Spawning Site Research Articles

Decomposition Rates of Suppression-Produced Fish Carcasses in a Large, Deep, High-Elevation Lake in North America

The decomposition of vertebrates in lake ecosystems has been largely understudied despite being a vital part of ecosystem processes. Invasive lake trout (Salvelinus namaycush) invaded Yellowstone Lake and caused a decline in the native Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) population. To restore Yellowstone cutthroat trout, lake trout were suppressed by gillnetting annually since 1995 and has continued to present, with most carcasses deposited in the profundal zone (>70 m). As a part of suppression management, a fraction of carcasses from gillnetting were ground and placed on littoral spawning sites (causing lake trout embryo mortality via hypoxia). We conducted experiments (2018 and 2019) to determine how carcass state (i.e., whole vs. ground) and location of deposition (i.e., profundal or littoral) affected decomposition rates. Whole carcasses in the depths of Yellowstone Lake decomposed nine times slower (rate of decay, k = −0.0075 day−1; 95% CI = −0.0063–−0.0089) than ground carcasses in the littoral zone (k = −0.0679 day−1; 95% CI = −0.0590–−0.0768). Whole carcasses had a half-life of 91 days while ground carcasses had a half-life of 10 days. We showed that carcass state and location cause a differential decomposition for lake trout carcasses in Yellowstone Lake. Understanding carcass persistence in lakes can inform the management of suppression-produced carcasses in large lakes and provide insight into potential effects of carcass deposition from other sources, such as spawning events or fish kills, on nutrient cycling.

Home range, space use, and vertical distribution of Nassau grouper (Epinephelus striatus) during non-spawning times in Western Puerto Rico

Understanding animal space use patterns is critical for ecological research and conservation efforts. An organism’s home range territory serves as the fundamental unit of space use and is the area repeatedly used for routine activities. Nassau grouper, Epinephelus striatus, once of high commercial fishery importance, are now on the IUCN’s Red List designated as Critically Endangered due to overexploitation. Known for the formation of large spawning aggregations, information on their movements and space use dynamics outside of the reproductive period are lacking. In this study, we used acoustic telemetry to quantify the non-spawning horizontal and vertical space use patterns of Nassau grouper at the Bajo de Sico seamount, a seasonally closed marine protected area (MPA) in Puerto Rico. Twenty-nine groupers were tagged with acoustic transmitters, of which, fourteen were tracked continuously over a three-year period. Tagged individuals displayed high site fidelity to home reef locations and individuals occupied home ranges of relatively small size that remained constant between years. There was a high degree of overlap of home range territories and in locations where multiple individuals occupied the same home reef, individuals maintained discrete vertical distributions. Nassau groupers were recorded making multiple forays to the spawning site outside of the reported spawning season, and two individuals underwent home reef site relocation. Results indicate relatively low contribution to ecological connectivity during the non-reproductive period, therefore high relative abundances of this species are needed to fulfill their ecological role at the community level. The results also highlight the importance of Bajo de Sico, an isolated seamount of relatively deeper depth, as critical habitat for primary home reef sites of Nassau grouper. These results provide a basis for adapting the current management strategy at this MPA to provide adequate protection to the non-spawning population of Nassau grouper.

Evaluating the cascade dam construction effects on endemic fish habitat and population status in spawning sites of Lancang River (in Tibet), China

Cascade dam constructions will alter the habitat of spawning sites and affect fish population in the Lancang River basin. This paper examines the impacts of cascade dam construction on four spawning sites, focusing on two co-distributed and endemic fish species: Schizothorax prenanti and Schizothorax davidi. An ecohydraulic modeling framework that combined hydro-morphodynamic, habitat, and population models was used to investigate changes in habitat quality and fish population under two scenarios: no-dam and with-dam. Fish habitat quality was evaluated using the habitat suitability index, and population fluctuations were assessed by the abundance and density of fish populations at all life stages. The simulation results indicated that cascade dam construction would fragment the spawning site habitat in the tailwater zone of the main stream and result in a decrease in fish population abundance and density. Conversely, spawning site habitats in backwater zone of tributaries would improve, and fish population abundance and density would increase. Additionally, the simulation results showed that the magnitude of fish population variations varied by species and life stages. These results highlight the different responses of spawning site location, fish species, and life stages to dam construction, which can help identify areas of the habitat with higher potential for finer-scale endemic fish conservation and recovery efforts. This study provides a comprehensive framework tool for fish ecological evaluation in dammed rivers, which has the potential to assist decision-makers involved in river ecosystem ecological conservation.

Balancing economic and ecological benefits for hydro-junction operation based on the ecological flow from the four major Chinese carps: a case study from Xinjiang River, China

The construction and utilization of the hydro-junctions would change the water flow and affect the hydrologic process required for the survival and reproduction of the aquatic organism in the river basin. To investigate the influence of the construction of the Jiepai (JP) and Bazizui hydro-junction (BZZ) on the hydrologic process in the Xinjiang River and coordinate the benefits between power generation and downstream ecological protection of the four major Chinese carps (FMCC), a one-dimensional hydrodynamic model is established to simulate the river hydrological regime of the spawning site before and after the construction of BZZ. Meanwhile, eleven ecological hydrologic parameters are used to evaluate the degree of hydrological changes for the spawning site caused by JP and BZZ, and four hydrological methods are applied to calculate the minimal and optimal ecological flows to satisfy the demands of FMCC. The multi-objective operation model combined with the non-dominated sorting genetic algorithm II(NSGA-II) is established to evaluate the relationship among the objective functions and design the ecological operation scheme of BZZ. The results indicate that the hydrologic changes in the spawning site has been moderately changed since the construction of the JP and would change more after the construction of BZZ. An obvious antagonistic relationship between electricity generating and ecological changes are presented in the simulation results, and the multiobjective operation model could clearly increase the comprehensive benefits under three typical years (dry, average, and abundant) by 20%, 19%, and 34% with the corresponding electricity generating lost by 4.9%, 3.5%, and 4.1%, respectively. This study is expected to provide scientific guidance to coordinate the restrictions and conflicts between economic and ecological benefits of hydro-junction operation in the lower reaches of the Xinjiang River.

Seascape genomics reveals limited dispersal and suggests spatially varying selection among European populations of sea lamprey (Petromyzon marinus).

Sea lamprey Petromyzon marinus is an anadromous and semelparous fish without homing behaviors. Despite being a freshwater, free-living organism for a large part of their life cycle, its adulthood is spent as a parasite of marine vertebrates. In their native European range, while it is well-established that sea lampreys comprise a single nearly-panmictic population, few studies have further explored the evolutionary history of natural populations. Here, we performed the first genome-wide characterization of sea lamprey's genetic diversity in their European natural range. The objectives were to investigate the connectivity among river basins and explore evolutionary processes mediating dispersal during the marine phase, with the sequencing of 186 individuals from 8 locations spanning the North Eastern Atlantic coast and the North Sea with double-digest RAD-sequencing, obtaining a total of 30,910 bi-allelic SNPs. Population genetic analyses reinforced the existence of a single metapopulation encompassing freshwater spawning sites within the North Eastern Atlantic and the North Sea, though the prevalence of private alleles at northern latitudes suggested some limits to the species' dispersal. Seascape genomics suggested a scenario where oxygen concentration and river runoffs impose spatially varying selection across their distribution range. Exploring associations with the abundance of potential hosts further suggested that hake and cod could also impose selective pressures, although the nature of such putative biotic interactions was unresolved. Overall, the identification of adaptive seascapes in a panmictic anadromous species could contribute to conservation practices by providing information for restoration activities to mitigate local extinctions on freshwater sites.

Modeling the interaction between salmon management and consumption by coastal brown bears

AbstractHarvest management policy for species with strong trophic connections can reverberate through food webs and cause unintended consequences, such as altering the abundance of a harvested species' predators or prey. Pacific salmon (Oncorhynchus spp.), a key food for many predators and an economically valuable harvested species, is generally managed for maximum sustained harvests without explicit consideration for the freshwater and terrestrial food webs that they support. The density of brown bear (Ursus arctos) populations in Alaska, USA, is correlated with the amount of salmon they can access and consume, so it seems likely their populations are inadvertently affected by salmon management. We simulated the effect of salmon management policy on brown bears by customizing a general bear–salmon model using empirical data from three watersheds in southwest Kodiak, Alaska. Our goal was to quantify the effect of current salmon management policy (i.e., escapement goals and early/late run allocations) on salmon consumption by brown bears. Bears in the individually‐based model evaluated the value of each foraging site based on salmon abundance, salmon vulnerability, and competition with other bears and made movement decisions (among salmon spawning sites) accordingly. A validation of the model based on empirical brown bear foraging data revealed that simulated bears selected the same salmon spawning locations but visited more sites and fished for more days compared to real bears. In simulations across variables (salmon abundance, phenological variation, bear competition, and bear density), consumption of salmon by bears was remarkably resilient to changes in salmon abundance within the range of current high and low escapement goals, as long as all run‐timing variation and salmon sub‐populations were preserved. Mean salmon consumption increased by ~20% as escapement approximately doubled from the regional lower escapement goal of 625,000 to the upper goal of 1,270,000, but rapidly declined if salmon abundance decreased below the minimum escapement goal. In this system, salmon management policy, designed to achieve maximum sustained yield, also provides adequate salmon for the current bear population. This model creates a potentially useful tool for assessing the knock‐on effects of future changes to salmon management policy.

Ecohydraulic modelling to evaluate cascade dam construction impact and support fish habitat restoration

The cascade dam constructions in the Lancang River basin will alter the river's hydrological status and affect the habitat quality of spawning sites. In this study, an ecohydraulic model was proposed to evaluate the effects of the cascade dam construction and support the restoration of spawning sites. Four spawning sites and two fish species were selected as computational domains and target fish species, respectively. The Schizothorax prenanti and Schizothorax davidi represent dominant and protected fish species in all four spawning sites. Typical annual flow discharges were used to represent the flow pattern in the Lancang River. The hydrodynamic parameters and habitat indicators were simulated and used for ecological status evaluation. Three scenarios were proposed: pre-dam construction, after dam construction, and restoration strategies. The results indicated that the quality of the Schizothorax prenanti habitat is better than that of the Schizothorax davidi habitat in all scenarios, with Schizothorax prenanti mainly distributed in the middle of the river and Schizothorax davidi scattered along the riverside. The cascade dam construction will fragment spawning Sites 1 and 2 while it will improve the habitat status in Sites 3 and 4. In addition, with restoration strategies applied, the prediction indicates that the degree of fragmentation of the habitat at spawning Sites 1 and 2 can be significantly reduced. The post-restoration effects also proved the feasibility of these two recommended restoration strategies. The analysis indicated that the investigation of the Lancang River could yield valuable information about hydropower development and habitat protection.

Synthesizing historic and current evidence for anadromy in a northern pike (Esox lucius L.) meta-population inhabiting brackish lagoons of the southern Baltic Sea, with implications for management

Pike (Esox lucius) populations across the central and southern Baltic Sea have undergone declines in recent decades. The underlying reasons are not fully understood but the loss of access to freshwater habitats in tributaries to brackish lagoons may be one important factor in some localities. Our objective was to synthesize evidence for the presence of historic and contemporary anadromy in pike from the brackish lagoon systems around the Fischland-Darß-Zingst peninsula and the islands of Hiddensee, Rügen and Usedom (Germany) by combining a review of grey literature, interviews with local citizens with knowledge tracing back to the mid-20th century, and field studies based on a range of methods, including telemetry, fyke netting and electrofishing of tributaries during the spawning seasons in the years 2020–2022. Genetic analyses were used to validate the existence of reproductively isolated subpopulations among pike migrating into different streams. The collective findings confirm the existence of freshwater spawning activity and genetic subpopulations across the entire study system in a multitude of tributaries, streams and ditches, but many populations appear to be small. The prevalence of anadromy across tributaries has likely suffered from water management activities in the 1970s and 1980s that blocked access to many rivers, ditches, streams and wetlands. Reduced access to freshwater streams through migration barriers associated with wetland management and agriculture could have fostered selection pressures to fully recruit in brackish environments, at the cost of declines and perhaps even local extinctions of once abundant anadromous subpopulations, most likely reducing stock resilience through the loss of genetic diversity and biocomplexity. Restoration of wetlands and access to freshwater spawning sites to recover subpopulations and anadromy can be recommended.

Intra-specific variation in responses to habitat restoration: Could artificial reefs increase spatiotemporal segregation between migratory phenotypes of lake sturgeon?

Habitat restoration is an important tool used to conserve biodiversity and restore species, but its effects are notoriously difficult to predict. Although outcomes of restoration projects are usually assessed using indices of species abundance and diversity, phenotypic differences among individuals within species are likely associated with differing responses to restored habitats. Here, we use lake sturgeon (Acipenser fulvescens) as a case study to illustrate how responses to habitat restoration can differ between phenotypes and potentially lead to unanticipated effects on populations. North America’s St. Clair River supports one of the largest remaining populations of lake sturgeon but has lost much spawning habitat due to its role as a major industrial corridor between the Laurentian Great Lakes Erie and Huron. Two artificial reefs were recently built in the lower and middle segments of the river to increase the available sturgeon spawning habitat. Interestingly, lake sturgeon in the St. Clair River express different migratory phenotypes that may be associated with different likelihoods of colonizing artificial reefs. Acoustic telemetry revealed that artificial reefs were more likely to be used by sturgeon that migrated downstream to overwinter in Lake St. Clair than those that migrated upstream to overwinter in Lake Huron. Furthermore, increasing time spent at the artificial reefs by Lake St. Clair migrants was associated with later arrival to and shorter occupancy of the river’s only natural spawning site, the primary location where the two phenotypes have opportunity to interbreed. Additional research is necessary to determine the ultimate impacts of the artificial reefs on lake sturgeon populations; nevertheless, our study showed phenotype-specific opportunity to colonize restored habitat and a mechanism through which this could lead to changes in gene flow. Our results illustrate the importance of considering intra-specific diversity when planning restoration projects and assessing the effects on populations.

Variability of hydrological conditions at spawning sites of East Kamchatka walleye pollock (Gadus chalcogrammus) в 2012–2022

Analysis of inter-annual variability of temperature and dynamic conditions at sites of mass spawning of East Kamchatka walleye pollock is made based on the data obtained in the course of spring ichthyoplankton surveys for the period from 2012 to 2022 and used data of remote (satellite) monitoring. Tight correlation is demonstrated between the temperatures in the water column in spring and “severity” of previous autumnwinter period in the south-western part of the Bering Sea. According to the results of remote monitoring, there is a noticeable intensification of the Kamchatka current in the last decade in the area of the research. At the same time, at the sites of mass spawning, the water transfer rate is much lower, especially in the area of Avachinsky Gulf. But even here an insignificant increase of current velocity with time can be traced.

Can seamounts in the Gulf of Alaska be a spawning ground for sablefish settling in coastal nursery grounds?

In addition to their prevalence on the continental shelf, adult sablefish have been found over the chain of seamounts far offshore in the Gulf of Alaska (GOA). Many of the females that were observed had recently spawned or were ready to spawn. However, to date, it is not known what role the seamounts play in sablefish life history and there are no observations of sablefish eggs or larvae over the GOA seamounts. Due to their depth and remoteness, there are no suitable shallow nursery areas in the vicinity of the seamounts. For successful recruitment, individuals hatching from eggs spawned over seamounts would need to be transported hundreds of miles to suitable areas inshore. Using an individual-based model (IBM) of sablefish, we have demonstrated that if spawning occurs over any of the seamounts in the GOA seamount province it is likely that at least some individuals will be successfully transported to shallow inshore nursery areas in the coastal GOA. As our simulated individuals only exhibit vertical movement behavior this on-shore transport results from the prevailing currents to which they were subjected and not from any geographic or environmental homing capabilities. Our analysis indicates that the strength of the on-shelf velocity is not the primary factor in determining the likelihood of transport to nursery areas. We speculate that the size, strength, location, and direction of the eddies that populate the GOA in any given year could be important in determining transport success. This idea is reinforced by our path analysis which shows that there are markedly different pathways taken by successful individuals among years. Our findings suggest that it may be necessary to expand what is considered suitable habitat for young sablefish. With seamounts being a potentially important spawning site for sablefish, future research priorities should include ground-truthing with fishery or fishery-independent data collected from seamounts. Potential applications of this expanded sablefish IBM include testing for connectivity between seamount and slope spawning areas and the Aleutian Islands and Bering Sea and contributing to the development of spatially explicit assessment models of sablefish.

Using fishers’ knowledge to determine the spatial extent of deep-water spawning of capelin (Mallotus villosus) in Newfoundland, Canada

IntroductionOn the Newfoundland-Labrador Shelf, Canada, capelin (Mallotus villosus) is a key forage fish that migrates annually from offshore to spawn within coastal embayments. Although capelin are thought to primarily spawn on beaches in this region, they also spawn subtidally in deeper water (5–40 m), where their eggs remain throughout incubation. The spatial extent of subtidal (i.e. “deep-water”) spawning habitat in coastal Newfoundland is unknown and is a research priority for fishers and management.MethodsWe collaborated with capelin fishers to identify putative deep-water spawning sites as a first step in determining the contribution of deep-water spawning to capelin recruitment. Given limited fine-scale coastal bathymetry and seabed habitat type data, which impeded spatial modeling to determine suitable capelin spawning habitat, this science-industry research collaboration was key to addressing this knowledge gap.ResultsThrough two years of multi-bay fisher interviews, 84% of interviewed fishers (56 interviewees) reported having observed deep-water spawning and identified a broad distribution of putative spawning sites throughout coastal Newfoundland. The majority of fishers indicated inter-annual variation in beach and deep-water spawning habitat use, and most interviewees linked this variation to temperature and capelin abundance. Further collaborations with fishers during boat-based surveys, we sampled 136 unique sites within 12 search areas in eastern Placentia Bay and 26 unique sites within six search areas in Bonavista Bay. Underwater video surveys combined with sediment sampling revealed seven previously undocumented deep-water spawning sites.ConclusionThe deep-water spawning areas derived from these fisher interviews can now be used to build a time series for monitoring capelin spawning habitat use alongside citizen-based beach monitoring data, as a general capelin stock health indicator in a weight of evidence approach for the science advisory process.

Numerical modelling for ecologically successful spawning-site restoration in Chin-sha River, China

Context The construction of dams on the Chin-sha River will affect fish spawning sites, leading to a decline in fish species. Aims This paper presents a model to evaluate the ecological status of restoration strategies aimed at fish species living at a spawning site. Methods The model comprises hydro-morphodynamic and habitat modules. The modelling approach was applied with two restoration strategies (side-channel addition and riverbank reconstruction) and their corresponding post-restoration effects. Key results Three indicators were utilised to assess the ecological status of the spawning site. Modelling results showed poor ecological status under current hydrological conditions, with weighted usable area and overall suitability index values of 1.07 × 106 m2 and 0.41. Without implementing a restoration strategy, the ecological status would continue to fragment and deteriorate. Conclusions The weighted usable area can be recovered to 2.86 × 106 and 1.67 × 106 m2 in scenarios of side-channel and bank construction respectively. The overall suitability index values increase to 0.67 and 0.63 respectively. Implications It is also noted that the ecological restoration strategy (side-channel addition) can considerably enhance the freshwater Reeves shad’s habitat status. Additionally, the restoration strategy illustrated the feasibility of the side-channel addition restoration strategy.

Otolith microchemical evidence revealing multiple spawning site origination of the anadromous tapertail anchovy (Coilia nasus) in the Changjiang (Yangtze) River Estuary

Otolith microchemical evidence revealing multiple spawning site origination of the anadromous tapertail anchovy (Coilia nasus) in the Changjiang (Yangtze) River Estuary

Does hatchery rearing of lake trout affect their reproductive behavior in the wild?

Stocking of hatchery-reared fishes has been used with variable success as a management action to promote the recovery of populations and species. The practice has been controversial for several reasons, including uncertainty about whether the hatchery rearing experience may affect reproduction after release. Fine-scale acoustic telemetry was used during three spawning seasons to test whether hatchery rearing affects the reproductive behavior of lake trout using a spawning shoal complex in northern Lake Huron. Within sex, wild- and hatchery-reared fish behaved similarly, but significant behavioral differences occurred between sexes. Lake trout of both sexes moved synchronously onto the spawning shoals at the completion of autumn thermal turnover and occupied the same spawning sites (confirmed visually by presence of fertilized eggs) on the shoals. Male lake trout tended to congregate directly on spawning sites, with duration of occupancy varying greatly among years. Female lake trout spent less time on spawning shoals than males and congregated less at spawning sites on shoals. Most fish visited multiple spawning sites among shoals per season, with many making multiple transits among individual spawning sites. We found no evidence to support the hypothesis that hatchery rearing impairs spawning behavior of lake trout and, therefore, conclude that behavior deficiencies on the spawning ground are likely not an impediment to rehabilitation of lake trout in northern Lake Huron. Our study narrows the field of possible impediments to lake trout rehabilitation in the Great Lakes and provides insights that expand the conceptual model of lake trout spawning behavior.

Spawning Atlantic cod (Gadus morhua L.) exposed to noise from seismic airguns do not abandon their spawning site

Abstract Seismic airgun surveys may disturb and displace fish at large ranges. If such displacement causes fish to abandon spawning grounds, reproductive success could be impacted. To investigate whether airgun sound causes cod (Gadus morhua L.) to leave their spawning grounds, acoustic telemetry arrays were deployed on two cod spawning grounds: a test and a reference site. From 2019 to 2021, 136 mature cod from the test site and 45 from the reference site were tagged with acoustic transmitters. Intermittent seismic shooting of two 40 in.3 airguns for 1 week during the spawning periods of 2020–2021 resulted in fluctuating sound exposure levels (SEL) at the test site, comparable to a full-scale industrial survey 5–>40 km away. Residency and survival of tagged cod were analysed with capture–mark–recapture models fitted to the detection and recapture data. Departure rate of the mature cod varied between spawning seasons but was similar between the test and reference sites. Neither survival nor departure significantly differed between seismic exposure and baseline periods. The results indicated that exposure to airguns at received SEL of up to ∼145 dB re 1 µPa2 s, comparable to a seismic survey occurring several kilometres away, did not displace tagged cod from spawning grounds.

Primed and cued: long-term acoustic telemetry links interannual and seasonal variations in freshwater flows to the spawning migrations of Common Snook in the Florida Everglades

BackgroundSpawning migrations are a widespread phenomenon among fishes, often occurring in response to environmental conditions prompting movement into reproductive habitats (migratory cues). However, for many species, individual fish may choose not to migrate, and research suggests that conditions preceding the spawning season (migratory primers) may influence this decision. Few studies have provided empirical descriptions of these prior conditions, partly due to a lack of long-term data allowing for robust multi-year comparisons. To investigate how primers and cues interact to shape the spawning migrations of coastal fishes, we use acoustic telemetry data from Common Snook (Centropomus undecimalis) in Everglades National Park, Florida, USA. A contingent of Snook migrate between rivers and coastal spawning sites, varying annually in both the proportion of the population that migrates and the timing of migration within the spawning season. However, the specific environmental factors that serve as migratory primers and cues remain unknown.MethodsWe used eight years of acoustic telemetry data (2012–2019) from 173 tagged Common Snook to investigate how primers and cues influence migratory patterns at different temporal scales. We hypothesize that (1) interannual differences in hydrologic conditions preceding the spawning season contribute to the number of individuals migrating each year, and (2) specific environmental cues trigger the timing of migrations during the spawning season. We used GLMMs to model both the annual and seasonal migratory response in relation to flow characteristics (water level, rate of change in water level), other hydrologic/abiotic conditions (temperature, salinity), fish size, and phenological cues independent of riverine conditions (photoperiod, lunar cycle).ResultsWe found that the extent of minimum marsh water level prior to migration and fish size influence the proportion of Snook migrating each year, and that high river water level and daily rates of change serve as primary cues triggering migration timing.ConclusionOur findings illustrate how spawning migrations are shaped by environmental factors acting at different temporal scales and emphasize the importance of long-term movement data in understanding these patterns. Research providing mechanistic descriptions of conditions that promote migration and reproduction can help inform management decisions aimed at conserving ecologically and economically important species.

A stakeholder-engaged approach to evaluating spawning aggregation management as a strategy for conserving bonefish (Albula vulpes) in Cuba.

Animals that congregate in large numbers to reproduce in spatially and temporally distinct locations are particularly susceptible to overexploitation. Many fishes form spawning aggregations that are intentionally targeted given ease of capture. Bonefish (Albula spp.) species aggregate to spawn and are culturally and economically important, but generally lack management such as spawning area protections to ensure that fisheries are sustainable. Here, we use Cuba as a case study to inform the development and refinement of management strategies for bonefish. Recommendations for the management of bonefish pre-spawning aggregations were based on international experiences, which have been adapted to the Cuban context from results of surveys and interviews with Cuban fisheries professionals and fishing guides. The achievability and feasibility of recommendations were further reviewed by additional experts in the field of fisheries, management and Cuban policy. The process revealed extensive data-limitations for bonefish fisheries and underscored the importance of including fishing guides, local ecological knowledge and the context of marine protected areas in Cuba for bonefish management. Recommendations include (1) initiating information exchange between Cuban management agencies and third-party institutions related to bonefish management; (2) utilizing local ecological knowledge to gather information, formulate management strategies and enforce regulations; (3) implementing spatial and temporal management measures for bonefish spawning sites; (4) using what is already in place, by protecting spawning sites in the context of existing marine protected areas; (5) collaborating with all stakeholders to manage bonefish spawning sites; and (6) reducing the commercial harvest of the species.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10641-022-01355-0.

Coupling natural and electronic tags to explore spawning site fidelity and natal homing in northeast Atlantic European seabass

The structure and connectivity of European seabass (Dicentrarchus labrax) populations remain poorly known and ecological evidence is missing to support the current delineation between the northern (southern North Sea, English Channel and Celtic Sea) and southern French stocks (Bay of Biscay). Adult spawning site fidelity and natal homing were analysed by coupling Data Storage Tag (DST) information and otolith microchemistry of recaptured fish to investigate, within the study area, the population structure and connectivity in European seabass. Trajectory reconstructions inferred from DST data were used to assign a spawning area (English Channel or Bay of Biscay) to each spawning winter record. In addition, otolith composition (Mg, P, Mn, Zn, Sr, Ba and δ18O) was measured in both larvae and adults otolith increments corresponding to a winter spawning event. We built a training dataset using coupled spawning area assignments and otolith elemental signatures (Mg, P, Mn, Zn, Sr and Ba) for winters with DST data. The training dataset was used to calibrate a Random Forest model and assign spawning areas based on otolith winter signatures outside the DST recording period. Results revealed that 64% of the seabass expressed spawning site fidelity. We also found a geographical gradient of site fidelity, with the highest proportions of spawning site fidelity found in seabass tagged at the northern and southern limits of the studied area. Significant ontogenetic effects were observed for trace elements and δ18O with ratios significantly lower in the larval stage than in the adult stage. These biases and the variability across cohorts prevented us to use the assignment model fitted on adults to study natal homing. At the larval stage, the analysis of spatio-temporal effects on otolith trace elements did not reveal any significant difference between spawning areas. However, the patterns of difference were similar for larval and adult Zn, Sr and Ba between the two spawning areas, suggesting a homing behaviour.

Influence of the lunar cycle and spatial gradients on size-dependent male and female reproductive investment decisions of a protogynous reef fish

Coral reef fish species experience variable environments and may employ a range of reproductive strategies to help them maximize fitness. Here, we explore patterns of variation in size- and sex-dependent spawning strategies (pair spawning, group spawning, and streaking tactics) of a sex-changing, highly iteroparous fish (the sixbar wrasse Thalassoma hardwicke) across the lunar month, and in relation to proximity to the reef edge. We test the hypothesis that adults vary their investment strategies as a function of body size. We evaluated reproductive behaviour patterns at 2–3 days intervals over 5 consecutive months, and found that frequencies of pair spawning, group spawning, and streaking attempts all significantly increased around the new moon and were greatest in the most exposed territories (i.e., those located closest to the reef edge). Smaller females and IP males largely curtailed reproductive activities during the full moon and third quarter moon, while larger individuals reproduced more consistently across the lunar month. Size-dependent reproductive decisions appeared to mediate frequencies of specific reproductive tactics (e.g., prevalence of pair spawning, group spawning, and streaking strategies). We speculate that (1) optimal tactics are shaped by size- and sex-dependent trade-offs between reproduction and growth in relation to environmental conditions, and that (2) individual investment decisions determine the prevailing reproductive mode at a spawning site. Variation in female choice might thereby act as a mechanism for maintaining these two reproductive modes (pair spawning and group spawning) in a population.