Feeding Grounds Research Articles

Using acoustic monitoring to reveal nearly year‐round presence of humpback whales (Megaptera novaeangliae) in the waters of southern Iceland

AbstractIcelandic waters are a crucial feeding ground for North Atlantic humpback whales, yet their occurrence in these subarctic waters remains underexplored. This study examined seasonal and diel patterns in humpback whale occurrence off the Vestmannaeyjar archipelago, southern Iceland, from June 2018 to May 2019, using automated acoustic detections from bottom‐moored hydrophones. Vocalizations were manually categorized into social calls, song fragments, or songs. Further classification identified seven social sound types and 25 unique song units. Humpback whales were detected on 126 out of 329 recording days and were present in nearly all months except April and May. Social calls were most common in summer and fall, while song fragments and songs were prevalent in winter. No diel singing pattern was observed. These findings suggest southern Iceland serves as a vital habitat for humpback whales, acting as a feeding ground in summer and a migration stopover or overwintering site in winter. The study underscores the potential of acoustic monitoring to uncover important habitats year‐round, especially when field observations are scarce, and emphasizes the need for ongoing monitoring of habitat use. Continued acoustic monitoring could provide further insights into the whales' behavioral patterns and preferences, essential for their conservation.

Bottom Trawling and Multi‐Marker eDNA Metabarcoding Surveys Reveal Highly Diverse Vertebrate and Crustacean Communities: A Case Study in an Urbanized Subtropical Estuary

ABSTRACTEstuarine habitats serve as critical feeding and nursery grounds for many aquatic species and support fisheries. However, monitoring these complex ecosystems using conventional trawling methods is destructive, costly, and labor‐intensive. This study compared trawling and a multi‐marker environmental DNA (eDNA) metabarcoding approach to monitor marine vertebrate and crustacean communities in an estuarine environment in subtropical Hong Kong. We analyzed 16 bottom trawl samples and the eDNA from 32 two‐liter water samples using primer sets specific to fishes and mammals (MiFish‐U, 12S‐V5, and Berry‐Fish) and decapod crustaceans (MiDeca). We found that the eDNA approach detected more pelagic and demersal fishes (237 vs. 106 in trawling) and elasmobranchs (6 vs. 3) than trawling. The eDNA approach was also more effective than trawling in detecting threatened vertebrates (16 vs. 4), including the Indo‐Pacific Finless Porpoise and the critically endangered Large Yellow Croaker. Among the detected fish at species level, 70 species were detected by both approaches, 32 species were detected by trawling only, and 142 species were detected by the eDNA approach only. Regarding crustaceans, the eDNA approach detected slightly fewer decapods (61 vs. 77) and stomatopods (5 vs. 8) than trawl surveys. However, the eDNA approach could be enhanced through the development of suitable decapod‐specific primers and the expansion of the local reference database. In addition, multivariate analyses of the eDNA data revealed spatial patterns of fish and crustacean assemblages that might be associated with sediment loading, oxygen, and nutrient levels. Furthermore, there was a positive correlation between eDNA read counts and trawl catch, but their correlation coefficient was low. We conclude that eDNA metabarcoding can provide high‐resolution detection of species, composition, and unravel community–environment relationships in estuarine ecosystems. Overall, integrating the non‐destructive eDNA approach can complement the conventional trawling method for better‐informed sustainable fishery management and conservation.

Lake shape and the characteristics of migration behavior modify Atlantic salmon smolt migration success through lakes.

Migration is a high-risk behavior. For the Atlantic salmon, Salmo salar, migrating from its river nursery area to marine feeding grounds, the magnitude of risk varies with habitat type. Passage through lakes, in particular, is associated with low rates of migration success. Downstream migrating salmon smolts are rheotactic when migrating in rivers, but lakes typically provide poorer directional currents for migrating salmon. In this study we tested if, in the absence of clear navigational cues in lakes, Atlantic salmon smolts switch to a random search strategy to find the outflowing river. We constructed random search simulations to test if lake basin shape has an effect on migration success. We also compared simulated migration characteristics with migrations of salmon smolts through five real lakes for which there are telemetry data for migrating salmon. Correlated random walk simulations showed that a random search strategy could be successful for all lake shapes tested but was more successful in curved (round and elliptical) than rectangular basin shapes. Rectangular basins with the migration start and stoppoints at the ends of the lake had a higher success than those where these points were perpendicular to the axis of the lake. In general, a random walk model predicted the migration success rate of fish tracked through real lakes. However, for two lakes the simulated migration success exceeded that of actual success, suggesting that fish passing through these lakes were not adopting a random search strategy. We speculate that this is the result of either conflicting navigational cues which inhibit smolts from finding the lake outlet or that they temporarily suspend migration (e.g., to feed). Modelling predicted that for small lakes, directional swimming in short steps (ca. 100 m) followed by turns with very low variation from the direction of travel resulted in the highest migration success. For larger lakes, longer step lengths but also with low turn variation (simulated turning angle drawn from distributions of standard deviation 2° and 5° around a mean of 0°) resulted in the highest migration success. We conclude that navigation in downstream migrating salmon smolts switches from rheotaxis in rivers to a random search tactic in lakes except where residual flow cues in some lakes prevent this, at times resulting in suboptimal navigation outcomes.

Seasonal Distribution of Key Small-Sized Fish in the South Inshore of Zhejiang, China

Small-sized fish are a vital food source for large predatory commercial fish and play a key role in marine food webs, bridging lower and higher trophic levels. They are indispensable in maintaining the energy flow and material cycling within aquatic ecosystems. This study utilized bottom-trawl survey data from 2017 to 2020 along the south inshore of Zhejiang, China, complemented by concurrent environmental data, to examine the influence of environmental factors on the resource density and seasonal distribution patterns of four dominant small-sized fish species. The research findings indicated that SSH (sea surface height) and Chl (chlorophyll-a concentration) emerged as the key environmental factors influencing resource densities, with all four species exhibiting similar preferences toward these variables. However, significant disparities were observed in their preferences for SST (sea surface temperature), SSS (sea surface salinity), and DO (dissolved oxygen). The various species’ resource density and distribution patterns underwent significant seasonal variations. Additionally, the seasons and regions with the highest resource densities consistently aligned, occurring predominantly in autumn within the northern waters of the study area. This research further elucidated the environmental predilections and seasonal spatial distribution traits of small-sized fish in the south inshore of Zhejiang, an important feeding ground for economic fish species in the East China Sea. This provides scientific backing for forecasting alterations in coastal fishery resources under environmental and climate change scenarios and supports ecosystem-based fisheries management strategies.

Seabird attacks contribute to calf mortality in a whale population

Reports of seabirds attacking marine mammals have become frequent in the 2000s. Southern right whales Eubalaena australis off Península Valdés (PV), Argentina, have suffered the effects of micropredation by kelp gulls Larus dominicanus since at least the 1970s. During 2003-2013, this population experienced 9 yr of unprecedented high calf mortality. Using a 25 yr dataset (1995-2019) of focal follows of gull-whale interactions, we studied long-term changes in gull attack intensity (attacks h-1) and frequency, and explored whether they influenced calf mortality. We also asked whether calf mortality was affected by prey density at maternal feeding grounds during gestation. Applying Bayesian models, we found that the intensity and frequency of attacks increased significantly from 1995 to the 2000s, and that in 2004-2019, calves received 2.85 times as many attacks as did mothers. Moreover, attacks significantly contributed to increase the probability of calves dying, such that a year with average overall harassment had 2.26 times the mortality of a hypothetical year with no attacks. In years of high intensity and frequency of attacks, many older calves died near the end of the season, probably reflecting the cumulative effect of gull harassment on calf health. However, calf mortality was not affected by prey density, and extremely high mortality was not related to extremely high frequency or intensity of attacks, indicating that deaths are also influenced by other unidentified factors. These findings imply that chronic micropredation contributed to the unprecedented high calf mortality observed in PV and that other marine mammal populations experiencing seabird attacks could be threatened.

Assessment of Migratory Bird Diversity in Key Wetlands and Forest Reserves of Lakhimpur District, Assam, India

Lakhimpur district of Assam has a rich biodiversity and is home to many birds and has good breeding, resting and feeding grounds for migratory birds as well. However, there is little information available regarding the diversity of migratory birds in the district's various locales. A study was conducted in different locations to document the diversity of migratory birds visiting the district. To better understand the diversity of migrating birds in the district, six locations were selected- Kakoi RF, Ranga RF, Pabha RF, Satajan wetland, Bordoibam-Bilmukh Bird Sanctuary and Ghagor Ghat. Data were gathered through surveys, conducted for 218 days from January 2022 – May 2024. A total of 80 migratory bird species were recorded under 26 families of which Anatidae was most diverse. Out of the 80 species, 56 were winter visitor, 18 were local migrants and 6 were summer visitors. Among the migratory birds, Palla’s Fish Eagle (Haliaeetus leucoryphus) is listed as endangered species in IUCN Red List. Three species viz. Ferruginous duck (Aythya nyroca), Falcated duck (Mareca falcata) and Greater Adjutant (Leptoptilos dubius) are listed as near threatened species in IUCN Red List. Out of all the recorded species, insectivorous species are found to be highest (39%) as compared to species with other feeding habits. The Shannon diversity index was highest for Satajan wetland (H′ = 3.86) and lowest for Bordoibam-Bilmukh BS (H′ = 2.79). Jaccard similarity index showed highest similarity between Ranga RF and Kakoi RF (0.312) and the lowest value between Ranga RF and Bordoibam-Bilmukh BS (0.069). The Satajan wetland, Ranga RF, Kakoi RF, Pabha RF, Bordoibam-Bilmukh BS, and Ghagor Ghat are vital habitats that require conservation to continue supporting diverse resident and migratory birds, as well as other wildlife.

Mass occurrences of Sandeels (Ammodytes spp.) causing aggregations of diving ducks

In autumn 1999, large, compact flocks of foraging diving ducks, particularly Common Eiders Somateria mollissima, were observed within and at the mouth of Trondheimsfjord in Central Norway. Some of these aggregations were at places previously not known as particularly rich feeding grounds. This situation continued through the winter, and still existed in March 2000. Investigations on these feeding grounds showed that the only possible prey species occurring in significant quantities was Sandeel (only Ammodytes tobianus was verified). Although most of the fish were swallowed before the birds reached the surface, some ducks (including Velvet Scoter Melanitta fusca and Goldeneye Bucephala clangula) were observed eating Sandeels. Sandeel populations fluctuate in size annually and shoals are very patchily distributed. Consequently, the very variable occurrence in time and space of this food resource may occasionally bring about unusually dense and patchy aggregations of various species of diving ducks. Due to the specific habitat requirements of the Sandeel, these aggregations may also occur at localities that are not generally preferred feeding grounds for diving ducks, as was the case here. These findings may be relevant for some monitoring projects involving populations of diving ducks in marine environments.

Seasonal and diel patterns in Black Sea harbour porpoise acoustic activity in 2020-2022.

The Black Sea is a semi-enclosed inland sea with an unevenly distributed extensive coastal shelf area and anoxic deep waters. It is inhabited by common and bottlenose dolphins, as well as harbour porpoises, all represented by local subspecies. Between September 2020 and October 2022, 19 F-PODs deployed by research teams from Bulgaria, Georgia, Romania, Türkiye and Ukraine collected data on acoustic activity of Black Sea harbour porpoises. Strong seasonal and diel patterns were found, which varied in three regions. In the south-eastern part of the Black Sea, harbour porpoise acoustic activity was higher from January to May, with a peak in April. This pattern agrees with the seasonal anchovy migration from the winter spawning grounds in warmer waters in the south-eastern region to feeding grounds on the productive shallow north-west shelf. The diel pattern showed strong nocturnal acoustic activity, which is consistent with anchovy vertical migration. Porpoises on the western side of the Black Sea exhibited a bimodal seasonal pattern in acoustic activity, with a larger peak in April and a smaller one in October. Diel activity was primarily nocturnal. On the north-west shelf, harbour porpoise acoustic activity was mostly recorded during the warm period from April to October. The diel pattern showed activity mainly during daylight with two peaks: a smaller one approximately at dawn and a larger one at dusk. This pattern is similar to the vertical migrations of sprat. Overall, the results of the study were consistent with the prey being an important driver of seasonal and diel dynamics of harbour porpoise acoustic activity.

Chlorophyll-a interannual and seasonal variability in Panay Gulf: Identification of potential productive sites in the municipal waters and offshore blooms aided by water currents

Chlorophyll-a (Chl-a) is often used as a substitute for marine primary productivity measurements in fishing grounds. Panay Gulf stands as one of the Philippines’ vital fishing grounds, however, there are limited studies on its Chl-a interannual and seasonal variability. As such, this study used remotely sensed Chl-a data from 2017-2023 to assess areas with high Chl-a concentrations, and high primary productivity. The relationship of Chl-a to location, month, year, and water current variables was evaluated using a generalized additive model (GAM). Chl-a value of >10mg.m-3 was observed approximately <6.5, <2km, and <1km from the coast of Negros, Guimaras, and Panay Island respectively. During the Northeast Monsoon, short-term offshore pockets with elevated Chl-a levels were noted 13-24km from the coast of Binalbagan, Negros Occidental that function as brief feeding grounds for marine organisms. These Chl-a pockets originated from the coast of Negros Occidental and were advected by the water currents to the center of the gulf. Furthermore, 2017 and 2022 have the highest Chl-a value in Panay Gulf, coinciding with the region's seasonal high fisheries production. Major peaks were regularly observed in January and December when offshore Chl-a pockets were present. A minor peak was observed in July corresponding to the Southwest Monsoon season and attributed to summer blooms. The lowest Chl-a values were observed in September during the transition months. Furthermore, high Chl-a values were found in low current speed near the coast and water moving west and southwest during the Northeast Monsoon. This study is the first to evaluate the Chl-a dynamics in Panay Gulf, which is valuable information to understand the influence of the environment on marine productivity. This study may prompt the local government to intensify monitoring efforts and coastal protection in these valuable areas within the municipal waters.

Amino Acid Content in the Muscles of the Red Deer (Cervus elaphus) from Three Types of Feeding Grounds

This study aimed to analyze the amino acid profile, with a particular focus on the nutritional value of the protein of the longissimus lumborum (LL) and the semimembranosus (SM) muscles of deer originating from three feeding grounds: forest (FFG); conventional (CFG) grounds; organic farm (OFG). This is the first time that deer from an organic farm feeding ground have been included in this study. The muscles were collected from 36 deer carcasses with equal proportions of sex and 31 months of age. This study demonstrated significantly higher essential amino acid (EAA) and non-essential amino acid (NEAA) contents in the muscles of deer from the FFG and CFG compared to the OFG. However, the EAA-to-NEAA ratio was significantly higher for the muscles of deer from the OFG. The muscles of the FFG and CFG deer were characterized by a higher concentration of lysine as well as acidic and tasty amino acids compared to the OFG deer, with the muscles of the latter exhibiting a higher percentage of branched-chain amino acids (BCAA). The results obtained can be used professionally by nutrition specialists in preventive and therapeutic diets and breeders to make decisions about farm location and deer feeding strategies.

Body size- and temperature-related metabolic traits of juvenile chum salmon during northward migration

Due to rapid ocean warming at higher latitudes, northward habitat shifts of the dominant anadromous fish in the Northern Hemisphere, chum salmon ( Oncorhynchus keta), have recently been reported. Physiological development is considered to be a trigger for habitat shifts during early life. However, the possibility of physiological adaptations to future ocean warming is not fully understood, because data on the physiological traits of juveniles, such as metabolic rate and swimming performance, are limited. Using swim tunnel respirometers, we identified the metabolic traits of different-sized chum salmon juveniles originating from the Sanriku coastal river, Japan, which is far from the northern feeding grounds. The weight gain of &gt;2 g steeply increased the prolonged swimming performance, and the metabolic cost of swimming against the southward current in the Sanriku coast decreased with weight gain under the sea water temperature range of 8–12 °C. These findings indicate weight gain and inhabiting areas with temperatures &lt; 13 °C might provide potential benefits for northward migration. These results will be valuable when assessing the increased costs associated with changing ocean conditions.

Beyond counting calls: estimating detection probability for Antarctic blue whales reveals biological trends in seasonal calling

We explore the utility of estimating the density of calls of baleen whales for better understanding acoustic trends over time. We consider as a case study stereotyped ‘song’ calls of Antarctic blue whales (Balaenoptera musculus intermedia) on their Antarctic feeding grounds over the course of a year-long, continuous recording from 2014. The recording was made in the Southern Ocean from a deep-water autonomous hydrophone moored near the seafloor in the Eastern Indian sector of the Antarctic. We estimated call density seasonally via a Monte-Carlo simulation based on the passive sonar equation, and compared our estimates to seasonal estimates of detection rate, which are commonly reported in acoustic studies of Antarctic blue whales. The resulting seasonal call densities at our Antarctic site were strongly influenced by seasonally varying noise levels, which in turn yielded seasonal differences in detection range. Incorporating the seasonal estimates of detection area into our analysis revealed a pattern of call densities in accord with historic (non-acoustic) knowledge of Antarctic blue whale seasonal distribution and migrations, a pattern that differed from seasonal detection rates. Furthermore, our methods for estimating call densities produced results that were more statistically robust for comparison across sites and time and more meaningful for interpretation of biological trends compared to detection rates alone. These advantages came at the cost of a more complex analysis that accounts for the large variability in detection range of different sounds that occur in Antarctic waters, and also accounts for the performance and biases introduced by automated algorithms to detect sounds. Despite the additional analytical complexities, broader usage of call densities, instead of detection rates, has the potential to yield a standardized, statistically robust, biologically informative, global investigation of acoustic trends in baleen whale sounds recorded on single hydrophones, especially in the remote and difficult to access Antarctic.

Tracking Whale Calls in the Lower St. Lawrence Seaway at Land Seismometers

The Lower St. Lawrence Seaway (LSLS) is critical to Canada’s economy both as part of a major marine shipping corridor and a site of intensive fishing. Every year, fin whales and blue whales frequent the LSLS feeding ground. Understanding the mechanisms driving whale habitat usage is key for making informed decisions on shipping and fishing, reducing whale collision risks and mitigating noise pollution. We detect whales in the LSLS with land seismometers by using a method that relies on the intervals of the regularly repeating low frequency calls. The resulting catalogue contains 14,076 fin whale detections and 3,739 blue whale detections between February 2020 and January 2022. These detections follow the overall pattern of hydrophones, with most detections from fall to early winter in the Estuary and until mid-winter/spring in the Gulf. High detection rates in the Northwest Gulf throughout the winter months demonstrate that this region is potentially utilized year-round. This labelled catalogue may be suitable for developing a deep learning-based whale call detection algorithm. Making use of seismometers and deep learning can increase whale monitoring coverage within the LSLS and elsewhere.

The contributions of primary sources to fauna and the trophic structure in tropical seagrass areas: A case study from Thai waters

AbstractSeagrass provides habitat and resources for various organisms in coastal areas. However, the productivity of a seagrass meadow might vary by its size, which can influence the contribution of primary sources to fauna and the food web structure. This study uses stable isotopes to investigate the contribution of sources to faunas and the associated food web structure in two tropical seagrass meadows. The carbon (δ13C) and nitrogen (δ15N) stable isotopes of primary sources such as mangrove leaf, coastal and riverine particulate organic matter, seagrass material and associated fauna (fish, bivalves, gastropods, crab, shrimp) were investigated from samples collected seagrass meadows of different sizes, at Libong Island and Tharai Island in Thailand. The contribution of the primary sources to the fauna diet showed that seagrass material was the main food source for fauna in both sites. Moreover, the trophic niche did not overlap among the groups of each fauna guild, reflecting the support seagrass provides to resident fauna. The study emphasizes the important role of seagrass as a habitat and feeding ground in tropical coastal ecosystems.

Feeding habits of splendid alfonsino Beryx splendens in the vicinity of Kuroshio, the south of Japan

AbstractGut contents and nitrogen isotope ratio (δ15N) analyses were conducted on splendid alfonsino Beryx splendens collected in the vicinity of Kuroshio from May 2015 to November 2016 (n = 708) to identify their feeding habits in the Western North Pacific. Micronektonic fish, shrimp, and squid were the dominant prey species, with the Decapoda Acanthephyra quadrispinosa, Prehensilosergia prehensilis, Cephalopoda Enoploteuthis chunii, Chiroteuthis calyx, Teleostei Sigmops gracilis, and Gonostoma elongatum. These micronektons are common in the Kuroshio Current; thus, B. splendens is a possible opportunistic feeder. Gut content weight (GCW), occurrence (%O) of fish and squid, and δ15N were significantly increased with the fork length (FL) of B. splendens. Only the %O of shrimp does not show a significant relationship with the FL of B. splendens. These indicated the ontogenetic shift of dominant prey from shrimp to fish. Fattened specimens could also prey on a greater number of fish. The seasonality of GCW and %O values was high in spring and autumn and low in summer and winter. This seasonality indicated that the feeding habits of B. splendens are controlled by primary productivity in the surface layer and/or by maturity. When the Kuroshio flowed in the north of Hachijojima Island, the GCW was significantly increased, and some organisms, including C. calyx, G. elongatum, and S. gracilis, were preyed on more. While the offshore area of the Kuroshio has low productivity, B. splendens can actively prey in this area, indicating that it is an important feeding ground for this species.

Genetic Sex and Origin Identification Suggests Differential Migration of Male and Female Atlantic Bluefin Tuna (Thunnus thynnus) in the Northeast Atlantic

ABSTRACTKnowledge about sex‐specific difference in life‐history traits—like growth, mortality, or behavior—is of key importance for management and conservation as these parameters are essential for predictive modeling of population sustainability. We applied a newly developed molecular sex identification method, in combination with a SNP (single nucleotide polymorphism) panel for inferring the population of origin, for more than 300 large Atlantic bluefin tuna (ABFT) collected over several years from newly reclaimed feeding grounds in the Northeast Atlantic. The vast majority (95%) of individuals were genetically assigned to the eastern Atlantic population, which migrates between spawning grounds in the Mediterranean and feeding grounds in the Northeast Atlantic. We found a consistent pattern of a male bias among the eastern Atlantic individuals, with a 4‐year mean of 63% males (59%–65%). Males were most prominent within the smallest (&lt; 230 cm) and largest (&gt; 250 cm) length classes, while the sex ratio was close to 1:1 for intermediate sizes (230–250 cm). The results from this new, widely applicable, and noninvasive approach suggests differential occupancy or migration timing of ABFT males and females, which cannot be explained alone by sex‐specific differences in growth. Our findings are corroborated by previous traditional studies of sex ratios in dead ABFT from the Atlantic, the Mediterranean, and the Gulf of Mexico. In concert with observed differences in growth and mortality rates between the sexes, these findings should be recognized in order to sustainably manage the resource, maintain productivity, and conserve diversity within the species.

Artificial wetlands providing space gain for the suitable habitat of coastal Pied Avocet

A large number of artificial wetlands have replaced natural wetlands along waterbird migration routes to supply breeding, resting and feeding grounds for waterbirds. Effective identification of potential artificial wetlands that could serve as suitable habitats for waterbirds can provide important reference for field investigation and waterbird conservation. In this study, the habitat suitability of the Pied Avocet in the Yellow River Delta (YRD), China was simulated with the optimized MaxEnt model based on its occurrence records and environmental variables. The results showed that the MaxEnt model could well predict the habitat suitability of the Pied Avocet (Recurvirostra avosetta) in the YRD. The suitable habitats were distributed in the specific areas of the coastal zone, and artificial wetlands such as salt pans and mariculture ponds were the main components in the high-suitability area. The top three environmental factors affecting habitat selection were the land use and land cover (LULC), distance to the coastline and normalized difference vegetation index (NDVI). This paper emphasizes the role of artificial wetlands in providing suitable habitat for waterbirds. In order to better protect the habitat of waterbirds and alleviate human-bird conflict in the YRD, some targeted suggestions were put forward for the management gap of artificial wetlands. This study has strong practical significance for the protection and habitat management of waterbirds in the YRD. The methodology we employed is transferable to other wetlands, where efficient management is inhibited due to a lack of comprehensive field investigations.

Spatial distribution and habitat suitability of seaweed on West Simeulue Island, Aceh Province, Indonesia

Seaweed is an important biological resource for human life, serving essential ecological functions, including providing shelter and feeding grounds for marine biota. Seaweed can be found in several Indonesian waters, growing naturally or through cultivation, including in the waters around Simeulue Island. This study aimed to assess the distribution of seaweed in relation to land suitability, using oceanographic parameters in Simeulue Island waters. The research was conducted at five stations within the West Teupah District, South Teupah District, and Alafan District. In situ measurements were taken to evaluate land suitability for seaweed growth based on oceanographic parameters such as current speed, depth, substrate type, salinity, temperature, pH, and dissolved oxygen. Results indicated that seaweed in Simeulue Island waters is distributed along the coastline and attached to coral reefs and rocks at depths of 2-5 meters. The total area of seaweed distribution is approximately 351.83 hectares along a coastline of 206.12 km. The measured parameters of seaweed habitats include a pH of 7.7 to 7.9, salinity of 31-35.3 ppt, temperature of 20-30 °C, dissolved oxygen levels of 3-4.8 mg/L, depth of 2-5 meters, current speed of 0.10 to 0.60 m/s, and a sandy coral substrate. Based on these water quality and substrate parameters, the seaweed habitats in Simeulue Island are classified as highly suitable, with suitability values ranging from 64 to 82. The recorded environmental conditions collectively support optimal seaweed growth.

Role of Mangroves as Fishery Resource: A Systematic Review

Mangroves are valuable for their fishery resources, coastline stabilization abilities, water quality and clarity benefits, provision of habitat to economically profitable and ecologically important species, carbon sequestration services, and climate regulation capabilities. For centuries, mangroves have contributed significantly to the socioeconomic lives of coastal dwellers; especially in coastal fishery by providing nursery grounds for finfishes. Fishery resource services provided by mangrove ecosystem play an important role as the habitat, nursery ground, feeding ground, and spawning ground for various marine fish species. Despite their enormous socio-economic value and ecological significance, mangrove ecosystems are under severe threat such as large scale clearing, small scale harvesting and grazing, and industrial threats. The productivity of mangrove ecosystems has been linked to the well-being of valuable fisheries because of the role mangroves play as nursery habitat for a variety of marine and estuarine species. Many species of mangrove-related fish and crab have served the coastal communities as a natural, cheap and balanced nutritional source. Mangroves provide vital ecosystem services to coastal fishing communities through the enhancement of fisheries production. Due to their economic and ecologic significance, it is important to look to the future of these systems in the face of ‘fishery resource’ so that policy makers may act quickly to preserve and protect these ecosystems. Present review provides recent information on role of mangroves as fishery resource by studying the updated published literature and the threats faced by the mangroves. It is suggested that strategies should be prepared and rigorously implemented for the conservation and restoration of mangrove ecosystem.

Ommastrephes caroli (Cephalopoda: Ommastrephidae) from the Adriatic Sea: Morphometry, Age, and Genetic Characterization

This study gives the first data on the body and beak morphometric characteristics, age, and genetic structure of neon flying squid, a rarely caught cephalopod in the Adriatic Sea. We identified specimens as recently resurrected Ommastrephes caroli species using two mitochondrial markers, 16S ribosomal RNA gene and cytochrome c oxidase subunit I gene. Overall, 23 juveniles (3 females, 3 males, and 17 unsexed), with a dorsal mantle range of 65–152 mm, were caught in September 2020 in the waters of the Korčula Channel, island of Palagruža, and island of Jabuka, thus providing the most abundant sample of this species in the Mediterranean waters. The length–weight relationship showed an isometric growth. The results of the beak/length regressions suggest hood length is a useful characteristic for biomass estimation studies, as it showed a good linear fit to the dorsal mantle length. Statolith growth increments were easily visible and statolith microstructure analysis was successfully used to determine the age of 22 individuals. The estimated age ranged from 36 to 64 days (mean = 48 days). The back-calculation analysis showed that the squid hatched during July and August 2020, indicating that O. caroli spawns during the warmer, summertime period. Considering the size and age of the caught individuals, the Adriatic Sea could represent a potential feeding ground for this species. The genetic structure analyses indicate the existence of separate Atlantic and Mediterranean/Adriatic subclusters; however, this warrants further investigation.