Rapid growth of popular and lucrative catch-and-release marine sportfisheries worldwide has high- lighted the need for reliable weight estimation methods for use in fishing tournaments, pursuit of fishing records, and to support scientific research that allows captured fish to be released alive. This paper describes new methods to predict weight from measurements of body size of game fish. Here we also evaluated efficacy of a widely used historical model and compared this to several new statistical and analytical weight estimation models that we developed herein. We applied these candidate models to a unique morphometric data set on Atlantic tarpon ( Megalops atlanticus ) which contained information on body weight W as a function of fork length L and dorsal girth G for more than 1100 individuals from Florida, the Gulf of Mexico, Caribbean Sea and western Africa. A popular formula ( W = G 2 L/800), devel- oped more than a century ago specifically for tarpon was originally derived from geometric and physical relationships between fish body weight and shape. [...]
We evaluated vertical depth and thermal habitat utilization of Atlantic tarpon Mega- lops atlanticus from high-resolution temporal data on 42 recovered pop-up archival transmitting (PAT) tags deployed and recovered from 2002 to 2010 to estimate vertical movement rates (swim speeds) during descents and ascents. All individuals strongly preferred shallow waters, spending > 80% of their time in water depths <10 m. Diel vertical distributions followed 4 patterns, but there was substantial variation within and among individuals. Vertical descent and ascent rates, defined as changes in depths extending ≥ 2 m over time, were estimated from tag data with 1 s sampling intervals. Descent rates ranged from 0.01 to 2.74 m s −1 , while ascent rates ranged from 0.01 to 4.5 m s −1 . Relatively uncommon deep diving behaviors might be associated with spawning activ- ity. The most preferred water temperature was ~26°C, particularly during the spring and fall migratory periods. However, these reached > 29°C in summer when tarpon were at their feeding grounds at the northern extreme of their range. Peaks of ‘rolling and jumping’ behaviors inferred from relative conductivity sensor data occurred with greatest frequency just after sunset and sunrise. [...]
Hammerschlag, N., Luo, J., Irschick, D.J., & Ault, J.S. 2012. A comparison of spatial and movement patterns between sympatric predators: bull sharks (Carcharhinus leucas) and Atlantic tarpon (Megalops atlanticus). PLOS ONE 7(9): 1-14.
Background: Predators can impact ecosystems through trophic cascades such that differential patterns in habitat use can lead to spatiotemporal variation in top down forcing on community dynamics. Thus, improved understanding of predator movements is important for evaluating the potential ecosystem effects of their declines. Methodology/Principal Findings: We satellite-tagged an apex predator (bull sharks, Carcharhinus leucas ) and a sympatric mesopredator (Atlantic tarpon, Megalops atlanticus ) in southern Florida waters to describe their habitat use, abundance and movement patterns. We asked four questions: (1) How do the seasonal abundance patterns of bull sharks and tarpon compare? (2) How do the movement patterns of bull sharks and tarpon compare, and what proportion of time do their respective primary ranges overlap? (3) Do tarpon movement patterns (e.g., straight versus convoluted paths) and/or their rates of movement (ROM) differ in areas of low versus high bull shark abundance? and (4) Can any general conclusions be reached concerning whether tarpon may mitigate risk of predation by sharks when they are in areas of high bull shark abundance? [...]
Hammerschlag, N., Gallagher, A., Wester, J., Luo, J., &Ault, J.S. 2012.Don’t bite the hand that feeds: Assessing ecological impacts of provisioning ecotourism on an apex marine predator. Functional Ecology 26(3): 567-576.
Summary: 1. There has been considerable debate over the past decade with respect to wildlife provisioning, especially resultant behavioural changes that may impact the ecological function of an apex predator. The controversy is exemplified by the shark diving industry, where major criticisms based on inference, anecdote and opinion stem from concerns of potential behaviourally medi- ated ecosystem effects because of ecotourism provisioning ( aka ‘chumming’ or feeding). 2. There is a general lack of empirical evidence to refute or support associated claims. The few studies that have investigated the behavioural impacts of shark provisioning ecotourism have generated conflicting conclusions, where the confidence in such results may suffer from a narrow spatial and temporal focus given the highly mobile nature of these predators. There is need for studies that examine the potential behavioural consequences of provisioning over ecologically relevant spatial and temporal scales. 3. To advance this debate, we conducted the first satellite telemetry study and movement analy- sis to explicitly examine the long-range migrations and habitat utilization of tiger sharks ( Gale- ocerdo cuvier ) originating in the Bahamas and Florida, two areas that differ significantly with regards to the presence ⁄ absence of provisioning ecotourism. [...]