Philip Matich’s research while affiliated with Texas A&M University at Galveston and other places

Shark and ray populations continue to decline in many regions around the world. The contribution of artisanal fisheries to these declines remains poorly understood for many locations. A rapid assessment framework using fisheries-independent sampling and fisher interviews was employed to study elasmobranch occurrence and use in coastal artisanal fisheries of Guadeloupe, Martinique, and Tobago. In-person interviews (n = 405) were conducted between June 2015-June 2017, and baited remote underwater video stations (BRUVS) (n = 50 video drops/reef) were deployed in nine reefs across the islands. The fate of elasmobranchs caught by artisanal fishers varied by island. Martinique reported the highest proportion of fishers keeping their catch for subsistence among the study locations. In Guadeloupe, fishers most frequently sold their catch, and Tobago fishers engaged in both subsistence fishing and sale. Fishers retained almost all animals caught and reported reduced catches of elasmobranch compared to when they started fishing. BRUVS revealed relatively low elasmobranch occurrence and a low Shannon diversity index compared to Caribbean nations with less fishing pressures on elasmobranchs. The present study highlights the need for improved data on, and monitoring of, artisanal fisheries.

Seasonal variability in environmental conditions is a strong determinant of animal migrations, but warming temperatures associated with climate change are anticipated to alter this phenomenon with unknown consequences. We used a 40‐year fishery‐independent survey to assess how a changing climate has altered the migration timing, duration and first‐year survival of juvenile bull sharks (Carcharhinus leucas). From 1982 to 2021, estuaries in the western Gulf of Mexico (Texas) experienced a mean increase of 1.55°C in autumn water temperatures, and delays in autumn cold fronts by ca. 0.5 days per year. Bull shark migrations in more northern estuaries concomitantly changed, with departures 25–36 days later in 2021 than in 1982. Later, migrations resulted in reduced overwintering durations by up to 81 days, and the relative abundance of post‐overwintering age 0–1 sharks increased by >50% during the 40‐year study period. Yet, reductions in prey availability were the most influential factor delaying migrations. Juvenile sharks remained in natal estuaries longer when prey were less abundant. Long‐term declines in prey reportedly occurred due to reduced spawning success associated with climate change based on published reports. Consequently, warming waters likely enabled and indirectly caused the observed changes in shark migratory behaviour. As water temperatures continue to rise, bull sharks in the north‐western Gulf of Mexico could forgo their winter migrations in the next 50–100 years based on current trends and physiological limits, thereby altering their ecological roles in estuarine ecosystems and recruitment into the adult population. It is unclear if estuarine food webs will be able to support changing residency patterns as climate change affects the spawning success of forage species. We expect these trends are not unique to the western Gulf of Mexico or bull sharks, and migratory patterns of predators in subtropical latitudes are similarly changing at a global scale.

Many shark populations are in decline around the world, with severe ecological and economic consequences. Fisheries management and marine protected areas (MPAs) have both been heralded as solutions. However, the effectiveness of MPAs alone is questionable, particularly for globally threatened sharks and rays (‘elasmobranchs’), with little known about how fisheries management and MPAs interact to conserve these species. Here we use a dedicated global survey of coral reef elasmobranchs to assess 66 fully protected areas embedded within a range of fisheries management regimes across 36 countries. We show that conservation benefits were primarily for reef-associated sharks, which were twice as abundant in fully protected areas compared with areas open to fishing. Conservation benefits were greatest in large protected areas that incorporate distinct reefs. However, the same benefits were not evident for rays or wide-ranging sharks that are both economically and ecologically important while also threatened with extinction. We show that conservation benefits from fully protected areas are close to doubled when embedded within areas of effective fisheries management, highlighting the importance of a mixed management approach of both effective fisheries management and well-designed fully protected areas to conserve tropical elasmobranch assemblages globally.

Coastal ecosystems are highly vulnerable to the impacts of climate change and other stressors, including urbanization and overfishing. Consequently, distributions of coastal fish have begun to change, particularly in response to increasing temperatures linked to climate change. However, few studies have evaluated how natural and anthropogenic disturbances can alter species distributions in conjunction with geophysical habitat alterations, such as changes to land use and land cover (LU/LC). Here, we examine the spatiotemporal changes in the distribution of juvenile bull sharks (Carcharhinus leucas) using a multi-decadal fishery-independent survey of coastal Alabama. Using a boosted regression tree (BRT) modeling framework, we assess the covariance of environmental conditions (sea surface temperature, depth, salinity, dissolved oxygen, riverine discharge, Chl-a) as well as historic changes to LU/LC to the distribution of bull sharks. Species distribution models resultant from BRTs for early (2003–2005) and recent (2018–2020) monitoring periods indicated a mean increase in habitat suitability (i.e., probability of capture) for juvenile bull sharks from 0.028 to 0.082, concomitant with substantial increases in mean annual temperature (0.058°C/yr), Chl-a (2.32 mg/m³), and urbanization (increased LU/LC) since 2000. These results align with observed five-fold increases in the relative abundance of juvenile bull sharks across the study period and demonstrate the impacts of changing environmental conditions on their distribution and relative abundance. As climate change persists, coastal communities will continue to change, altering the structure of ecological communities and the success of nearshore fisheries.

A global survey of coral reefs reveals that overfishing is driving resident shark species toward extinction, causing diversity deficits in reef elasmobranch (shark and ray) assemblages. Our species level analysis revealed global declines of 60 to 73% for five common resident reef shark species and that individual shark species were not detected at 34 to 47% of surveyed reefs. As reefs become more shark-depleted, rays begin to dominate assemblages. Shark-dominated assemblages persist in wealthy nations with strong governance and in highly protected areas, whereas poverty, weak governance, and a lack of shark management are associated with depauperate assemblages mainly composed of rays. Without action to address these diversity deficits, loss of ecological function and ecosystem services will increasingly affect human communities.

Understanding the factors shaping patterns of ecological resilience is critical for mitigating the loss of global biodiversity. Throughout aquatic environments, highly mobile predators are thought to serve as important vectors of energy between ecosystems thereby promoting stability and resilience. However, the role these predators play in connecting food webs and promoting energy flow remains poorly understood in most contexts. Using carbon and nitrogen isotopes, we quantified the use of several prey resource pools (small oceanic forage, large oceanic prey, coral reef, and seagrass) by 17 species of elasmobranch fishes (n = 351 individuals) in The Bahamas to determine their functional diversity and roles as ecosystem links. We observed remarkable functional diversity across species and identified four major groups responsible for connecting discrete regions of the seascape. Elasmobranchs were responsible for promoting energetic connectivity between neritic, oceanic, and deep-sea ecosystems. Our findings illustrate how mobile predators promote ecosystem connectivity, underscoring their functional significance and role in supporting ecological resilience. More broadly, strong predator conservation efforts in developing island nations, such as The Bahamas, are likely to yield ecological benefits that enhance the resilience of marine ecosystems to combat imminent threats such as habitat degradation and climate change.

Understanding how intraspecific variation in the use of prey resources impacts energy metabolism has strong implications for predicting long-term fitness such as reproductive success and survival and is critical for predicting population-to-community level responses to environmental change. Here we examine the energetic consequences of variable prey resource use in a widely distributed marine carnivore, juvenile sand tiger sharks (Carcharias taurus). We used carbon and nitrogen isotope analysis to identify three primary prey resource pools – demersal omnivores, pelagic forage, and benthic detritivores and estimated the proportional assimilation of each resource using Bayesian mixing models. We then quantified how the utilization of these resource pools impacted the concentrations of six plasma lipids and how this varied by ontogeny. Sharks exhibited variable reliance on two of three predominant prey resource pools: demersal omnivores and pelagic forage. Resource use variation was a strong predictor of energetic condition, whereby individuals more reliant upon pelagic forage exhibited higher blood plasma concentrations of very low-density lipoproteins, cholesterol, and triglycerides. These findings underscore how intraspecific resource use variation may impact the energy metabolism of animals, and more broadly, that natural and anthropogenically-driven fluctuations in prey resources could have longer term energetic consequences.

Ecological monitoring is critical for conservation efforts, particularly in marine ecosystems. Recently, greater emphasis on analyses of data resultant from long‐term ecological research has allowed for broader questions pertaining to climate change, species range shifts and reproductive phenology to be assessed, which may improve ecosystem management. Data collected via ecological monitoring, however, often feature strong class imbalances, complicating the development of models to predict such events. Here, we propose two modelling frameworks—a boosted regression tree (BRT) model and an artificial neural network (ANN)—for predicting exceptionally rare aggregatory behaviour of bull, Carcharhinus leucas and blacktip sharks, C. limbatus along the Gulf coast of Texas. In tandem with aggressive techniques for handling zero‐inflated data, both methods produced accurate predictions of aggregations of three or more individuals in one survey event, with the BRT outperforming the ANN in minimizing type I error. Additionally, both models maintained relatively high area under the receiver operating characteristic (ROC AUC) values when the threshold for defining aggregative behaviour was raised, though there was a measurable drop‐off in the precision‐recall (PR) AUC at each successive threshold increase. These results provide support for both modelling approaches as highly viable in generating predictions based on monitoring data, even in situations where negative cases outweigh positive cases by more than 10‐fold. This is promising for conservation and management of species that exhibit biologically and ecologically significant, but rare, behaviours like aggregations, and species that are rare in abundance and thus vulnerable to future declines. More accurately predicting aggregation events provides the information necessary to improve the protection of species that gather during key life‐history events (e.g. mating, parturition, migration), and assess the spatiotemporal consistency of such events, thereby improving the efficacy of adaptive management. Synthesis and applications. Conservation and management programmes serve a critical role in maintaining the health of ecosystems, and regularly make use of ecological monitoring to collect data relevant to population studies. In marine systems, particularly, monitoring is often expensive and time‐consuming, which can result in incomplete or sparse datasets. Especially where an ecological event of interest is rare, subsequent analyses are particularly affected by the many limitations of zero‐inflated datasets. When training predictive models to classify these events, special care must be taken to avoid simply predicting negative events in every case. Here, we propose and compare two machine learning approaches: gradient boosting and the artificial neural network (ANN), to predict aggregatory behaviour of two shark species: bull, Carcharhinus leucas and blacktip sharks, C. limbatus in the Gulf of Mexico. Applied to a large dataset considering many spatial and environmental variables, and in tandem with negative case downsampling, our results support the application of each method to improve analyses of sparse monitoring datasets, with the gradient boosting machine performing particularly well in classifying positive cases.

The Bahamas is among the last remaining refuges for the Critically Endangered smalltooth sawfish, Pristis pectinata , and the presence of a distinct ‘beacon of hope’ population on Andros Island may prove critical to their recovery. Although legislation in The Bahamas protects sharks from exploitation, no such national protection exists for rays, which include sawfishes. Targeted efforts to protect essential habitats coupled with community‐led conservation actions provide a path forward for sawfish conservation and recovery. Structured interviews were conducted in 2021 ( n = 77) with community members that frequent Andros waters to describe the temporal and spatial patterns of sawfish distribution in Andros, and to identify key regions or habitats for sawfish‐specific monitoring and potential protection. Sawfish encounters ( n = 99) included all life stages and were located throughout coastal and tidal waters of Andros. Comparable numbers of animals were encountered along both coastlines, predominantly on shallow (<2 m), muddy flats close to shore (<1 km). Most notable were encounters with young‐of‐the‐year sawfishes in new regions of Andros, indicating the potential discovery of undocumented nursery habitats. Although most encounters were sightings, 22% ( n = 20) of the sawfishes were caught, with just under half of these harvested for food, bait, and/or to keep the rostrum as a decorative item. There is an urgent need for more expansive protection and monitoring of smalltooth sawfishes across their range in Andros and improved education and outreach to prevent further harvest. Recommendations include: (i) the formal development of a national strategy for sawfish conservation; (ii) adding sawfish to the existing shark sanctuary to provide national protective measures; and (iii) community‐led outreach and education activities to develop and lead conservation initiatives, including ecotourism and wildlife guiding and a Bahamian sawfish reporting network.