Aquatic Conservation: Marine and Freshwater Ecosystems

Microtidal estuaries in Mediterranean climates are particularly vulnerable to the effects of anthropogenic degradation. This study provides the first data on the fish and benthic macroinvertebrate fauna of Hill Inlet, the northernmost estuary in south-western Australia. Sampling was conducted in June 2019 (Austral winter), when water levels were very high due to recent heavy rainfall and the bar at the mouth of the estuary was intact. Surface salinities were oligohaline and declined along the longitudinal axis, ranging from 12 to 3. A marked halocline was present at most sites, resulting in pronounced hypoxia. High water levels precluded the use of a seine net at some sites to sample the nearshore fish fauna, however, two species were recorded (Pseudogobius olorum and Acanthopagrus butcheri), both of which complete their life-cycle within the estuary. Deeper, offshore waters, sampled using gill nets, yielded only four species (Mugil cephalus, A. butcheri, Adrichetta forsteri and Pomatomus saltatrix), due to the bar at the mouth of the estuary being closed prior to sampling thus limiting recruitment from marine species. Ten benthic macroinvertebrates species were collected, representing mainly polychaetes, molluscs and crustaceans. The low number of species was likely caused by the hypoxia present throughout most of the bottom waters. Although these data represent a benchmark against which future changes can be detected, it is recommended that additional sampling is conducted when water levels are lower and the bar has been open to provide a more holistic assessment of the fauna of Hill Inlet.

Sharks play a crucial role in the structure of marine ecosystems but are heavily threatened by overfishing globally. Due to their slow life history traits, even low fishing pressure can have an extreme influence on shark populations. The Mediterranean Sea, which has had historical overexploitation over the course of many centuries, is considered a hotspot for elasmobranchs. One particular species is the bluntnose sixgill shark, Hexanchus griseus, which has recently become more prominent in sightings and landings. Because of its deep range, H. griseus is difficult to study in situ so we used opportunistic data from sharkPulse, a crowd-sourcing platform that collects and organizes image-based shark occurrence records from all over the world, to better understand the abundance and distribution of H. griseus over the past decade. Additionally, we explored historical data to create a baseline of the species abundance starting from the late 1800s. We found that H. griseus underwent a quadratic-shaped change in their abundance where they started out as a rare catch, became increasingly more prominent in fisheries data, and now is declining like many other cartilaginous fishes in the Mediterranean Sea. This work is important because H. griseus is not yet threatened according to the IUCN so research is not heavily focused on this species but the decreasing trend we detected here is concerning while in line with the degree of exploitation of one of the most exploited regions of the world, as well as illustrative of a broader ecological process that will likely occur in many other large marine ecosystems worldwide.

Many populations of Atlantic salmon (Salmo salar) native to the Baltic Sea are endangered. A significant group targeting salmon in this region is the recreational trolling fisheries. Due to frequent changes in fisheries regulations and conditions, both the conservation of the species and the fishers are impacted. This study aims to enhance our understanding of the spatial extent and population dynamics of salmon trolling boat skippers in the Baltic Sea by estimating their population size and resource utilization. The study utilizes participation lists of skippers from recreational fishing tournaments and Automatic Identification System (AIS) data to track their movements. These lists are formatted as encounter histories for spatial capture-recapture models, while AIS data are integrated as telemetry data to estimate resource selection. The results reveal a 51% decrease in the number of skippers from two time periods: years 2014-2020 and 2021-2023, with the count dropping from 5,343 individuals (95% CI: 4,622-6,178) to 2,604 individuals (95% CI: 2,273-2,983). The decline may be attributed in part to heavy regulations imposed on recreational salmon fisheries in 2022. Furthermore, the resource selection analysis indicates that these skippers target various species also outside of the Baltic Sea, such as Bluefin tuna (Thunnus thynnus) in Skagerrak, and endangered salmon stocks elsewhere, such as in Lake Vanern. The results of this study suggests that regulations and changes in the Baltic Sea salmon trolling fishery may have broader impacts on seemingly unrelated species and ecosystems.

O_LISeagrasses are marine angiosperms that potentially provide habitat for crabs, shrimps and fish. However, these types of data are lacking for the seagrass species (Zostera muelleri/rimur[e]hia) that inhabit intertidal estuaries on the South Island of New Zealand. C_LIO_LIAbundances of crabs, shrimps and fish were therefore quantified from 361 non-destructive seine tows done in seagrass beds and bare mudflats in Duvauchelle bay and two sites in the Avon-Heathcote/Ihutai estuary between October 2019 and February 2020. C_LIO_LIA total of 2549 crabs, 5824 shrimps and 1149 fish (75% were juvenile flounders) were identified and counted in the seine-net and immediately released back in healthy condition to the exact location from where they were caught. C_LIO_LIOnly few seagrass leaves were caught in the net and these leaves may have been previously uprooted drift fragments. The instant catch-and-release methodology therefore leaves, literally, nothing but a footprint. C_LIO_LIMore fish taxa, including two species of pipefish, were found in seagrass beds in Duvauchelle bay than in the Avon-Heathcote estuary. Fish (minus juvenile flounders) were also more abundant in these seagrass beds. Furthermore, juvenile flounders and shrimps were more abundant in Duvauchelle bay compared to the Avon-Heathcote estuary, but were found in similar abundances in seagrass beds and on bare flats. C_LIO_LIIt is possible that more fish were found in Duvauchelle seagrass beds because these beds have adjacent deeper areas, and may have high connectivity to seagrass beds in nearby bays. This hypothesis should be tested by sampling more seagrass beds in different types of estuaries and bays. C_LIO_LIBy contrast, crabs were more abundant in the Avon-Heathcote estuary, where spider crabs were most abundant in the seagrass beds, but other crabs were found in similar abundances in seagrass beds and bare habitat. We hypothesize that crab abundances were higher in the Avon-Heathcote estuary because of lower fish predation pressure and/or larger populations of prey like mollusc and polychaetes. C_LIO_LIOur results suggests that (a) superficially similar Zostera beds in relatively close proximity can provide very different habitat values for fish and crustaceans, (b) seagrass beds with higher diversity and abundances of fish may be prioritized in conservation and management (assuming other important ecosystem functions are similar between beds), and (c) that pipefish may be useful indicator organisms, representing healthy, extensive, dense and connected seagrass beds. C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=177 SRC="FIGDIR/small/120055v1_ufig1.gif" ALT="Figure 1"> View larger version (111K): org.highwire.dtl.DTLVardef@1c21731org.highwire.dtl.DTLVardef@180c521org.highwire.dtl.DTLVardef@10e2875org.highwire.dtl.DTLVardef@824c21_HPS_FORMAT_FIGEXP M_FIG C_FIG

Conservation of exploited fish populations is a priority for environmental managers. Spatio-temporal knowledge on reproductive sites is mandatory for species and habitat conservation but is often difficult to assess, particularly over vast geographic areas. Regular and long-term standardized surveys are necessary to identify reproductive sites, assess population trends and their distribution. Here we emphasize the utility of Passive Acoustic Monitoring (PAM) for the survey and management of a depleted vulnerable Mediterranean fish species, the brown meagre, Sciaena umbra. Acoustic surveys of reproductive calls were conducted combining 1) spatial data from standardized surveys within three MPAs and from 49 unprotected sites throughout the Northwestern Mediterranean basin, as well as 2) temporal data from a two-year-long survey at a presumed spawning location. The MPA surveys, which rapidly scanned ~30-50 km of the rocky coastlines per MPA, unveiled maps of distribution and reproductive activity of the brown meagre, including potential spawning sites. They were also effective in emphasizing effects linked to management actions: Full-protection zones had a higher number of vocalizations (70% of the listening sites) compared to less protected zones (30% of the sites) or sites outside MPAs (45% of the sites). This was also reflected in the number of singers that was generally low (< 3 individuals) in less protected zones and outside MPAs, implying lower fish densities. Highest calling aggregations were observed in potential spawning areas that represented only 0.04% of all listening sites, and were almost all in older, fully protected MPAs, which thus play a key role for fish stock recovery. The two-year survey revealed a 5-month reproductive season (from May to October) with a strong positive correlation between calling activity and temperature. Overall this study confirms the role of PAM as an efficient, replicable and standardized non-invasive method for population management that can identify functional sites and key protection zones, provide valuable information on reproduction, spatial and temporal occurrence, but also on population trends and climate-driven changes. HighlightsO_LIMonitoring of threatened species and their key habitats is critical for environmental managers. C_LIO_LIManagement requires methods to assess population trends at large spatial and temporal scales. C_LIO_LIPassive acoustics (PA) is efficient in mapping and monitoring vulnerable fish species. C_LIO_LIDistribution, reproductive sites and population dynamics can be assessed over vast geographical areas. C_LIO_LIWe show the utility of PA to identify key conservation zones and assess effects of management actions. C_LI

The spatial scale at which temporal change in a population is measured has the potential to skew the inferences drawn on patterns of change from monitoring data. This study analysed data from rod catches of anadromous sea trout (Salmo trutta) in Scotland over a period of 72 years and over three spatial scales (National, Regional and District). The pattern of temporal change evident at the national scale mostly did not clearly manifest at Regional or at District spatial scales; which were also generally decoupled (67% of Regions and 80% of Districts exhibited a different pattern from the National pattern). At the National level, very clear and substantive declines over the study period were evident. At Regional levels (N=9) change in rod catches was more nuanced with some Regions showing no change, one Region showing an increase in sea trout caught and 6 (67%) exhibited a different pattern from the National one. At the District levels (N=64) opposing patterns of change were observed over the study period, even in adjacent Districts with 80% of Districts exhibiting a different pattern from the National one. A conclusion of this study is that, as a national resource, sea trout numbers have declined substantively over the last seven decades (by around 50%). However, this general picture is not applicable across all geographic Regions nor all Districts. Two logical inferences derive from these results. Firstly, for best effect, the application of limited resources for management should be focused at smaller scales than at countrywide. Secondly, that monitoring population change at small spatial scales, for example in several index rivers, is unlikely to capture the highly nuanced patterns of change in species with high levels of intra-specific structuring as is commonly exhibited by the Salmonidae.

Herbivorous reef fishes are critically important for maintaining the health and resilience of coral reefs. In the Egyptian Gulf of Aqaba (GoA), many of these herbivores are important fishery targets, however, little is known about their biomass and size structure patterns. Here, we conduct a large-scale ([~]250 km of coastline) assessment of the status of herbivorous fish populations on 30 reef sites from eight coastal regions in the GoA. These regions are subjected to three levels of fishing and protection, ranging from almost no fishing (No-take, NT), and moderately fished (via Gear-restriction, GR) to heavily fished (Open-access, OA). We found that the NT fishery reserve was the most effective in maintaining herbivorous fish richness, body-size, and biomass across all functional groups, though numerical density was not. Total herbivore biomass was 4.3 and 2.8 times higher on NT reefs and GR reefs respectively than on OA reefs. Among GoA regions, only Ras Mohammed and Sharm El-Sheikh (unfished), and Nabq (moderately fished) met the global mean herbivore biomass target of [~]30 kg/500 m2. Our work also highlights three important results regarding the impacts of fishing and fisheries management on herbivorous fish populations: (i) size structure was heavily skewed toward smaller individuals, with fishes less than (20 cm) accounting for 81.1% of the population in heavily fished OA reefs vs. 52.8% at unfished NT reefs, (ii) biomass of larger herbivore individuals (>35 cm) accounted for less than 1% of the total biomass in OA reefs vs. 37% at NT reefs, and (iii) large-bodied target species, Cetoscarus bicolor, Naso unicorn, and Kyphosus spp., accounting for 15.9% of the total biomass at NT reefs on average, while they were virtually absent from OA reefs. Collectively, these findings suggest that many principal fishery species in the central-northern regions of the GoA have been overexploited, which in turn can lead to reef degradation. Therefore, there is an urgent need to develop a participatory management approach and enforce restrictions on destructive fishing gear in order to promote recovery of herbivore biomass. HighlightsO_LILarge-scale assessment of the status of herbivorous fishes in the northern Red Sea. C_LIO_LIComparison of herbivorous fish assemblages across three levels of fishing pressure. C_LIO_LILarge-bodied herbivore species were either rare or absent at heavily fished reefs. C_LIO_LILoss of these key herbivores may boost algal dominance, thus diminish reef functionality. C_LIO_LIPromoting local community participation in the fishery management process. C_LI

Segregation of older adult males from females and immature males is known to occur in some beluga whale populations, but it is unclear if adults accompanied by calves segregate in Hudson Bay, where the largest summering population is found. Using imagery from a photographic aerial survey conducted in August 2015, we considered a number of environmental variables that might explain distribution by age class of beluga near two of three main estuaries (Churchill and Seal River) used by Western Hudson Bay belugas in the summer season. Belugas were identified and classified by age manually using an identification decision tree and GPS coordinates were plotted in ArcGIS. Distribution by age class was examined in relation to distance to coastal habitat and bathymetry to test the predation risk hypothesis, sea surface temperature (thermal advantage hypothesis), and extent of river plume (forge-selection hypothesis). Habitat characteristics and the proportion of age classes in both estuaries were similar between age class groups (with and without calves) indicating no segregation and suggesting the environmental data assessed were not driving patterns of distribution and density of age classes at the spatial and temporal scale being investigated. Results provide a greater understanding of spatial patterns of beluga whale habitat use in western Hudson Bay and information useful in conservation and management advice.

Recent developments in assessing species-specific seabird bycatch risks demonstrated that fine-scale approaches are essential tools to quantify interactions with fishing vessels and understand attraction and attendance behaviours. Matching boats movements with birds tracking data specifically allows to investigate seabird-fishery interaction for cryptic species for which on-board information is critically lacking. The sooty albatross (Phoebetria fusca) overlaps with fisheries throughout its range and is known to be vulnerable to incidental bycatch. Combining GPS and behaviour data from individuals from Crozet Islands and boat locations during the incubation period, we investigated interactions of sooty albatrosses with fisheries in the southern Indian Ocean. Individuals foraged mostly in sub-tropical international waters, where they only encountered a small number of boats. The low interaction rate during this period may suggests that sooty albatrosses are not strongly attracted towards fishing vessels. However, this result should be interpreted with caution due to the low sample size and fishing effort during the study period, as these observations may conceal a higher bycatch risk during intense fishing effort and/or energetically demanding periods. The species conservation status requires further data to be collected throughout the annual cycle to provide an accurate assessment of the threat.

Golden redfish (Sebastes norvegicus) are a long-living (>50 years), late maturing (>10 years) species of commercial interest, distributed along the coast, shelves and continental slope of Norway, down to approximately 400 m depth in the water column. In recent years, analyses of size-at-age data have revealed variable growth trajectories for this species. Whilst some individuals appear to grow slowly after sexual maturity (37cm at ~ 15 years), others continue to grow throughout their lifetime up to 100 cm or more. To investigate how depth and latitude affect golden redfish growth patterns, we developed non-linear mixed effects statistical models. Alongside this, small scale experiments were also conducted to assess the quality of age-determination. The results showed that individuals found in deeper, northern waters present a higher growth potential, even when uncertainty in age determination and species identification were considered. The proximal causes for variations in the growth potential of S. norvegicus are still unresolved and the existence of a possible cryptic species remains a fundamental issue that will need to be addressed, in order to understand the causes behind observed growth variations.

Overexploitation is a major threat to marine ecosystems, causing collapse of numerous fisheries since the 19th century. The Hong Kong Grouper (Epinephelus akaara) is a commercial fish species that suffered at least 50-80% population declines in the past 40 years throughout its distribution range. Yet there has been minimal research or specific management, resulting in insufficient data on abundance, reproduction and habitat utilization. Here we aim to develop a novel species-specific quantitative PCR (qPCR) assay to detect potential occurrence of E. akaara through non-invasive environmental water samples. We developed a qPCR assay amplifying 71 bps of the mitochondrial ND2 gene which offers high sensitivity and specificity. To quantify the E. akaara population with the emerging environmental DNA (eDNA) tool, however, species-specific shedding and decay rates are crucial. The decay rate of E. akaara was similar to that of reported values of other marine fish species. However, the shedding rate of E. akaara was found to be few orders of magnitude lower which may be related to the relatively low activity and energy use from solitary and sedentary behavior of groupers. This highlights the importance of empirically determining species or taxon-specific shedding and decay rates to inform accurate abundance estimates with modelling tools for eDNA concentrations. Only 6 out of 88 water samples (6.81%) collected across 4 sampling seasons and 11 sites around Hong Kong showed positive signals at a concentration below limit of detection of the assay, implying its rarity in Hong Kong nowadays. Overall, we demonstrate that eDNA with our qPCR assay is efficient and sensitive in detecting the target species and is a promising tool in documenting endangered species for species management and conservation.

The endangered North Atlantic right whale (Eubalaena glacialis) showed limited recovery from the cessation of industrial whaling until 2011, and has since been in decline. Research is therefore focused on identifying what factors are limiting recovery and what conservation actions will be most effective. A compromised reproductive rate is one of the primary reasons for this lack of recovery, yet there is no consensus on how to quantify reproductive performance. As one potential solution, we propose a relatively simple approach where we calculate the theoretical maximum number of calves each year. Comparing this expected number to those observed provides a means to quantify the degree to which reproduction is being compromised and trends thereof over time. Implementing this approach shows that, between 1990 and 2017, the number of calves born never came close to the theoretical maximum, resulting in overall reproductive performance being only about 27% of that expected. In addition to quantifying the magnitude of the reproductive problem, this approach should also be useful for quantifying the role of reduced reproductive performance in limiting species recovery, and for aiding research programs focused on identifying what factors are compromising reproduction.

We followed landings of dusky grouper, Epinephelus marginatus, from 2013 to 2019. We observed 1,896 individuals of dusky grouper, Epinephelus marginatus, in Copacabana, Rio de Janeiro, from September 2013 to February 2019. The total weight of the catches was 6,065.57 kg, with an average of 1,442.50 kg/year and a std of 147.30 kg.\n\nWe integrated fishers in our study through citizen science (CS): individuals were trained to monitor grouper gonads and supplied information on fishing spots and prices. After comparing catch curves (based on weight) and curve prices (in the Brazilian monetary currency of reals), our results showed that catches in the Copacabana fishery have been stable (the results of the Kruskal-Wallis test showed no significant difference for either the weight of the catches or the average prices of dusky groupers in the years compared). Copacabana has been a sustainable fishery when considering its catches of dusky grouper. This is a very important result for conservation and management, considering the importance of small-scale fisheries in terms of their low fishing efforts and their possible effects on vulnerable species, as well as their ecological and economic importance in developing countries. Citizen science, alomng with local ecological knowledge, helps integrate research and fisheries as well as researchers and fishers and allows for larger sampling efforts and management training for fishers.

O_LIIn intertidal environments, land subsidence may change the local flooding regime and sediment composition, two main drivers of the macrozoobenthic community structure. In the Dutch Wadden Sea, a UNESCO world heritage site, gas extraction has resulted in an average subsidence of up to 2 mm y-1 of intertidal mudflats. These mudflats support a highly productive macrozoobenthic community, which offers important resources for birds and fishes. To what extent land subsidence due to gas extraction affects sediment and macrozoobenthos remains unknown and increasingly important given sea level rise. C_LIO_LITaking advantage of a monitoring program, we evaluated the effect of anthropogenically caused land subsidence on sediment composition and intertidal macrozoobenthos. Nearly 4600 points were sampled yearly (2008-2020) across the Dutch Wadden Sea, allowing us to compare sediment composition and macrozoobenthos biomass within and outside the subsidence area while controlling for the main drivers of these variables. We also compared population trends within and outside the subsidence area for 31 species with different habitat use in terms of depth and sediment composition. C_LIO_LISediment median grain size decreased in the subsided area at 1 {micro}m y-1 while on average remaining constant in other intertidal mudflats. Mud fraction was 3% higher within the subsided area throughout the studied period. This had no effect on the total biomass of macrozoobenthos. The biomass of species that use deeper areas increased within the subsidence area compared to outside, and the opposite was true for species using shallower places, but comparable patterns were also found in an area not affected by subsidence. C_LIO_LIChanges in median grain size could be happening, and minor changes in macrozoobenthic community composition. For a successful implementation of the "hand on the tap" principle in the Wadden Sea, it is necessary to define beforehand the relevant variables that represent the natural values, implement proper monitoring, and define threshold values above which effects are not acceptable. We propose median grain size, mud fraction and macrozoobenthic biomass as good measures of the natural values of the Wadden Sea, and the methods used here as a way for identifying anthropogenic effects on them. C_LI

Among cetaceans, the Cuviers beaked whale is considered an extreme diver, very challenging to be studied with standard monitoring methods due to its elusive behaviour and a preference for deep offshore waters. These limitations seem to be mitigated by the use of new molecular methodologies capable of intercepting small traces of DNA left in the environment (eDNA) by marine organisms. Moreover, the collection of water from the superficial layer of the sea represents a perfect case study for the targeting of marine mammals, as the constraints imposed by their nature implies periodic and frequent surfacing. Therefore, we designed and tested a taxon-specific primer set to infer the Cuviers beaked whale presence, with the aims of 1) examining the effectiveness of the eDNA technique to detect the presence of deep-diving cetacean in open waters, using the Cuviers beaked whale as case study; 2) providing data on the spatiotemporal occurrence of this species within the Canyon of Caprera; and 3) assessing the species occurrence in central northern Mediterranean Sea based on molecular traces. Results from this study demonstrated that collection of superficial waters is a valid approach to monitor deep-diving cetacean species, without the need for complementary visual survey monitoring. Specifically, this study provides evidence of the regular presence of the Cuviers beaked whale in the Canyon of Caprera, with a preference for bathymetry in the range of 700-1000 m. This study also showed a potential inshore movement of this species during fall, which is possibly related to migration of its cephalopod prey or a shift in prey preferences. Overall, the data presented here are particularly relevant in the optic of proposing the Caprera Canyon as an Important Marine Mammal Area (IMMA) in the Mediterranean Sea. At a wider level, this study also showed that the stronger positive signals were recorded in sampling stations located on submarine canyon systems, demonstrating the importance of these areas as elective habitats for the Cuviers beaked whale, thus the pivotal priority to their conservation.

Landings by the multi-gear coastal fleet operating off the Portuguese continental coast include near 300 species, from which only a few are the object of management plans. In this study, daily landings (kg trip_1) are used, along with an effort indicator, vessel length overall (LoA), to obtain landings per unit of effort (LPUE) as a proxy for the species relative abundance for a total of 48 species. LPUE indices were then used as a response variable in linear models where year (2012-2016), season, region (north and south) and NAO index were included as explanatory variables. Season and region effects were found to significantly affect species abundance for a total of 41 and 40 species respectively, while interannual effects were found to be significant for 19 species, and finally, the NAO index for 3 species. Global LPUE density maps are presented for a number of selected species and a subsample of trips where VMS records were available. For the species analysed, it is proposed that geographic and seasonal changes in LPUE indexes can be used to understand trends in abundance and obtain information that can be used in support of the definition of regional management plans.

Catadromous eels are found in more habitats than any other fish and are capable of inhabiting marine, brackish and freshwater environments. In this study we used the American Eel (Anguilla rostrata) as a bioindicator organism to create a novel method of using spatial analysis to study species conservation over landscape scales. We built a model of the subwatersheds of the Chesapeake Bay using a Digital Elevation Model (DEM) and overlaid eel density data (> 1 million eels sampled), dam density data and land use in ArcGIS. Dam construction in the study area peaked between 1955 and 1975, possibly as a result of flood control measures. Effects of land use were localized and most pronounced in areas around Baltimore, Maryland, Washington, D.C. and Richmond, Virginia, USA. Results indicate the Potomac and Rappahannock rivers appear to be areas of lesser concern while the upper James and York rivers are ideal for follow-up studies, since these area rank poorly in both eel density and barriers to fish passage. Because these rivers have high eel density downstream, the dams appear to be the limiting factor. Sampling methods have been inconsistent over time, making it is difficult to determine where eel densities are low vs. the area having had little sampling effort. This is partially resolved with catch per sampling event (CPSE), which appears to show a relationship between eels sampled and the number caught per sample. Potential strategies for improving watersheds include dam removal, fish passage and habitat restoration.

Large boreal rivers in Sweden are generally impounded by hydropower dams and a large proportion of their main stem shallow flowing habitats have been lost. Tributaries often contain relatively undisturbed habitats and could be important for the conservation of species diversity. Tributary mouth areas could be biodiversity hot-spots, due to the vicinity to the main stem and favorable environmental conditions. In this study, we investigate whether tributary mouth areas in two impounded boreal rivers (Ume- and Lule River) could be regarded as biodiversity hot spots for fish. Based on electrofishing in 20 tributary mouths, we found that overall fish diversity is generally low. The highest species richness and diversity was found in mouth areas dominated by intermediate substrate sizes (gravel - cobble). Few, if any, species were found in association with fine sediment substrates (smaller than sand). The tributary mouth areas had similar species richness and diversity as areas in the tributaries located 1-km upstream of the mouth, but the fish community composition often differed between these sites. Management action favoring fish diversity in the tributary mouth areas could include protection or rehabilitation of areas dominated by medium sized substrate and reduction of erosion and transport of fine sediments in the tributaries. Overall, we find no support for tributary mouths being hot-spots for fish biodiversity and while some patterns in diversity gives hints on suitable management action, it is important to further understand impacts in tributaries and their mouths especially in relation to temporal dynamics of the fish community.

The long-term monitoring of long-lived animal populations often requires individual identification. For cetacean populations, this identification is mostly based on morphological characters observable from a boat such as shape, spots and cuts of the back, caudal and dorsal fins. This is well suited for species easily displaying their caudal fins, such as the humpback whales Megaptera novaeangliae, or those whose skin pigmentation patterns enable individual identification. However, for elusive or shier species such as the sperm whales Physeter macrocephalus, this approach may be more challenging as individuals display a rather uniform skin pigmentation. They also do not show very often their caudal fin that must be photographed perpendicularly to the water surface, vertically and fully emerged, uneasing the individual identification from a boat. Immature sperm whales that usually have a caudal fin without any distinctive marks may sometimes be excluded from photo-identification catalogues. Within the framework of the Maubydick project, focusing on the long-term monitoring of sperm whales in Mauritius, passive underwater observation and video recording were used to identify long-lasting body markers (e.g., sex, ventral white markings, cut outs of fins) to improve individual identification. A catalogue of individual identity cards was developed and 38 individuals were recorded (six adult males, 18 adult females and 14 immatures). This catalogue was used in the field and enabled observers to record some nearly-daily and yearly recaptures. Advantages and disadvantages of this method are presented here. Such catalogues represent a robust baseline for conducting behavioural, genetic and acoustic studies in marine megafauna social species. Benefits of such newly acquired knowledge are of first importance to implement relevant conservation plans in the marine realm.

The northern Adriatic Sea is an important foraging ground for the loggerhead sea turtle Caretta caretta (Linnaeus, 1758) within the Mediterranean Sea. Here, spatial-temporal patterns of loggerhead sea turtles strandings along a short portion ([~]18 km) of the coast south of the Po River delta (Italy) during a three-year period (2019-2021) were investigated. A total of 244 records (alive, n=7; dead, n=237) were analysed and the curved carapace lengths (CCL, notch to tip, cm) mainly reflected sub-adults (average CCL=55.2 cm; 95% CI= 53.3-57). The month of July was identified as the critical month with the highest number of strandings, mirroring migratory processes toward this area during warmer months. Interaction with the trawl fishery was hypothesized as the main cause of mortality and a small fraction of deaths (6%; n=16) could be linked to boat strikes and net entanglement. The number of stranded turtles*km-1 as well as the absolute number of strandings along the short portion of monitored coast confirmed this area as the most impacted in Italy and perhaps in the whole Mediterranean Sea. This study provides valuable information to improve conservation efforts for this species and highlight that, with all due caution, monitoring stranding events can offer useful insights into the geographic ranges, seasonal distribution, and life history of marine species of conservation interest such as the loggerhead sea turtle.