small free-floating species. Due to its buoyancy and mat-forming abilities, it is spread by moving waters. In 1994, salvinia was reported to be present in 247 water bodies in the state (out of 451 surveyed public waters, Schardt 1997). It is a small, rapidly growing species that can become a nuisance due to its explosive growth rates and its ability to shade underwater life (Oliver 1993). Any efforts toward management of salvinia populations must consider that, in reasonable amounts, its presence is desirable since it plays an important role in the overall ecosystem balance. New management alternatives need to be explored besides the conventional herbicide treatments; for example, it has been shown that the growth of S. molesta can be inhibited by extracts of the tropical weed parthenium (Parthenium hysterophorus) and its purified toxin parthenin (Pande 1994, 1996). We believe that cattail, Typha spp. may be a candidate for control of S. minima infestations. Cattail is an aggressive aquatic plant, and has the ability to expand over areas that weren't previously occupied by other species (Gallardo et al. 1998a and references cited there). In South Florida, T. domingensis is a natural component of the Everglades ecosystem, but in many cases it has become the dominant marsh species, outcompeting other native plants. In Florida public waters, this cattail species is the most dominant emergent species of aquatic plants (Schardt 1997). Several factors enable it to accomplish opportunistic expansion, including size, growth habits, adaptability to changes in the surroundings, and the release of compounds that can prevent the growth and development of other species. We have been concerned in the past with the inhibitory effects of the T. domingensis extracts, and the phenolic compounds mentioned before, towards the growth and propagation of S. minima (Gallardo et al. 1998b). This investigation deals with the impact of cattail materials on the rates of oxygen production of salvinia, as determined through a series of Warburg experiments (Martin et al. 1987, Prindle and Martin 1996).

Survey Assessment of Semi-pelagic Gadoids: The Example of Walleye Pollock, Theragra chalcogramma, in the Eastern Bering Sea

Assessment of walleye pollock, Theragra chalcogramma, in the eastern Bering Sea is complicated because the species is semi-pelagic in habit. Annual bottom trawl surveys provide estimates of demersal abundance on the eastern Bering Sea shelf. Every third year (starting in 1979), an extended area of the shelf and slope is surveyed and an echo integration-midwater trawl survey provides estimates of pollock abundance in midwater. Overall age-specific population and biomass estimates are obtained by summing the demersal and midwater results, assuming that the bottom trawl samples only pollock inhabiting the lower 3 m of the water column. Total population estimates have ranged from 134 x 109 fish in 1979 to 27 x 109 fish in 1988. The very high abundance observed in 1979 reflects the appearance of the unusually large 1978 year class. Changes in age-specific abundance estimates have documented the passage of strong (1978, 1982, and 1984) and weak year classes through the fishery. In general, older fish are more demersally oriented and younger fish are more abundant in midwater, but this trend was not always evident in the patterns of abundance of 1- and 2-year-old fish. As the average age of the population has increased, so has the relative proportion of pollock estimated by the demersal surveys. Consequently, it is unlikely that either technique can be used independently to monitor changes in abundance and age composition. Midwater assessment depends on pelagic trawl samples for size and age composition estimates, so both surveys are subject to biases resulting from gear performance and interactions between fish and gear. In this review, we discuss survey methodology and evaluate assumptions regarding catchability and availability as they relate to demersal, midwater, and overall assessment.

A general framework for integrating environmental time series into stock assessment models: model description, simulation testing, and example

We present a method to integrate environmental time series into stock assessment models and to test the significance of correlations between population processes and the environmental time series. Parameters that relate the environmental time series to population processes are included in the stock assessment model, and likelihood ratio tests are used to determine if the parameters improve the fit to the data significantly. Two approaches are considered to integrate the environmental relationship. In the environmental model, the population dynamics process (e.g. recruitment) is proportional to the environmental variable, whereas in the environmental model with process error it is proportional to the environmental variable, but the model allows an additional temporal variation (process error) constrained by a log-normal distribution. The methods are tested by using simulation analysis and compared to the traditional method of correlating model estimates with environmental variables outside the estimation procedure. In the traditional method, the estimates of recruitment were provided by a model that allowed the recruitment only to have a temporal variation constrained by a log-normal distribution. We illustrate the methods by applying them to test the statistical significance of the correlation between sea-surface temperature (SST) and recruitment to the snapper (Pagrus auratus) stock in the Hauraki Gulf–Bay of Plenty, New Zealand. Simulation analyses indicated that the integrated approach with additional process error is superior to the traditional method of correlating model estimates with environmental variables outside the estimation procedure. The results suggest that, for the snapper stock, recruitment is positively correlated with SST at the time of spawning.

Climatic effects on flood frequency: an example from southern Arizona

EXTRACT (SEE PDF FOR FULL ABSTRACT): After 1960, the Santa Cruz River at Tucson, Arizona, an ephemeral stream normally dominated by summer floods, experienced an apparent increased frequency of flooding coincident with an increased percentage of annual floods occurring in fall and winter. This shift reflects large-scale and low-frequency changes in the eastern Pacific Ocean, in part associated with El Niño-Southern Oscillation (ENSO) phenomena. ... Questions are raised about the validity of standard methods of flood-frequency analysis to estimate regulatory and designed floods.

The fish stocks in Uganda aquatic systems: opportunities and challenges for transformation

The status of fish stocks in a water body at any one time is a function of several factors affecting the production of fish in that water body. These include: total number (abundance) and biomass(weight) present, growth (size and age), recruitment (the quantity of fish entering the fishery) including reproduction, mortality which is caused by fishing or natural causes, Other indirect factors of major importance to the status of the stocks include production factors (water quality and availability of natural food for fish), the life history parameters of the different species making up the stocks (e.g. sex ratios, condition of the fish, reproductive potential (i.e. fecundity) etc), Changes in fish stocks do occur when any of the above listed factors directly influence aspects of growth, reproduction and mortality and therefore, numbers and standing stock (biomass). In the exploited fisheries, major research concerns regarding stocks relate to the listed factors especially: estimates of stock abundance/biomass, the quantity of fish being caught,where the fish are caught, which species are caught (relative abundance)when the fish are caught, how the fish are caught. The balance between stock abundance and amount of fish caught provides the basis for intervention. Due to the diverse characteristics of the physical water environment, fishes are in general, not evenly distributed throughout a water body. Shallow and vegetated areas tend to support higher abundance and diversity of fish species. In addition, seasonal variations in fish abundance are so strong that fluctuations in catch have to be expected at fish landings.