The Response of Gastric pH and Motility to Fasting and Feeding in Free Swimming Blacktip Reef Sharks, Carcharhinus melanopterus

In many fish and reptiles, gastric digestion is responsible for the complete breakdown of prey items into semi-liquid chyme. The responses of the stomach to feeding and to periods of fasting are, however, unknown for many lower vertebrates. We inserted data loggers into the stomachs of free-swimming captive adult blacktip reef sharks (Carcharhinus melanopterus) to quantify gastric pH, motility and temperature during fasting and following ingestion of food. Gastric acid secretion was continuous, even during long periods of fasting, with a mean pH of 1.66 ± 0.40 (± 1 SD) when the stomach was empty. Stomach contractions were greater following meals of mackerel than for those of squid. Gastric motility following feeding on mackerel, was positively influenced by ambient temperature, and followed a quadratic relationship with meal size, with maximum motility occurring after meals of 0.8–1.0% body weight. Diel changes in gastric motility were apparent, and were most likely caused by diel changes in ambient temperature. Gastric digestion in blacktip reef sharks is affected by both biotic and abiotic variables. We hypothesize that behavioral strategies adopted by sharks in the field may be an attempt to optimize digestion by selecting for appropriate environmental conditions

Etmopterus lailae Sp Nov., a New Lanternshark (Squaliformes: Etmopteridae) from the Northwestern Hawaiian Islands

A new species of lanternshark, Etmopterus lailae (Squaliformes: Etmopteridae), is described from the Northwestern Hawaiian Islands, in the central North Pacific Ocean. The new species resembles other members of the “Etmopterus lucifer” clade in having linear rows of dermal denticles, and most closely resembles E. lucifer from Japan. The new species occurs along insular slopes around seamounts at depths between 314–384 m. It can be distinguished from other members of the E. lucifer clade by a combination of characteristics, including a longer anterior flank marking branch, arrangement of dermal denticles on the ventral snout surface and body, flank and caudal markings, and meristic counts including number of spiral valve turns, and precaudal vertebrate. A key to species of the Etmopterus lucifer-clade is included

Reef shark science - key questions and future directions

The occurrence of sharks on coral reefs has been well documented for decades, especially since the advent of SCUBA diving. Despite this, it is only within the last decade that substantial research effort has been directed at these species. Research effort has increased in conjunction with the realization that reef shark populations have experienced significant declines throughout their distribution. However, trends in declines have been coupled with reports of high abundance in some areas providing confusion about what healthy reef shark populations should look like. Given that coral reefs are among the most biologically diverse and productive habitats, but also are one of the most threatened by climate change due to the effects of rising temperature and declining pH, there is a need to understand reef sharks to better predict consequences for their populations. Studies of reef sharks also have the potential to provide insights into the functioning of their populations and ecosystems more broadly because of the spatially constrained nature of their distributions, and high water visibility in most locations. These aspects make studying reef shark populations integral to understanding coral reef ecosystem dynamics and resilience to pressures. This paper synthesizes a number of key questions about coral reef sharks based on our experience researching this group of species over the past decade. Key research gaps and critical questions include aspects of life history, population dynamics, ecology, behavior, physiology, energetics, and more. This synthesis also considers the methods used to date, and what new and emerging techniques may be available to improve our understanding of reef shark populations. The synthesis will highlight how even basic questions relating to reef shark population sizes, how large they should be, and what impacts do they have on reef ecosystems, remain either unanswered or highly controversial

Spline-based nonparametric inference in general state-switching models

State‐switching models combine immense flexibility with relative mathematical simplicity and computational tractability and, as a consequence, have established themselves as general‐purpose models for time series data. In this paper, we provide an overview of ways to use penalized splines to allow for flexible nonparametric inference within state‐switching models, and provide a critical discussion of the use of corresponding classes of models. The methods are illustrated using animal acceleration data and energy price data.PostprintPeer reviewe

Drivers of Daily Routines in an Ectothermic Marine Predator: Hunt Warm, Rest Warmer?

Animal daily routines represent a compromise between maximizing foraging success and optimizing physiological performance, while minimizing the risk of predation. For ectothermic predators, ambient temperature may also influence daily routines through its effects on physiological performance. Temperatures can fluctuate significantly over the diel cycle and ectotherms may synchronize behaviour tomatch thermal regimes in order to optimize fitness. We used bio-logging to quantify activity and body temperature of blacktip reef sharks (Carcharhinus melanopterus) at a tropical atoll. Behavioural observations were used to concurrently measure bite rates in herbivorous reef fishes, as an index of activity for potential diurnal prey. Sharks showed early evening peaks in activity, particularly during ebbing high tides, while body temperatures peaked several hours prior to the period of maximal activity. Herbivores also displayed peaks in activity several hours earlier than the peaks in shark activity. Sharks appeared to be least active while their body temperatures were highest and most active while temperatures were cooling, although we hypothesize that due to thermal inertia they were still warmer than their smaller prey during this period. Sharksmay be most active during early evening periods as they have a sensory advantage under low light conditions and/ or a thermal advantage over cooler prey. Sharks swaminto shallow water during daytime low tide periods potentially to warm up and increase rates of digestion before the nocturnal activity period, which may be a strategy to maximize ingestion rates. Hunt warm, rest warmer may help explain the early evening activity seen in other ectothermic predators

Growth and life history variability of the grey reef shark (Carcharhinus amblyrhynchos) across its range

For broadly distributed, often overexploited species such as elasmobranchs (sharks and rays), conservation management would benefit from understanding how life history traits change in response to local environmental and ecological factors. However, fishing obfuscates this objective by causing complex and often mixed effects on the life histories of target species. Disentangling the many drivers of life history variability requires knowledge of elasmobranch populations in the absence of fishing, which is rarely available. Here, we describe the growth, maximum size, sex ratios, size at maturity, and offer a direct estimate of survival of an unfished population of grey reef sharks (Carcharhinus amblyrhynchos) using data from an eight year tag-recapture study. We then synthesized published information on the life history of C. amblyrhynchos from across its geographic range, and for the first time, we attempted to disentangle the contribution of fishing from geographic variation in an elasmobranch species. For Palmyra’s unfished C. amblyrhynchos population, the von Bertalanffy growth function (VBGF) growth coefficient k was 0.05 and asymptotic length L∞ was 163.3 cm total length (TL). Maximum size was 175.5 cm TL from a female shark, length at maturity was estimated at 116.7–123.2 cm TL for male sharks, maximum lifespan estimated from VBGF parameters was 18.1 years for both sexes combined, and annual survival was 0.74 year-1. Consistent with findings from studies on other elasmobranch species, we found significant intraspecific variability in reported life history traits of C. amblyrhynchos. However, contrary to what others have reported, we did not find consistent patterns in life history variability as a function of biogeography or fishing. Ultimately, the substantial, but not yet predictable variability in life history traits observed for C. amblyrhynchos across its geographic range suggests that regional management may be necessary to set sustainable harvest targets and to recover this and other shark species globally

Activity seascapes highlight central place foraging strategies in marine predators that never stop swimming

Background: Central place foragers (CPF) rest within a central place, and theory predicts that distance of patches from this central place sets the outer limits of the foraging arena. Many marine ectothermic predators behave like CPF animals, but never stop swimming, suggesting that predators will incur ‘travelling’ costs while resting. Currently, it is unknown how these CPF predators behave or how modulation of behavior contributes to daily energy budgets. We combine acoustic telemetry, multi-sensor loggers, and hidden Markov models (HMMs) to generate ‘activity seascapes’, which combine space use with patterns of activity, for reef sharks (blacktip reef and grey reef sharks) at an unfished Pacific atoll. Results: Sharks of both species occupied a central place during the day within deeper, cooler water where they were less active, and became more active over a larger area at night in shallower water. However, video cameras on two grey reef sharks revealed foraging attempts/success occurring throughout the day, and that multiple sharks were refuging in common areas. A simple bioenergetics model for grey reef sharks predicted that diel changes in energy expenditure are primarily driven by changes in swim speed and not body temperature. Conclusions: We provide a new method for simultaneously visualizing diel space use and behavior in marine predators, which does not require the simultaneous measure of both from each animal. We show that blacktip and grey reef sharks behave as CPFs, with diel changes in activity, horizontal and vertical space use. However, aspects of their foraging behavior may differ from other predictions of traditional CPF models. In particular, for species that never stop swimming, patch foraging times may be unrelated to patch travel distance

Reef Shark Science – Key Questions and Future Directions

The occurrence of sharks on coral reefs has been well documented for decades, especially since the advent of SCUBA diving. Despite this, it is only within the last decade that substantial research effort has been directed at these species. Research effort has increased in conjunction with the realization that reef shark populations have experienced significant declines throughout their distribution. However, trends in declines have been coupled with reports of high abundance in some areas providing confusion about what healthy reef shark populations should look like. Given that coral reefs are among the most biologically diverse and productive habitats, but also are one of the most threatened by climate change due to the effects of rising temperature and declining pH, there is a need to understand reef sharks to better predict consequences for their populations. Studies of reef sharks also have the potential to provide insights into the functioning of their populations and ecosystems more broadly because of the spatially constrained nature of their distributions, and high water visibility in most locations. These aspects make studying reef shark populations integral to understanding coral reef ecosystem dynamics and resilience to pressures. This paper synthesizes a number of key questions about coral reef sharks based on our experience researching this group of species over the past decade. Key research gaps and critical questions include aspects of life history, population dynamics, ecology, behavior, physiology, energetics, and more. This synthesis also considers the methods used to date, and what new and emerging techniques may be available to improve our understanding of reef shark populations. The synthesis will highlight how even basic questions relating to reef shark population sizes, how large they should be, and what impacts do they have on reef ecosystems, remain either unanswered or highly controversial

Spatial Connectivity and Drivers of Shark Habitat Use Within a Large Marine Protected Area in the Caribbean, The Bahamas Shark Sanctuary

Marine protected areas (MPAs) have emerged as potentially important conservation tools for the conservation of biodiversity and mitigation of climate impacts. Among MPAs, a large percentage has been created with the implicit goal of protecting shark populations, including 17 shark sanctuaries which fully protect sharks throughout their jurisdiction. The Commonwealth of the Bahamas represents a long-term MPA for sharks, following the banning of commercial longlining in 1993 and subsequent designation as a shark sanctuary in 2011. Little is known, however, about the longterm behavior and space use of sharks within this protected area, particularly among reef-associated sharks for which the sanctuary presumably offers the most benefit. We used acoustic telemetry to advance our understanding of the ecology of such sharks, namely Caribbean reef sharks (Carcharhinus perezi) and tiger sharks (Galeocerdo cuvier), over two discrete islands (New Providence and Great Exuma) varying in human activity level, over 2 years. We evaluated which factors influenced the likelihood of detection of individuals, analyzed patterns of movement and occurrence, and identified variability in habitat selection among species and regions, using a dataset of 23 Caribbean reef sharks and 15 tiger sharks which were passively monitored in two arrays with a combined total of 13 acoustic receivers. Caribbean reef sharks had lower detection probabilities than tiger sharks, and exhibited relatively low habitat connectivity and high residency, while tiger sharks demonstrated wider roaming behavior across much greater space. Tiger sharks were associated with shallow seagrass habitats where available, but frequently transited between and connected different habitat types. Our data support the notion that large MPAs afford greater degrees of protection for highly resident species such as Caribbean reef sharks, shark, acoustic telemetry, marine protected area, MPA, seagrass, coral reef, Bahamas, Caribbea