Automated, objective texture segmentation of multibeam echosounder data - Seafloor survey and substrate maps from James Island to Ozette Lake, Washington Outer Coast

Without knowledge of basic seafloor characteristics, the ability to address any number of critical marine and/or coastal management issues is diminished. For example, management and conservation of essential fish habitat (EFH), a requirement mandated by federally guided fishery management plans (FMPs), requires among other things a description of habitats for federally managed species. Although the list of attributes important to habitat are numerous, the ability to efficiently and effectively describe many, and especially at the scales required, does not exist with the tools currently available. However, several characteristics of seafloor morphology are readily obtainable at multiple scales and can serve as useful descriptors of habitat. Recent advancements in acoustic technology, such as multibeam echosounding (MBES), can provide remote indication of surficial sediment properties such as texture, hardness, or roughness, and further permit highly detailed renderings of seafloor morphology. With acoustic-based surveys providing a relatively efficient method for data acquisition, there exists a need for efficient and reproducible automated segmentation routines to process the data. Using MBES data collected by the Olympic Coast National Marine Sanctuary (OCNMS), and through a contracted seafloor survey, we expanded on the techniques of Cutter et al. (2003) to describe an objective repeatable process that uses parameterized local Fourier histogram (LFH) texture features to automate segmentation of surficial sediments from acoustic imagery using a maximum likelihood decision rule. Sonar signatures and classification performance were evaluated using video imagery obtained from a towed camera sled. Segmented raster images were converted to polygon features and attributed using a hierarchical deep-water marine benthic classification scheme (Greene et al. 1999) for use in a geographical information system (GIS). (PDF contains 41 pages.)

The head-body weight and head-body length relationship of Synodontis schall (Bloch and Schneider 1801) in Asa Lake, Ilorin, Nigeria

A total of 710 specimens of Synodontis schall were analyzed for the head body weight and head body length relationship. The head constituted 40% of the total body weight and 30% of the total body length. The mean head weight for male and female computed was 23.90g and 29.13g respectively. Head weight in both male and female was significantly different (P<0.01) while the head length for the combined sexes showed no significant difference (P>0.05). Fat accumulation in the body tissue was prominent in the females than males usually before the breeding season. The significance of the cephalo-nuchal shield in the bony head of Synodontis species compared with some other catfishes in the lake was also discussed

James's rule and causes and consequences of a latitudinal cline in the demography of John's Snapper (Lutjanus johnii) in coastal waters of Australia

Demographic parameters were derived from sectioned otoliths of John’s Snapper (Lutjanus johnii) from 4 regions across 9° of latitude and 23° of longitude in northern Australia. Latitudinal variation in size and growth rates of this species greatly exceeded longitudinal variation. Populations of John’s Snapper farthest from the equator had the largest body sizes, in line with James’s rule, and the fastest growth rates, contrary to the temperature-size rule for ectotherms. A maximum age of 28.6 years, nearly 3 times previous estimates, was recorded and the largest individual was 990 mm in fork length. Females grew to a larger mean asymptotic fork length (L∞) than did males, a finding consistent with functional gonochorism. Otolith weight at age and gonad weight at length followed the same latitudinal trends seen in length at age. Length at maturity was ~72–87% of L∞ and varied by ~23% across the full latitudinal gradient, but age at first maturity was consistently in the range of 6–10 years, indicating that basic growth trajectories were similar across vastly different environments. We discuss both the need for complementary reproductive data in age-based studies and the insights gained from experiments where the concept of oxygen- and capacity-limited thermal tolerance is applied to explain the mechanistic causes of James’s rule in tropical fish species.

Age, growth and mortality of the toadfish, Halobatrachus didactylus (Schneider, 1801) (Pisces: Batrachoididae), in the Bay of Cádiz (southwestern Spain)

Age, growth and mortality of the toadfish, Halobatrachus didactylus, were determined by examination of the whole sagittal otoliths of fish sampled in the Bay of Cádiz (southwestern Spain) from March 1999 to March 2000. A total of 844 specimens (425 males, 416 females, and 3 of indeterminate sex), ranging from 95 to 470 mm in total length were examined. Eighty-nine percent of the otoliths could be read allowing an age estimation. The opaque zone was formed between April and May coincident with the maximum reproductive peak, while the translucent zone formed mainly in summer-fall (June to December). Maximum ages for males and females were 12 and 10 years, respectively. The samples were dominated by 2- to 6-year-old specimens. Males matured at an age of approximately 2 years and females at 3 years. Fish total length and otolith radius were closely related. The von Bertalanffy growth curve was used to describe growth. The parameters were derived from back-calculated length-at-age. Significant differences in the growth parameters were found between sexes. Although the growth analysis revealed that this species is slow-growing, males reached larger sizes than females. Females appeared to experience higher natural mortality rates than males.

Anchorage of air bladder with the interspinous bone of the anal fin in Lactarius lactarius (Bloch and Schneider, 1801)

Specimens of the false trevally (Lactarius lactarius ), 127 to 221 mm in total length, were studied for the mode of anchorage of the air-bladder with the interspinous bone of the anal fin. The 1st and 2nd interspinous bones are fused together into a single piece (named here as the anchor bone) which pierces through the air-bladder, dividing it into two intercommunicating chambers at its upper end, and ultimately articulates with the 10th vertebral bone. The lower end of the bone is broad, fan like with one side affording articulation with the 1st and 2nd anal spines. This is an unique feature of great taxonomical importance to L. lactarius, the only species in the family Lactariidae. The anal fin counts (23-27) and vertebral counts (23) are also given.