Growth dynamics of the spinner shark (Carcharhinus brevipinna) off the United States southeast and Gulf of Mexico coasts: a comparison of methods

The age and growth dynamics of the spinner shark (Carcharhinus brevipinna) in the northwest Atlantic Ocean off the southeast United States and in the Gulf of Mexico were examined and four growth models were used to examine variation in the ability to fit size-at-age data. The von Bertalanffy growth model, an alternative equation of the von Bertalanffy growth model with a size-at-birth intercept, the Gompertz growth model, and a logistic model were fitted to sex-specific observed size-at-age data. Considering the statistical criteria (e.g., lowest mean square error [MSE], high coefficient-of-determination, and greatest level of significance) we desired for this study, the logistic model provided the best overall fit to the size-at-age data, whereas the von Bertalanffy growth model gave the worst. For “biological validity,” the von Bertalanffy model for female sharks provided estimates similar to those reported in other studies. However, the von Bertalanffy model was deemed inappropriate for describing the growth of male spinner sharks because estimates of theoretical maximum size (L∞) indicated a size much larger than that observed in the field. However, the growth coefficient (k= 0.14/yr) from the Gompertz model provided an estimate most similar to that reported for other large coastal species. The analysis of growth for spinner shark in the present study demonstrates the importance of fitting alternative models when standard models fit the data poorly or when growth estimates do not appear to be realistic

Signal theoretic characterization of a function using positive exponential basis functions

A signal theory characterization of a time function or signal is a representation of the function throughout a sample interval by an orthogonal basis function expansion. The characterization described here obtains the coefficients in the expansion by processing the input waveform, in real time, through a system of three terminal passive RC filters. The outputs of the filters are sampled periodically and the coefficients of the basis function expansion in that interval are related to these values. The basis functions result from an exponential transformation applied to the Legendre polynomials and are orthogonal in time over the sample interval. The basis functions and the resulting reconstruction appear as summations of positive exponential terms. Different signals may require different sampling intervals and/or different number of terms in their orthogonal expansions. As a result, the input waveforms have been classified in the time domain by two methods. One is a graphical method. The worst case input to the system is bounded by simple test functions. The shortest duration of the resulting test functions gives the sample interval. The rate of convergence of the mean-square error of the approximation is also given for the various forms of the test function. The graphical technique is easy to use, but gives conservative error estimates. The input waveform is also classified in terms of the pole locations of the Laplace-transformed input function. Using conventional time domain synthesis techniques, the pole locations of the transformed input function can be located in the complex-S plane. Bounding these poles by circles, with center at the origin of the S plane, will give the maximum signal reconstruction error for a given number of filters. The sampling period is based on a normalized rate and the frequency scaling required to move the poles into desirable maximum error regions of the S plane determines the actual sampling rate. These regions are very broad and thus a considerable change in the pole positions can be tolerated without affecting the parameters of the system. This method is more analytical than the first method, although more work is required to find the pole locations --Abstract, page ii-iii

Age and Growth of the Sandbar Shark (Carcharhinus plumbeus) from the Northern Gulf of Mexico and the Western North Atlantic Ocean

Age and growth analysis of the sandbar shark, Carcharhinus plumbeus, from the northern Gulf of Mexico and western North Atlantic Ocean was completed with vertebral samples (n = 1,194). Three parameter von Bertalanffy growth curves were run for male and female sandbar sharks separately, and growth parameters were estimated: theoretical maximum length (L∞) = 172.9 ± 1.3 cm straight-line fork length [FL], growth coefficient (k) = 0.15 ± 0.01 yr-1, x-intercept (t0) = 22.3 ± 0.2 SE (male); and L∞ = 181.2 ± 1.5 cm FL, k = 0.12 ± 0.01 yr-1, t0 = 23.1 ± 0.2 SE (female). The oldest sandbar shark was a 27-yr-old female, and the oldest male was 22 yr old. The age and growth parameters estimated during this study differed from those in previous studies. The differences in the age and growth parameters may indicate growth overfishing, or they may be due to the bias in sampling from a fishery that targets a limited size range of sharks

High Post-Capture Survival for Sharks, Rays and Chimaeras Discarded in the Main Shark Fishery of Australia?

Most sharks, rays and chimaeras (chondrichthyans) taken in commercial fisheries are discarded (i.e. returned to the ocean either dead or alive). Quantifying the post-capture survival (PCS) of discarded species is therefore essential for the improved management and conservation of this group. For all chondrichthyans taken in the main shark fishery of Australia, we quantified the immediate PCS of individuals reaching the deck of commercial shark gillnet fishing vessels and applied a risk-based method to semi-quantitatively determine delayed and total PCS. Estimates of immediate, delayed and total PCS were consistent, being very high for the most commonly discarded species (Port Jackson shark, Australian swellshark, and spikey dogfish) and low for the most important commercial species (gummy and school sharks). Increasing gillnet soak time or water temperature significantly decreased PCS. Chondrichthyans with bottom-dwelling habits had the highest PCS whereas those with pelagic habits had the lowest PCS. The risk-based approach can be easily implemented as a standard practice of on-board observing programs, providing a convenient first-step assessment of the PCS of all species taken in commercial fisheries

Atlas of marine bony fish otoliths (Sagittae) of Southeastern - Southern Brazil Part I: Gadiformes (Macrouridae, Moridae, Bregmacerotidae, Phycidae and Merlucciidae); Part II: Perciformes (Carangidae, Sciaenidae, Scombridae and Serranidae)

The drawings, detailed pictures, precise descriptions and measurements that characterize otoliths must be made available for studies in various areas, including taxonomy, phylogeny, ecology, fisheries, paleontology, diversity, predator-prey relationships and modeling. The Collection of Teleostei Fish Otoliths of Southeastern-Southern Brazil (COSS-Brasil) of IOUSP contains 45,000 pairs of otoliths from 210 species. This publication is the first in a series that will constitute an atlas of Teleostei otoliths for southeastern-southern Brazil and presents the results of the morphologic and morphometric analyses of 11 Gadiformes and 36 Perciformes species by means of the most commonly used features, measurements and indices. Three otoliths of each species were illustrated and photographed whenever possible. The frequency of occurrence was calculated for each characteristic by total length classes (TL), and the ontogenetic differences were analyzed (multiple χ2 test; significance 0.05). Morphometric analyses were conducted for each characteristic per total length (TL) class and for the whole sample, and the ontogenetic differences were analyzed

Deepwater fisheries of the MesoAmerican Region

Deepwater (>150 m) fishes tend to have life history characteristics, such as slow growth, late age of maturity, and long lives, which make them especially vulnerable to overfishing. World-wide, deepwater fisheries are often overexploited and in a state of collapse prior to the collection of biological data or oversight by fisheries managers. In the western Caribbean, shallow coastal fisheries are overfished, leading fishers to explore the nearshore deepwater fishing grounds to supplement income. Though deepwater fisheries are widespread throughout the Caribbean Sea, little information is available about the grouper and snapper species targeted across the region. This thesis aims to fill crucial data gaps on the fish and fisheries in the MesoAmerican countries of Mexico, Belize, Guatemala, and Honduras in the western Caribbean and to provide practical, low cost, and meaningful tools for managers and conservation groups to inform management going forward. In Chapter I, I characterize the fishery in each of the four MesoAmerican countries to determine the scope and history of deepwater fishing in the region. Chapter II focuses on the spatial and depth distributions of targeted grouper and snapper species in Belize and Honduras, and investigates whether higher fishing rates have already affected deepwater species in Honduras. For Chapter III, several life history characteristics of an important deepwater snapper species are investigated, using bomb radiocarbon dating to validate the ageing protocol and determine the longevity of a snapper species that is important to the fishery across the region. The analysis introduces a low-cost method for ageing cardinal snappers using otolith morphology. Finally, Chapter IV brings these data together to provide an Ecological Risk Assessment for the Effects of Fishing and Management for ten commercially important species, as well as a practical toolkit for stakeholders that is user-friendly and open access. The toolkit provides guidance for producing a Productivity and Susceptibility Assessment, and gives specific recommendations based on user inputs. This dissertation provides evidence that deepwater fishes are vulnerable to overexploitation by small-scale fisheries, and shows that practical conservation and management measures, such as time area closures are necessary for the continuation of the fishery

Acoustic telemetry of grey reef sharks in Micronesia

VEMCO vrl files, cleaned and aggregated in R. Each row represents one detection by one of 20 tagged grey reef sharks. Data columns include Station Name for each receiver, Latitude and Longitude for each receiver, Date.Time (the date and time of each transmitter detection), Detections (dummy variable equal to 1 for ease of summarization), Transmitter_ID (the Transmitter unique identification number), and Source (where the shark was originally tagged)

Grouper (Epinephelidae) spawning aggregations affect activity space of grey reef sharks, Carcharhinus amblyrhynchos, in Pohnpei, Micronesia.

Fish spawning aggregations (FSA) act as biological hotspots that concentrate food and nutrients across a broad trophic spectrum. In Pohnpei (Federated States of Micronesia), 20 female grey reef sharks (Carcharhinus amblyrhynchos) were acoustically tagged at two multi-species grouper (Epinephelidae) FSA to examine the likelihood that these mesopredators utilize FSA as a seasonal food source. Both FSA sites are within small-scale MPAs, thus providing a secondary opportunity to examine their conservation potential during these ephemeral events. Shark movement and residency was gauged against known spatial and temporal grouper reproductive patterns using an array of 15 and 50 acoustic receivers at Ant Atoll and Pohnpei (Island), respectively. Activity space was investigated using Kernel Density estimates of individual sharks, and residency indices (RI) were analyzed based on daily and monthly occurrence at the array. Three distinct residency patterns were identified: transient, semi-transient, or resident (Daily RI 0.40 to 0.80, or >0.80, respectively). Generalized linear mixed models (GLMMs) were used to identify biological and environmental factors influencing shark activity space, including month, temperature, shark size, spawning month, and residency pattern. Findings revealed significant changes in average monthly residency indices and kernel densities during spawning months in support of an opportunistic foraging strategy around FSA. Monthly residency was higher during spawning months among semi-resident and transient sharks, while average monthly activity space was concentrated around FSA. Best-fit models for the GLMM indicated that activity spaces were most influenced by month and grouper spawning month. Seven of 20 sharks demonstrated inter-island movement and wide variations in individual movement and spatial requirements were shown. The concentration of sharks and groupers at unprotected FSA sites increases their vulnerability to fishing and supports the need for combined area and non-area management measures to effectively protect these species

Data from: Grouper (Epinephelidae) spawning aggregations affect activity space of grey reef sharks, Carcharhinus amblyrhynchos, in Pohnpei, Micronesia

Fish spawning aggregations (FSA) act as biological hotspots that concentrate food and nutrients across a broad trophic spectrum. In Pohnpei (Federated States of Micronesia), 20 female grey reef sharks (Carcharhinus amblyrhynchos) were acoustically tagged at two multi-species grouper (Epinephelidae) FSA to examine the likelihood that these mesopredators utilize FSA as a seasonal food source. Both FSA sites are within small-scale MPAs, thus providing a secondary opportunity to examine their conservation potential during these ephemeral events. Shark movement and residency was gauged against known spatial and temporal grouper reproductive patterns using an array of 15 and 50 acoustic receivers at Ant Atoll and Pohnpei (Island), respectively. Activity space was investigated using Kernel Density estimates of individual sharks, and residency indices (RI) were analyzed based on daily and monthly occurrence at the array. Three distinct residency patterns were identified: transient, semi-transient, or resident (Daily RI 0.400.80, respectively). Generalized linear mixed models (GLMMs) were used to identify biological and environmental factors influencing shark activity space, including month, temperature, shark size, spawning month, and residency pattern. Findings revealed significant changes in average monthly residency indices and kernel densities during spawning months in support of an opportunistic foraging strategy around FSA. Monthly residency was higher during spawning months among semi-resident and transient sharks, while average monthly activity space was concentrated around FSA. Best-fit models for the GLMM indicated that activity spaces were most influenced by month and grouper spawning month. Seven of 20 sharks demonstrated inter-island movement and wide variations in individual movement and spatial requirements were shown. The concentration of sharks and groupers at unprotected FSA sites increases their vulnerability to fishing and supports the need for combined area and non-area management measures to effectively protect these species