Environmental Biology of Fishes最新文献

During elasmobranch ontogeny, increasing body size has been proposed to result in a tradeoff between increased sensitivity and decreased spatial resolution of the electrosensory system, but this hypothesis has not previously been tested. Further, the sensitivity of the electrosensory system has not been examined in any large sharks. In the present study, we examined the behavioral electrosensitivity of large (likely adult) sandbar sharks to prey-simulating electric fields, compared with previously published results for small (juvenile) sandbar sharks. We found that the large sandbar sharks, which were approximately three times larger than the small juveniles previously tested, had lower minimum (0.002 nV/cm) and median (0.5 nV/cm) response thresholds. These represent the lowest sensitivity thresholds of any elasmobranch studied to date. Since electric field detection plays an important role in feeding behavior, increases in sensitivity of the electrosensory system and the corresponding increase in electric field detection distance with growth may be linked to ontogenetic dietary changes.

One of the most conspicuous impacts of dam construction on fish is the blocking of their migratory routes. However, the formation of the reservoir, a lentic environment with distinct hydrological and ecological characteristics, can also constitute an obstacle to migration. This impact, however, is poorly explored in the scientific literature. Therefore, this study aimed to assess the movements of Prochilodus argenteus tagged with radio telemetry transmitters and manually translocated across the Três Marias Dam in the São Francisco River. The Três Marias reservoir covers an area of 1090 km² and ranks among the largest artificial reservoirs in Brazil. Individuals translocated to the Três Marias reservoir showed reduced movement rates and home ranges. They appeared disoriented in the new environment, with many of them settling near fish farms and remaining there throughout the study period. A comparative analysis with existing literature on Neotropical species’ reproductive migration through artificial reservoirs revealed a trend: the ability of migratory fish to navigate reservoirs diminishes with their area, especially those exceeding 50 km² or with a residence time surpassing 30 days. These results indicate that caution is needed when designing fish passage facilities for dams that form larger artificial reservoirs in the Neotropics. Even if these facilities are efficient in attracting and translocating migratory species, behavioral and physiological thresholds may prevent them from reaching suitable areas to complete their reproductive cycle in the new environment formed.

The silvertip shark (Carcharhinus albimarginatus) is a reef-associated shark widely distributed across the Indo-Pacific. However, it has been poorly studied and little is known about its spatial ecology, particularly about long-range travels. In this study, we investigated the residency and movement patterns of silvertip sharks in a widespread remote archipelago offshore the Pacific coast of Mexico, the Revillagigedo Archipelago. An array of 10 VR2W receivers was deployed around the archipelago to monitor the movement of 45 silvertip sharks during 11 years. Among the 40 sharks detected during the study, 34 exhibited high site fidelity with 70% of their daily detections recorded in one particular site. Residency index ranged from 0.049 to 0.99 with an average residency of 0.49 ± 0.27 (SD). The sharks exhibited strong diurnal patterns in horizontal and vertical movements with two peaks of detections at sunrise and sunset and a presence in deeper waters during daytime. Eleven individuals (7 adult females) traveled from one island to another (separated by distances ranging from 60 to 425 km). Geographical ontogenetic segregation was observed within the archipelago with juveniles being present only around San Benedicto and Socorro islands. Five sharks tagged as juveniles left their tagging island once they had reached adulthood, three males between 8 and 10 years old and two females at 11 years old.

Abstract

Studying the behavior of pelagic sharks can be challenging due to the logistical difficulties of locating migratory individuals in the open ocean. This is further compounded by their rarity in certain ocean regions due to overfishing. The accessibility of deep-water basins in The Bahamas provides a unique model system for describing how pelagic sharks connect surface and deep ocean habitats through vertical behavior. Using custom deep-sea landers in The Bahamas, we provide novel depth data for two species of pelagic sharks: a depth range extension for the dusky shark at 767 m and novel occurrence at twilight zone depth for the silky shark at 470 m. These observations expand the vertical niche for these two species, suggesting that deep diving behavior is likely more common than previously thought and likely important for ecosystem connectivity.

This study employed aerial surveys to quantify the spatial and temporal abundance of the whitespotted eagle ray, Aetobatus narinari, and the giant manta ray, Mobula birostris, in southeast Florida. Aetobatus narinari abundance did not differ along the north-south axis of the coast, whereas M. birostris was more abundant at lower latitudes. Similarly, A. narinari did not exhibit any seasonal difference in abundance, whereas M. birostris was more abundant during December and February. Neither species exhibited a clear trend in abundance over the study period (2014–2021). In addition, the abundance of both species failed to correlate with water temperature, chlorophyll-a concentration, or photoperiod. Both M. birostris and A. narinari are protected species in Florida state waters, and M. birostris is designated as threatened under the US Endangered Species Act. In addition, both species are classified by the IUCN as endangered worldwide. Insufficient data exist to establish critical habitat designations for M. birostris so that the provided information on their distribution and abundance is useful for the development of effective management.

The vulnerability of fish populations to climate change is driven primarily by impacts on their most vulnerable life stages. The earliest life stages may, in many cases, be more thermally sensitive than juvenile and adult fish, as developing embryos cannot behaviourally thermoregulate. We quantified the survivorship of brook trout (Salvelinus fontinalis) embryos under a range of winter thermal regimes. In the laboratory, embryos from four populations with varying amounts of native or hatchery-introgressed ancestry were reared under four simulated winter thermal regimes relevant to the central portion of the species’ range: ambient stream temperatures, ambient + 2 °C, ambient with a simulated winter snowmelt event, and ambient followed by an early rise to spring temperatures. Embryo survival (hatching success) differed significantly among populations across all thermal regimes, with the pure native population having the lowest survival. No consistent differences in survivorship across thermal regimes were detected, although native populations exhibited more among-family variability in response to thermal stress. Our study does not align closely with others that found reduced embryo survival under thermal stress, but concurs with observations of substantial intraspecific variation in thermal performance in coldwater fishes. Our results suggest that brook trout embryos may be somewhat resilient in the face of warmer and more variable incubation conditions, but it is likely that their resiliency varies among populations. Future experiments that include more extreme and variable conditions to clarify environmental limits of early life stages of brook trout would be useful for conservation planning.

The Media Luna spring, Mexico, is the main reservoir of the endemic and endangered fish Ataeniobius toweri. In the last decades, the ecosystem has been modified by tourism, and the habitat has changed for this species. Therefore, for better conservation management of the natural fish population, it is necessary to understand its abundance status and suitable habitat conditions, in ecological and spatial scenarios, on a temporal scale. In the present study, we modeled A. toweri’s ecological responses and spatial distribution for adult and juvenile life stages, in three summer periods (years 1999, 2009, and 2019). As habitat variables, we used water depth and underwater coverage. Ecological response curves were obtained from a Generalized Linear Model; distribution models were obtained with DOMAIN. In the modeling evaluation, for the Linear Regression Model, we obtained true statistical skills metric > 0.30 and, for DOMAIN, an area under the curve (AUC) > 0.70 with an AUC ratio > 1.00. In general, as the summer periods progressed, we found the highest probability of occurrence (P > 0.20) and distribution (P > 0.60) in areas with conditions of large coverage of underwater vegetation, in the first 1.5 m of depth, and near the shores of the spring. Also, the variations of relative abundance were always observed at sites with these habitat conditions. Thus, we concluded that our models had the performance to discern between suitable and unsuitable habitat conditions for A. toweri, and that areas with little or no anthropogenic pressure are more important for this species.

Abstract

In many fisheries, such as trawl fisheries, sharks appear among the catches as bycatch or discards, and these species include velvet belly (Etmopterus spinax) and blackmouth catshark (Galeus melastomus). The objective of this study was to research the feeding habits of both species in the Gulf of Cádiz and to identify possible differences in diet depending on size and time of day. The most frequent sizes were 12–16 cm for E. spinax and 14–20 cm for G. melastomus. Both species preyed mainly on euphausiaceans and teleosts; their Index of Relative Importance (IRI) per species were as follows: E. spinax 42.30% IRI, 21.66% IRI; G. melastomus 52.33% IRI, 27.26% IRI, respectively. Only Etmopterus spinax showed significant variation in diet as a function of the time of day (p < 0.05), although both species showed similar patterns of feeding throughout the day. With respect to size, E. spinax consumes more cephalopods and teleosts as its size increases, while G. melastomus increases its consumption of decapods.

The white shark (Carcharodon carcharias) is the largest macropredatory fish in the world. Yet, there remains a paucity of data on the early life history and reproduction of this iconic shark. Here, we present aerial observations of an individual white shark that appears to be sloughing a white film from its body. We propose two possibilities for the possession of the white film: (1) this is a newly born white shark with intrauterine substances still adhered to its body, or (2) this white shark has an unknown skin disorder resulting in shedding, discharge, or possibly a microbial growth over the dermal layer. We discuss the possibility that this individual is a newborn and its implications for the Southern California region as a critical birthing location.