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Deep-water snapper fisheries in the Mariana Archipelago are important commercial, recreational and subsistence fisheries. Pristipomoides zonatus, one of the top four deep-water snapper species harvested in Guam, lacked life-history information. To fill this gap, a comprehensive life-history assessment for P. zonatus, which included age, growth, mortality and reproduction, was conducted in Guam. The size range of P. zonatus sampled for life history was from 11.5 cm to 40.4 cm (fork length), with ages ranging from 0.5 to 30 years. Von Bertalanffy growth model-combined sex parameters were L∞ = 36.91 cm and K = 0.29. Males obtained a larger average size and a larger asymptotic size (+3.03 cm) than did females. Pristipomoides zonatus matures at a small size and age (L50 ≤ 24.0 cm and A50 ≤ 2.1 years) relative to their maximum size (40.4 cm) and age (30 years). Additionally, P. zonatus has a long spawning season and a short spawning interval, suggesting high reproductive output. Our results expand knowledge on Pristipomoides life history (fast early growth, moderately long-lived, high productivity), providing the necessary information for the management of P. zonatus in Guam.

Concentrations of total mercury (THg) in the axial musculature of northern pike (Esox lucius), walleye (Sander vitreus), lake whitefish (Coregonus clupeaformis), and sauger (Sander canadensis) were analyzed from several regions of Lake Winnipeg and three main inflows, focusing on Mossy Bay in the North Basin of the lake. Length-standardized means (standard means) indicated THg concentrations in pike of 550 mm fork length (0.44 ppm) and walleye measuring 400 mm (0.38 ppm) from Mossy Bay were highest in 1971 and declined to 0.13 and 0.22 ppm, respectively, by 1974. Standard means of both these species have been similar since 2010 (walleye; approximately 0.11 ppm) and 2013 (pike; approximately 0.17 ppm), except for a significant increase to 0.15 ppm in walleye in 2019, potentially related to concurrent changes in trophic interactions with invasive fish and invertebrate species. Standard means of 300 mm long sauger (0.23–0.29 ppm) did not decline significantly between 1971 and 1974, and those of 350 mm long whitefish ranged from 0.006 to 0.028 ppm from 1983 to 2016 with no clear temporal trend. In concert with data from other areas of Lake Winnipeg and the three inflows for 2000–2019, these results indicate higher contemporary concentrations in the South Basin of the lake. This latitudinal gradient in fish THg is assumed to be a result of continuous mercury inputs from the Red and the Winnipeg River, whereas a former point source of industrial mercury in the Saskatchewan River is no longer relevant. According to human consumption limits based on tolerable daily intake calculations and current THg concentrations of fish from Mossy Bay, substantial quantities of whitefish, pike, and walleye fish can be safely eaten.

Liver and skin tumours in brown bullhead (Ameiurus nebulosus) and white sucker (Catostomus commersoni) have been associated with contamination of the aquatic environment. In this study, we present a Bayesian hierarchical logistic-Bernoulli framework that considers the role of fish covariates (e.g., age, total weight, gonad weight, liver weight, fork length) on tumour prevalence to identify the presence of “hot-spots” around the Canadian waters of the Great Lakes, where high fish tumour frequencies are registered. We developed methods to discern the degree of impairment that are either based on the comparison of tumour frequencies in contaminated (or impacted) sites against those predicted in their corresponding reference areas, or the assessment of the prevailing conditions in impaired sites independently, without the need to establish baseline conditions for comparison purposes. Our modelling study predicts low frequencies of neoplastic tumours in all the impacted locations. In contrast, the same comparisons with the preneoplastic lesions provided evidence of distinct differences between impacted and reference sites in Jackfish Bay, St. Mary’s River, Niagara River, Hamilton Harbour, and Bay of Quinte. We also found weak to moderately strong relationships between tumour occurrence and fish physical characteristics that varied considerably in terms of their strength and nature (sign) among the different locations. Our study concludes that the prevalence of neoplastic tumours appears to have reached acceptable levels around the Great Lakes, but the distinctly higher levels of preneoplasms in several impacted locations underscore the need to improve our understanding of the lesions that may lead to carcinogenesis.

The invasive rainbow smelt (Osmerus mordax) was an abundant food source for Lake Winnipeg walleye (Sander vitreus), especially in the north basin of the lake, until the smelt’s collapse in approximately 2013. We quantified changing length-at-age (≈ growth rates) and relative mass (≈ body condition) in Lake Winnipeg walleye caught for a gillnet index data set. Here, walleye showed smaller length-at-age, particularly young fish in the north basin, over time. This approach to assessing growth suggests a constraint in the north basin fish, possibly a nutritional limitation between 2017 and 2018, that was not present in the south. We then analyzed a separate group of walleye (≥452 mm in fork length) sampled in 2017 as part of a large-scale tracking study, which had a similar slope in length-mass relationship to large walleye caught in that year for the gillnet index data. A panel of metabolites in whole blood samples associated with amino acid metabolism and protein turnover was compared. These metabolites revealed elevated essential amino acids in fish caught in the Dauphin River, and suggest that protein degradation may be elevated in north basin walleye. Therefore, based on both growth estimates and metabolites associated with protein balance, we suggest there were spatially distinct separations affecting Lake Winnipeg walleye with decreased nutritional status of walleye in the north basin of Lake Winnipeg being of particular concern.

We studied life‐history traits focusing on the growth and condition of the pikeperch Sander lucioperca to evaluate its phenotypic plasticity when introduced to new environments. Pikeperch is a non‐native fish introduced to Iberian freshwater fauna in 1998 that quickly spread to other river basins through human‐mediated activities, occupying now a wide variety of habitats along mainland Portugal. Condition (K and SMI), fork length at age, and length–weight relationships were studied for Portuguese populations. Pikeperch fork length for ages 1, 2, 3, and 4 was different between several populations. We applied generalized linear models (GLM) to study the influence of habitat type, latitude, altitude, time after first detection, and fish prey richness on pikeperch populations size at age 4 and condition. We observed higher condition values on populations from lower altitudes at lentic systems more recently introduced. But higher fork length at age 4 was found in populations from higher altitudes, on older populations with higher prey richness. Habitat type, time since first detection, and fish fauna composition are discussed as the main environmental factors explaining the observed phenotypic plasticity with concerns on predatory impact on native fauna., Sander lucioperca is a non‐native fish which colonized a variety of Portuguese freshwaters and showed adaptive phenotypic plasticity on condition and growth to such new environments. Habitat type, time since first detection, and fish fauna composition are discussed as the main environmental factors explaining the observed phenotypic plasticity with concerns on predatory impact on native fauna.

The fish monitoring effort has been increasing over the past years, due to conservation and management requests demanding more accurate data and consequently raising costs. This is an important challenge especially for remote and disperse locations where fish sampling poses unbearable costs, leading to limited spatial sampling schemes, limited data on rare and occasional landed species, and erroneous and biased observations. In this article, we propose a new autonomous system that can be installed on monitoring spots or on board fishing vessels, which is able to remotely acquire all the landed or captured fish and measure it automatically without any physical interaction. The system uses (i) a camera and a 3D sensor to obtain a complete XYZ reading of the fish and (ii) a convolutional neural network, trained for a representative set of species to detect and measure the individuals visible in a box. The system was validated in real conditions, using continuous observations of the landed fish in three islands of the Azores Archipelago, for 2 years. The aim of this article is to provide an overview of the measuring system and an analysis of the sampled data, by comparing the results of the proposed method with the traditional sampling methodology for a given period.

The morphometric analysis was carried out in indigenous cyprinid food fish, Schizothorax labiatus (a species of snow trout) collected from Vishav stream, a perennial cold water stream of Kashmir valley, India, wherein various morphometric characters viz., Total Length (TL), Standard Length (SL), Fork Length (FL), Pre-dorsal Length (PDL), Pre-pectoral Length (PPL), Pre-pelvic Length (PPeL), Pre-anal Length (PAL), Anal Fin Length (AL), Head Length (HL), Height of Dorsal Fin (HOD), Snout Length (SnL), Body Depth (BD), Eye Diameter (ED), Inter Orbital Length (IOL), Caudal Fin Length (CL) and Caudal Depth (CD) of 104 fish specimens were measured, correlated and analysed. The morphometric data was calculated in the percentage of total length except SnL, ED and IOL which were calculated in the percentage of HL. The result revealed that the correlation coefficient ranged from 0.770 to 0.995 in proportion to TL and 0.706 to 0.859 in proportion to HL which indicates that all the morphometric characters are highly correlated. All the correlations were significant at the level of p

Biometric indices of Pomadasys jubelini from Obuama Creek, Rivers state, Nigeria were investigated using length frequency distributions (LFDs), length-weight relationships (LWRs), length-length relationships (LLRs), condition factors (allometric, K A , Fulton’s, K F and relative, K R ). Specimens were captured in a stretch of the creek from March to September 2019. A total of 229 specimens were examined with the total length (TL) and weight (W) ranging from 8.7 to 50.4 cm and 8.7 to 834.5 g respectively. The standard length (SL) ranged from 5.3 to 46.8 cm, fork length (FL) was between 6.5 to 48.7 cm and the girth length (GL) varied from 4.7 to 38.7 cm. The relationships of weight-length showed a negative allometric growth pattern with a value of "b" of 2,666. Fulton's condition factor (K F ) ranged from 0.10 to 5.45, with an average of 1.21±0.66 indicating perfect wellbeing for the species. The LLR's allometric coefficient ' b ' between TL vs. FL and TL vs. GL showed positive allometric growth, while SL vs. FL, SL vs. TL, SL vs. GL, and GL vs. TL showed negative allometric growth, although the values were close to 1. These findings also provided some new and updated information on some of the morphometric characters of Pomadasys jubelini in Obuama Creek that could be useful for fisheries management and fish species protection measures in the creek and adjacent habitats.

Determining which factors are most effective for mitigative strategies in conservation management can be difficult for species with complex life cycles. Salmon (Oncorhynchus spp.) migrating through a hydroelectric power system experience conditions that can affect their survival directly within a life stage and indirectly in subsequent life stages through carryover effects. We quantified the association of covariates with survival across life stages of Chinook salmon (O. tshawytscha): juveniles migrating downstream, juveniles in the estuary, subadults in the ocean, and adults migrating upstream. We applied a hierarchical Bayesian mark–recapture model to ~400,000 wild Snake River Chinook salmon (Pacific Northwest, USA). Modeled covariates of survival included migration timing, river temperature, flow, percent of water spilled over dams, snow water equivalent, juvenile fish transportation, juvenile fish length, dam powerhouse passage, sea surface temperature, and the North Pacific Gyre Oscillation. By analyzing these covariates in a unified model, we evaluated their relationships to survival within and across life stages in a common currency. Among direct effects, the negative relationship of sea surface temperature to ocean survival had the largest marginal effect size. Carryover effects also had substantial marginal effect sizes. Ocean survival was associated positively with juvenile length and snow water equivalent and negatively with river temperature. In comparison, direct effects on juvenile and adult survival generally showed smaller marginal effect sizes. Both juvenile and adult survival were negatively associated with river temperature. Juvenile survival increased with fish length, while adult survival was positively related to flow and negatively to percent water spilled at dams. The greatest variability in survival, however, was in the ocean stage. Thus, as the ocean continues to warm and as the human population exerts more pressure on the ecosystem, carryover effects will be increasingly important for recovering salmon and other migratory species.

Background Acoustic telemetry is a widely used tool to study the movement and survival of juvenile fish and often requires a surgical procedure to implant the transmitter, which may impact overall fitness and survival following release. This is an important consideration when implementing large-scale acoustic telemetry projects aimed at estimating outmigration survival. The objective of this study was to examine the effects of water temperature, tag type, size at tagging, and surgeon experience on tag retention and growth rate of juvenile Chinook salmon (Oncorhynchus tshawytscha). We tagged 128 spring-run Chinook salmon (81–97 mm fork length, 5.2–10.0 g, tag burden 2.4–6.0%) with one of two types of acoustic transmitters; a shorter, heavier model (‘standard’) and a longer, lighter model (‘injectable’). Fish were tagged by either a novice or experienced surgeon. An additional 64 untagged fish served as a control group and were split between temperature treatments. Fish were reared in either cool (mean 13.4 °C) or warm (mean 17.8 °C) water for 60 days, prior to being euthanized, weighed and measured. Results Tag retention was similar for both transmitter types, but varied with water temperature, with significantly higher tag loss in the warm treatment (21.9%, 14 tags expelled), compared to the cold treatment (7.8%, 5 tags expelled). In the warm treatment, fish growth in the injectable tag group was significantly lower compared to the control group, and lower than the standard tag group, but not significantly lower. There was no significant difference between the control and standard tag groups for the warm treatment. In the cool temperature treatment, fish growth was not significantly different among any of the factors tested. Surgery time differed between surgeons; however, surgeon experience did not significantly affect tag shedding or growth. Conclusion Total tag loss was 14.8% over the 60-day trial, with higher and earlier loss in the warmer treatment. Tag length may be a more important factor than tag weight in smaller size fish. This suggests that tag shedding is a significant factor to consider when estimating survival, as the actual survival rate may be higher than estimates based solely on receiver detections.

Transport of salmonids allows upstream migrating adults to bypass barriers to migration, for example hydroelectric dams or adverse habitats. Downstream movement (“fallback”) after transport is common and removes individuals from spawning populations, with possible detrimental consequences for population productivity. Time‐to‐event analysis was used to determine effects of fish characteristics, transport conditions and environmental variables on fallback by adult Atlantic salmon transported to an inaccessible river reach as a population enhancement strategy on the Riviere Sainte‐Marguerite Nord‐Est (Quebec, Canada). Of 68 salmon transported, 19 exhibited post‐transport fallback within seven days of transport. Fork length (FL) was the only factor that increased risk of post‐transport fallback; there was a 5% increase in the proportion of large salmon (≥780 mm FL) exhibiting post‐transport fallback relative to individuals of median size (750 mm FL). Although the present study was limited by small sample size, the findings will help inform design of transport programmes in freshwater systems.

An animal's performance during its early life stage can greatly influence its survival to adulthood. Therefore, understanding aspects of early life history can be informative, particularly when designing management plans to rebuild a population. For a threatened population of fall Chinook salmon (Oncorhynchus tshawytscha) in the Snake River of Idaho, we reconstructed the early life history for 124 returning wild and hatchery adults using information recorded in their otoliths. Of our sampled wild adults (n = 61), 43% and 49% reared within the Snake River and Clearwater/Salmon rivers. We also found that only 21% of our sampled wild adults exhibited the historically common subyearling out‐migration strategy, in which juveniles exit freshwater shortly after hatching, while the remaining wild adults exhibited the yearling out‐migration strategy (i.e., individuals delay their freshwater exit). As expected, yearlings had, on average, a significantly larger body size than subyearlings at ocean entry. However, 35% of wild yearlings overlapped in size with wild subyearlings suggesting that spending more time in freshwater might not necessarily result in a larger body size. Lastly, we observed that variability in fork length at Snake River egress and ocean entry were best explained by migration strategy and where it reared, followed by hatch year and sex. Results from this study highlight the utility of adult otoliths in providing details about early life history, an understanding of which is critical to the conservation of Snake River fall Chinook salmon.

The tiger shark (Galeocerdo cuvier) is believed to be a fast-growing shark that has shown regional variation in growth. Vertebrae samples were taken from 124 tiger sharks (60 females, 38 males, 26 of unknown sex) caught in Western Australia (WA) from 1994 to 1998. Samples were aged using standard vertebral ageing techniques, and the data were used to create length-at-age curves. Dahl-Lee back-calculation was used because of the low number of small juveniles (

Tunas can elevate their red (slow-twitch, oxidative) skeletal muscle, visceral and cranial temperatures significantly above the ambient water temperature (Ta) with the aid of specialized blood vessels (retia mirabilia) that conserve metabolic heat. The ontogeny of this phenomenon, known as regional endothermy, was studied in young [18.5–62.5 cm fork length (FL), 71–5350 g body mass, 2–16 months of age] Pacific bluefin tuna (Thunnus orientalis). Maximal red muscle, visceral and cranial temperatures were measured in parallel with measuring red muscle mass and the size of the red muscle and visceral retia. The maximal thermal excess (maximal tissue temperature – Ta) increased from 1.1 ± 0.3 °C (mean ± SD) to 11.1 ± 3.4 °C in the red muscle, from 0.6 ± 0.3 °C to 3.5 ± 1.4 °C in the viscera and from 0.5 ± 0.4 °C to 2.0 ± 0.6 °C in the cranium in the smallest individuals compared with the largest. Thus, red muscle endothermy was well developed, but visceral and cranial endothermy were still developing, in the largest individuals studied. The scaling coefficients, relative to body mass, for total red muscle mass (0.90 ± 0.03, mean ± SE), red muscle rete (RMR) length (0.84 ± 0.06), maximum number of RMR blood vessel rows (0.43 ± 0.04) and visceral rete cross-sectional area (0.90 ± 0.08), indicated negative allometry for total red muscle mass ( 0.33) and the area of the visceral rete (> 0.67).

In Australian and New Zealand waters, current knowledge on white shark (Carcharodon carcharias) movement ecology is based on individual tracking studies using relatively small numbers of tags. These studies describe a species that occupies highly variable and complex habitats. However, uncertainty remains as to whether the proposed movement patterns are representative of the wider population. Here, we tagged 103 immature Australasian white sharks (147–350 cm fork length) with both acoustic and satellite transmitters to expand our current knowledge of population linkages, spatiotemporal dynamics and coastal habitats. Eighty-three sharks provided useable data. Based on individual tracking periods of up to 5 years and a total of 2,865 days of tracking data, we were able to characterise complex movement patterns over ~45° of latitude and ~72° of longitude and distinguish regular/recurrent patterns from occasional/exceptional migration events. Shark movements ranged from Papua New Guinea to sub-Antarctic waters and to Western Australia, highlighting connectivity across their entire Australasian range. Results over the 12-year study period yielded a comprehensive characterisation of the movement ecology of immature Australasian white sharks across multiple spatial scales and substantially expanded the body of knowledge available for population assessment and management.

Fish of the genus Thunnus are unusual because they are regional endotherms. In this study, archival tag data were used to demonstrate behavioural and physiological thermoregulation in juvenile yellowfin tuna, Thunnus albacares (35−52 cm fork length). Tags inserted into the peritoneal cavity were recovered from 23 yellowfin tuna caught mainly around Ishigaki Island, Japan, in 2009−2012. Peritoneal and environmental temperatures and depth data revealed that juvenile yellowfin tuna made daytime bounce dives repeatedly with a median dive duration of 16 min, and they remained at the surface during night-time. Body temperature daily averages were slightly higher than those of ambient temperature, and the body temperatures varied according to ambient temperature changes associated with vertical movements. Heat exchange coefficients (λ) during dives were estimated by a heat budget model. The thermal inertia component of λ was estimated in an experiment with dead juvenile yellowfin tuna. The value of λ exceeded the measured thermal inertia and varied between ascents and descents, thus providing evidence that physiological thermoregulation contributes to λ in juvenile yellowfin tuna and varies according to environmental temperature. Physiological thermoregulation helps maintain relatively stable body temperatures during dives in which tuna behaviourally escape cool deep waters and enter warm surface waters. Comparison of the obtained physiological parameters of λ and heat production ($${\dot{T}}_{\mathrm{m}}$$) with those previously recorded in Pacific bluefin tuna indicate that yellowfin tuna has a higher λ and lower $${\dot{T}}_{\mathrm{m}}$$ than Pacific bluefin tuna, which may restrict yellowfin tuna to warm tropical and subtropical surface waters.

In 1979, the Shortnose Sturgeon (Acipenser brevirostrum) population of the Saint John River, New Brunswick, was estimated at 18,000 &plusmn, 5400 individuals. More recently, an estimate of 4836 &plusmn, 69 individuals in 2005, and between 3852 and 5222 individuals in 2009 and 2011, was made based on a single Shortnose Sturgeon winter aggregation in the Kennebecasis Bay of the Saint John River, a location thought to contain a large proportion of the population. These data, in combination with the Saint John River serving as the sole spawning location for Shortnose Sturgeon in Canada prompted a species designation of &ldquo, Special Concern&rdquo, in 2015 under Canada&rsquo, s Species at Risk Act (SARA). A three-decade span of scientific observations amplified by the traditional knowledge and concerns of local indigenous groups have pointed to a declining population. However, the endemic Shortnose Sturgeon population of the Saint John River has not been comprehensively assessed in recent years. To help update the population estimate, we tested a rapid, low-cost side-scan sonar mapping method coupled with supervised image classification to enumerate individual Sturgeon in a previously undescribed critical winter location in the Saint John River. We then conducted an underwater video camera survey of the area, in which we did not identify any fish species other than Shortnose Sturgeon. These data were then synchronized with four years of continuous acoustic tracking of 18 Shortnose Sturgeon to produce a population estimate in each of the five identified winter habitats and the Saint John River as a whole. Using a side-scan sonar, we identified &gt, 12,000 Shortnose Sturgeon in a single key winter location and estimated the full river population as &gt, 20,000 individuals &gt, ~40 cm fork length. We conclude that the combined sonar/image processing method presented herein provides an effective and rapid assessment of large fish such as Sturgeon when occurring in winter aggregation. Our results also indicate that the Shortnose Sturgeon population of the Saint John River could be similar to the last survey estimate conducted in the late 1970s, but more comprehensive and regular surveys are needed to more accurately assess the state of the population.

The present study illustrates the first complete temporal variations of sex ratio (SR), length-frequency distributions (LFDs), growth pattern based on length-weight relation (LWR), length-length relationships (LLRs) and physiological status of Eutropiichthys vacha in the Ganges River, Bangladesh. A total of 1386 specimens (male = 652, female = 734) were collected from the fishers catch during January to December, 2016. For each individual, total length (TL), fork length (FL), standard length (SL) and body weight (BW) were measured using digital slide calipers and electronic balance with 0.01 cm and 0.01 g precision. The overall SR differed statistically from the expected 1:1 ratio, although females were greater in percentage throughout the year, except in April. The TL of males and females ranged from 6.2–19.9 cm and 6.5–20.6 cm, respectively. The overall growth pattern was negative allometric for both sexes, though ANCOVA reveals significant difference in LWRs. All LLRs were highly significant wi...

International audience; Fisheries management requires knowledge on the population dynamics of exploited stocks. To that end, the present study used a mark–recapture approach to characterise the population demographics of roundjaw bonefish Albula glossodonta (Forsskål) and their interaction with a data-limited fishery on Anaa Atoll in the Tuamotu Archipelago of French Polynesia. Over the course of the study, 2,509 bonefish were tagged and12.3% were recaptured. The L ∞ of bonefish was estimated at 71 cm fork length (FL) with a K of 0.17, based on changes in FL between capture events. Artisanal fish traps located in the migratory corridors of the atoll accounted for 94% of recaptures and these movements occurred during the waning moon. Fishing mortality increased as bonefish reach sexual maturity, recruiting to the trap fishery at age 4 with the onsetof spawning behaviour. Bonefish abundance between ages 3 and 5 was estimated to be 29,079 individuals. This case study demonstrated the utility of mark–recapture in filling knowledge gaps that impede the management of data-limited fisheries. Ultimately, these results supported the creation of an Educational Managed Marine Area and the resurgence of rahui (seasonal closure) to manage this fishery.

Different methods used to store specimens, even for short periods, can notably affect morphometric characteristics such as colour, length and shape. As a consequence, in the case of samples that have to be analysed morphometrically, the right preservation method is crucial. In this study, two comparably easy applicable methods, the effects of freezing and moderate cool storage on morphological traits, were studied on specimens of the scaleless North American channel catfish Ictalurus punctatus, an alien species to European freshwaters of increasing concern. Results revealed that freezing, like preservation with alcohol or formalin, affected the generally considered characteristics (colour, standard length, fork length, total length, shape), while cool storage was shown to preserve most traits without notable alteration, an important difference when studying potentially adapting alien species. Implications are discussed.

We examined the reproductive cycle, sexuality, and length at 50% maturity ( L 50 ) of the deep-sea snappers Etelis coruscans, Paracaesio caerulea, Pristipomoides filamentosus, and Pr. sieboldii from Okinawan waters based on gonadal histology. The overall sex ratios of E. coruscans and Pr. sieboldii were significantly female-biased, whereas those of Pa. caerulea and Pr. filamentosus were not significantly sex-biased. The spawning season was estimated to occur from May to November for E. coruscans, from April to September for Pa. caerulea, and from March to October for Pr. filamentosus and Pr. sieboldii. Their initial reproductive activity coincided with an increase in sunlight duration. Of the four species examined, E. coruscans and Pr. filamentosus indicated significant peaks of spawning around a specific lunar phase. We observed the presence of multiple oocyte maturation stages with postovulatory follicles (POFs) during the spawning season of each species. Transitional gonads were not observed in these four snappers. The L 50 of the females and males were 67.1 cm fork length (FL) and 37.6 cm FL for E. coruscans; 34.8 cm FL and 26.1 cm FL for Pa. caerulea; 35.7 cm FL and ≥ 20.0 cm FL for Pr. filamentosus; and 24.6 cm FL and ≥ 24.0 cm FL for Pr. sieboldii, respectively. Thus, the reproductive traits of E. coruscans, Pa. caerulea, Pr. filamentosus and Pr. sieboldii are characterized by a long spawning season and iteroparity. The E. coruscans and Pa. caerulea show relatively slow maturation compared to the two species of Pristipomoides. The implications of our results vis-a-vis the conservation and management of Okinawan bottom fisheries are discussed.

The longevity of blue marlin (Makaira nigricans) remains unresolved. The use of fin spines and sagittal otoliths for age reading has led to unconfirmed longevity estimates near 20–30 years. Age validation has been elusive because large individuals are uncommonly caught, and a technique that can be applied to structures that provide estimates of age was absent. The use of otolith chemical signatures has been limited by sagittal otoliths that are very small — whole otolith mass of adult blue marlin rarely exceeds 10 mg for the largest fish. Recent advances in the detection limits of radiocarbon (14C) with accelerator mass spectrometry — coupled with recently acquired knowledge of marine bomb 14C signals spanning the tropical Pacific Ocean — have led to an opportunity to age blue marlin from small amounts of otolith material. In this study, otoliths from a recently collected 1245 lb (565 kg) female blue marlin at a measured 146-inch (371 cm) lower jaw fork length were analyzed for 14C. Estimated longevity was either 12–21 or 32–44 years on the basis of bomb 14C dating. Using multiple lines of evidence, it was determined that the young age scenario was most likely, with evidence for an age close to 20 years using a series of deductions in the bomb 14C dating method.

Upwelling and the El Nino “Southern Oscillation” (ENSO) are recurrent climatic phenomena in the southeastern Pacific Ocean that severely affect the reproduction and growth of pelagic fish populations. However, there are not long-term growth data from demersal fish populations to test these interconections in a long-term analysis. For this reason, a first extensive growth chronology was reconstructed from the annual growth of sagittal otoliths as a proxy for somatic growth for the cardinalfish (Epigonus crassicaudus). Adult fish ranging from 35 to 40 cm in fork length and from 39 to 63 years in age were collected off Chilean waters. The master chronologies were estimated for the period from 1974 to 2014, using the regional curve standardization approach (RCS) and linear mixed models (LMMs). Growth indexes derived from both approaches followed a similar trend and were positively correlated with the Humboldt Current Index (HCI) and negatively with ENSO, Pacific Decadal Oscillation and sea surface temperature. LMMs showed that a 75% of growth variability was explained by the age of increment formation and HCI was the environmental index that most significantly affected the annual growth of cardinalfish followed by the sea surface temperature in spring. A reduced growth phase from 1974 to 1996 contrasted with a higher growth period from 1997, matching the 1997/1998 climatic regime shift, demonstrating that the enhanced growth for cardinalfish was associated with upwelling of nutrient rich water to the surface, triggering an increase of the primary and secondary productivity during the prevalence of a cold regime period in the Humboldt Current System. The consistence between RCS and LMM methods was indicative that both approaches are promising to evaluate the influence of environmental drivers on the growth condition of a demersal fish population in a highly productive marine ecosystem.

The food and feeding habits of the sawtooth barracuda, Sphyraena putnamae, from the southeastern Arabian Sea, India, were studied from 1367 specimens having a fork length range of 16.5–76 cm. The sawtooth barracuda consumed diverse prey items, which were grouped into three categories: teleosts, molluscs, and crustaceans. Teleosts were the preferred and dominant food component, while molluscs and crustaceans constituted the secondary and accessory food items, respectively. The chief constituents of the teleost group on basis of their dominance were identified to be carangids, scombrids, engraulids, leiognathids, and synodontids. The empty stomach ratio and stomach fullness index did not differ significantly between the sexes. The juveniles of both sexes exhibited a significantly higher stomach fullness index compared with the adults. A clear ontogenetic shift in the feeding pattern was observed, with only the crustaceans forming the diet in lower size class (

Red Snapper (Lutjanus campechanus) is a popular reef-associated fish species in the northern Gulf of Mexico (GOM) that supports both commercial and recreational fisheries. In this region, there is a large overlap in fork length (FL, 90%) and age (93%) range between mature and immature females. Therefore, here we investigate how age and FL of mature and immature female Red Snapper vary by artificial reef type and depth. Red Snapper (n = 695) were sampled using vertical long lines from March or April through November of 2016–2018 off the coast of Mississippi at different artificial structure types (platforms, artificial reefs, rigs-to-reefs) and depths (shallow, 20 m; mid, 20–49 m; deep, 50–100 m). To investigate habitat use of mature and immature fish respectively, we developed linear mixed-effects models. For both immature and mature fish, FL and age increased significantly with depth. Immature fish captured at artificial reefs were older than those captured at platforms, and mature fish were older and had longer FL at rigs-to-reefs than platforms and artificial reefs. The effect of depth on FL or age did not differ between mature and immature fish while the effect of structure types did. Structure types were important to predict FL for mature fish, but not for immature fish. In addition, the differences in age between rigs-to-reefs and both platforms and artificial reefs were significantly larger in mature fish than in immature fish. Larger and older mature females are found at deeper depths where fishing pressure is lower, while smaller and younger, immature fish are most often found in shallower, reef-based areas where pressure is highest. These spatial differences in maturity can help inform management regulations for the species.

Alewife (Alosa pseudoharengus) passage through 3 fishways was assessed during the 2013–2016 spawning runs in 3 rivers of the Isthmus of Chignecto, Canada. From April 24 to June 10, 5,423 alewife with a mean ± SD fork length of 227 ± 18 mm were tagged with passive integrated transponders. During their tagging year, approximately half of individuals (40% to 64%) went undetected whereas those detected used fishways from April 16 to July 8. Detected alewife were significantly longer than those undetected. Attraction rates to fishway entrances in 2015 and 2016 ranged from 85% to 98%. Annual fishway passage rates for pooled fish tagged that year and returnees, varied from 64% to 97% for 2 Denil style fishways. A pool-and-weir fishway that was dysfunctional (2013), repaired (2014), and replaced (2015–2016) yielded 0.5%, 25%, 60%, and 73% annual pooled passage rates, respectively. Larger individuals, previously tagged returnees, and males compared to females of a similar size had higher passage success suggesting some fishways may apply population-level selective pressures. Alewife passage rates related to fishway style, design, and proper function, with greater passage for the 2 Denils than the pool-and-weir fishway in our study. Regular structural maintenance and fish passage reviews are essential management considerations to ensure fishway functioning and river connectivity. Replacement of a fishway with poor fish passage may be the best option to improve passage rates. Future research should address the effects of multiple anthropogenic instream obstructions, environmental variables, negative sublethal post-tagging effects, and the importance of returnees on fish passage rates in fishways.

We examined the diet of a common midwater predator, the longnose lancetfish ( Alepisaurus ferox , n=1371), with respect to fork length, season, and capture location within the North Pacific Subtropical Gyre (NPSG). While A. ferox fed diversely across 97 prey families, approximately 70% of its diet by wet weight consisted of seven prey families (fishes: Sternoptychidae, Anoplogastridae, Omosudidae, Alepisauridae; hyperiid amphipods: Phrosinidae; octopods: Amphitretidae; polychaetes: Alciopidae). Altogether, these micronekton prey families constitute a poorly known forage community distinct from those exploited by other pelagic predators and poorly sampled by conventional methods. We demonstrate ontogenetic variation in diet between two size classes of A. ferox ( A. ferox consumed more fish and octopods, fewer crustaceans, and were more cannibalistic than small A. ferox . Ontogenetic shifts in vertical foraging habitat were observed as the consumption of larger and more mesopelagic prey with increasing fork length. Spatial and seasonal variation in the diet of A. ferox is consistent with expected patterns of variation in prey distribution with respect to oceanographic features of the NPSG. Within both size classes, the diets of specimens collected from the oligotrophic core of the NPSG were more diverse than those collected near the boundaries of the gyre and appeared to track seasonal variation in the position of the northern boundary of the gyre. Our data suggest seasonal and spatial variability in the composition of midwater forage communities exploited by A. ferox across the NPSG, and demonstrate that sustained monitoring of diet could provide valuable insights into long-term changes in these understudied communities.

One method with considerable potential for understanding fishing and environmental impacts on fish assemblages is size spectra (SS) and diversity size spectra (DSS) analysis—a regression of Ln abundance or Shannon diversity against the natural logarithm of body size of fish assemblages. But the usefulness of this method for application to tropical freshwater fish assemblages is uncertain. Here, we assessed the extent to which SS and DSS analyses explained changes in the exploited fish assemblage related to fishing effort and river droughts. To do this, we used correlation analyses on historical datasets of river water level, fishing effort, and fish length measurements for 56 fish species in three of the largest rivers of the Amazon Basin. In calculating the SS and DSS analysis statistics, we found that linear regressions adjusted well to the diversity and Ln(abundance) data plotted against Ln(fork length). In analysing SS and DSS statistics in relation to fishing and environmental impacts, we found that the slope of SS was negatively correlated to drought intensity with a lag of zero years in all rivers. The slope of SS also was negatively correlated to fishing effort with a lag of three years in two rivers and a lag of two years in one year. The slope of DSS was not correlated to drought intensity and fishing effort in any of the rivers. Our results provide support for the use of SS analysis to investigate fishing and environmental effects on exploited fish assemblages in tropical freshwater environments.

To better understand habitat-specific predation risk for stream fish, we used an approach that assumes animals trade off food for safety and accurately assess risk such that predation risk can be measured as a foraging cost: animals demand greater harvest rates to occupy riskier locations. We measured the foraging cost of predation risk for juvenile salmonids within enclosures in a natural stream at locations that varied in water depth and distance to cover. Measurements relied on a food delivery apparatus and direct observations that allowed estimation of “giving-up” harvest rates – food delivery rates at which animals left the feeding apparatus. Juvenile steelhead about 120 mm fork length exhibited sharp increases in giving-up harvest rate with decreasing water depth and refused to use the feeding device even when offered extreme food delivery rates in water ≤20 cm deep. Giving-up harvest rates were less affected by the distance to cover. Assuming the gradients we observed in giving-up harvest rates reflect predation risk, the results of this study can be applied to spatially explicit models of stream fish populations that incorporate risk into both habitat selection and mortality due to predation.

Underwater stereo–video systems are widely used for counting and measuring fish in aquaculture, fisheries, and conservation management. Length measurements are generated from stereo–video recordings by a software operator using a mouse to locate the head and tail of a fish in synchronized pairs of images. This data can be used to compare spatial and temporal changes in the mean length and biomass or frequency distributions of populations of fishes. Since the early 1990s stereo–video has also been used for measuring the lengths of fish in aquaculture for quota and farm management. However, the costs of the equipment, software, the time, and salary costs involved in post processing imagery manually and the subsequent delays in the availability of length information inhibit the adoption of this technology. We present a semi-automatic method for capturing stereo–video measurements to estimate the lengths of fish. We compare the time taken to make measurements of the same fish measured manually from stereo–video imagery to that measured semi-automatically. Using imagery recorded during transfers of Southern Bluefin Tuna (SBT) from tow cages to grow out cages, we demonstrate that the semi-automatic algorithm developed can obtain fork length measurements with an error of less than 1% of the true length and with at least a sixfold reduction in operator time in comparison to manual measurements. Of the 22 138 SBT recorded we were able to measure 52.6% (11 647) manually and 11.8% (2614) semi-automatically. For seven of the eight cage transfers recorde,d there were no statistical differences in the mean length, weight, or length frequency between manual and semi-automatic measurements. When the data were pooled across the eight cage transfers, there was no statistical difference in mean length or weight between the stereo–video-based manual and semi-automated measurements. Hence, the presented semi-automatic system can be deployed to significantly reduce the cost involved in adoption of stereo–video technology.

Pop-up satellite archival tags (PSATs) have been used since the 1990s to document the movements and post-release survival of numerous fish species. The effects of PSAT attachment on metabolic rate, cost of transport, and swimming kinematics have, however, not been broadly investigated. We therefore quantified the acute effects of PSAT attachment on these parameters in juvenile (47–87 cm fork length) sandbar shark Carcharhinus plumbeus. Using a water tunnel, we also measured the lift and drag forces of PSATs from three manufacturers which allowed us to calculate the theoretical power costs of towing these devices. We found no evidence that PSAT attachment results in increases in metabolic rate or cost of transport, or influences swimming kinematics of juvenile sandbar shark at volitional swimming speeds. Applying drag force measurements obtained for PSATs to our data showed that the predicted fractional increase in metabolic rate engendered by towing one of these devices at a specified velocity, normalized by the metabolic rate when swimming at that velocity minus the standard metabolic rate, would be below 5%. Our results are therefore congruent and suggest that PSAT attachment does not negatively impact juvenile sandbar shark (and by extension other elasmobranch species of equivalent or larger body sizes and employing a similar swimming mode).

Assimilation of mercury (Hg) into food webs is directly influenced by ecological factors such as local habitat characteristics, species feeding behavior, and movement patterns. Total Hg concentrations ([THg]) in biota from Subarctic latitudes are driven both by broad spatial processes such as long-range atmospheric transport and more local influences such as biovectors and geology. Thus, even relatively pristine protected lands such as national parks are experiencing Hg accumulation. We analyzed [THg] and stable isotopes of carbon (δ13C) and nitrogen (δ15N) in 104 Dolly Varden (Salvelinus malma) collected from two rivers in southeastern Alaska, upstream and downstream of apparent anadromous migration barriers in watersheds with and without glacial coverage. To assess the potential magnitude of marine-derived THg returning to freshwater, we analyzed [THg] in ten adult pink salmon from each study system. There were no differences in Dolly Varden mean [THg] between sites after the data were standardized for fork length, but unadjusted [THg] varied relative to fish size and δ15N values. While previous studies generally show that [THg] increases with higher δ15N values, we found that Dolly Varden below migration barriers and foraging on salmon eggs had the highest δ15N values among all sampled individuals, but the lowest [THg]. Dolly Varden residing below anadromous barriers had δ13C values consistent with marine influence. Since salmon eggs typically have low [Hg], our results suggest that abundant salmon populations and the dietary subsidy they provide may reduce the annual exposure to [Hg] in egg-eating stream fishes such as Dolly Varden. In addition to identifying a suitable species for freshwater Hg monitoring in southeastern Alaska, our study more broadly implies that river characteristics, location within a river, fish size, and feeding ecology are important factors influencing Hg accumulation.

Accurate descriptions of life history profiles are important for effective conservation and stock assessment efforts. We examined the reproductive cycle, sexual maturity, sexuality, growth, and longevity of the pagrinae sparid Argyrops bleekeri inhabiting bays in Okinawa Island, Ryukyu Archipelago, southwestern Japan based on gonadal histology and age determination, using sectioned otoliths. The overall sex ratio was not significantly sex-biased. The spawning season was estimated to occur from November to June, peaking from January to May. Opaque zones can be considered an annual ring formed from November to March. The three growth parameters of the von Bertalanffy growth equation were L ∞ = 43.1 , K = 0.245 , and t 0 = − 1.503 for females and L ∞ = 46.8 , K = 0.261 , and t 0 = − 0.671 for males. Their growth was rapid during the first 3 years of life and reached a size of >30 cm, and then the males grew larger than the females. The maximum ages observed were 19.3 years for females and 17.4 years for males. The observed lengths at 50% maturity were 20.0 cm fork length (FL) for females and ≥ 18.0 cm FL for males, which was already reached at 2 years old (females) and 1 year old (males). Transitional gonads were not observed. The species also had similar size and age ranges for both sexes. These results imply that the species may not undergo a sex change. Thus, the life history traits of A. bleekeri are characterized by functional gonochorism (juvenile hermaphroditism and/or gonochorism), relatively early maturation, and a long life span.

Steelhead trout (Oncorhynchus mykiss) reared under two different regimes: high food ration for 1 year (S1; typical strategy) or low ration for 2 years (S2) were subjected to a seawater challenge during the corresponding spring outmigration period. The S1smolts were smaller and suffered greater seawater challenge mortality (23.9% compared with 0.7% for the S2smolts) that was significantly and negatively related to body size. Heritability of body size was similar for the two treatments during the parr stage (fork length: S1= 0.181, S2= 0.245; mass: S1= 0.372; S2= 0.447), but higher for the S1treatment during the smolt stage for length (S1= 0.212, S2= 0.002) and body mass (S1= 0.145, S2= 0.015). Strong family effects for both traits and significant family by environment interactions for parr mass and smolt length indicated significant phenotypic plasticity. A genetic response to size-selective mortality caused by insufficient growth opportunity in the S1treatment is plausible and may affect fitness in the natural environment through effects on correlated traits.

Investigations were carried out for evaluating the design and selectivity of Pampus argenteus gillnets used along the Satpati coast. Satpati, an important marine fish landing centre of Maharashtra, India has the maximum Silver pomfret, P. argenteus landing by mechanized gillnetters. Among the maritime states, maximum landing of pomfret was recorded from Gujarat and Maharashtra in the northwest coast. They are highly relished table fishes in domestic and export markets and command high unit value. In India, the species is available in all the coastal states. Gillnet selectivity plays an important role in fish resource management and helps in maintaining sustainability of the stock. The gillnetters used for pomfret fishing in Satpati carried only one net per vessel and the total fleet length ranged from 10620 m to 11400 m. Gillnets are operated as column and bottom drift and depth of operation ranged from 35 m to 50 m. Gillnets made of Polyamide (PA) monofilament of diameter 0.23 mm to 0.28 mm and mesh size that ranged from 110 mm to 130 mm are commonly used. They are rigged with hanging coefficient between 0.42 and 0.51. Hung length varied from 114 m to 143 m and hung depth from 7.66 m to 9.50 m. The estimated optimum length of small mesh and large mesh was 131.40 mm and 155.29 mm respectively. Findings of the present study indicate a drastic decline in the length at first maturity of Silver pomfret to 199 mm fork length and the optimum mesh size estimated is 166 mm. Selectivity in terms of mesh size selectivity in accordance with the size at first maturity and size at first capture helps to eliminate juveniles from the gear. The knowledge of size selectivity of fishing gear types is crucial to fisheries management in order to achieve sustainable yield.

Knowledge of the influence of both spatial and temporal environmental gradients on life history traits and population demographics is a critical requirement in the management of exploited fish populations. This study examined variation in the demographics of Arripis trutta, an economically-important pelagic fish species with a broad latitudinal distribution in the waters of coastal south-eastern (SE) Australia, a region dominated by the influence of the East Australian Current (EAC). A validated ageing protocol was first developed using sectioned sagittal otoliths, which in turn permitted examination of latitudinal variation in A. trutta growth, size compositions and age compositions. The von Bertalanffy growth function parameters for A. trutta in SE Australia were estimated to be L∞ = 63.20 ± 0.37 cm fork length (FL), k = 0.26 ± 0.01 yr−1 and to = −0.14 ± 0.03 yr, with a maximum estimated age of 12.7 years. Growth was shown to be faster with decreasing latitude likely due to a simple relationship with the latitudinal gradient in water temperature; fastest growth occurring in northern NSW and slowest growth occurring in Tasmania. Latitudinal patterns in growth were remarkably similar to those previously reported for this species, despite age being estimated using scale readings some 40 years ago. This consistency in latitudinal growth patterns of a temperate fish can be attributed to the life history-related movements undertaken by A. trutta in this region. This temporally-consistent movement pattern is supported by the spatial gradient in the size and age composition of A. trutta sampled from different latitudes in both the current and historical research, whereby numbers of large and old fish increase progressively from Tasmania to northern NSW. These results highlight the need to consider the potential for spatial size- or age-structuring in the development of sampling designs and interpretation of results for any study examining spatial or temporal variation in demographic parameters of exploited fish populations.

The composition of walleye pollock diets from the eastern Bering Sea continental shelf was determined from 25 years of sampling during summer surveys from 1987 through 2011. Substantial differences in the stomach contents of walleye pollock were found among the sizes and geographic strata that correspond to geographic distribution of the prey. With increasing pollock size, copepods decreased in importance in middle and outer shelf areas while mysids decreased in importance in the inner shelf. Euphausiids increased in importance with increasing pollock size in southeastern areas of the shelf, and fishes and shrimp increased in importance with increasing pollock size in northeastern areas of the middle and outer shelf. The biomass-weighted average diet composition of eastern Bering Sea pollock in each year׳s survey indicated perennial but variable importance of euphausiids and copepods as prey. An index of partial fullness indicated an interannual pattern of below-average consumption of copepods by the surveyed pollock from 1993 to 2004, but during this period the amount of euphausiids consumed continued to fluctuate about a mean that was similar to years surveyed before and after that period. The summer feeding success, as indicated by average stomach fullness, of intermediate sizes of pollock appears to be closely related to the consumption of copepods (especially for pollock 30–39 cm fork length (FL)) and prey other than euphausiids (especially for pollock 40–49 cm FL). Length-specific predator–prey relationships with copepods and euphausiids correspond to patterns in pollock feeding migrations. Interannual trends in the biomass of copepods in the EBS are reflected most closely in the diet of 20–29 cm FL pollock, and trends in the biomass of euphausiids in the EBS are reflected most closely in the diet of the largest pollock (60+ cm FL). Climate-mediated changes in the zooplankton community will likely have differential impacts across the demographic spectrum of pollock in the EBS.

Variations in marine prey availability and nutritional quality can affect juvenile salmon growth and survival during early ocean residence. Salmon growth, and hence survival, may be related to the onset of piscivory, but there is limited knowledge on the interplay between the prey field, environment, and salmon ontogeny. Subyearling Chinook Salmon (Oncorhynchus tshawytscha) and their potential prey were sampled in coastal waters off Willapa Bay, USA to explore this issue. Three seasonal prey assemblages were identified, occurring in spring (May), early summer (June – July), and late summer (August – September). The onset of piscivory, based on salmon stomach contents, fatty acids, and stable isotopes occurred later in 2011 compared to 2012, and coincided with the appearance of Northern Anchovy (Engraulis mordax). Salmon fork length (FL) and carbon isotope values (δ13C) increased with a fatty acid biomarker for marine phytoplankton and decreased with a freshwater marker, indicating dietary carbon sources changed as salmon emigrated from the Columbia River. Salmon FL also increased with nitrogen isotope ratios (δ15N), trophic position, and a fatty acid marker for piscivory – a consequence of the ontogenetic shift in diet to fish. Salmon grew faster and obtained larger size and condition by September 2011 compared to 2012, which was related to inter-annual differences in ocean conditions and the duration over which Northern Anchovy were available. Our results support the idea that juvenile salmon growth depends on the onset and duration of piscivory, suggesting both of these factors may be important components of lifetime growth and fitness.

We provide a detailed characterisation of the life histories of two commercially important tropical goatfish species, Parupeneus barberinus and Mulloidichthys flavolineatus, from the Commonwealth of the Northern Marianas Islands (CNMI). Two years of continuous fishery-dependent data were used to assess age, growth, mortality and reproduction. Both species are short-lived, with a maximum age of 5 years and maturation within the first year of life. Female and male P. barberinus reach 50% maturity at 15.4- and 20.2-cm fork length (FL) respectively. The M. flavolineatus females and males reach 50% maturity at 15.8- and 16.1-cm FL. Temporal variation in the reproductive cycle of M. flavolineatus indicated that average monthly gonadosomatic index had a clear reproductive period of May–June and an anomalously high peak in November. The reproductive seasonality of P. barberinus was less clear, owing to the abnormally high proportion of inactive physiologically mature females found throughout the year in the fishery across a wide size range. Migrations of P. barberinus into and out of the main fishing area (Saipan lagoon) may explain why the fishery does not encompass the actively spawning population.

Onaga Etelis coruscans is an important component of the commercial deep-water handline fishery in Hawaii and is one of the more valuable species because of its local popularity. This species is part of a management unit called the Deep 7, a data-poor fishery comprising six snapper and one grouper species for which information about age, growth, longevity and maturity is incomplete. Although some life history information is available for onaga, prior estimates of maximum age (~10–20 years) likely suffered from underestimation of age, whereas two recent studies provided estimates that were similar to the work presented here—a refined age reading protocol revealed age estimates up to 55 years. This maximum age estimate and the age reading protocol used on onaga otoliths were validated using bomb radiocarbon dating. Using an otolith reference image age reading protocol that relied on the validated otolith sections, almost all onaga otoliths covering nearly the full body size range were used to generate valid growth parameters that may be sexually dimorphic. An empirical estimate of age at the length at which 50% of individuals reach maturity (L50) is 11 years, and fish near the minimum retention size in Hawaii (1 lb (~0.45kg) or ~30-cm fork length) may be just 2–3 years old.

The migratory and endemic Labeobarbus platydorsus and Labeobarbus tsanensis are threatened by extinction. This study is the first to use otolith microstructural analyses to infer life history traits of these species to assist in future conservation. We examined whole asterisci otoliths from 750 L. tsanensis and 542 L. platydorsus collected monthly between May 2016 and April 2017. The size of the L. tsanensis and L. platydorsus individuals collected was in the range 123–363- and 115–630-mm fork length respectively. For both species, 4- and 5-year-old individuals were dominant, whereas specimens older than 6 years were rarely recorded. The maximum ages recorded for L. tsanensis and L. platydorsus were 11 and 17 years respectively. Of the different growth models evaluated, the logistic growth model yielded the best fit to age-at-length data. For both species, growth parameters differed significantly between males and females, and sexual maturation proceeded faster in males than in females. Natural mortality estimates based on longevity were higher than the estimates based on growth parameters. For both species, females were predominant over males and the length–weight relationships were curvilinear. The estimated life history traits are important input parameters in further stock assessment evaluation of the species and should allow fisheries managers to optimise future conservation strategies.

Intraspecific variability in life-history patterns is well documented in elasmobranchs, and defining regionally specific parameters is essential for proper management and sustainability of species. Studies on the reproductive biology of finetooth sharks (Carcharhinus isodon) have noted a potential disparity in periodicity within North American waters. To better define regional variability, the current study collected 1490 finetooth sharks (831 female, 659 male) from the northern Gulf of Mexico. The size-at-maturity was determined to be 995- and 961-mm fork length for females and males respectively. In males, the peak gonadosomatic index (GSI) in March and presence of semen in the seminal vesicles in April suggested spermatogenesis occurs from March to April. In females, ovulation occurred from May to June, with a peak GSI occurring in May and maximum vitellogenic follicle diameter occurring in May and June. Gestation was found to be 11–12 months, with parturition occurring in May and June and a mean brood size was 3.8±0.1 embryos. Of the 50 females examined during the ovulatory period, 32 exhibited annual and 18 exhibited biennial reproductive periodicity. The results from this study will be impactful, because regionally distinct reproductive parameters can now be considered for future assessments.

Green sturgeon (Acipenser medirostris) is a highly migratory, marine oriented species that congregates in non-natal estuaries during summer and early fall. Individuals from the threatened Southern Distinct Population Segment (SDPS) and non-listed Northern Distinct Population Segment (NDPS) regularly co-occur in non-natal estuaries including the Columbia River estuary, Willapa Bay, and Grays Harbor in relative proportions not explained by abundance or distance from natal river. We used genetic markers to assign green sturgeon sampled in these estuaries from 2010 to 2012 to distinct population segments (DPS). We then examined interannual differences in DPS composition among estuaries. Fork length distributions were compared between SDPS and NDPS green sturgeon to determine whether size varied within and among DPSs and estuaries. The majority of green sturgeon sampled in the Columbia River estuary and Willapa Bay were assigned to the SDPS, while we assigned nearly even DPS proportions to our Grays Harbor samples. NDPS green sturgeon were significantly smaller than those originating from the SDPS within and among estuaries. We used these findings to develop several hypotheses about the mechanisms that may lead to specific patterns of non-natal estuary use. Genetic markers also assigned a single age-0 green sturgeon sampled in the Columbia River to the NDPS, although our analyses suggest that this individual’s parents may not have originated from known NDPS spawning populations. Because the Columbia River may serve as alternative spawning habitat for green sturgeon as climate change occurs, we recommend monitoring the Columbia River more closely for further evidence of green sturgeon spawning.

In this study, we examined summer and fall freshwater rearing habitat use by juvenile coho salmon (Oncorhynchus kisutch) in the quickly urbanising Big Lake drainage in south-central Alaska. Habitat use was assessed by regressing fish count data against habitat survey information across thirty study sites using generalised linear mixed models. Habitat associations were examined by age-0 and age-1+ cohorts separately, providing an opportunity to compare habitat use across different juvenile coho salmon life stages during freshwater rearing. Regression results indicated that the age-0 cohorts were strongly associated with shallow, wide stream reaches with in-stream vegetation, whereas age-1+ cohorts were associated with deeper stream reaches. Furthermore, associations between fork length and habitat characteristics suggest cohort-specific habitat use patterns are distinct from those attributable to fish size. Habitat use information generated from this study is being used to guide optimal fish passage restoration planning in the Big Lake drainage. Evidence for habitat use partitioning by age cohort during freshwater juvenile rearing indicates that pooling age cohorts into a single “juvenile” stage for the purposes of watershed management may mask important habitat use dynamics.

Stocking of hatchery-raised fish is an important part of the pallid sturgeon Scaphirhynchus albus recovery program. In the wild, juvenile pallid sturgeon consume primarily aquatic insects, although little is known about specific dietary needs. In hatchery settings, pallid sturgeon are fed commercial diets that are formulated for salmonids. To compare food consumption, growth, and energy status of pallid sturgeon fed artificial or natural diets, we conducted a laboratory study using 24 juvenile pallid sturgeon (initial fork length 153–236 mm). Pallid sturgeon were fed a daily ration of either commercial pellets (1 mm, slow sinking; 45% protein, 19% fat) or chironomid larvae for 5 wk. Natural-fed pallid sturgeon exhibited a greater specific growth rate (2.12% d−1) than pellet-fed fish (0.06% d−1). Similarly, relative condition was greater for natural-fed sturgeon (Kn = 1.11) than that observed for pellet-fed fish (Kn = 0.87). In contrast, the hepatosomatic index was significantly higher in pellet-fed fish (2.5%), indicating a high lipid diet compared with natural-fed sturgeon (1.4%). Given the importance of natural diets to fish digestion and growth, it is suggested that a more holistic approach be applied in the development of a practical diet for pallid sturgeon that incorporates attributes of natural prey.

Passive integrated transponder (PIT) tags are an important technology used to study ecology and behavior of animals including several stream fishes. In this study we investigated feasibility of using PIT technology to study ecology of juvenile Mugil cephalus (striped mullet) in Hawaiian streams. We quantified retention rates of PIT tags relative to an alternative tagging approach, visible implant elastomer (VIE) tags in the postorbital adipose tissue, for juvenile M. cephalus through a laboratory study. Next we conducted a field study of movement patterns of PIT-tagged juvenile mullet in a lowland Hawaiian stream (Waiāhole Stream) from early to mid-August 2014. For the laboratory portion of the study, 30 individuals (5–7 cm fork length) were randomly distributed among three treatments: PIT, VIE, and control (no tag) and held for 48 days. Tag retention was 100% for PIT-tagged and 0% for VIE-tagged fish. For the field study, 19 individuals (14.6–18.7 cm fork length) collected from Waiāhole Stream were implanted with PIT tags, and the movement of tagged individuals between the stream and its stream-mouth estuary/Kāne‘ohe Bay was inferred using a stationary PIT antenna array for 7 days. During that period, the antenna array registered 189 detections (97% during daylight hours, one missed detection) from five individuals, translating into 27 visits in total. Trip lengths to the estuary ranged from 45 min to 22 hr, with longer forays (≥10 hr) occurring primarily at night and shorter forays (

Large, mesopelagic teleost fishes have a potentially keystone position in the ecology of the pelagic water column, yet remain relatively unstudied when compared with large, commercially important, epipelagic fishes. Here, the ecological roles of four, large, vertically migrating teleosts were examined. Stomach content analyses were performed on 48 oilfish (Ruvettus pretiosis), 35 escolar (Lepidocybium flavobrunneum), 32 snake mackerel (Gempylus serpens) and seven lancetfish (Alepisaurus spp.) collected from pelagic longline gear in the Western North Atlantic Ocean from 2007 to 2010. Of these specimens, stable carbon and nitrogen isotope analyses were also performed on white dorsal muscle tissue from 33 oilfish, 16 escolar, 27 snake mackerel and seven lancetfish. Based on literature length-at-maturity values, all escolar, snake mackerel and lancetfish specimens were mature, while 13 of the 33 oilfish were juveniles. Crustaceans, annelids, salps, cephalopods and teleosts were present in the stomachs and were presumed to be prey items. A Kruskal–Wallis test showed the four species to be isotopically segregated in both δ13C and δ15N. Escolar were the most depleted in δ13C, followed by adult oilfish, juvenile oilfish and lancetfish, with snake mackerel the most enriched. The depletion in δ13C of adult oilfish and escolar may have been attributable to high C/N values, which were strongly correlated with length in oilfish, weakly correlated with length in escolar and moderately correlated with length in snake mackerel and lancetfish. The high C/N was likely due to the high lipid concentration of these fishes. Other factors that may have contributed to the depletion in δ13C may include spawning or a change in carbon source within the ecosystem. Large escolar occupied the highest trophic level (δ15N = 10.20), followed by snake mackerel (δ15N = 9.66), adult oilfish (δ15N = 9.32), lancetfish (δ15N = 9.05) and juvenile oilfish (δ15N = 7.83). A marked change in oilfish δ13C and C/N at 30–35 cm fork length coincided with a presumed length-at-maturity.

The age, growth and reproduction are described for 411 individuals of abu mullet from the Orontes River in Turkey between May 2011 and April 2012. The overall male to female ratio was 1:1.29. Fork length of all individuals ranged from 2.2 to 18.5 cm and total weight from 1.85 to 66.40 g. Isometric growth was observed for males (b=2.938) and all individuals (b=2.907); positive allometric growth was observed for females (b=3.246). The von Bertalanffy growth parameters based on data from otoliths were L∞ = 19.48 cm, k=0.258 year−1 and t0=−1.738 years for males, L∞ = 20.31 cm, k=0.313 year−1 and t0=−1.432 years for females. The growth performance index (Φ) was found to be 1.99 for males, 2.11 for females and 2.18 for all individuals. The mean condition factor (K) was calculated as 0.792±0.027 for males and 0.835±0.030 for females. Length at maturity was 11.49 cm for males and 11.82 cm for females. The fecundity was 14413±1569 with an egg diameter of 0.44±0.07 mm. Spawning period was between April and August. Abu mullet has acclimated well in the Orontes River and is capable of successful reproduction. Its calculated age and size at maturity was smaller and younger than for other populations.

Baited stereo-camera surveys of fish assemblages provide conservative estimates of abundance and length-frequency distributions. While underwater camera systems have numerous advantages over traditional fishing and diver surveys, limitations in sampling capacity, data processing time, and resultant data still exist. Previous studies have shown that shorter camera soak times can increase sampling efficiency and reduce per-sample data processing time without affecting overall data quality. Using data from stereo-video surveys of bottomfish in the main Hawaiian Islands, this study evaluates the effect of camera soak time on relative abundance metrics, fish length data, sampling efficiency, and power to detect differences in relative abundance and fish lengths. A soak time of 15 min was found to be the shortest duration able to capture bottomfish abundance and length metrics while 30 min generated data that did not significantly differ from the standard 40-min soak time. These shorter soak times allow for better survey efficiency and improved cost–benefit through increased levels of field sampling and reductions in video-processing time, while maintaining the power to detect differences in bottomfish relative abundance and lengths. The main drawback to shortening soak time was the concurrent reduction in the number of length measurements collected per species. An increased sample yield can alleviate this effect but only for bottomfish with a higher frequency of occurrence. Species-specific patterns in abundance were apparent in this study suggesting a strong influence of fish behavior on stereo-video abundance metrics. While a soak time of 15 to 30 min was found to be sufficient for effectively sampling bottomfish, the cost–benefit of employing a given soak time in future stereo-video surveys should be assessed based on the target species and survey goals.

Age and growth of the dolphinfish Coryphaena hippurus caught off north-eastern Brazil were studied by counting growth increments on scales and otoliths. A sample (n = 2338) measuring 7·7-195 cm fork length (LF ) was collected from September 2001 to February 2003. The scales (n = 69) removed from six different regions of the body were examined and those from the caudal region exhibited greater morphological regularity, symmetry and a smaller rate of regeneration. The regression between caudal scale radius (RS ) and LF displayed was linear (LF = 28·334 RS + 9·186; r(2) = 0·754). Otolith micro-increments were counted assuming daily periodicity. Ages estimated from otoliths ranged from 64 to 659 days. The von Bertalanffy growth model was fitted based on the otolith readings generating L∞ = 194·1 cm LF , k = 0·912 year(-1) and t0 = 0·081 years. Species longevity was estimated to be c. 4 years. Ninety-eight per cent of the overall sample was adult specimens well above the age of first maturity in the study area. The large variability between scale length and LF and the failure to ascertain increment deposition periodicity suggest that scales are not appropriate for ageing C. hippurus and analysis of otolith micro-increments is deemed the best structure for ageing this species in the study area.