Predator-prey landscapes of large sharks and game fishes in the Florida Keys.

Interspecific interactions can play an essential role in shaping wildlife populations and communities. To date, assessments of interspecific interactions, and more specifically predator-prey dynamics, in aquatic systems over broad spatial and temporal scales (i.e., hundreds of kilometers and multiple years) are rare due to constraints on our abilities to measure effectively at those scales. We applied new methods to identify space-use overlap and potential predation risk to Atlantic tarpon (Megalops atlanticus) and permit (Trachinotus falcatus) from two known predators, great hammerhead (Sphyrna mokarran) and bull (Carcharhinus leucas) sharks, over a 3-year period using acoustic telemetry in the coastal region of the Florida Keys (USA). By examining spatiotemporal overlap, as well as the timing and order of arrival at specific locations compared to random chance, we show that potential predation risk from great hammerhead and bull sharks to Atlantic tarpon and permit are heterogeneous across the Florida Keys. Additionally, we find that predator encounter rates with these game fishes are elevated at specific locations and times, including a prespawning aggregation site in the case of Atlantic tarpon. Further, using machine learning algorithms, we identify environmental variability in overlap between predators and their potential prey, including location, habitat, time of year, lunar cycle, depth, and water temperature. These predator-prey landscapes provide insights into fundamental ecosystem function and biological conservation, especially in the context of emerging fishery-related depredation issues in coastal marine ecosystems.

Global trends in aquatic animal tracking with acoustic telemetry.

Acoustic telemetry (AT) is a rapidly evolving technique used to track the movements of aquatic animals. As the capacity of AT research expands it is important to optimize its relevance to management while still pursuing key ecological questions. A global review of AT literature revealed region-specific research priorities underscoring the breadth of how AT is applied, but collectively demonstrated a lack of management-driven objectives, particularly relating to fisheries, climate change, and protection of species. In addition to the need for more research with direct pertinence to management, AT research should prioritize ongoing efforts to create collaborative opportunities, establish long-term and ecosystem-based monitoring, and utilize technological advancements to bolster aquatic policy and ecological understanding worldwide.

The importance of spawning behavior in understanding the vulnerability of exploited marine fishes in the U.S. Gulf of Mexico.

The vulnerability of a fish stock to becoming overfished is dependent upon biological traits that influence productivity and external factors that determine susceptibility or exposure to fishing effort. While a suite of life history traits are traditionally incorporated into management efforts due to their direct association with vulnerability to overfishing, spawning behavioral traits are seldom considered. We synthesized the existing biological and fisheries information of 28 fish stocks in the U.S. Gulf of Mexico to investigate relationships between life history traits, spawning behavioral traits, management regulations, and vulnerability to fishing during the spawning season. Our results showed that spawning behavioral traits were not correlated with life history traits but improved identification of species that have been historically overfished. Species varied widely in their intrinsic vulnerability to fishing during spawning in association with a broad range of behavioral strategies. Extrinsic vulnerability was high for nearly all species due to exposure to fishing during the spawning season and few management measures in place to protect spawning fish. Similarly, several species with the highest vulnerability scores were historically overfished in association with spawning aggregations. The most vulnerable species included several stocks that have not been assessed and should be prioritized for further research and monitoring. Collectively, the results of this study illustrate that spawning behavior is a distinct aspect of fish ecology that is important to consider for predictions of vulnerability and resilience to fisheries exploitation.

Application of machine learning algorithms to identify cryptic reproductive habitats using diverse information sources.

Information on ecological systems often comes from diverse sources with varied levels of complexity, bias, and uncertainty. Accordingly, analytical techniques continue to evolve that address these challenges to reveal the characteristics of ecological systems and inform conservation actions. We applied multiple statistical learning algorithms (i.e., machine learning) with a range of information sources including fish tracking data, environmental data, and visual surveys to identify potential spawning aggregation sites for a marine fish species, permit (Trachinotus falcatus), in the Florida Keys. Recognizing the potential complementarity and some level of uncertainty in each information source, we applied supervised (classic and conditional random forests; RF) and unsupervised (fuzzy k-means; FKM) algorithms. The two RF models had similar predictive performance, but generated different predictor variable importance structures and spawning site predictions. Unsupervised clustering using FKM identified unique site groupings that were similar to the likely spawning sites identified with RF. The conservation of aggregate spawning fish species depends heavily on the protection of key spawning sites; many of these potential sites were identified here for permit in the Florida Keys, which consisted of relatively deep-water natural and artificial reefs with high mean permit residency periods. The application of multiple machine learning algorithms enabled the integration of diverse information sources to develop models of an ecological system. Faced with increasingly complex and diverse data sources, ecologists, and conservation practitioners should find increasing value in machine learning algorithms, which we discuss here and provide resources to increase accessibility.

Seasonal occupancy and connectivity amongst nearshore flats and reef habitats by permit Trachinotus falcatus: considerations for fisheries management.

We used acoustic telemetry to quantify permit Trachinotus falcatus habitat use and connectivity in proximity to the Florida Keys, USA, and assessed these patterns relative to current habitat and fisheries management practices. From March 2017 to June 2018, 45 permit tagged within 16 km of the lower Florida Keys were detected at stationary acoustic receivers throughout the south Florida region, the majority of which remained within the Special Permit Zone, where more extensive fisheries harvest regulations are implemented. There was a high level of connectivity between nearshore flats (i.e., <3 m water depth) and the Florida reef tract (FRT; 15-40 m water depth), with 75% of individuals detected in both habitats. These locations probably function primarily as foraging and spawning habitats, respectively. Permit occupancy on the FRT peaked during the months of March-September, with the highest number of individuals occurring there in April and May. Specific sites on the FRT were identified as potentially important spawning locations, as they attracted a high proportion of individuals that exhibited frequent visits with high residency durations. There were also significant positive relationships between seasonal habitat-use metrics on the FRT and an empirical permit gonadosomatic index. Large aggregations of permit at spawning sites on the FRT are potentially vulnerable to the effects of fishing (including predation during catch and release) at a critical point in their life cycle. These data on permit space use and movement, coupled with knowledge of stressors on their ecology, provide insights for implementing science-based strategic management plans.

Reproductive resilience of an estuarine fish in the eye of a hurricane.

Spatial and temporal patterns of spawning activity are important measures of resilience in fishes that directly link environmental disturbances with reproductive success. We acoustically monitored spawning in spotted seatrout (Cynoscion nebulosus) from April through September 2017 at 15 sites near Port Aransas, Texas, which coincided with the landfall of a category 4 hurricane (Harvey) on 25 August. Spawning sounds were recorded every day of the study across all sites and were also confirmed during the hurricane at two sites located within the eye of the storm. Daily spawning continued after the hurricane, but the onset of spawning shifted 2.12 h earlier for 5 days, after which it returned to the pre-storm schedule. These results illustrate the resilience of seatrout to intense, episodic disturbances and offer insights on the phenotypic plasticity of estuarine fishes to cope with projected increases in environmental variability.

Acoustic telemetry and fisheries management.

This paper reviews the use of acoustic telemetry as a tool for addressing issues in fisheries management, and serves as the lead to the special Feature Issue of Ecological Applications titled Acoustic Telemetry and Fisheries Management. Specifically, we provide an overview of the ways in which acoustic telemetry can be used to inform issues central to the ecology, conservation, and management of exploited and/or imperiled fish species. Despite great strides in this area in recent years, there are comparatively few examples where data have been applied directly to influence fisheries management and policy. We review the literature on this issue, identify the strengths and weaknesses of work done to date, and highlight knowledge gaps and difficulties in applying empirical fish telemetry studies to fisheries policy and practice. We then highlight the key areas of management and policy addressed, as well as the challenges that needed to be overcome to do this. We conclude with a set of recommendations about how researchers can, in consultation with stock assessment scientists and managers, formulate testable scientific questions to address and design future studies to generate data that can be used in a meaningful way by fisheries management and conservation practitioners. We also urge the involvement of relevant stakeholders (managers, fishers, conservation societies, etc.) early on in the process (i.e., in the co-creation of research projects), so that all priority questions and issues can be addressed effectively.

Timing and locations of reef fish spawning off the southeastern United States.

Managed reef fish in the Atlantic Ocean of the southeastern United States (SEUS) support a multi-billion dollar industry. There is a broad interest in locating and protecting spawning fish from harvest, to enhance productivity and reduce the potential for overfishing. We assessed spatiotemporal cues for spawning for six species from four reef fish families, using data on individual spawning condition collected by over three decades of regional fishery-independent reef fish surveys, combined with a series of predictors derived from bathymetric features. We quantified the size of spawning areas used by reef fish across many years and identified several multispecies spawning locations. We quantitatively identified cues for peak spawning and generated predictive maps for Gray Triggerfish (Balistes capriscus), White Grunt (Haemulon plumierii), Red Snapper (Lutjanus campechanus), Vermilion Snapper (Rhomboplites aurorubens), Black Sea Bass (Centropristis striata), and Scamp (Mycteroperca phenax). For example, Red Snapper peak spawning was predicted in 24.7-29.0°C water prior to the new moon at locations with high curvature in the 24-30 m depth range off northeast Florida during June and July. External validation using scientific and fishery-dependent data collections strongly supported the predictive utility of our models. We identified locations where reconfiguration or expansion of existing marine protected areas would protect spawning reef fish. We recommend increased sampling off southern Florida (south of 27° N), during winter months, and in high-relief, high current habitats to improve our understanding of timing and location of reef fish spawning off the southeastern United States.

Assessing reproductive behavior important to fisheries management: a case study with red drum, Sciaenops ocellatus.

Spawning site selection and reproductive timing affect stock productivity and structure in marine fishes but are poorly understood. Traditionally, stock assessments measure reproductive potential as spawning stock biomass or egg production and do not include other aspects of reproductive behavior. Red drum make an excellent case study to assess these other aspects, as (1) they are highly fecund, pelagic spawners, like most exploited marine fishes; (2) their life cycle is delineated between nursery (estuarine) and adult (coastal and offshore) habitat; and (3) they are managed at these two spatial scales. This study was conducted from August 2012 to December 2013 and integrates data from multiple methods and spatial scales. Aerial surveys were used for large-scale monitoring of aggregations off two known estuarine nursery areas, Tampa Bay and Charlotte Harbor, Florida, USA. Capture-based sampling in Tampa Bay coastal (n = 2581) and estuarine waters (n = 158) was used to assess reproductive state and to confirm coastal spawning. To assess spatial dynamics, we acoustically tagged two population components in the Tampa Bay system, subadults from the estuary (n = 20) and adults from the coastal spawning site (n = 60). Behavioral plasticity was seen in subadult recruitment to coastal habitat, with some subadults maturing and recruiting before or during the spawning season and others (14 of 20 acoustically tagged fish) recruiting at the end of the 2012 spawning season. Both adults and recruited subadults (n = 29) were consequently detected in the Charlotte Harbor array, 132 km to the south. Spawning-site fidelity to the Tampa Bay spawning site occurred at both the population and individual scales. Aggregations consistently occurred in Tampa Bay coastal waters during the spawning season, and approximately two-thirds of tagged adults returned in the 2013 spawning season. A similar proportion of subadults returned to the Tampa Bay spawning site, exhibiting natal homing. However, these first-time spawners arrived later than repeat spawners and were detected over shorter time periods. This study, and others like it, demonstrates how integrating data from individuals tracked over space and time with more traditional population-based sampling is changing our understanding of ecological processes that affect marine fish productivity and our ability to manage for sustainablity.

Egg boons: central components of marine fatty acid food webs.

Food web relationships are traditionally defined in terms of the flow of key elements, such as carbon, nitrogen, and phosphorus, and their role in limiting production. There is growing recognition that availability of important biomolecules, such as fatty acids, may exert controls on secondary production that are not easily explained by traditional element-oriented models. Essential fatty acids (EFAs) are required by most organisms for proper physiological function but are manufactured almost entirely by primary producers. Therefore, the flow of EFAs, especially docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA), through aquatic food webs is critical for ecosystem functioning. A meta-analysis of data on the EFA content of marine organisms reveals that individual eggs of marine animals have exceptionally high concentrations of EFAs, and that superabundances of eggs released in temporally and spatially discrete patches create rich, but temporary, nutritional resources for egg predators, called "egg boons." Mortality rates of fish eggs are disproportionately higher than animals of similar size, and those eggs are consumed by predators, both larger and smaller than the adults that produce the eggs. Thus, egg boons are a major trophic pathway through which EFAs are repackaged and redistributed, and they are among the few pathways that run counter to the main direction of trophic flow. Egg boons can transport EFAs across ecosystems through advection of patches of eggs and spawning migrations of adults. Recognizing the significance of egg boons to aquatic food webs reveals linkages and feedbacks between organisms and environments that have important implications for understanding how food webs vary in time and space. Examples are given of top-down, bottom-up, and lateral control mechanisms that could significantly alter food webs through their effects on eggs. Our results suggest that trophodynamic food web models should include EFAs generally, and egg production and egg EFA content in particular.