Important Nursery Areas Research Articles

The function of the Wadden Sea in the life cycle of small pelagic fish

Most fish species require different habitats to complete their life cycle, with coastal areas often playing a crucial role as nursery areas for juveniles. The Wadden Sea is an important nursery area for juvenile fish in the North Sea ecoregion. Despite extensive research on the nursery function of the Wadden Sea for demersal species, its role in the life cycle of small pelagic fish (SPF) remains largely unknown. This limits our understanding of the Wadden Sea ecosystem, as SPF are the dominant component of the overall fish biomass and serve as important food source for higher trophic levels. We studied the role of the Wadden Sea in the life cycle of Atlantic herring (Clupea harengus), European sprat (Sprattus sprattus), European smelt (Osmerus eperlanus) and European anchovy (Engraulis encrasicolus) through monthly stow net and seasonal trawl surveys. Our study showed that SPF use the Dutch Wadden Sea primarily as juvenile habitat, with herring being the dominant marine juvenile representative. Length frequency distributions and genetic analysis revealed that the juvenile herring originated predominantly from southwestern waters, such as the English Channel. Additionally, the Wadden Sea still provides spawning grounds for herring and anchovy, with no substantial spawning observed for sprat. While smelt can complete nearly its entire life cycle in the Wadden Sea, it depends on connectivity to nearby freshwater for spawning. In summary, the Wadden Sea functions as a nursery for juveniles, and to a lesser extent as spawning grounds for adults. A thorough understanding of these functions is crucial for identifying bottlenecks and implementing effective conservation and management strategies.

Kinship assessment and insights into reproductive behaviour of the Critically Endangered green sawfish Pristis zijsron in Western Australia

Abstract In this study, single nucleotide polymorphisms were used to investigate kinship and philopatry for the Critically Endangered green sawfish, Pristis zijsron, in Western Australia. Sampling was conducted in an important nursery area: the Ashburton River estuary and adjacent tidal creeks. Kinship was inferred from the genotypes of 104 sawfish sampled between 2011 and 2014 (n = 31), and 2020 and 2022 (n = 73). The total number of dams contributing across all sites and time periods was estimated to be between 50 and 56. Fifty‐two full sibling dyads, 90 half sibling dyads and 72 third‐degree dyads were detected, involving 58, 67, and 46 P. zijsron, respectively. Of these, 34 half sibling dyads were related maternally and 56 related paternally, including multiple maternal and paternal half siblings pupped in different years, suggesting both female and male philopatry. Catch data indicated that two groups of maternal half siblings were littermates, demonstrating multiple paternity. A high degree of relatedness was found across the study area, with 88% of P. zijsron related to at least one other individual up to the third‐degree. Evidence for female philopatry in P. zijsron highlights the importance of protecting nursery areas for this species. The occurrence of philopatric behaviour in male and female P. zijsron suggests that dispersal might be limited in both sexes of this species, highlighting the need to investigate the amount of genetic diversity and incidence of inbreeding within remaining populations.

Lakeshore areas of conservation interest: Characteristics of nursery areas of the threatened lake‐dwelling grayling, Thymallus thymallus

AbstractResearch‐based knowledge is essential for effective conservation and restoration of threatened aquatic species and habitats. Here, our aim was to gather this knowledge on the lake‐dwelling grayling (Thymallus thymallus), typically a riverine fish. Such atypical populations are particularly vulnerable to anthropogenic impacts, including fishing pressure, climate change, eutrophication and waterway construction, some of which affect especially the early life stages. However, there is little information available to guide management and conservation of grayling in lakes. Accordingly, we assessed characteristics of the nursery areas in the threatened grayling population of Lake Puruvesi (eastern Finland). In particular, we used beach seines in two consecutive years to sample lakeshore sites (including islands) that were a priori presumed suitable for grayling. We assessed the occurrence of grayling fry (larvae and post‐larvae <40 mm in length) regarding depth, year, the site's exposure (fetch), bottom shear stress, substrate coarseness and shoreline's north–south orientation. Overall, we found grayling fry in low numbers at every fourth site, with the sites’ exposure and dominant substrate coarseness being most relevant variables. In particular, more exposed sites (i.e. with higher fetch values) and fine‐grained substrates dominated by sand or gravel had more grayling fry. Average depth, bottom shear stress or shoreline orientation along the north–south axis did not have a significant effect. Together, the results suggest that the most important nursery areas for lake‐dwelling grayling are lakeshore zones that are barren and exposed. Hence, the sites share characteristics with those used for reproduction by the more common riverine grayling. We hope that these findings will facilitate lake‐dwelling grayling's management and conservation efforts.

NURSERY AREA FOR THE THREATENED GUIANA DOLPHIN, SOTALIA GUIANENSIS, ON THE NORTHEAST COAST OF BRAZIL

Cetacean calves are considered fragile and vulnerable, especially in the first year of life. To guarantee safety and increase the likelihood of survival, females with calves use habitats with unique characteristics, called nursery areas. In the present study, we investigated whether the Guiana dolphin Sotalia guianensis, considered a threatened species in Brazil, uses the Tibau do Sul Coastal Wildlife Reserve (REFAUTS) as a nursery area. We identified the Guiana dolphins through photographs and recorded the composition of the groups during the 41-day sampling period, between 2013 and 2019. We identified 17 adults/juveniles in the company of calves, five of which were recorded in three or more years of the study. The average size of the Guiana dolphin groups (mean±SE) was 2.4±0.08 individuals, ranging from 2 to 5 individuals (n = 98). Groups with calves were recorded in every year of the study and on 53.7% of the sampling days. A total of 35.8% of the Guiana dolphin groups had calves. These results suggest that REFAUTS is an important nursery area for Guiana dolphins on the Northeast coast of Brazil.

Fish community, seasonal movement and habitat use in a subtropical coastal lagoon

Coastal lagoons are environmentally and naturally dynamic areas crucial for fish reproduction and nursery. Thus, this research aims to evaluate the importance of the species performing their biological processes and development in this ecosystem. For this purpose, a subtropical coastal lagoon in the Gulf of California was taken as a case study, where four sampling seasonal campaigns were performed within the lagoon (internal zones) and the marine environment (external) nearby zones from 2016 to 2017. Diversity, evenness, and dominance indices were determined, and the number of individuals, size, length at first maturity, and reproductive period of each species were analyzed to obtain fish use of the lagoon. This coastal lagoon shows a high abundance of juvenile organisms in the cold season, whereas mature adults were mostly present during the warm season. Environmental variables influencing fish species development and distribution, such as sea surface temperature, salinity, and chlorophyll-a, were detected. To conclude, the subtropical coastal lagoon in the Gulf of California is an important nursery area where reproduction occurs mostly near adjacent areas.

Consequences of Juvenile Fish Movement and Seascape Connectivity: Does the Concept of Nursery Habitat Need a Rethink?

Estuarine and adjacent inshore habitats have long been recognised as important nursery areas for fishes before they disperse to coastal habitats. Assessing nursery function supports spatial and fisheries management, yet work commonly focusses on singular habitat types. Re-considering how juvenile fish connect habitats may improve our understanding of nursery function and the scales that recruits are supplied to coastal fisheries. This study quantified the juvenile movements of two harvested fishes in south-eastern Australia, luderick (Girella tricuspidata) and yellowfin bream (Acanthopagrus australis). Acoustic tags were used to track 33 luderick and 20 yellowfin bream from seagrass meadows for up to ~400 days in Jervis Bay Marine Park. Both species had relatively small home ranges (< 7 km2) and exhibited site attachment to seagrass meadows where they were released. Most luderick and yellowfin bream were detected moving 100’s metres to kilometres to reefs adjacent to seagrass, although these movements were not habitat shifts. Rather, reef-ward movements represented repeated visits that lasted days to months before fish returned to seagrass, suggesting that these movements may be explorations in search of suitable adult habitat. Strong retention within an existing marine reserve was observed, with only five of 33 fish tagged within reserves crossing the boundary into fished waters. Overall, our results demonstrate that juvenile fish use and connect multiple habitat types during their movements. These findings support the broadening of the nursery concept from single habitats to a mosaic of functionally connected habitat patches (dubbed ‘seascape nurseries’).

Response of demersal fishes to low dissolved oxygen events in two eutrophic estuaries

Coastal ecosystems serve as important nursery areas, yet they are facing many challenges. For example, eutrophication-induced hypoxia is one of the major threats to the functioning of coastal ecosystems, particularly estuaries. The Sundays and Swartkops estuaries both experience persistent eutrophic conditions, with frequent phytoplankton blooms (>20 μg Chl-a l−1) that result in instances of bottom-water oxygen depletion (<4 mg/l). Bi-seasonal sampling of both physico-chemical parameters and demersal fishes between February 2018 and September 2019 in the Swartkops and Sundays estuaries allowed for the quantification of low dissolved oxygen (<4 mg/l) and hypoxic (<2 mg/l) events in both estuaries and the impact of low dissolved oxygen (DO) and hypoxic events on overall fish species abundance, richness and distribution. Low DO conditions were typically observed in the bottom waters of the vertically-stratified meso-to polyhaline middle and upper reaches of the Sundays and Swartkops estuaries, respectively. Hypoxic conditions ( DO = 0.5 mg/l) were recorded in the Sundays Estuary during the study, whereas in the Swartkops Estuary the lowest DO recorded was 2.4 mg/l. Low DO events resulted in a decrease in fish species richness and overall abundance in the Sundays Estuary, while in the Swartkops Estuary fish species richness declined during low DO events, with little effect on fish abundance. Fish only completely avoided areas where DO was <1 mg/l or >10 mg/l. As such, the low DO concentrations recorded in the Swartkops Estuary did not have a noticeable impact on fish distribution, although the abundance of Rhabdosargus holubi and Caffrogobius gilchristi declined in the upper reaches of the Swartkops Estuary when DO was <3 mg/l. The results from this study provide much-needed insights into the impact of low DO and hypoxic conditions on the spatial distribution of demersal fish species.

Too young to die: Mapping nursery areas for early juveniles of the endangered sandbar shark (Carcharhinus plumbeus) to inform conservation in the Mediterranean Sea

Abstract Globally, elasmobranch species have been declining in abundance due to fishery activities. This conservation issue calls for effective management strategies and increasing efforts to protect these species. The declining status of elasmobranchs in the Mediterranean Sea is alarming as well. Reversing such dramatic trends requires tackling fishing pressure using multiple methods, including a fine‐tuned spatial resolution in conservation strategies incorporating robust evidence on species spatial use at different life stages and its overlap with fishing pressure. In particular, a scientifically sound identification of nursery grounds is crucial to define key spatial management targets promoting the recruitment of such depleted species. Here we focused on the sandbar shark (Carcharhinus plumbeus), listed as endangered by the IUCN, and on the nursery of its early juveniles such as newborns (i.e. a few months old) and young‐of‐the‐year individuals (i.e., &lt; 1 year old), both characterized by a total length below 71 cm. First, by monitoring a small‐scale fishery fleet in the North‐Western Adriatic Sea, we unambiguously identified a local multiyear nursery site for early juveniles of this species. Then, we combined such novel information with a bibliographic review on the presence and absence of early juveniles across Mediterranean regions to construct a species distribution model predicting favourable nursery areas throughout the entire Mediterranean Sea. To do so, a Bayesian approach was applied to construct a generalized linear model with spatial effect estimated by a Gaussian random field (INLA‐SPDE). Model‐based inference indicates that, in summer, which is the main pupping season, important nursery areas for this species are found along the North‐Western coast of the Adriatic Sea, in the coastal area of the Gulf of Gabes, and in the Gulf of Iskenderun (North‐Eastern Levantine Sea). Synthesis and applications: These key areas should be prioritized to apply conservation measures to foster the recruitment of this species since intense fishing activities were also documented. Model predictions also allowed to determine where unknown nursery grounds may potentially occur, a valuable information to direct future monitoring efforts and clarify any further occurrence of nursery areas.

Residency and Use of an Important Nursery Habitat, Raja Ampat’s Wayag Lagoon, by Juvenile Reef Manta Rays (Mobula alfredi)

The behaviour and spatial use patterns of juvenile manta rays within their critical nursery habitats remain largely undocumented. Here, we report on the horizontal movements and residency of juvenile reef manta rays (Mobula alfredi) at a recently discovered nursery site in the Wayag lagoon, Raja Ampat, Indonesia. Using a multi-disciplinary approach, we provide further corroborative evidence that the lagoon serves as an important M. alfredi nursery. A total of 34 juvenile rays were photo-identified from 47 sightings in the sheltered nursery between 2013–2021. Five (14.7%) of these individuals were resighted for at least 486 days (~1.3 years), including two juveniles resighted after 641 and 649 days (~1.7 years), still using the nursery. Visually estimated (n=34) disc widths (DW) of juveniles using the nursery site ranged from 150–240 cm (mean ± SD: 199 ± 19), and the DW of two juveniles measured using drones were 218 and 219 cm. Five juveniles were tracked using GPS-enabled satellite transmitters for 12–69 days (mean ± SD: 37 ± 22) in 2015 and 2017, and nine juveniles were tracked using passive acoustic transmitters for 69–439 days (mean ± SD: 182 ± 109) from May 2019–September 2021. Satellite-tracked individuals exhibited restricted movements within Wayag lagoon. The minimum core activity space (50% Utilisation Distribution-UD) estimated for these five individuals ranged from 1.1–181.8 km2 and the extent of activity space (95% UD) between 5.3–1,195.4 km2 in area. All acoustically tagged individuals displayed high residency within the nursery area, with no acoustic detections recorded outside the lagoon in the broader Raja Ampat region. These juveniles were detected by receivers in the lagoon throughout the 24 h diel cycle, with more detections recorded at night and different patterns of spatial use of the lagoon between day and night. The observed long-term residency of juvenile M. alfredi provides further compelling evidence that the Wayag lagoon is an important nursery area for this globally vulnerable species. These important findings have been used to underpin the formulation of management strategies to specifically protect the Wayag lagoon, which will be instrumental for the survival and recovery of M. alfredi populations in Raja Ampat region.

Using acoustic telemetry to locate flatfish spawning areas: Estuarine migrations of turbot Scophthalmus maximus and European flounder Platichthys flesus

Estuaries are complex environments that provide important nursery areas for several fish species, but anthropogenic activities as well as low salinities may affect fish reproductive potential. This study investigated spawning migrations of turbot (Scophthalmus maximus) and European flounder (Platichthys flesus) in the estuary of Roskilde Fjord using acoustic telemetry. For turbot, migratory behaviour was coupled with salinity measurements to estimate likelihood of successful spawning. Turbot inRoskilde Fjord are stocked fish, whereas the European flounder represents a naturally occurring population. Telemetry data suggested that the two species exhibited different migration behaviours towards the spawning season. The migratory behaviour of turbot indicates that they remain in the southern parts of Roskilde Fjord where successful development of eggs and larvae may be limited by low salinity. In contrast, the majority of European flounder migrated towards more marine waters prior to the spawning season, and only a minority of the fish remained inside Roskilde Fjord during the spawning season. Consistent with previous studies, the present results indicate that European flounder perform partial spawning migration. Thus, European flounder may utilize a diversity of spawning areas, including the brackish waters inRoskilde Fjord estuary as well as more marine waters with elevated salinities. Our results are important for future management of spawning areas, recruitment dynamics and selection of suitable turbot populations for stocking.

Environmental influences on the ichthyoplankton in hypersaline estuaries located in a Semiarid Northeastern Brazilian coast

ABSTRACT Hypersaline estuaries are commonly found in the Semiarid Northeast Brazilian coast. However, the utilization of these estuaries by early life stages of fishes is less well documented. This study aimed to evaluate the effects of environmental factors on the ichthyoplankton, and to describe their spatial and temporal variation in two estuaries (Tubarão and Casqueira). The sampling were diurnally in four excursions carried out during two dry-season months (November and December 2017) and two rainy-season months (May and July 2018). A total of 423 larvae representing 30 species (14 families) and 2,762 eggs (five families) were collected. Although the community structures were similar in both estuaries, there was strong seasonal variation, with higher abundances observed during the dry season. Low rainfall was the primary environmental driver affecting ichthyoplankton in both estuaries. Other environmental factors, such as depth, water temperature, and channel width, were also predictor variables for the distribution of eggs and larvae. The ichthyoplankton was dominated by marine estuarine-dependent species in both estuaries, accounting for 76% of individuals. The presence of the early life stages of typically marine species suggests that hypersaline environments provide important nursery areas and play an essential role for some coastal fish species.

Inter‐sexual comparison of body biomass, proximate biochemical composition, and fatty acid profiles of new juvenile squat lobsters (Pleuroncodes monodon) in the Southeast Pacific Ocean

AbstractIn the wide distribution range of the red squat lobster Pleuroncodes monodon in the Southeast Pacific Ocean, there is an important nursery area on the southern coast of Chile. The new juvenile individuals from this nursery area are directly recruited into the adult squat lobster population, which is exploited by industrial fisheries. Despite the importance of new P. monodon juveniles for recruitment estimations in fishery management models, their bioenergetic condition and/or nutritional status at the onset of their benthic phase remain unknown, as are the differences in the biochemical composition and energy reserves of the two sexes, which could help explain the cost of the first breeding event in females. Therefore, in new juvenile squat lobsters with the same degree of immaturity, we quantified and compared between the sexes (female vs. male): the size (cephalothorax length, CL), body biomass (dry weight and organic matter), biochemical composition (proteins, glucose, and lipids), and fatty acid profiles (FAs). The results indicate that the CL of new juveniles was similar between the sexes, while the dry weight and organic matter presented significant differences, with higher values in new juvenile females (NJF) than new juvenile males (NJM). Similarly, the NJF had a higher content of proteins, glucose, and lipids than NJM. The FAs also showed significant differences between the sexes; the NJF had a higher content than NJM in all fatty acid classes (i.e., saturated, monounsaturated, and polyunsaturated), with the FAs DHA (C22:6n‐3), EPA (C20:5n‐3), oleic (C18:1n‐9), palmitic (C16:0), and eicosatrienoic (C20:3n‐3) significantly contributing to the differentiation of FA profiles between the sexes. All of the aforementioned differences among the multiple variables of the bioenergetic condition can indicate biochemical adaptations in the storage capacity of energy reserves, particularly among NJF that must support the high energy cost of the first reproductive event (characterized by embryo production and incubation), which occurs during the austral winter, a period predominated by cold‐water temperatures and scarce food availability in the habitat. Overall, our findings have significant implications in fishery management models. In this case, defining the bioenergetic condition of the new juvenile squat lobsters can aid in predicting the density and stability of the adult population, which is exploited by commercial fisheries.

Effects of pesticides and metals on penaeid shrimps in Maputo Bay, Mozambique – A field study

Estuaries are important nursery areas for many species and these habitats are often affected by anthropogenic activities. We investigate possible negative effects of pesticides and metals on penaeid shrimps in Maputo Bay, Mozambique. Shrimps and water samples were collected in three estuaries and one coastal area for biomarker and chemical analysis. Acetylcholinesterase (AChE) and glutathione-S transferase activities were analysed as biomarkers for pollutants. 37 different pesticides were analysed in water samples and shrimp muscle tissue was analysed for 10 metals. Risk assessment showed that the environmental thresholds were exceeded for several herbicides in three of four of the assessed nursery areas. Lower AChE activities were detected in shrimps captured close to an agriculture area and this location had the lowest shrimp densities. Metal analysis in shrimp showed low levels. Despite localized effects, results highlight the need to improve the regulation of pollutants in the Espírito Santo estuary in Maputo bay.

Prey selectivity and feeding rates of the scyphozoan Catostylus tagi (Haeckel, 1869)

Abstract The occurrence of scyphozoan blooms is frequently reported in coastal areas, suggesting a need to assess its impacts on trophic webs. However, many scyphozoan species remain understudied with regard to their feeding ecology. Here, feeding selectivity experiments were conducted to learn about the possible prey preference of Catostylus tagi among mesozooplankton prey and estimate feeding rates. In general, C. tagi demonstrated a relative positive selection on small prey as cyclopoid copepods (Oithona spp. and Oncaea spp.), copepod nauplii as well as non-swimming prey (fish eggs), and ingestion rates increased with prey concentration. Further in situ studies must be conducted during summer blooms, to determine the predatory impact, retrieving data of C. tagi and prey abundance, particularly in important nursery areas such as estuaries.

Assemblage structure and distribution of fish larvae on the North Kenya Banks during the Southeast Monsoon season

The North Kenya Banks (NKB) is the broadest area of continental shelf along the Kenyan coast, and experiences higher productivity relative to neighbouring shelf regions. It is an area of great importance to Kenya with new emerging fisheries that have the potential to improve the livelihoods of local impoverished fishing communities. Managing these emerging fisheries successfully however is challenged by insufficient data on the fisheries and the local marine environment, and the lack of a management plan specifically for the NKB region. Here, baseline information on the ichthyoplankton assemblage across the NKB region during the Southeast Monsoon season is described and analysed to understand the effect biophysical parameters have on larval composition, abundance and distribution. The dominant fish larvae families were Engraulidae (29.5% of total) followed by Sphyraenidae (8.6%), Carangidae (8.2%), Scombridae (6.2%) and Lutjanidae (5.5%), whilst the dominant species within these families were Encrasicholina sp., Sphyraena sp., Thunnus albacares, T. alalunga and Lutjanus sp., respectively. A high prevalence of larvae from migratory species such as T. albacares, T. alalunga and Gempylus serpens was found across the northern part of the NKB, suggesting that the area may be an important nursery area for migratory fish with implications for fisheries across the wider Western Indian Ocean. Zooplankton abundance, temperature and conductivity played a positive role in determining the structure and composition of fish larvae assemblages across the NKB region. The high larval densities encountered out to the shelf break (200 m contour) imply that the NKB is a productive fishery and as such requires appropriate management oversight. Furthermore, the identification of a clear influence by temperature on larval distributions suggests that the NKB fishery may be susceptible to predicted future warming in this region with implications for both management of the resource and those fishing communities who benefit from the fisheries.

Climate Change Impacts on Salt Marsh Blue Carbon, Nitrogen and Phosphorous Stocks and Ecosystem Services

Salt marshes are valuable ecosystems, as they provide food, shelter, and important nursery areas for fish and macroinvertebrates, and a wide variety of ecosystem services for human populations. These ecosystem services heavily rely on the floristic composition of the salt marshes with different species conferring different service values and different adaptation and resilience capacities towards ecosystem stressors. Blue carbon, nitrogen, and phosphorous stocks are no exception to this, and rely on the interspecific differences in the primary production metabolism and physiological traits. Furthermore, these intrinsic physiological characteristics also modulate the species response to any environmental stressor, such as the ones derived from ongoing global changes. This will heavily shape transitional ecosystem services, with significant changes of the ecosystem value of the salt marshes in terms of cultural, provisioning, regulating, and supporting ecosystem services, with a special emphasis on the possible alterations of the blue carbon, nitrogen, and phosphorous stocks retained in these key environments. Thus, the need to integrate plant physiological characteristics and feedbacks towards the expected climate change-driven stressors becomes evident to accurately estimate the ecosystem services of the salt marsh community, and transfer these fundamental services into economic assets, for a fluid communication of the ecosystems value to stakeholders, decision and policy makers, and environmental management entities.

Using historical and citizen science data to improve knowledge about the occurrence of the elusive sandbar shark Carcharhinus plumbeus (Chondrichthyes - Carcharhinidae) in the Adriatic Sea.

The Mediterranean Sea is an extinction hotspot for sharks, skates, and rays, with at least half of all species being threatened. The sandbar shark Carcharhinus plumbeus is among the most threatened species and is declared endangered (EN) in the Mediterranean according to the IUCN Red List of Threatened Species. The Adriatic Sea was previously proposed to be an important nursery area for this species based on sporadic sightings of neonates and juveniles. However, this species is generally considered to be rare in this region, and reports of its presence are scarce. Here, we present new records for the sandbar shark in the Adriatic Sea and review spatial and temporal data accumulated from literature, museum specimens, and citizen science initiatives in an attempt to assess the distribution and seasonality of this species. The majority of the records were from neonate and juvenile sandbar sharks, and three hotspots for their occurrence could be identified: (1) the Emilia-Romagna region, (2) the Veneto region, and (3) the Gulf of Trieste. Our data indicate a high concentration of sandbar sharks around the delta of the Po river, emphasising the need for scientific surveys in this confined area in order to confirm a possible nursery ground. Data collected by citizen science initiatives reveal that this species is still present in the Adriatic Sea and might be more abundant than previously thought, underlining the potential of citizen science as a valuable tool to monitor the distribution of rare and endangered species.

Reproductive aspects of seven threatened shark species captured by artisanal fisheries in the southern Caribbean Sea

Venezuela is among the top four Latin American countries with the greatest elasmobranch biodiversity. The country is also characterised by extensive artisanal fisheries, but there is a paucity of regional life-history data for many important species. Here, we provide reproductive information for one local (Carcharhinus acronotus) and six cosmopolitan species (C. brevipinna, C. falciformis, C. limbatus, Galeocerdo cuvier, Sphyrna lewini and Isurus oxyrinchus) landed by artisanal fisheries at Margarita Island, Venezuela. For two years (2006–2007), three ports and two fish markets were weekly sampled for the total length (TL), sex, and maturity stages for specimens of the assessed species. A total of 664 specimens were analysed, of which 96% were immature. We found no significant differences in the sex ratios of all species, except for C. falciformis (1.5F:1M). Based on the numbers of neonates with unhealed umbilical scars, parturition appeared to peak in the first half of the year for C. acronotus (April–June) and S. lewini (May–June). Conversely, the second half of the year appeared important for parturition in C. brevipinna (August–September), C. limbatus (July–September) and G. cuvier (September–November). Both C. falciformis and I. oxyrinchus (individuals <1.5 m TL) showed non-seasonal parturition. The large percentages of small sizes of individuals in landings imply the waters surrounding Margarita Island might represent an important nursery area, and it is likely that historical and ongoing harvest rates represent a threat for regional populations of various elasmobranchs.

Littoral habitats as major nursery areas for fish species in estuaries: a reinforcement of the reduced predation paradigm

For many decades, the role of estuaries as important nursery areas for fishes was accepted as fact by scientists and environmental managers. At the turn of the 21st century, a question mark was raised in relation to the reduced predation component of the nursery function, with some scientists contending that both large and small piscivorous fish species had access to the estuarine habitats that juvenile fishes in estuaries occupied. If true on a global scale, the nursery designation for these habitats would be compromised and the long-held paradigm that estuaries are important nursery areas for fishes would need to be revised. In this review, I examine the nature of fish nursery areas in estuarine littoral habitats from a mainly predation perspective and, based on a variety of ichthyofaunal and avifaunal studies, come to the conclusion that apart from a few selected estuarine systems, there is limited predation on juvenile fishes in these particular areas. This, coupled with the abundant suitable food resources for juvenile fish from different trophic categories, shelter from high-energy marine wave action and biological connectivity between a variety of submerged and emergent macrophyte communities, renders shallow estuarine littoral areas ideal nursery areas for the juveniles of mostly euryhaline marine fish species, the dominant component of estuarine ichthyofaunas globally. In addition, there are strong indications from the fossil record that these littoral estuarine nursery areas have been functioning since the Devonian, more than 350 million years ago.

The decline of short‐beaked common dolphin (Delphinus delphis) in the waters off the island of Ischia (Gulf of Naples, Italy)

Abstract This study presents data on a local population of short‐beaked common dolphin monitored in the waters off Ischia Island (Gulf of Naples, Italy) over a 16‐year period (2000‐2015). We examine dolphin occurrence and distribution and perform photoidentification analysis. The data presented support the hypothesis that the waters around Ischia Island represent a feeding area, as well as a calving and an important nursery area for this local population, providing favourable conditions in which to give birth and raise calves. The levelling‐off of the photoidentification curves together with the continuous decline of the encounter rate lead us to believe that the area has been a hotspot for a local population (mainly resident) for years and that now this population is dying (has died) or is moving (has moved) to other locations. Several expanding human activities at sea have the potential to impact on the common dolphin in the study area, the most significant possibly being habitat disturbance and degradation (including traffic and noise pollution) and overexploitation of food resources by the fishery. The data presented in this study offer a strong argument for explicit and urgent population‐specific conservation and management strategies to be developed and applied locally for common dolphins, considering that they rely on the region for important biological processes.