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The catch of butterfly kingfish Gasterochisma melampus, a large pelagic species in southern temperate waters, is strongly biased (73%) towards females. Whether this is caused by differences in sex-specific spatiotemporal distributions or mortality of sexes is investigated herein. Analysis of sex ratios using a generalized additive model (GAM) for year, month, latitude, longitude, sea surface temperature, and fork length from Japanese longline catch data for areas where immature and adult fish occur revealed the influence of space and time on sex ratios to be small, and that of fork length to be large. Based on observation of the increments in vertebrae of immature fish (N = 179), the fork length at the time of increment formation was back-calculated from distances between increments on the anterior and posterior cones, generating 2–8 measurements per vertebra and 865 data points in total. Growth equations were calculated for each sex, with females growing faster. The age composition of males and females in the catch was similar, meaning that the mortality rate in males is unlikely to be higher than that of females. The data suggest that biased sex ratios in catches are representative of the natural sex ratio in a population for fish more than 60 cm in fork length.

Brown trout Salmo trutta (L.) is a facultative anadromous species, where a portion of individuals in populations with access to the sea perform migrations to use the richer feeding resources. We investigated the effect of salmon lice Lepeophtheirus salmonis (Krøyer 1837) infestation on the survival and behaviour of wild trout post-smolts (average fork length = 180 mm) during their marine migration. Comparisons of the marine migratory behaviour were made between an artificially infested group (n = 74) and a control group (n = 71) in an area with low natural lice infestation pressure. Artificial infestation was estimated to cause 100% prevalence and a mean intensity of 65 lice fish−1 (mean relative intensity of 2.4 lice g−1 fish). Survival analysis showed limited statistical power but revealed lice-induced mortality, with an estimated hazard ratio of 2.73 (95% CI = 1.04−7.13) compared to the control group, when data from a previous pilot study were included. Surviving individuals in the infested group additionally responded by residing closer to fresh water while at sea, and by prematurely returning to fresh water. On average, infested fish returned to fresh water after only 18 d at sea, while control fish spent on average 100 d at sea. The residency in the inner part of the fjord and the premature return to fresh water represent an adaptive behavioural response to survive the infestation, at the probable cost of reduced growth opportunities and compromised future fitness.

Defining the home range of vulnerable species is critical for designing effective spatial management strategies. However, animal home ranges often change with ontogeny, and quantifying the associated temporal and spatial changes is particularly challenging for mobile marine species. Here, we investigated how the space use of a top predatory reef-associated fish (giant trevally Caranx ignobilis) scales with body size. Fish were tagged with acoustic transmitters and passively tracked for >3 yr at a tropical island and atoll in the Republic of Seychelles. A sheltered atoll environment was critical for juvenile fish (<60 cm fork length, FL) that exhibited a shift in home range location and area as they matured into adults. Small (60−100 cm FL) and large (>100 cm FL) adult fish appeared to favour shallow coral reefs and associated reef drop offs whilst sharing a similar core home range location. Large adult fish utilized a greater diversity of habitat types and had significantly (p <0.05) greater annual dispersal distances (mean = 35.29 km, max = 91.32 km) than small adults (mean = 13.72 km, max = 21.55 km). Additionally, the home range of large adults (mean = 209.74 km²) was significantly (p 0.05) larger than that of juveniles (mean = 38.73 km²) and small adults (77.32 km²) and there was a significant (p = 0.02) relationship between fish length and home range size. Furthermore, tagged fish took up to 34 mo (mean = 18.54 mo) to utilize the full extent of their home range. The habitat shift and expansion in home range size throughout ontogeny should be taken into account when designing effective spatial management plans for C. ignobilis.

Ghosh, S., 2023. Reproductive biology and feeding habits of razorbelly scad, Alepes kleinii (Bloch, 1793), in the northeastern Arabian Sea. Journal of Coastal Research, 39(6), 1094–1104. Charlotte (North Carolina), ISSN 0749-0208. Alepes kleinii is subject to a commercial fishery in the northern Indian Ocean. The present study provides new information on the diet and reproductive biology of this species, based on the examination of 1109 specimens caught by gillnet off the coast of Veraval (north-eastern Arabian Sea). These samples ranged from 8.6–16.9 cm fork length (LF), and the sex ratio (male:female) was 1:1.45. Females and males reached sexual maturity at 12.25 cm and 12.57 cm LF, respectively. A. kleinii spawn throughout the year, though the peak spawning period was January–March. Monthly percentage of spawning capable individuals ranged from 11.8–60.4% (females) and 12.5–52.6% (males). The gonadosomatic index of females varied from 2.55–6.93, and absolute batch fecundity ranged from 30,653 to 70,275 eggs. Egg diameter (ranging from 230–720 µm) distribution was bimodal with the dominant peak at 601–700 µm, indicating group-synchronous ovarian development. In relation to the diet, A. kleinii <10.0 cm LF were zooplanktivorous, with zooplanktonic crustaceans the predominant prey category; whereas crustaceans were the principal diet of larger (≥10.0 cm LF) individuals followed by juvenile teleosts. Variations in feeding preferences were insignificant with respect to three climatological seasons (18.14%–18.50%) and two length classes (17.73%). Feeding intensity was low, although it increased with fish length, and was at a minimum during the peak spawning months.

Differences in the reproductive traits of Pacific bluefin tuna Thunnus orientalis (PBF) in the Sea of Japan (SOJ) were investigated to evaluate the reproductive potential in 3 fishing grounds (i.e. northern, central and southern areas). The size distribution of PBF differed among the fishing grounds, with smaller fish (100–130 cm in fork length, FL) being caught in the central and northern areas of the SOJ. Spawning-capable females were found at sea surface temperatures (SSTs) between 17 and 25°C, with most SSTs >21°C. Seasonal changes in SST differed among the fishing grounds, and the period when SST exceeded 21°C differed in each fishing ground. Spawning-capable females were found at different times among the fishing grounds, and were observed throughout the fishing season in the southern area of the SOJ. The mean ± SD relative batch fecundity was estimated to be 69.8 ± 45.3 and 92.7 ± 43.1 oocytes g−1 in the central and southern areas of the SOJ, respectively. The total spawning fraction was 0.2, 0.38 and 0.73 in the northern, central and southern areas of the SOJ, respectively. SST and FL were positively correlated with the batch fecundity. In addition, FL, SST and location affected the probability of occurrence of spawning-capable fish among mature fish. Therefore, the difference in the observed reproductive potential of PBF among fishing grounds in the SOJ can be linked to the differences in seasonal increases in SST and the size distribution of adult fish.

For anadromous fish entering the marine environment, we expect the probability of avoiding predation and starvation to increase with the quality and/or quantity of dietary resources consumed during the period immediately prior to, and following, ocean entry. Here, we report the results of research examining trophic history in relation to fork length, mass, and body condition in juvenile Chinook salmon captured in the southern Bering Sea using δ 13 C and δ 15 N analysis of skeletal muscle and liver samples. Our results show little inter-individual variability in δ 15 N, but variability in δ 13 C among tissues and within and among years was observed. Further, we found few relationships between δ 15 N and morphological or condition metrics, but strong relationships between δ 13 C and fork length, body mass, and Fulton’s K. We attribute the similarity in δ 15 N among individuals to high trophic level feeding ( i.e ., piscivory) associated with the prolonged duration of freshwater residency observed for juvenile Chinook salmon in our study area. Variation in δ 13 C, as well as relationships between δ 13 C, fork length, body mass, and Fulton’s K can be attributed to variability in carbon sourcing resulting from the large spatial footprint of our study area. In addition to relating these findings to Chinook salmon ecology, we offer guidance for future use of δ 13 C and δ 15 N analysis in studying early marine trophic interactions in anadromous fish.

We quantified cephalopods consumed by longnose lancetfish (Alepisaurus ferox, n = 1267 stomachs containing cephalopod remains) from 2009 to 2018 in the central North Pacific Ocean (between 0–35° N and 135–175° W). When cephalopods identified from beak remains in the stomach contents were included in diet analyses, clear increases in the abundance of gelatinous taxa and the inferred foraging depths of lancetfish were evident. Ontogeny in cephalopod consumption was evident for lancetfish, corroborating past diet studies. Small lancetfish (fork length < 97 cm) fed on smaller, muscular cephalopods from shallow habitats (0–500 m, e.g., Ommastrephidae, Onychoteuthidae), while large lancetfish (fork length ≥ 97 cm) consumed larger, gelatinous cephalopods from deeper waters (depths greater than 500 m, e.g., Amphitretidae, Cranchiidae). Cephalopod beaks were more abundant in the diets of large lancetfish, representing 37.8% of identified cephalopods, numerically. Although beaks likely remain in stomachs longer than soft tissues, they did not simply accumulate with increasing predator size. Cephalopods identified from beaks were also significantly larger than those identified from soft tissues. Despite having low average energy densities, large gelatinous cephalopods are important prey for lancetfish in deep habitats, with energetic values that are comparable to smaller, more muscular cephalopods (95.3 ± 125.8 kJ and 120.2 ± 169.4 kJ, respectively). Holistic consideration of cephalopod beaks in diet analyses will help to elucidate predator foraging behaviors and the trophic and ecological roles of gelatinous cephalopods in deep pelagic food webs.

The behaviour of returning Salmo salar (Linnaeus, 1758) approaching, and attempting to pass low-head weirs remains relatively unknown. A radio telemetry array was created at a low-head weir to enable the behaviour of S. salar (n = 120) to be observed as they approached and attempted to pass the barrier. The majority of fish successfully passed the barrier on their first or second attempt, some individuals required 11 attempts prior to successful passage occurring. Mean delay at the barrier per fish was 47.8 h (±SD 132.0 h), range 15 min to 31 days. Passage success on a fish’s initial attempt was significantly predicted by the amount of searching a fish undertook, fork length, and fat content. Fish were more likely to have a successful first passage attempt if it was smaller with a low fat content and exerted a greater effort in searching for a passage channel. Small-scale barriers cause delays and increased energy expenditure in migrating fish. Barriers may be creating an anthropogenic selection pressure for traits which enable passage success. The impact of a delay at a barrier and increased energy expenditure on reproduction and gonad development remains unknown but is likely to be negatively impacted by instream anthropogenic structures.

Baeck, G.W.; Seong, G.C.; Kang, D.Y.; Jin, S.; Soh, H.Y., and Kim, D.-G., 2023. Feeding habits of jack mackerel, Trachurus japonicus, in the coastal waters of South Sea, Korea. In: Lee, J.L.; Lee, H.; Min, B.I.; Chang, J.-I.; Cho, G.T.; Yoon, J.-S., and Lee, J. (eds.), Multidisciplinary Approaches to Coastal and Marine Management. Journal of Coastal Research, Special Issue No. 116, pp. 573-577. Charlotte (North Carolina), ISSN 0749-0208. To investigate the feeding habits of the jack mackerel, Trachurus japonicus, in the coastal waters of South Sea, Korea, fish samples were collected by a set net and purse seine fishery in March 2020 to February 2022. The Fork Length (FL) of these specimens was from 5.1 to 50.7 cm. T. japonicus were a carnivore that fed mainly on euphausiids and fishes. In addition, T. japonicus fed on small quantities of copepods, shrimps, cephalopods etc. T. japonicus underwent an ontogenetic dietary shift. The proportion of fishes and copepods decreased as body size increased, whereas the consumption of euphausiids increased gradually. Examination of the feeding habits according to ontogenetic feeding patterns in the diets of T. japonicus revealed that the mean number of prey (mN/ST) and mean weight of prey (mW/ST) continuously increased. Euphausiids most common prey during spring, autumn and winter, whereas fishes were mainly consumed during summer. Permutational Multivariate Analysis of Variance (PERMANOVA) revealed significant dietary differences by size class, and the interaction between the season and size class. T. japonicus were specialized feeders with euphausiids and fishes as their dominant prey.

The age, growth, and maturity of bonnetheads, Sphyrna tiburo, inhabiting estuarine and coastal waters of the U.S. Gulf of Mexico (GOM) were investigated. Based on results of a concurrent population genetics study, two populations were examined, the eastern GOM and western GOM. Vertebrae were collected and aged from 1081 females and 811 males ranging in size 261–1060 mm and 227–898 mm fork length (FL), respectively. The von Bertalanffy growth model provided the best fit to length-at-age data. Eastern GOM von Bertalanffy parameters (length parameters in mm FL) were L∞ = 844, k = 0.23, to = -1.99, and Lo = 310 for females and L∞ = 680, k = 0.39, to = -1.44, and Lo = 294 for males. Western GOM von Bertalanffy parameters were L∞ = 1005, k = 0.20, to = -1.81, and Lo = 298 for females and L∞ = 807, k = 0.30, to = -1.44, and Lo = 285 for males. Maximum observed age was similar between populations with an overall maximum of 17.1 years for females, and 12.1 years for males. Length and age at 50% maturity for the eastern GOM was 661.5 mm and 4.9 years for females, and 564.1 mm and 3.5 years for males and for the western GOM 772.7 mm and 5.3 years for females, and 644.9 mm and 4.4 years for males. Bonnetheads in the eastern GOM generally grow faster and to smaller asymptotic lengths than those from the western GOM; however, longevity is similar between the two populations.